HK1081250B - Exhaust after-treatment system for reducing pollutants from diesel engine exhaust - Google Patents

Description

Exhaust aftertreatment system for reducing pollutants from diesel exhaust

This application claims priority from U.S. provisional application 60/398473 filed on 25/7/2002 and U.S. provisional application 60/454046 filed on 12/3/2003.

Technical Field

The present invention generally relates to a diesel engine. More particularly, the present invention relates to a method for capturing and removing or destroying diesel exhaust pollutants such as particulate matter, labile organic compounds (VOCs), nanoparticle numbers, NOx, HC, CO, and SO₂The post-processing system of (1).

Background

Worldwide, governmental regulatory agencies are very concerned with particulate emissions from diesel engines. Important investigations of their health impact show that: the deleterious effects on human health are much more severe than originally recognized. Most of the toxicity of diesel exhaust pollutants is generated by the phenomenon of VOC compounds and nano-particle formation and number. Although VOCs compounds and nanoparticle counts cannot be controlled, methods may be employed to limit their discharge to the atmosphere to a minimum, which will be the subject of future government regulation. Nitrogen oxide is the cause of smog and acid rain, and sulfur dioxide is the main factor for acid rain.

Engine technology has improved dramatically over the past decade. Modern diesel engines can achieve emissions of 0.1gm/bhp.hr compared to 0.60gm/bhp.hr, 1988. Although modern diesel engines are significantly cleaner than older diesel engines, there is still a need to purify the exhaust gases until close to 0 emissions. The present USEPA and CARB regulations are aimed at reducing particulate emissions to 0.01gm/bhp.hr and NOx emissions to 0.2gm/bhp.hr, starting in heavy duty truck model year 2007. It is very difficult from today's perspective, if not impossible, to achieve such target emissions using only engine technology. That allows exhaust after-treatment to be selected as the most effective alternative to comply with the regulations.

Aftertreatment technologies used to trap diesel particulate matter and reduce NOx have received significant attention over the last 25 years. Most of the technologies focus on capturing particulate matter on filter media such as cordierite ceramic wall flow filters, ceramic fibers wound on perforated tubes and metal fiber filter media. These devices are generally known as particle traps.

Although the particle trap has proven to be an effective filter medium with an efficiency of 80-95%, it requires that the accumulated smoke be removed from the filter medium to return it to its original condition for another filtration cycle. This required leads to what is now known as the "regeneration process". Although the principle of the regeneration process according to burning the accumulated fumes is simple, they are still unreliable in particulate applications. In this regard, regeneration processes and particle traps have many limitations in practical social applications. For example, regeneration must begin when the filter load reaches a threshold, wherein, above the threshold, the pressure drop across the filter media begins to increase rapidly and affect engine performance operation. From a statistical point of view, when it is needed, the exhaust gas temperature during operation of the diesel truck is not high enough to start the regeneration process. Methods are employed to facilitate regeneration such as "forced regeneration" in which an external heat source is used to raise the temperature of the filter media above the ignition temperature of the smoke to initiate combustion. In addition, noble metal and or base metal catalysts are proposed in the form of a spray on filter media or added as additives to diesel fuels. The catalyst may lower the light-off temperature of the smoke from 620 degrees celsius to 320 degrees celsius, which increases the likelihood that: during engine operation, regeneration is effected by relying on the exhaust gas temperature distribution, especially at high engine loads. Relying on a catalyst to effect regeneration creates other problems: the catalyst is poisoned by sulfur compounds in the diesel. This results in the addition of very little sulfur diesel to ensure durable performance of the catalyst. Although the likelihood of successful regeneration in real-life applications has increased in recent years, the regeneration problem has not been completely eliminated. In the final analysis, complex, expensive hardware with elaborate logic is deployed into operation in harsh exhaust environments, which exacerbates other problems such as operational reliability and useful life.

The most critical limitation associated with the regeneration process in particle traps relates to the reliability of operation, which is a critical factor, especially in mobile applications. Diesel vehicles do not follow one mode of the road travel cycle. Of course, some diesel powered vehicles extend the idle condition while others operate in a congested traffic area. All these factors cause the exhaust gas temperature to be distributed too low to achieve regeneration in a passive system. This can occur even with a catalyst. As a result, during operation, an impermissible problem arises. While these problems are typically accommodated by "forced regeneration," the associated moving components such as fuel injection in the exhaust, valves, microprocessors, thermocouples, and the like have proven to produce extensive maintenance and poor reliability in harsh exhaust environments. Elements in or near the exhaust system mitigate high vibration loads to 30 g's and also mitigate thermal vibration loads. The reliability of moving elements in the exhaust environment of diesel engines has proven to be poor.

Service life is another major challenge to date: according to the EPA, particle trap systems are required to achieve 450,000 mile service life with 150,000 miles of non-maintenance intervals. Most active components and systems lack the ability to meet this service life requirement due to impermissible vibration loading, thermal vibration applications, and other related factors.

NOx control technologies are diverse. Important control techniques include: a lean burn catalyst; a plasma-assisted catalyst; an adsorbent; a selective catalytic reducing agent; and exhaust gas recirculation.

Almost all of these known techniques can effectively reduce NOx emissions by 25% -90%. However, each technique has some problems similar to particle traps. To date, exhaust gas recirculation is the most promising technology to easily address these issues. In diesel engines, EGR issues include: (1) smoke contaminates the exhaust gas, which creates problems in the air intake system of the engine; (2) higher exhaust gas temperatures affect engine performance; and (3) not having a large enough pressure differential to drive the required exhaust flow into the engine intake to maintain proper circulation. These problems have hindered the use of EGR technology in diesel applications. These improvements have led to the development of new EGR theory for diesel engines if high and low pressure methods and their combinations. Known EGR systems are complex and employ a large amount of hardware that also potentially results in poor service life, poor reliability, and large fuel consumption.

In summary, despite the improvements, these issues of regeneration and EGR adaptation still confuse researchers. In particular, trapping smoke in a filter medium has proven to be a very difficult, confusing task without fully addressing the warranty acceptance in mobile and stationary diesel applications. There is a complete need to improve the technology concerned.

Disclosure of Invention

The present invention relates to the field of particle traps and replaces the currently known technology with different solutions to solve the above problems. The process of the present invention is based on agglomerating fine smoke particles into large size particles that are easily separated from the exhaust stream. Two methods can be used to achieve separation of the agglomerated particles. These are centrifugal separations and the agglomerated smoke is removed by reverse pulse injection. The separated particles can be collected and compacted into solid pellets and sold commercially. Furthermore, the separated particles can be incinerated continuously in a controlled environment, which can eliminate sudden temperature rises and hot spots, thus improving reliability and service life. The use of the teachings of the present invention will simplify and enhance the EGR system, which solves the primary EGR problem in diesel applications. The system lends itself to the control of unregulated emissions at suitably high levels, such as reduced nanoparticle numbers, complete elimination of harmful air pollutants (VOCs), reduction of pressure drop in particulate converters, and separation of NOx and sulfur compounds from diesel exhaust.

The invention is based on the following: various well-known physical phenomena and properties are utilized to remove controlled and uncontrolled pollutants from diesel engine exhaust by overall system methods. Known exhaust particulate traps are based on providing a filtering action. The main product of the present invention is a particle converter. The first method of the invention, which has absorption capacity for stationary engines, is based on: a caking process is used instead of the filtration process. Having the particle agglomerator totally smoky will result in complete agglomeration of the incoming particulate matter, i.e., all particles entering the agglomerator are collected and combined into a larger size form for subsequent removal at the downstream end. Once the agglomerator is loaded with smoke particles, the capture efficiency of the incoming particles is greatly improved, even higher for finer particle size sizes. This results in the known highest nanoparticle capture efficiency. The particles blown off at the downstream side of the agglomerator are broken dendrites and therefore their size is large. Depending on the operating conditions and whether the dendrite is dry or wet, the size of the dendrite particles ranges from 1-100 microns in size, while the incoming particles range from nano-size to 1 micron, and average 0.1 micron. With particle size in the range of 1-100 microns, new opportunities can be created to separate them and finally dispose of them by incineration or simple collection. In each case, as is known today, the regeneration process can be replaced entirely with a more reliable alternative. The compression of the separated particles to form the soot pellets is a more efficient and reliable method than known filtration techniques. The incineration process is of course also passive, continuous and also very reliable, long-lived, and it solves a well-known problem in regeneration processes.

