US20010003898A1

US20010003898A1 - Method and apparatus for reducing pollutants

Info

Publication number: US20010003898A1
Application number: US09/780,955
Authority: US
Inventors: Robert Miller; Robert Caren; Jack Ekchian
Original assignee: Lockheed Martin Corp
Current assignee: Lockheed Martin Corp
Priority date: 1996-12-09
Filing date: 2001-02-09
Publication date: 2001-06-21

Abstract

A method and apparatus are provided for improving the conversion efficiency of a catalytic converter for treating exhaust gases produced from the combustion of a fuel to at least reduce pollutants from incomplete combustion, wherein the reduction in pollutants is achieved by the introduction of ozone, upstream from the catalytic converter, to improve the efficiency of the catalytic converter.

Description

This is a continuation of application no. 09/414,452, filed Oct. 7, 1999 which is a continuation of application Ser. No.09/103,249, filed Jun. 3, 1998, now U.S. Pat. No.6,012,283 which is a continuation of application Ser. No.08/761,955, filed Jun. 28, 1996, now U.S. Pat. No. 5,806,305. [0001]

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a method and apparatus for reducing pollutants by improving the conversion efficiency of a catalytic converter for treating exhaust gases produced from the combustion of fuels, and more particularly, to such a method and apparatus wherein the reduction in pollutants is achieved by the use of ozone.

2. Background

Internal combustion engines, which operate by the controlled combustion of hydrocarbon fuels, produce exhaust gases containing complete combustion products of CO ₂and H₂0 and also pollutants from incomplete combustion, such as CO, which is a direct poison to human life as well as unburnt hydrocarbons (HC). Further, due to the very high temperatures produced by the burning of the hydrocarbon fuels, thermal fixation of nitrogen in the air results in the detrimental formation of NO_x.

The quantity of pollutants varies with many operating conditions of the engine but is influenced predominantly by the air-to-fuel ratio in the combustion cylinder such that conditions conducive to reducing carbon monoxide and unburnt hydrocarbons (a fuel mixture just lean of stoichiometric and high combustion temperatures) cause an increased formation of NO _xand conditions conducive to reducing the formation of NO_x(rich fuel mixture and low combustion temperatures) cause an increase in carbon monoxide and unburnt hydrocarbons in the exhaust gases of the engine. As a result, within the region of stable operation of the internal combustion engine, a significant amount of CO, HC and NO_xis emitted into the atmosphere.

Although the presence of pollutants in the exhaust gases of internal combustion engines has been recognized since 1901, the need to control internal combustion engine emissions in the U.S. came with the passage of the Clean Air Act in 1970. Engine manufacturers have explored a wide variety of technologies to meet the requirements of the Clean Air Act. Catalysis has proven to be the most effective passive system.

Auto emission catalytic converters are typically located at the underbody of the automobile and are situated in the exhaust stream from the engine, just before the muffler, which is an extremely hostile environment due to the extremes of temperature as well as the structural and vibrational loads encountered under driving conditions.

Nearly all auto emission catalytic converters are housed in honeycomb monolithic structures that are generally made of cordierite, a low-thermal-expansion ceramic with excellent strength and crack resistance under thermal shock. The honeycomb construction provides a relatively low pressure drop and a high geometric surface area that enhances the mass-transfer-controlled reactions.

An adherent washcoat, generally made of stabilized gamma alumina into which the catalytic components are incorporated, is deposited on the walls of the honeycomb. The active catalyst contains about 0.1 to 0.15% precious metals, primarily platinum (Pt), palladium (Pd) or rhodium (Rh). The honeycomb is set in a steel container and protected from vibration by a resilient matting.

The first generation of catalytic converters, from 1976 to 1979 focused solely on the oxidation of CO and HC.NO _xwas decreased by engine modification and operating conditions and not addressed by use of catalysis. In contradistinction, the second generation of catalytic converters, from 1979 to 1986, not only oxidized CO and HC, but also reduced NO_x.

Because NO _xreduction is most effective in the absence of 0₂while the abatement of CO and HC requires 0₂, the construction of an effective means of reducing these emissions requires that the engine be operated close to the stoichiometric air-to-fuel ratio, because, only under these conditions can all three pollutants be converted simultaneously. The use of an oxygen sensor, which is positioned before the catalyst, makes it possible to maintain the air-to-fuel ratio within the narrow window required so that three-way catalysis (TWC) is possible.