Replacing the regeneration process with an agglomeration and separation process creates new opportunities to reduce contaminants. For example, reducing the exhaust gas temperature as low as possible, as opposed to the known particle trap approaches, provides a number of advantages in reducing emissions, which were previously unattainable. For example, but not by way of limitation, such advantages include: (1) reducing the exhaust gas temperature can reduce the exhaust gas flow rate and viscosity, resulting in a reduction in pressure drop by a factor of 3.1; (2) the lower exhaust gas temperature forces a significant amount of VOC to partially condense into millimeter-sized particles that can be captured with very high efficiency and eliminated from the tailpipe; (3) reducing the exhaust gas temperature forces more nano-sized particles to condense and become trapped in the particle converter, rather than occurring after the tailpipe; (4) adding platinum catalyst withoutIs a diesel oil oxidation catalyst and can be used for treating SO₂Oxidation to sulphate nano-particles which can be collected together with the soot particles, thereby eliminating the emissions of sulphur compounds from the tailpipe; (5) these active platinum catalysts also oxidize 50-70% of the NO to NO₂. If the exhaust gas is cooled to 200F or less, a large amount of NO₂Can be absorbed by water, thus reducing NOx emissions in an effective and simple manner; (6) the performance of the particle converter is not dependent on the exhaust gas temperature distribution, which is not the case with other known techniques. These advantages and additional advantages will become apparent to those of ordinary skill in the art upon reading the details of the present invention as set forth below.

The particle agglomeration and separation converter, other ancillary devices and retrofit devices underlying the present invention were developed into a system design designed to reduce all known pollutants emitted from diesel exhaust. In mobile applications, the exhaust gas by-product of incineration is freed of particulate matter and can therefore be re-directed to the engine intake as clean exhaust gas for Exhaust Gas Recirculation (EGR). EGR provides NOx reduction functionality. The exhaust gas recirculation flow may be further regulated by a diverter valve at the tailpipe.

In the case where the exhaust stream reaches the settling chamber rather than the incinerator, the chamber collects smoke during engine operation until it is full, typically this occurs over a period of 3-6 months. When the chamber is full, it is unloaded during routine maintenance procedures such as oil change. In the service repair station, the particles are passed into a fume drum and processed into compressed pellets. This can be achieved by inserting a tail pipe and allowing the exhaust stream at idle to sweep the accumulated smoke (sweep stream) into the smoke drum. The process of emptying the chamber into the smoke drum takes about 5 minutes. One smoke drum may service 10 to hundreds of mobile engines. In stationary applications, marine applications or multi-engine applications, and where space is warranted for installation of the smoke drum, the scavenging flow is processed directly into the smoke drum without the need for a smoke chamber. Furthermore, the settling chamber may be replaced by a bag for collecting the fumes.

The system of the invention can effectively reduce PM, NOx, toxic Substances (VOCs), nano-particle number and SO₂HC and CO. Furthermore, the primary balance of the attributes and system of a simple, passive particle converter is the most promising approach to address the lifetime, reliability, and other safety of known post-processing techniques.

Another embodiment of the present invention is attractive for small diesel applications such as trucks and SUVs. In almost all of these applications, the size of the post-processing hardware is critical, especially in mobile application improvements. Furthermore, the engine operates in a transient mode, which does not allow the centrifugal separator to function properly under optimum conditions, due to the addition of turbulence, swirl effects and the modification of the centrifugal acceleration of the centrifugal separator. This embodiment includes an integrated hardware without a centrifugal separator. The agglomeration process is replaced with a similar agglomeration filtration process. The hardware was fitted with a synthetic wire mesh that employed wire mesh media augmented by a filter screen. A similar cake-filter medium is a depth filter (depth filter) which operates on the cake principle, followed by one or more stages of filtration. The media is not intended to function as a full agglomerator. Therefore, when the particle collection efficiency starts to deteriorate (measured by an increase in the pressure drop over the medium), some method has to be used to purify the medium. This results in the use of reverse pulse ejection to remove a large amount of smoke stored in the media. The agglomerated, blown-off smoke on the upstream side falls into the bottom of the housing. To prevent the agglomerated fumes from agitating and reloading them onto the wire mesh media, perforated sheets may be used to separate the collected fumes, which fall under the perforated sheets due to gravity and vibration, and thus are separated from the main exhaust flow. The spaces between the perforated sheet and the synthetic wire mesh are all dedicated to the flow of the main exhaust stream.

Similar cake-filter media embodiments may be, but are not limited to, rectangular in shape, wherein the rectangular shape is of a height suitable for underground installation on mobile sources such as trucks and buses. On the other hand, this embodiment may take the shape of a cylindrical device, which is also suitable for vertical mounting on some trucks and buses. In each embodiment, the number of chambers in which the wire mesh media is installed may be one, two, or more. The number of chambers in which the wire mesh is installed is increased, pressure drop can be reduced, the holding ability of smoke can be improved, and the smoke trapping efficiency can be improved.

Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

Drawings

The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:

FIG. 1 is a schematic diagram of a completely passive particulate converter system for use in stationary applications, illustrating exhaust flow in accordance with the teachings of the present invention.

FIG. 2 is a schematic diagram of a particulate converter system showing exhaust gas flow with emphasis on controlling exhaust gas recirculation according to the teachings of the present invention.

FIG. 3 is a longitudinal cross-sectional view of a particle converter with a agglomeration tube and outlet showing gas inlet, agglomeration and separation.

Fig. 3A is a cross-sectional view taken along line a-a of fig. 3.

Fig. 3B is a cross-sectional view taken along line B-B of fig. 3.

Fig. 3C is a cross-sectional view taken along line C-C of fig. 3.

FIG. 4 is a longitudinal cross-sectional view of a particulate converter having a two-stage separator and an incinerator integrated within a cylinder.

Fig. 4A is a cross-sectional view taken along line a-a of fig. 4.

Fig. 4B is a cross-sectional view taken along line B-B of fig. 4.

Fig. 4C is a cross-sectional view taken along line C-C of fig. 4.

Fig. 5A and 5B show detailed cross-sectional views of an integrated incinerator engaged screen element and an ongoing incineration process.

Fig. 6 is a longitudinal cross-sectional view of a particle converter having a plurality of agglomerate tubes.

Fig. 6A is a cross-sectional view taken along line a-a of fig. 6.

Fig. 6B is a cross-sectional view taken along line B-B of fig. 6.

Fig. 6C is a cross-sectional view taken along line C-C of fig. 6.

FIG. 7 is a longitudinal cross-sectional view of a particle converter with a multiple agglomeration tube and a two-stage particle separator.

Fig. 7A is a cross-sectional view taken along line a-a of fig. 7.

Fig. 7B is a cross-sectional view taken along line B-B of fig. 7.

Fig. 7C is a cross-sectional view taken along line C-C of fig. 7.

FIG. 8 is a side view of an auger in a particle separator with multiple bypass holes for sound attenuation.

Fig. 9 is a cross-sectional view showing the principle of window design and temporary particle ejection and separation.

Figure 10 is a cross-sectional view of a composite wire mesh agglomerator.

Fig. 11 shows the results of an analysis of the amount of movement of 2 micron particles as a function of flow path and position of the window aperture within the centrifugal separator, the spacing between two successive arrows being equal to the amount of movement produced by a fall cycle rotation (360 degrees). The graph was generated by 3-dimensional fluid mechanical analysis and particle movement is highlighted by size and collision with vortex action.

FIG. 12 shows the results of an analysis of the 5 micron particle movement and the position of the window aperture within the centrifugal separator. The interval between two consecutive arrows is equal to the amount of movement produced by a full cyclic rotation (360 °).