Because the exhaust oscillates from slightly rich to slightly lean as a result of system time lag in adjusting the ratio, an oxygen storage medium is added to the washcoat that adsorbs (stores) oxygen during the lean part of the cycle and releases it to react with excess CO and HC during the rich portion. CeO ₂is most frequently used for this purpose due to its desirable reduction-oxidation response.

TWC technology for simultaneously converting all three pollutants comprises the use of precious metals Pt and Rh (Pt-to-Rh ratio of 5-to-1), with Rh being most responsible for the reduction of NO _x, although it also contributes to CO oxidation along with Pt. The basic operation of the catalyst is to oxidize CO and HC to CO₂and H₂0 and reduce NO/NO₂to N₂.

Third generation converters, i.e., those from 1986 to 1992, evolved as auto operating strategies shifted to include greater fuel economy at higher operating speeds, by shutting off fuel during deceleration, which exposed TWC's to higher temperatures and a highly oxidizing atmosphere, causing Rh to react with the gamma alumina of the washcoat and form an inactive aluminate. Properly designed catalysts recover their activity to a great extent under rich fuel mixtures, however, Rh may also react with CeO ₂at high temperature, reducing the activity of both. This drawback is overcome by segregating the two in washcoats with multiple layers or by stabilizing the ceria with oxides of Zr, Ba and La.

In fourth generation TWC's, which began to appear in 1995, less expensive Pd was substituted for or used in combination with Pt and Rh. While the operation of fourth generation TWC's is consistent with prior catalytic converters, there is still a significant amount of pollutants emitted into the atmosphere by the catalytically treated exhaust gases of internal combustion engines.

The recent passage of the 1990 amendment to the Clean Air Act requires further significant reductions in the amount of pollutants being released into the atmosphere by internal combustion engines. In order to comply with these requirements, restrictions on the use of automobiles and trucks have been proposed, such as, employer compelled car pooling, HOV lanes, increased use of mass transit as well as rail lines and similar actions limiting automobile and truck utilization at considerable cost and inconvenience.

An alternative to diminished automobile and truck usage is decreasing emissions by increasing the efficiency of the internal combustion engine. This approach presents a considerable challenge because studies show that 70% of automobile originated pollution is contributed by only 30% of the vehicles on the road, these vehicles typically being older models having inefficient engines that inherently produce a lot of pollution. Moreover, these older vehicles oftentimes have difficulty passing required emission tests, resulting in an increased cost to the owner for tune-ups or new catalytic converters, such maintenance procedures sometimes failing to adequately cure the problem so that the vehicle still cannot pass the required emissions test.

In addition, while considerable gains have been made in recent years to reduce the amount of pollutants in the exhaust gases of the internal combustion engine of vehicles such as automobiles and trucks, it is difficult and expensive to further reduce the amount of pollutants in the exhaust gases of the internal combustion by increasing the efficiency of engines now being designed for use in new vehicles, even though exhaust emissions of automobiles and trucks currently being manufactured do not meet proposed Environmental Protection Agency standards.

In lieu of decreasing exhaust emissions by increasing the efficiency of the internal combustion engine or decreasing the use of automobiles, a further alternative would be to increase the efficiency of the catalytic converter, however, only minimal success has been achieved.

In this regard, the conversion efficiency of a catalytic converter is measured by the ratio of the rate of mass removal in the catalytic converter of the particular constituent of interest to the mass flow rate of that constituent into the catalytic converter. The conversion efficiency of a catalytic converter is a function of many parameters including temperature, stoichiometry, the presence of any catalysts' poisons (such as lead, sulfur and carbon) the type of catalyst and the residence time of the exhaust gases in the catalytic converter. At start-up the conversion efficiency of a catalytic converter is low.

SUMMARY OF THE INVENTION

One object of the present invention to provide a method and apparatus for reducing pollutants in the exhaust gases of an internal combustion engine having a catalytic converter by improving the conversion efficiency of the catalytic converter without the need for major modifications to the internal combustion engine or the catalytic converter.