Figure 13 is a plan view of the smoke collection chamber.

Figure 14 is a cross-sectional view of the smoke collection chamber.

FIG. 15 is a cross-sectional view of a smoke collection chamber with an integrated incinerator.

FIG. 16 is a plan view of a smoke collection chamber with an integrated incinerator.

Figure 17 is a longitudinal cross-sectional view of a smoke treatment drum with reverse pulse ejection.

Figure 18 is a modified cross-sectional view of a smoke treatment drum having a mechanical shaker.

FIG. 19 is a schematic diagram of a particulate converter and EGR system for use in mobile applications.

FIG. 20 is a schematic of a flat, cake-like, filtered particulate converter and EGR for use in mobile applications, illustrating exhaust flow in accordance with the teachings of the present invention.

FIG. 21 is a schematic diagram of a flat agglomerate-filter particulate converter for use in mobile applications, showing exhaust gas flow with emphasis on different reverse pulse injection schemes and the use of smoke collection bags.

Fig. 22 is a cross-sectional view of a cylindrical agglomeration/filter particle converter for use in mobile applications.

Fig. 23A and 23B each show the sliding door mechanism in the open and closed positions.

Fig. 24A and 24B are cross-sectional views of a cake/filter synthetic wire mesh media and similar fiber and screen filter media.

Figure 25 shows a passive incinerator arrangement in combination with the particle converter of figures 20 and 22.

FIG. 26 is a schematic diagram of control logic for controlling reverse pulse injection in a similar agglomeration-filter particle converter.

Figure 27 shows typical collection efficiency and backpressure characteristics for similar wire mesh media with and without a filter screen.

FIG. 28 is a logic diagram illustrating the use to capture, process and destroy VOCs, SO₂And the principle of NOx.

Detailed Description

The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.

Short description of the A System

Referring initially to FIG. 1 of the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, FIG. 1 shows an aftertreatment system for reducing pollutants from engine exhaust gases. The system shown in fig. 1 may be used to aftertreatment exhaust from various internal combustion engines, such as diesel, compressed and liquid natural gas engines, which operate lean and have a high amount of particulate matter. The system of the present invention may be designed to destroy/separate/remove all pollutants in the exhaust gas collectively. This includes: particulate matter and nano-sized particles, volatile organic compounds, nitrogen oxides, hydrocarbons, carbon monoxide and sulphur dioxide. By combining treatments, the exhaust gases released into the atmosphere can be efficiently freed of all said pollutants, which can render these highly polluted engines environmentally safe.

With continuing reference to fig. 1, and with further reference to fig. 2-7, various preferred embodiments of the present converter system for use in stationary diesel applications are shown. The oxidation catalyst 10 is connected to an engine exhaust manifold. Catalyst 10 may be a diesel oxidation catalyst or an active precious metal catalyst (e.g., in a gasoline engine application). Following the catalytic converter 10 is an exhaust system 50, which exhaust system 50 is designed to cool the exhaust gas to the greatest possible extent before the exhaust gas enters the particle converter 100. This possible cooling pattern can be generally divided into three sections representing different patterns of heat transfer: a radiant section 60 followed by an air convection section 70 followed by a liquid convection section 80.

The particle converter used in stationary applications is shown in more detail in figures 3, 4 and 6. The particle converter mainly comprises: an air intake portion 110; a agglomerator 120; a centrifugal separator 130; and an outlet portion 140. The outlet portion 140 may employ an incineration apparatus 150 as shown in fig. 4 and 5A and 5B. The ventilation air flow passage at the end of the converter is ducted into the smoke collection chamber 170. The cleaned exhaust gas exiting the smoke collection chamber 170 forms an Exhaust Gas Recirculation (EGR)200 to reach the air cleaner of the engine. The EGR system may employ an axial flow boost pump 241 to properly measure EGR flow. The fumes collected in the fume collection chamber 170 are ducted outwardly into the fume treatment drum 200, thereby recovering the spherical fumes.

B oxidation catalyst

The oxidation catalyst 10 of the present invention is selected to have a composition that is capable of substantially reducing small amounts of VOC compounds but allows large amounts of VOCs compounds to pass through, condense in the exhaust and eventually collect in the particulate converter. The condensed VOCs act as a binding material that forms larger sized agglomerated particles and prevents separation due to turbulence or vortex phenomena encountered in the cyclone separator. Thus, for the purposes of the present invention, the use of smaller sized diesel oxidation catalysts is usefulIt is sufficient. Diesel oxidation catalysts also function in oxidizing hydrocarbons, carbon monoxide, and sulfur dioxide (SO)₂) Has a smaller effect. On the other hand, the active noble metal catalyst has a great effect on the oxidation of hydrocarbons, carbon monoxide and small amounts of VOCs, and efficiently converts SO₂Oxidation to sulfate compounds and oxidation of NO to NO₂. To remove SO₂Oxidation to sulfate is widely known in the industry as being a very poor catalytic activity in diesel exhaust applications because it leads to increased particulate emissions. On the other hand, if the temperature of the exhaust gas after passing through the catalyst is cooled to less than the sulfate condensation temperature, nanometer sized sulfate particles may be formed, which may be collected in the converter together with the soot particles. The mixture of smoke and sulphate formed wet brown granules. Where adequate cooling can be achieved, the process can efficiently remove SO₂An exhaust gas of the pollutant. It should also be noted that NO is oxidized to NO with an efficiency of about 50-70%₂. Due to NO₂Is active and therefore after passing through the converter the exhaust gas is purified by water so that it is absorbed together with sulphate compounds.

C. Exhaust gas cooling system

The means designed to cool the exhaust gases vary depending on the engine application and the resulting liquid cooling medium, such as water. The method of the present invention is based on the use of the properties of the heat transfer mode. The radiant exhaust section 60 is used when the exhaust gas exits the oxidation catalyst 10 at high temperatures. The radiation section 60 is characterized in that it has a large surface area or a large tube, and the surface finish has the highest radiation characteristics such as matte black (matte black). This is followed by an air/exhaust heat exchange section 70. This portion 70 depends on the relative velocity of the outside air through the exhaust pipe due to vehicle motion. The exhaust pipe is corrugated in the axial direction to enlarge the surface. Multiple tubes may also be used. All the pipes need to be affected by wind factors.

The last part being liquid/exhaust heat exchangeAnd a device 80. This portion 80 relies on the use of a fluid such as engine coolant (which is typically used in automobiles) or water to provide the required cooling. It should be noted that the exhaust temperatures of most diesel engines reach approximately 900-. Target exhaust gas temperatures at the inlet to the converter of about 250 ° F to 300 ° F where adequate cooling can be achieved, such as water and NO₂The purification is required and the exhaust temperature needs to be further reduced to a range of about 150F to 200F after passing through the converter. The choice of three different cooling mechanisms varies over a wide range from one engine application to another. Generally, the radiating portion 60 provides, among other things, maximum cooling and minimal cost. The second or third cooling mechanisms may be used together or independently, depending on the application.

D. Particle converter, full agglomeration

Fig. 3, 4, 6 and 7 further illustrate a preferred embodiment of the particle converter 100. The inlet section 101 of the converter 100 diverts the incoming flow from a circular or rectangular tube into the space between the housing 113 and the agglomerator 102 by gradually expanding the flow channel into the space that feeds the agglomerator to minimize pressure drop.

The agglomerator portion 102 in the converter 100 may be a single housing as shown in fig. 3 and 4, or a multiple tube design as shown in fig. 6 and 7. In both embodiments, a larger surface area is required to enhance the caking effect. In the multi-tube design of fig. 6 and 7, all flow is towards the centrifugal separator. In the single shell agglomerator of fig. 3 and 4, this flow is fed and processed into the centrifugal separator on a continuous basis. The flow processed in each channel is a fraction of the total flow.

The flow rate in the channels may be selected based on the path of movement of the exhaust gas stream from the agglomerator to the inner tube 104 and the length of the agglomerator. It is desirable to treat a portion of the total flow in each channel because turbulence and swirling effects can be reduced. Further, the process of treating the particles by centrifugation is limited to keeping the particles separated on the inside diameter of the agglomerator while the clean exhaust gas stream moves inwardly into the core tube 107.

The agglomerator is formed of an integrated wire mesh medium having variable wire size and having a packing density as particularly shown in fig. 24A. The upstream side of the agglomerator 102 is formed of coarse wire having a lower packing density and modified to finer wire having a higher packing density at the downstream side as shown in FIG. 10. This selection criterion enables the capture of larger particles on the outer layer while capturing smaller particles on the more finely assembled wires. This method enables maximum particle capture efficiency, even distribution of smoke over the media, while minimizing pressure drop. In addition, there are open holes on the upstream side of the agglomerator, allowing particles to be trapped in the agglomerator and preventing a smoke layer (cake) from forming in front of the agglomerator, which results in an increase in pressure drop. The treatment of the agglomerated particulate matter is shown in fig. 10.

The thickness of the agglomerator is in the size of about 10mm to about 30mm, and in most applications is on average in the size of about 10mm to 20 mm. This thickness, combined with the smaller flow velocity of the dendrites forming in the interstitial spaces between the wires, can result in efficient capture of submicron or nano-sized particles from diesel exhaust, with a reduction in particles ranging from 104 to 105. This greatly reduces the main component of exhaust gas toxic pollutants.

The agglomerators of the present invention are in sharp contrast to other known soot filter technologies such as ceramic wall flow integration, which have wall thicknesses averaging 0.1mm to 0.3mm, making their capture of submicron and nano-particles less efficient. By cooling the exhaust gas, the nanoparticle capture efficiency is further improved. It is known that during the exhaust gas cooling process, a substantial amount of nanoparticles are formed and that a maximum amount is reached when the exhaust gas is cooled to ambient temperature. Cooling the exhaust from 900F-1000F to about 250F-300F can result in forcing a significant amount of the nano-particles to condense before the converter. It is believed that the small amount of VOC compounds, which is dependent on further formation of residual nanoparticles, is primarily destroyed by the oxidation catalyst. The combined effect of the oxidation catalyst, exhaust gas cooling and agglomerator of the present invention is a wide and significant reduction in the number of nano-sized particles commercially before the exhaust gas exits the tailpipe.

E centrifugal separator

The centrifugal separator of the preferred embodiment of the invention is shown in figures 3, 4 and 7. The centrifugal separator of fig. 3 is formed by an auger 105 mounted on a concentric core (tube) 111. The off-gas from the agglomerator is fed through the entire length of the centrifugal separator in a continuous and uniform manner. The concentric core tubes are provided with windows 109 which are equally spaced along the flow passage. The windows are spaced at an angle of about 120 degrees along the direction of rotation of the auger. To begin the swirling flow pattern, no window is used at the entrance to the auger. A combination baffle 103 is added which gradually creates a spiral motion to the flow. As the flow within the channel is established, the bonding plate gradually moves radially into the inner core tube. Likewise, the adhesive sheet starts on the outside diameter and moves helically towards the inner core. The auger rotation is required to make approximately 1.5 revolutions to form the entire rotating flow channel. No window is employed in the cross-section forming the rotational flow channel. The first window crosses 120 degrees over the end of the bonding plate to perform particle separation in the exhaust layer adjacent to the core tube. The window design then captures a clean layer of exhaust gas flow at the same velocity as the incoming flow from the agglomerator. This allows the flow velocity in the flow channel to remain substantially constant. The starting cross section of the centrifugal separator and the position of the first window are chosen such that the number of spin cycles of the exhaust gas before entering the window is formed. Typically, about two spin cycles are sufficient to separate agglomerated particles having a size of about over 2 microns. More spin cycles result in cleaner exhaust.

Fig. 11 and 12 show a typical particle separation (movement) of a centrifugal separator as a function of particle size versus number of revolutions. The movement of the particles for one complete cycle (360 degrees of rotation) is indicated by the gap between two consecutive arrows. It is clear that larger sized particles move more massive in the radial direction than smaller particles. However, two phenomena have opposite effects on the radial movement of particles in a centrifugal separator: turbulence and vortex effects. Both are studied by 3-dimensional fluid-mechanical analysis, which employs aerosol models of particles of different sizes. For smaller particles, the vortex action is dominant and may cause the particles to move in a direction opposite to the centrifugal direction, and therefore separation cannot be achieved. However, the vortex is limited to only those local regions which are close to the two sides of the auger, as shown in figures 11 and 12. The window opening is therefore selected so that the vortex region remains clean to avoid re-entry of contaminated exhaust gas into the window.

During the experiment, it was experimentally observed that smaller sized particles, which did not completely agglomerate to about 1.0 micron or more, or which may break off into smaller particles due to turbulence or vortex effects, collected on the outside surface of the core tube. This observation is contrary to the effect of centrifugation. It is assumed that such smaller particles are transported into the core tube due to the vortex action and are collected by the propagation mode of particle collection. These particles are considered to be flowing, agglomerate on the surface of the core tube and then start moving in the flow direction as soon as their size reaches a certain threshold to ensure sufficient drag in the flow direction. Although these particles constitute only a small fraction of the total particles, they can almost entirely be entrained into the window flow unless some method is employed.

A simple particle ejector 117 or separator is mounted in front of the window 107 as shown in figure 9. By releasing the agglomerated particles before the window opens, the centrifugal action will move the particles radially a sufficient radial distance to avoid entering the space of the window designed for clean flow. Due to the inertia of the particles, they form flow channels that are separate from the flow stream entering the window. This phenomenon is referred to in aerosol science as the anisokinetic phenomenon.

Upon advancement, a clean exhaust flow enters the window opening. The collected clean exhaust gases in the core tube are released to the atmosphere. All agglomerated particles remain separated and continuously accumulate at or near the outside diameter of the centrifugal separator. At the downstream end of the centrifugal separator, a portion of the exhaust gas carries all separated particles and reaches an outlet or an electric incinerator. This portion of the exhaust gas is referred to as the sweep stream. The exit mechanism is shown in cross-sectional views in fig. 3C, 6C and 7C. The bonded spiral plates 112 are used to assist the sweep gas flow out through the outlet 116.

Where the electric incinerator 117 is used as an integral component of the particle converter, as shown in fig. 4, two conical screen assemblies are connected at their ends to the inner core 111 and outer shell 115, with the two mating ends being secured together. This arrangement provides a large surface area that is required to provide a low exhaust flow velocity through the composite screen assembly. The sweep gas flow is divided between two conical screen assemblies. The surface area is doubled by doubling the number of conical screen assemblies (not shown).

F incinerator, preferred embodiment A

The resulting screen assembly is shown in fig. 24A and 24B. These screens have different functions. The first screen 120 is selected to have larger sized wires and wider openings. The downstream side of the screen 120 is coated with an electrically insulating material such as a ceramic substance. The screen 120 is connected to a 12 or 24V power supply. The second screen 121 is identical to the first screen 120, except that electrical insulation is applied to the surface that mates with the first screen 120. The third screen 122 is a spacer screen and is selected to have openings less than 50 microns. The fourth screen 123 is a wire mesh screen and is selected to provide structural support for the three first screens 120, 121 and 123. The ceramic sprayed on the mating sides of the first and second screens 120 and 121 provides a double protection against shorting of the screen metals.

As the sweep gas stream passes through the screen assembly in the sequence of the present invention, the agglomerated smoke collects on the outside surface of the screen 122, which screen 122 acts as a baffle. The smoke particles continue to form a smoke layer in the upstream direction until it reaches the first screen 120. The smoke particles collected on the first and second screens 120 and 121 come into contact with the bare metal of the two screens 120 and 121. Because of the high conductivity of the smoke, an electrical circuit is formed and current flows through the smoke layer. The smoke is heated to a high temperature in 3 to 6 seconds and is incinerated quickly due to the presence of oxygen in the scavenging air stream.