Another object of the present invention is to provide a method and apparatus for reducing pollutants of incomplete combustion in the exhaust gases treated by a catalytic converter which are inexpensive to employ and manufacture, simple in structure and operation.

A particularly advantageous feature of preferred embodiments of the present invention is that it provides a relatively inexpensive way to reduce pollution by retrofitting those engine and catalyst combinations already on the road which contribute the most pollution and are most likely to fail an emission test as well as providing easy installation in new engine systems.

A further particularly advantageous feature of preferred embodiments of the present invention is that the improved efficiency of the catalytic converter is achieved by adding ozone to modify the composition of the gases entering the catalytic converter in real-time without the need to store special chemical additives on-board.

Yet another advantageous feature of preferred embodiments of the present invention is that it can be applied to a variety of different types of internal combustion engines, including, but not limited to, automobiles, trucks, stationary power generators, motorboats, motorcycles, motorbikes, lawn mowers, chain saws or leafblowers which may use a variety of different fuels such as gasoline, gasoline-based formulations, diesel fuel, alcohol, natural gas and any other fuel where a catalytic converter can be used to reduce at least one pollutant.

These and other objects, advantages and features of the present invention are achieved, according to one embodiment of the present invention, by an apparatus comprising: 1) a combustion chamber having a pre-combustion flow stream, including air, to the combustion chamber and a post-combustion flow stream of exhaust from the combustion chamber, 2) a catalytic converter for treating the exhaust gases to reduce the amount of at least one pollutant from incomplete combustion of fuel and/or oxides of nitrogen, and 3) a device for adding ozone to at least one of the pre-combustion flow stream to the combustion chamber and the post-combustion flow stream from the combustion chamber upstream from the catalytic converter to reduce the amount of the at least one pollutant in exhaust gases treated by the catalytic converter.

According to one embodiment of the present invention, the device for adding ozone comprises an ultraviolet light emitting lamp that emits light having a wavelength of about 185 nanometers which is inserted into at least one of the pre-combustion flow or post-combustion flow streams so that the oxygen in the intake air, air/fuel mixture and/or exhaust gases are exposed to ultraviolet light to generate ozone which enhances the conversion efficiency of the catalytic converter.

According to another embodiment of the present invention, the device for adding ozone is positioned remotely of the pre-combustion and post-combustion flow streams and ozone enriched air is piped into the combustion flow stream. In this embodiment, the device draws in ambient air independently of the operation of the engine, for example, using a pumping mechanism. The ambient air is converted to ozone enriched air by exposure, for example, to UV light, and added to at least one of the precombustion or the post-combustion flow streams in accordance with the teachings of the present invention. A particularly advantageous feature of this embodiment is that it provides the flexibility of installing the ozone generator at a convenient location in the engine compartment or elsewhere on the vehicle. Another advantageous feature of this embodiment is that the ozone could be introduced at most any desirable point in the intake or exhaust streams. A further advantageous feature of this embodiment is that the flow rate of ozone from the ozone generator is independent of engine speed, i.e., flow of air to the combustion chamber or flow of exhaust gases from the combustion chamber. Thus, at low engine speeds, the mass flow rate of ozone will not be affected by low air mass flow through the combustion chamber.