To improve the incineration process, the bare metal of the second and third screens 121 and 122 may be coated with platinum. The precious metal coating greatly improves the incineration process by reducing the ignition temperature of the smoke. Furthermore, the platinum coating keeps the incineration process efficient despite the low oxygen content in the exhaust gas. The byproducts of the incineration process are CO and CO₂And steam, all of which are harmless gases and may pass through the third screen 122.

The formation of ash potentially affects the function of the incinerator because it gradually forms in the space between the first and second screens 120 and 121. Most of the ash is shaken off by the vibration and falls into the cavity at the bottom of the incinerator. The remaining ash that clogs the screen assembly can be removed by a conventional maintenance process using back pressure pulsations.

The incineration process occurs only in localized areas where smoke formation reaches the point where an electrical circuit can be formed. This makes the incineration process intermittent and somewhat continuous. The incineration process is believed to occur in a controlled environment due to the very low flow velocity over the synthetic screen, the distribution of smoke over a large area of the screen, the small amount of smoke being incinerated, and the thermal inertness of the first and second screens 120 and 121. It was observed that the exhaust gas temperature did not increase significantly between the upstream side and the downstream side of the incinerator. Further, the material selected for the screens 121 and 122 is stainless steel, which has high corrosion resistance at high temperatures and high resistance to chemicals that prevent attack by carbon and sulfur. A selected special grade alloy, such as the commercial grade known as a grade a alloy, with higher nickel, chromium and aluminum is sufficient for the screen material.

The scavenging flow leaving the converter employing an incinerator is cleaned of particulate matter and may be used as Exhaust Gas Recirculation (EGR) and thus passed to the engine intake after passing through an air filter element. The vacuum pressure after the air filter is a large enough driving force to create a scavenging (EGR) flow. This system arrangement is completely passive. However, EGR flow is small and uncontrollable, NO_xThe amount of reduction is small, in the range of 15-20%. Furthermore, when the engine is at idle, no EGR flow is formed because the negative pressure behind the air filter element is very small.

G. Smoke collecting chamber

Another preferred embodiment as a replacement for incinerators is the use of a fume collection chamber 170, as shown in fig. 13 and 14. The smoke chamber 170 is a simple chamber having an outlet at the bottom 171 for the scavenging air flow and a second outlet 173 at the upper side for the clean exhaust air. The clean exhaust gas leaving the chamber becomes exhaust gas recirculation as previously described.

The smoking chamber has two chambers separated by a screen 174. The screen 174 acts as a smoke barrier. In addition to the small sweep flow, the screen 174 is selected to have a large surface area and to have an interstitial space of less than about 50 microns, which results in very low flow velocities over the screen. This allows the screen 174 to act as a barrier to agglomerated smoke. The smoke is formed on the surface of the screen 174 in the shape of a layer (block). As layers of smoke are continuously formed on the underside of the screen, these smoke layers eventually fall into the bottom of the chamber due to vehicle vibration and impact loads.

The process of releasing the smoke layer can be enhanced by using a system with a spring and a steel ball that vibrates at its own natural frequency. The vibration system is excited by the load and engine vibrations. The smoke box may be designed to collect smoke produced by a truck operating for 3 to 6 months, depending on the level of engine smoke emissions. The smoke collects in the bottom half of the chamber, up to the screen. The chamber may employ an incinerator. The smoke chamber incinerator consists of two staggered rows of stainless steel tubes which are coated with platinum and the furnace is placed in the bottom. The lower row is grounded and the upper row is connected to a 12 or 24V power supply. The smoke bridging the gap between the ground pipe and the power pipe is continuously incinerated. The incinerator used in the smoke chamber is stable and simple in design. The incinerator by-product is a harmless gas that is recycled to the engine intake as part of the EGR system.

SO conversion for diesel applications (where an active platinum oxidation catalyst is used)₂Oxidation to sulfate compounds and smoke collection should replace the incineration process. This is convenient since the sulfate compound cannot be incinerated. Sulfated compounds are recirculated into the engine as part of the EGR, which can result in undesirable damage to the engine's air intake system. This results in one such preferred embodiment: the smoke is collected in a smoke chamber and then eventually processed into smoke spheres in a smoke processing drum 220 for eventual sale as commercially known carbon black. By connecting the second outlet 178 at the bottom of the chamber 170 into the smoke handling drum 220, the smoke chamber 170 is emptied, the tail pipe of the truck is temporarily plugged, and the engine is operated at near idle for approximately 5 minutes. The engine exhaust flow sweeps the collected smoke at the bottom of the smoke chamber 170 into the smoke drum.

H-shaped smoke treatment drum

Some applications, where it is advantageous to collect the smoke rather than incinerate it, require the use of a smoke treatment drum as shown in figures 17 and 18. The function of the drum 200 is to separate and collect the smoke at the bottom of the cavity and to compress it periodically until a compressed solid ball is formed. The balls are shipped in containers (plastic bags) and sold as commercial products to the chemical industry for applications such as printing. Sulphate and sulphamic acid fumes are collected together and the spheres may be brown in colour.

The smoke drum 200 has an inlet flow distribution auger. Two or four concentric conical baffle screens 202 fit into the enclosure. The rear side of the screen 202 is connected to an outlet manifold 203. The outlet manifold 203 is connected to a vacuum booster blower 204 which is used to generate a sufficient vacuum level to drive a minimum amount of flow through the drum 200.

When the agglomerated smoke collects on the screen 202, a smoke layer is formed and the back pressure on the screen 202 increases. Therefore, a mechanism is required to blow off the smoke layer. Two preferred embodiments may be employed: a back pressure pulse as shown in fig. 17, or a screen shaker as shown in fig. 18.

The back pressure pulse is created by a small compressor 205, which compressor 205 delivers compressed air to an air tank 206. An air box 206 opens to the rear of the screen 202 and compressed air is released through a control valve 207. The valve 207 is periodically actuated to allow pulses of high pressure air to flow to the back side of the screen 202, thereby releasing the smoke layer. The released smoke falls into the bottom of the cavity. A spring loaded check valve 208 is employed to prevent pulse air bypass.

In the core of the drum 200, a motor-operated shaft 209 drives a tensioner 210 down to compress the falling smoke into the cylindrical cavity until a certain calibration load is reached. The motor is stopped and the impactor is returned to the upper position in preparation for the second cycle. After repeating some compaction cycles, the pellet grows until it reaches a certain height. An electrical signal is developed representing the entire ball and another motor-operated shaft 211 moves the bottom retainer plate 213 away from the cavity. In subsequent cycles of operation of the motor shaft 209, the impactor drives the ball into the bottom platform 214. The pellets are released into the bag 212 for movement and transport.

The operation of the two motor shafts is controlled by means of a microcomputer (not shown) having logic to indicate the sequence of steps. When it is connected to the smoke collection chamber, the smoke treatment drum control is driven. For truck applications, the process of evacuating the chamber takes an average of 5 minutes. Since loading the smoke chamber requires trucks to operate for 3 to 6 months, the smoke treatment drum can service many trucks, 10 to hundreds.

Another preferred embodiment for releasing the smoke layer is a mechanical pulser or shaker, as shown in fig. 18. The mechanical shaker 218 sufficiently removes the tobacco pieces from the screen 202. For applications where the VOC content is high and the smoke is wet, a reverse pulse spray method is desirable. On the other hand, where the VOC fraction is small and the smoke is relatively dry, the mechanical pulser/shaker approach is preferred because it is relatively simple and inexpensive.

I particle converter-like agglomeration/filtration

Similar agglomeration/filtration particle converters are used in applications with motive sources. The particle converter has one or more chambers. Fig. 20 shows a transducer with two chambers, which shows a preferred embodiment for a major underground mobile application. In a two-chamber configuration, the intake air flow is divided into two chambers. Each flow section is directed toward a synthetic wire mesh or similar synthetic fleece and filter screen media, as shown in fig. 24A and 24B. The synthetic steel wool (wool) media is characterized in that it may be a coalescer media having low pressure drop and having less smoke retention capacity. On the other hand, a retaining screen with suitably sized openings is used, which increases the filtering function. The screen causes the smoke to accumulate on the upstream side of the exhaust gas stream, depending on the exhaust gas temperature and the ratio of the VOC fraction in the smoke. The accumulated smoke may form a cake. These phenomena improve the smoke retention/smoke collection efficiency of the synthetic wire mesh media; and with an accompanying increase in pressure drop.

The flattened, similar agglomeration/filtration converter shown in fig. 19 has inlet air 255 to convert and expand the inlet flow into the chamber. The chambers are separated by a separation plate 257. Each chamber has a similar coalescing/filter media 258. The driven sliding door mechanism 265 is shown in fig. 23. The outlet 271 collects the cleaned exhaust gas and conducts it out through a pipe. Passive incinerator 280 embodiment B is shown in fig. 25.

The similar agglomeration/filtration media of fig. 19 can be formed in one layer or multiple layers having different design objectives. For maximum smoke retention and efficiency, the upstream layer is therefore designed to capture the larger particles. The downstream layer is designed to trap smaller particles. This will result in a nearly uniform smoke load throughout the media and reduce the formation of back pressure as opposed to smoke load. Fig. 24A and 24B each show three layers of steel wool and screen.

The steel wool of the upstream layer has an average fiber diameter (also called average hydraulic fiber diameter) of 16-25 microns and has a packing density (defined as the percentage of the weight of the steel wool to the weight of solid steel of the same volume) of 3% -6%. The screen has a mesh count (mesh count is defined as the number of openings per inch) of 50 x 50 or 20 x 50. The latter layers have smaller fiber diameters, higher packing densities and higher mesh counts per inch such as 25-32um fiber diameter, 4% -8% packing density and 75 x 75, 100 x 100 mesh or 40 x 100 mesh. Smoke with a higher percentage of VOC compounds requires a larger fiber size, a smaller packing density and a smaller mesh count to cope with the "sticky effect" which increases the pressure drop.

Another preferred embodiment of a similar agglomeration/filter particle converter is a circular configuration as shown in fig. 22. An embodiment of the wire mesh medium is based on a cylindrical design, in which the wire mesh is cylindrical, the separator sheet is cylindrical, and the housing is also cylindrical. The transducer may have one or more chambers. This embodiment is desirable in certain truck applications such as those having a vertical muffler. Figure 22 shows a typical circular structure with two chambers. All elements and logics of the circular embodiment are substantially the same as those of the flat embodiment.

J reverse pulse injection system

When the synthetic wire mesh/steel wool medium is loaded with smoke on the upstream side, the smoke dendrites move in the direction of the flow stream. The downstream layer of media is eventually laden with smoke and, beyond a certain threshold, the smoke begins to blow off (as agglomerated particles). As a result, the smoke collection efficiency of the medium is reduced, which finally has a very small value.

Once the smoke begins to blow away, a reverse pulse jet is driven. This condition is triggered once a pressure drop threshold on the transducer is reached. By pulsing high pressure compressed air on the downstream side of the wire mesh, the collected fumes are blown off in the opposite direction of the incoming untreated exhaust flow. The reverse pulse jet is designed to blow off a sufficient amount of smoke to allow the web media to discharge the accumulated amount of smoke. The blown-off smoke is placed into the bottom of the chamber by gravity. To prevent the smoke from being agitated by the incoming exhaust gas, a perforated screen may be inserted into the lower chamber of each chamber. The smoke falls through the perforations in the screen. The exhaust gas passes through the top of the screen while the smoke contained at the lower portion of the screen is collected because no flow is generated. Ideally, the pulsations of compressed air are generated in the lower exhaust gas flow, for example, during idle conditions or during engine shut-down conditions. It is desirable to maximize the effectiveness of smoke removal. The exhaust flow is in the opposite direction to the direction of the pulsating air and therefore the exhaust flow has the opposite effect on the pulse injection. Furthermore, to maximize the effectiveness of the pulse injection, sliding doors may be used on the clean exhaust outlet of each chamber. During the pulse, the door is temporarily closed for one to two seconds to ensure that all the pulsed air passes through the wire mesh media.

Control logic for K-pulse injection system

The main method of the control logic of the present invention is to remove the smoke accumulated on the wire mesh media when the threshold is reached, pulse the media and return it to the original condition to begin another loading cycle. In real life, during operation of the vehicle, the smoke load on the medium is measured by a pressure drop measurement on the medium. However, the pressure drop can also be influenced by the exhaust gas flow. Since it is desirable to limit the pressure drop during operation of the vehicle, a simple logic based on pressure drop measurements is employed by employing a pressure switch. When the threshold is reached, the pressure switch drives the circuit. The momentary high pressure drop is not indicative of the smoke load on the media. However, during cyclic vehicle operation, repeated high pressure drops may be used to measure the threshold smoke load in the medium. The control logic is based on the duration of the addition when a threshold of high pressure drop is reached, and begins the pulsing process when the total time accumulation reaches a predetermined value. A typical threshold for high pressure drop is in the range of about 40-60 inches of water. In the case of this pressure threshold or greater, a typical threshold for accumulation time is in the range of 3 to 5 minutes. An exemplary control logic for reverse pulse injection is shown in fig. 26.

When these conditions relating to the start of the pulse injection cycle are satisfied, and the start process is driven, other conditions have to be satisfied. The first condition relates to engine RPM. The engine RPM has to approach idle speed or shut down the engine. Since the pulsing process is less than one second, a small RPM condition is instantaneously satisfied, which can be conveniently achieved once the vehicle is stopped. The second condition relates to the time required to refill the compressed air tank to pulse the next chamber. The time interval is two to 10 minutes depending on the source of compressed air on the vehicle. The control logic diagram is shown in fig. 26.

L incinerator-preferred embodiment B

An incinerator particularly suited for flat or round embodiments is shown in figure 4. The incinerator comprises a series of plates, electrically insulated from each other and alternately charged. The plates may be solid plates or perforated plates. Furthermore, it is desirable that the plates be formed of high temperature resistant stainless steel and coated with a highly active catalyst such as platinum. Where incinerators are used, it is desirable that the flat converter be slightly inclined to facilitate movement of smoke into the incinerator under the influence of gravity, exhaust gas pulses and the resulting rocking and vibratory loads on the road. Once the smoke bridges the gap between adjacent plates with opposing loads, the incinerator is driven. This increases the discharge of the current, which results in a more rapid incineration of the smoke.

The incinerator is large enough to store ash, incineration by-products. It is estimated that incinerators require periodic disassembly and ash removal. Such a cleaning interval may be anywhere in the range of 25,000 to 150,000 miles of vehicle travel, depending on the basic particulate discharge and drive cycle.

M exhaust gas recirculation

Exhaust Gas Recirculation (EGR) in the present invention solves a major problem commonly encountered with EGR in diesel applications. The first problem relates to the case: under idle and light load engine operating conditions, the pressure on the EGR terminal is not large enough, which reduces the flow required for the target NOx reduction. Such conditions are prevalent at idle and under light engine load conditions. Installing an efficient axial flow booster blower 241 can solve this problem. Blower 241 delivers the required flow rate to achieve the desired NOx reduction and to ensure continuous sweep flow at all engine operating conditions. Upon adjustment to a high engine load condition, blower 241 will throttle the EGR flow due to the high pressure differential across the EGR terminals, acting almost as an EGR control valve, and therefore consuming virtually no power. It regulates power consumption at idle and low engine load conditions.

EGR flow is controlled by a simple control device 242, which device 242 has logic based on an engine RMP signal 243 and a throttle position signal 244. This arrangement is particularly preferred for diesel retrofit applications. The EGR control logic is greatly simplified compared to the OEM logic. The EGR logic of the present invention is based on maximum NOx reduction and minimum fuel consumption, but can increase visible emissions such as particulate, HC, and CO. The amount of visible base emissions and particulate increase is reduced by the converter system.

An EGR system for a similar caking/filtration converter employs a converter valve 276. The position of the converter valve is controlled by means of signals from the ECU as shown in fig. 20. The unique design of the converter valve enables the EGR flow to be accurately delivered into the tailpipe by restricting the flow area, thus increasing the pressure, and delivered into the engine intake within the EGR tube. The EGR flow is injected before the intake filter. Such an arrangement removes the escaping agglomerate particles even further before they enter the engine air intake system.