In accordance with the present invention, a method is also provided for improving the conversion efficiency of a catalytic converter for treating exhaust gases to at least reduce one pollutant from incomplete combustion produced from the combustion of a fuel in a combustion chamber having a pre-combustion flow stream of at least ambient air to the combustion chamber and a post-combustion flow stream of exhaust gases from the combustion chamber, the method comprising the steps of: adding ozone to at least one of the pre-combustion and the post-combustion flow streams at at least one point upstream from a catalytic converter for treating exhaust gases produced from the combustion of the fuel to at least reduce one pollutant from incomplete combustion, and treating the exhaust gases with the catalytic converter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side perspective view, of a known configuration of an internal combustion engine having a catalytic converter: [0031]
FIG. 2 is a side view, partially-in-section, illustrating one embodiment of the apparatus of the present invention wherein an ozone generating device is inserted into at least one of the pre-combustion flow or post-combustion flow streams; and [0032]
FIG. 3 is a front view, partially-in-section, illustrating a further arrangements of the apparatus of FIG. 2; [0033]
FIG. 4 is a block diagram illustrating another embodiment of the apparatus of the present invention wherein the device for adding ozone is positioned remotely of the pre-combustion and post-combustion flow streams and ozone enriched air is piped into the combustion flow stream; and [0034]
FIG. 5 is a block diagram illustrating the method of the present invention. [0035]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Referring to FIG. 1, a known configuration of an [0036] automobile engine 11 having a catalytic converter 13 is illustrated. The catalytic converter 13 is positioned at the underbody of the automobile (not shown) and is situated in the exhaust stream from the engine, downstream from the exhaust manifold 15 and just before the muffler 17.
The [0037] catalytic converter 13, as contemplated for use in the present invention, includes any device which is provided for treating exhaust gases from the combustion of a fuel, such as, for example, gasoline, gasoline-based formulations, diesel fuel, alcohol, natural gas and any other fuel where a catalytic converter can be used to reduce at least one pollutant from incomplete combustion, such as, for example, CO, and unburnt hydrocarbons (HC), and/or NO_x, including, but not limited to, a three way catalyst typically used in today's modem automobile engines.
The [0038] catalytic converter 13 comprises, therefore, any device that catalytically removes at least one pollutant from an exhaust stream generated by combusting a fuel, including, but not limited to, those with monolithic or granular ceramic substrates, metallic substrates, or substrates of any kind, and devices with noble metals or any other type of catalytic material. It would also include, without limitation, devices having semiconductor catalysts, such as, oxides or sulphides of transition elements, and devices having ceramic type catalyst, such as alumina, silica-alumina, and zeolites individually, in combination with each other or in combination with metal catalysts.
As is well understood in the art, an internal combustion engine draws in ambient air which is mixed with fuel for combustion in a combustion chamber or cylinder and the resulting exhaust gases are expelled. Ignition of the air/fuel mixture in the cylinder is typically achieved by an ignition device, such as, for example, a spark plug or the like, or adiabatic compression to a temperature above the fuel's ignition point. [0039]
The flow of air to any combustion chamber, including the flow of the air/fuel mixture if applicable, is hereinafter referred to as the pre-combustion flow stream, and the resulting flow of exhaust therefrom is hereinafter referred to as the post-combustion flow stream. As used herein, the pre-combustion and post-combustion flow streams are hereinafter collectively referred to as the combustion flow stream. [0040]
In certain internal combustion engines, such as for example, gasoline engines commonly in use today, air is inducted via an air intake duct or port which conveys the ambient air to a carburetor or fuel injection arrangement where the air is mixed with fuel to create a air/fuel mixture. The air/fuel mixture is then conveyed via an intake manifold to the combustion chamber or cylinder of the engine. In diesel-type engines and certain spark ignition engines, the air and fuel are mixed in the combustion chamber or cylinder of the engine. After the air/fuel mixture has been burnt, the resulting exhaust gases are expelled from the combustion chamber to an exhaust manifold. The exhaust gases are then conveyed, via at least one exhaust pipe to the catalytic converter where pollutants are removed. [0041]