The EGR method of the present invention solves the main known problems related to EGR and is summarized as follows: (1) EGR flow is increased and controlled with a boost blower; (2) the EGR flow is free of contaminants that can foul or contaminate the engine intake system; and (3) the exhaust gas is cooled to a low temperature before entering the particulate converter. The EGR return line provides additional cooling. Exhaust gas recirculated back into the engine may be considered sub-cooled EGR to address issues related to volumetric efficiency and engine performance.

N water scrubber

Where water is available, water is injected into the exhaust pipe behind the converter to capture reactive NO from the exhaust stream₂A gas. The water scrubber may also capture sulfate compounds. Adding alkali to water to increase NO₂The capture effect of (1).

O System operation

In most stationary applications, the system of fig. 1 and 2 may be employed. The system includes a small diesel oxidation catalyst, a cooled exhaust pipe, and a particulate converter. During the engine start-up phase, temporary heavy smoke is generated and the oxidation catalyst is not active, but a significant amount of VOC compounds are relatively cold. In other words, these VOC compounds and particles condense into the shape of liquid or solid nanoparticles. These particles are efficiently collected and agglomerated in the agglomerator. Cooling the tubes during engine warm-up may provide less or no appreciable cooling effect. At small engine loads, and during idle conditions, exhaust gas temperatures and flow rates are small. As a result, the centrifugal separation effect in the circulation separator is greatly reduced, which impairs the centrifugal separation of the particles. However, this phenomenon is balanced by two other phenomena: retains the smoke in the agglomerator and significantly reduces turbulence and vortex effects. When the exhaust gas flow is small, for example at engine idle, the aerodynamic drag forces on the smoke dendrites interlaced on the wire mesh are greatly reduced. This will result in reduced smoke movement in the composite wire mesh media and a reduced change of the mode of operation of the agglomeration to the retention mode. In this case, the agglomerator acts as a filter. Turbulence and eddies are also reduced. The net effect is still to remove particulate and VOC compounds from the exhaust.

As the engine warms up and the engine load increases, the exhaust gas temperature and flow rate increase. This drives the oxidation catalyst, resulting in the burnout of hydrocarbons, carbon monoxide, and small amounts of VOC compounds. The cooling tube provides the function of: the exhaust gas temperature is reduced to a target low temperature of 250F to 300F under subsequent engine operating conditions.

Cooling the exhaust gas to 250F-300F can reduce the exhaust gas flow at full load by 40%. In addition, the reduction in the viscosity of the exhaust gas was 40% by cooling the exhaust gas at 1000 ℃ F. to the range of 300 ℃ F. to 250 ℃ F. The net effect is to reduce the pressure drop across the particle converter by a factor of up to 3.1 compared to that of a converter without cooling tubes. This factor is extremely important for meeting the engine maximum allowable back pressure specification and it results in reduced fuel consumption. Since the converter can provide a sound damping function, the muffler can be replaced by a converter system, the back pressure in both cases being the wash flow. The net effect is that fuel consumption is not increased in the case where the muffler is replaced with a converter.

Wire mesh agglomerators have heretofore been the most effective media for capturing submicron particles, as compared to other known filter media. The mechanism of particle capture in wire mesh media is divided into three modes: inert impingement, interception and diffusion. The first two collection modes are not effective for small particle size but have considerable single fiber rates once the particle size increases. Diesel exhaust is characterized by very small particles, with an average size of 0.1 micron and apparently a large number of nano-sized particles. The diffusion collection mode of the particles is formed as the primary mode that traps diesel soot particles. Small particles exhibit considerable random diffusive motion, known as brownian motion, and these particles collide with gas molecules and thus tend to deviate from the gas streamlines. Finally, the particles are deposited on a rigid surface, such as a fiber surface, or the smoke is deposited between fibers upon collision with the rigid surface. Equations representing the small particle single fiber collection efficiency (diffusion mode) and the total collection efficiency are given by the following equations:

due to diffusion (xi)_d) The resulting single fiber collection efficiency was:

ξ_d＝2.7Pe^-2/3[1+0.39K^-1/3.Pe^1/3.Kn]+0.624Pe^-1

here, Pe is the peclet number, which is given by the following equation: Pe-Vd_f/D

Where V is the linear velocity of the gas, d_fIs the effective fiber diameter, and D is the diffusion coefficient or particle diffusivity, which is calculated by the following formula:

D＝C K_b T/3πμ_g d_p

where C is the Cunningham correction factor, K_bIs the Boltzman constant, T is the absolute gas temperature, μ_gIs the gas viscosity, d_pIs the particle diameter, and K_nIs the Knudsen number, which is calculated by the following equation:

K_n＝2λ/d_f

where λ is the mean free path of the gas molecule, d_fEffective fiber diameter.

The total collection efficiency in the fiber medium is given by the following equation:

ξ_l＝1-EXP^-4ξ _d ^αH/πd _f

here, α is the fiber packing density, and H is the filter thickness.

The above formula is only for the diffusion mode of particle collection, which is the dominant mode. The other two modes or particle collection may simply not be considered because their effect is small, but when considered, the overall collection efficiency is somewhat higher. The different values of particle size are used to solve the above equation: as the particle size decreases, the individual fiber efficiency increases exponentially. For example, a particle size of 1.0 micron has an individual compacted fiber efficiency of 0.001. Particles having a size of 0.1 micron had a single fiber rejection of 0.0007 and a single diffusion fiber rate of 0.05. Particle size sizes in the nano-range, such as 0.02 microns (20 nm), have a single fiber rejection of 0.0001, while single particle diffusivity is 0.300. These figures are for the typical case of wire mesh media, where α is 0.005 and d is_f10 microns, V8 cm/sec, T200 degrees.

It should also be noted that the foregoing formula applies to green fiber media (i.e., no smoke dendrite formation). Once the smoke begins to form on the fibrous media, it acts as another fibrous media with very small fiber size, further increasing the particle capture efficiency. The capture efficiency of the nanoparticles can be as high as 10⁵Size step (i.e., only one particle passes through the fiber media from 10)⁵By the number of particles captured) are used. Furthermore, in the agglomerator design, the wire size is large and the scavenging air space between the wires exceeds 50 microns. This feature allows collected/trapped dendrites to proceedMove until they exit the fiber media. The effect of trapped smoke dendrites on the fibrous media is shown by experimental data to be the primary mode of particulate collection compared to metal fibers. This has led to the term green agglomerator which relates to new fiber media.

One of ordinary skill in the art will appreciate that the primary difference between the filter and the agglomerator is the retention efficiency, which should be high in the filter and 0 in the agglomerator. In diesel applications, the flow rate varies significantly between idle and full load. At idle, the agglomerator acts as a filter medium due to the low flow velocity and accumulates a significant amount of smoke. At full load, the agglomerator blows more agglomerated smoke dendrites than the incoming smoke. However, over a wide range of operation including idle, medium load and full load conditions, the average agglomerator retention (collection) rate is zero. Where smoke is blown off at a certain point, in the agglomerator, this situation is self-correcting. Where the smoke is blown off, more flow is rushed into that area, thus more smoke is formed, until an equilibrium condition is achieved by equilibrium of the medium. The back pressure in the particle converter can be increased by approximately 50% at an idle speed extended by 5 hours. When the engine speed increased from 800RPM to 1100RPM in 5 to 10 seconds, the backpressure decreased by 40%. This is a self-correcting mode of excessive smoke formation.