Referring to FIG. 2, one embodiment of an apparatus of the present invention is illustrated generally at [0042] 19. The apparatus 19 comprises a device for generating ozone, for example, an ultraviolet light emitting lamp 21, for example, a mercury vapor arc lamp having a light transmitting envelope for transmitting ultraviolet light having a wavelength of about 185 nanometers, because this emission is capable of producing ozone in air.
The type of envelope preferred for transmitting light at a frequency of about 185 nanometers is fused silica or its equivalent, synthetic quartz. The [0043] lamp 21 is connected to a transformer 23, for example, a Bodine Model 12R25E/GS transformer, which converts 12 volt battery power to the voltage and frequency required to operate the lamp 21.
The [0044] transformer 23 is connected to the electrical system 25 of the engine 11 in order to provide power for operating the lamp 21. The transformer 23 is directly connected to the electrical system 25 of the automobile by splicing into the hot wire (not shown) of the system, for example, as original equipment on a new vehicle. Alternatively, the transformer 23 is connected to the electrical systems 25 by using a plug adapted to be inserted into a cigarette lighter receptacle in the passenger compartment of the vehicle.
In the [0045] apparatus 19 as illustrated by FIG. 2, the lamp 21 is positioned upstream from he engine's carburetor or fuel injection system, generally indicated at 31 in FIG. 1, for example, between an air filter 27 and air intake duct 29, however, the present invention additionally contemplates positioning the device for generating ozone upstream from the air filter 27.
In order to retro-fit the [0046] apparatus 19 to an existing engine 11, the air filter casing 33 is opened and the lamp 21 is placed between the air filter 27 and the air intake duct 29 and the electrical wire leads of the lamp 21 are placed so that they pass beneath the air filter cover (not shown) so that they are routed out of the casing 33, for example, between the casing 33 and its removable cover (not shown) for connection to the transformer 23.
In order to increase the effective absorption coefficient of the oxygen in the air being inducted into the [0047] engine 11, the walls adjacent to the lamp 21 are provided with a surface highly reflective to ultraviolet light in the required range, for example, made of aluminum, in order to increase the mean free path of the 185 nanometer photons, since aluminum maintains its reflectance to ultraviolet light down to 185 nanometers.
According to teaching of the present invention, it is possible to also mount the [0048] lamp 21 downstream from the engine's carburetor or fuel injection system 31 and prior to the combustion chamber, for example, in the intake manifold 35 as best seen in FIG. 3. Alternatively, the lamp 21 is mounted downstream from the engine's combustion chamber, for example, in the exhaust manifold 37 as best seen in FIG. 3. In addition, the lamp 21 can be mounted both upstream and downstream of the combustion chamber.
Referring to FIG. 3, a further embodiment of the present invention is illustrated wherein the device for generating ozone is positioned remotely of the precombustion and post-combustion flow streams and ozone enriched air is piped into the combustion flow stream. In this embodiment, an [0049] auxiliary ozone generator 37 for generating ozone from air, draws in ambient air independently of the operation of the engine, for example, using a pumping mechanism 39. The ambient air is converted to ozone enriched air by exposure, for example, to UV light or by means of an electrostatic discharge device, and added to at least one of the pre-combustion or the post-combustion flow streams in accordance with the teachings of the present invention. In this regard, a mixing device 41 can be used to enhance mixing of the ozone enriched air with the combustion flow stream. It should be noted that in lieu of pumping mechanism 39, ambient air can be drawn in using the vacuum generated by the engine 11.
Table 1 compares the results obtained utilizing the [0050] ozone generating apparatus 19 which generates a trace amount of ozone and is situated in the pre-combustion flow stream, upstream from the carburetor or fuel injection system of an engine as illustrated in FIG. 2. The results of the base line tests were conducted without the ozone generating apparatus 19. The engine tested was a 1990 Ford Taurus engine equipped with a production catalytic converter.