The agglomerated particles can enter the electric incinerator where incineration occurs when smoke formation reaches a threshold, i.e. a point of passage into the electric circuit. The streaming immediately heats the smoke due to its higher electrical conductivity. When oxygen is present in the exhaust gas and platinum is coated on the incinerator grate (screen), the smoke is incinerated very quickly at low temperatures, typically within 3-5 seconds. Since incineration is localized and intermittent on the incinerator grid, the temperature rise downstream of the incinerator is insignificant. Furthermore, since a limited amount of smoke is incinerated at a given location, there is a limited amount of oxygen in the exhaust gas and the exhaust velocity on the grid is very small, local temperature increases are regulated and do not cause damage to the grid. The by-product of incineration is CO₂、H₂O and ash. The ash falls into the bottom of the incinerator chamber due to vibration and gravity. Because of the large size of the chamber, ash accumulations traveling 200,000 to 400,000 miles can be stored before the chamber needs to be cleaned. However, the recommended cleaning interval is 150,000 to 200,000 miles.

The exhaust gas leaving the incinerator is free of particulate matter and is cold. They can be used as EGR to moderately reduce NOx emissions. If the greater the reduction in NOx, the better, then boost pumps are used to boost and control EGR flow. The control logic of the booster pump allows for keeping the scavenging flow at a small engine load and ensuring that a suitable amount of exhaust gas flow is recirculated for maximum NOx reduction. To minimize the impact on fuel economy, EGR flow is therefore controlled at all engine operating conditions. Minimization of particulate engine emissions has no EGR control logic because the aftertreatment system treats these excess emissions very efficiently.

In stationary, marine and flooded diesel applications where sufficient cooling water is available, it is possible to increase NOx reduction beyond that produced by EGR. In this case, it is recommended to use an active platinum oxidation catalyst. The catalyst is used for removing SO₂To sulphate and, depending on the exhaust gas temperature, 50-70% of the NO is oxidized to NO₂. So long as the exhaust gas is cooled to a temperature below the sulfate condensation temperature and is collected with the particulates of the converter, the sulfate is collected with the particulate matter. The exhaust gas exiting the converter may be flushed with water to reduce the exhaust gas temperature to 200-. This allows for the capture of the reacted NO by water₂A gas. Ideally, the alkali substance is added to the water. NO is reduced₂Dissolution into water can result in the formation of nitric acid. The highly diluted portion of nitric acid has no significant effect on larger bodies of water and may be beneficial for irrigation applications. In summary, sulfuric acid and particulates collect in the flue chamber while the nitric acid is partially expelled and dissolved in water rather than being expelled into the air.

Small diesel applications (which perform transient modes of operation) need to accommodate reduced aftertreatment hardware. The important factors are the size and complexity of the hardware. This results in another embodiment using a similar cake/filter media. The media is characterized by a low filtration efficiency, but an increased collection efficiency when the first layer of smoke is collected. The presence of the filter screen increases the collection efficiency because the smoke layer collects on the upstream side of the screen. The smoke collection efficiency remains substantially constant for a longer period of time, which varies from 8 to 40 operating hours, depending on engine emissions. Thereafter, when the composite media is saturated with smoke, the smoke begins to be blown off and the pressure drop continues to increase. At a certain pressure drop threshold, the media needs to be regenerated or regenerated to the original condition, which is equivalent to the beginning of the smoke load cycle, and some smoke remains in the composite media to maintain high smoke collection efficiency. This results in a technique that can employ reverse pulse ejection. Typical collection efficiency and backpressure characteristics for similar media are shown in fig. 27, which show the effect of reverse pulse injection and the start of a new duty cycle.

The reverse pulse jet technique is most particularly characterized in that it lasts for fractions of a second; it may be driven when the engine is off or at idle. This maximizes the effect of the reverse pulse injection as it flows in the opposite direction of the exhaust flow. In this way, the exhaust flow attenuates the effect of the reverse pulse injection. Once the pulse jet is driven, the smoke is blown from the media to the upstream side and the media is rejuvenated and ready for another cycle of smoke filtration and collection.

Experiments conducted on a similar cake/filter converter on an old 1985 diesel truck showed that on the "green" converter, the smoke filtration efficiency was 40%. After accumulating about 400 miles, the efficiency rose to 90%. Continuously working for an additional 500 miles, the back pressure can be raised to 60 inches H at 55mph₂And O. The system is then pulsed by compressed air. After that, the collection efficiency did not significantly improveAnd (6) changing. It is also observed that vibrations are generated by levitation on the transducer due to road conditions, which vibrations are related to the reduction in the speed at which the pressure drop is formed as a function of mileage. Upon inspection of the device, larger cake formation was observed on the synthetic media and filter screen. The aforementioned smoke mass falls out of the medium due to the vibrations generated by the road, which vibrations can reduce the back pressure. After 1000 miles of travel, approximately three pounds of smoke could be removed from the bottom of both chambers.

When a converter is used in an incinerator, the converter is mounted at an incline so that the incinerator is at the lowest position to facilitate movement of smoke into the incinerator chamber. Such converters with incinerators are expected to be maintenance-free devices that require cleaning of the accumulated ash every 150,000- & 200,000 miles.

The converter with the smoke collection bag 272 shown in figure 21 does not necessarily require an incinerator. These converters also do not have to have such a reverse pulse injection system: the system is installed as an integral part of the converter. Of course, the pulse system may be stationary and used to service a variety of vehicles. The reverse pulse air system is driven by the tailpipe and the pulse injection works simultaneously in all converter chambers. The size of the bag should be sufficient to expand to accommodate the volume of the pulse of air at ambient temperature. The pulsed air sweeps the fumes collected in the bottom of the converter into the bag. For this operation, smoke is swept into the pocket during the course of each reverse pulse. When the bag is filled with cigarettes, it can be replaced with an empty bag. It is estimated that the bags are replaced every 6-30 months, depending on the basic discharge. This system arrangement is attractive for retrofit to motor truck and bus applications when these vehicles are installed at service stations at least once a week.

Of course, the description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.

Claims (10)

1. A diesel exhaust aftertreatment system for removing controlled and uncontrolled pollutants from the exhaust of a diesel engine, the system comprising:

a diesel particulate converter having an agglomerator for agglomerating particulate matter, the agglomerator being formed of a synthetic wire mesh media, the particulate converter also having a region for collecting smoke;

an exhaust gas cooling system for cooling the exhaust gas; and

an air pulse system in fluid communication with the diesel particulate converter.

2. The exhaust aftertreatment system of claim 1, further comprising an exhaust gas recirculation system fluidly connecting exhaust gas exiting the particulate converter to the diesel engine, and a valve selectively diverting exhaust gas from the particulate converter to the exhaust gas recirculation system, wherein the exhaust gas exiting the particulate converter has been subcooled and substantially cleaned of any hard-to-capture pollutants.

3. The exhaust aftertreatment system of claim 1, further comprising an oxidation catalyst upstream of the particulate converter.

4. The exhaust aftertreatment system of claim 1, wherein the synthetic wire mesh has a variable wire size and a dense density, the agglomerator wires and density having a spacing in excess of 50 microns.

5. The exhaust aftertreatment system of claim 1, further comprising:

a sensor for detecting a pressure drop across the particle converter and generating a control signal in response to the pressure drop exceeding a predetermined value; and

a controller for activating the air pulse system to remove particulate matter from the wire mesh media.

6. The exhaust aftertreatment system of claim 1, wherein the air pulse system is a reverse pulse injection system having a compressed air tank and a pulse valve within or outside of the particulate converter, wherein the pulse air entering from the compressed air tank blows soot from the media.

7. The exhaust aftertreatment system of claim 1, further comprising a soot collection chamber having a retarding screen for collecting agglomerated soot, wherein accumulated soot cake on an upstream side of the retarding screen falls to a bottom of the soot collection chamber.

8. The exhaust aftertreatment system of claim 1 further comprising an incinerator in the particulate converter to incinerate the soot.

9. The exhaust aftertreatment system of claim 1, wherein the exhaust cooling system includes a radiation mode cooling section that cools the exhaust with an ambient air source, a first convection mode cooling section that cools the exhaust with a liquid source, and a second convection mode cooling section that cools the exhaust with a liquid source, the radiation mode cooling section having a portion with a black outer surface.

10. The exhaust aftertreatment system of claim 1, wherein the diesel particulate converter has a first chamber and a second chamber separated by a partition, each chamber having an agglomerator.