BASELINE WITH OZONE REDUCTION

CARBON MONOXIDE 0.28 0.02 92.8%

(%)

HYDROCARBONS 154 12 92.2%

(ppm)
More extensive tests have been conducted with a 1996 Ford Taurus 3.0 L engine using the embodiment of FIG. 3, during which NO[0051] _x, HC, CO, and CO₂levels were measured upstream as well as downstream of the catalytic converter. It should be noted that this type of engine has two catalytic converters, one connected to the right exhaust manifold and another connected to the left exhaust manifold. The results of these tests are as forth below.

IDLE

CONDI- PPM/

TIONS PER- LEFT CAT- LEFT CAT- RIGHT RIGHT

EMISSIONS CENT IN OUT CAT-IN CAT-OUT

WITH DEVICE OFF

BASELINE

NOX PPM 131 2.5 116 1.2

HC PPM 2593 278 2484 137

CO PPM 5000 400 5000 10

CO₂ % 13.72 14.26 13.8 14.6

WITH DEVICE ON

NOX PPM 127 0.2 117 1.1

HC PPM 3048 2 2731 2

CO PPM 5000 0 5000 0

CO₂ % 13.87 13.9 13.99 14.27
It should be noted that the embodiments of the present invention discussed above are illustrative examples. In this regard, while the use of radiant energy to produce ozone is described above, the present invention is not so limited and other devices, well known in the art, which produce ozone are envisioned as sources for adding ozone to the combustion flow stream in accordance with the teachings of the present invention. [0052]
In addition, it should be noted that the only requirement of the present invention is that the ozone is added to the combustion flow stream at at least one point upstream of the catalytic converter, for example, the air intake duct to the carburetor or fuel injection systems of the combustion chamber, the air/fuel intake manifold to the combustion chamber, the combustion chamber directly or the exhaust manifold of the combustion chamber, or the exhaust pipe A as shown in FIG. 1. [0053]
Referring to FIG. 4, the method of the present invention is illustrated and comprises the steps of: 1) adding ozone to the combustion flow stream at at least one point upstream from a catalytic converter for treating exhaust gases produced from the combustion of a fuel to at least reduce one pollutant from incomplete combustion and/or oxides of nitrogen, and 2) treating the exhaust gases with the catalytic converter. [0054]
Although the present invention has been described with particular reference to its preferred embodiments, it should be understood that many variations and modifications will now be obvious to those skilled in that art, and it is preferred, therefore, that the scope of the invention be limited, not be the specific disclosure herein, but only by the appended claims. [0055]

Claims

What is claimed is:

1. In a method of processing exhaust gases formed from combustion of diesel fuel wherein the exhaust gases are passed through an exhaust passageway and thereafter through at least one device provided for reducing products of incomplete combustion in the exhaust gases, the improvement comprising:

positioning at least a portion of at least one generator, which produces ozone in ambient air, in the exhaust passageway;

providing high frequency current to the generator;

exposing at least a portion of the exhaust gases to the effects of the generator; and

passing at least a portion of the exhaust gases exposed to the effects of the generator through at least a portion of the device;

thereby enhancing a decrease in the concentration of at least one product of incomplete combustion in the exhaust gases.

2. The method according to

claim 1

, further comprising:

positioning the device a predetermined distance downstream of the generator.

3. The method according to

claim 2

, used for treating the exhaust gases produced by at least one diesel engine.

4. The method according to

claim 3

, applied to the exhaust system of a mobile vehicle.

5. The method according to

claim 1

, wherein the generator consumes low power.

6. The method according to

claim 3

, wherein the generator consumes approximately 0.01% to approximately 0.1% of the rated engine power.

7. The method according to

claim 1

, wherein the high frequency current has a frequency of at least about 1,000 Hertz.

8. The method according to

claim 6

conducted in the absence of any reducing agent added to the exhaust gases prior to their exposure to the generator.

9. The method according to

claim 1

, wherein the generator is continuously powered whenever exhaust gases are present.

10. The method according to

claim 1

, wherein the device comprises honeycombed, monolithic substrates.

11. The method according to

claim 10

, wherein the honeycombed, monolithic substrates contain catalytically active material.

12. The method according to

claim 1

, wherein the generator comprises an electric discharge device.

13. The method according to

claim 12

, wherein the electric discharge device comprises a corona discharge device.

14. In a device for processing exhaust gases formed from combustion of diesel fuel wherein the exhaust gases are passed through an exhaust passageway and thereafter through at least one device provided for decreasing products of incomplete combustion in the exhaust gases, the improvement comprising:

at least a portion of at least one generator, which produces ozone in ambient air, positioned in the exhaust passageway;

a power supply which provides high frequency current to the generator; whereby in at least a portion of the exhaust gases exposed to the effects of the generator and passed through the device, there is an enhanced decrease in the concentration of at least one product of incomplete combustion.

15. The device according to

claim 14

, wherein at least a portion of the device is positioned downstream of the generator.

16. The device according to

claim 15

, used for treating the exhaust gases produced by at least one diesel engine.

17. The device according to

claim 16

, applied to the exhaust system of a mobile vehicle.

18. The device according to

claim 14

, wherein the generator consumes low power.

19. The device according to

claim 16

20. The device according to

claim 14

21. The device according to

claim 14

, wherein no reducing agent is added to the exhaust gases prior to their exposure to the generator.

22. The device according to

claim 14

23. The device according to

claim 14

, wherein the device comprises honeycombed, monolithic substrates.

24. The device according to

claim 23

25. The device according to

claim 21

, wherein the generator comprises an electric discharge device.

26. The device according to

claim 25

, wherein the electric discharge device comprises a corona discharge device.