CN1332126C - Adaptive controllable thermal premixing direct injection diesel engine combustion system and method - Google Patents

Abstract

The invention discloses a combustion system and a method of a self-adaptive controllable hot premixed direct injection diesel engine, belonging to the field of internal combustion engines. The combustion system comprises a porous oil nozzle, a multi-communication space combustion chamber and an air inlet channel. The multi-communicating space combustion chamber is composed of two or more connected spaces, can control the propagation path of premixed combustion, is matched with fuel injection and fuel supply at regular time, can effectively control the time-space distribution of mixed gas and the ignition starting point and the combustion rate under different working conditions, and enables a combustion system to have self-adaptability and controllability. The combustion chamber may form a plurality of annular streams to facilitate formation of a homogenous mixture. The system has the advantages that the air inlet swirl ratio omega is 0-2, the aperture of the oil nozzle is 50-180 mu m, the oil injection pressure is more than 800bar, the flame temperature, soot, NOX and HC can be obviously reduced, and the combustion efficiency is improved.

Description

Adaptive controllable thermal premixing direct injection diesel engine combustion system and method

technical field

The invention belongs to the field of internal combustion engines, and more specifically, the invention relates to a direct-injection diesel engine combustion system and a combustion method.

Background technique

The combustion process of the traditional direct injection diesel engine includes both premixed combustion and diffusion combustion, and the diffusion combustion is the main one. In the past hundred years, people have successfully developed different diesel engine combustion systems. By their nature, most systems are diffusion combustion. Due to the extremely uneven formation of the diffusion combustion mixture, there is an insurmountable contradiction between smoke exhaust and NOX. In recent years, with the development of technologies such as electronic control and high-pressure injection, the combustion and emission of diesel engines have been greatly improved, but the essential problem of diffusion combustion still needs to be solved. With the increasingly stringent emission regulations in various countries, the combustion and emission of diesel engines are facing greater challenges.

In recent years, homogeneous compression ignition combustion (HCCI) has received international attention. The goal of HCCI is to form a homogeneous mixture before ignition, and eliminate diffusion combustion in principle, so it has the potential to eliminate soot and reduce NOX at the same time. However, the main problem facing HCCI at present is that it is difficult to control the ignition point and combustion rate, and it can only operate normally under some working conditions, so its practical application is facing great challenges. Chinese scholars have proposed the idea of thermal premixed combustion, and use umbrella nozzles to promote uniform mixing (Chinese patents 86104093, 90106022). Umbrella jet combustion has better performance under low load, but it is easy to generate black smoke under high load. Because of the fast oil supply rate and small spray penetration distance of umbrella jet, it is difficult to control the spatio-temporal distribution of oil and gas under high load.

The key to the success of the ultra-low pollution and high-efficiency direct-injection diesel engine is to eliminate diffusion combustion as much as possible, but at the same time it is self-adaptive and controllable, that is, it can effectively optimize the time-space distribution of oil and gas, ignition start point, and combustion rate under different working conditions control. The current optimization control technology, such as US Patent No. 6,230,683, is complicated in control technology and thus high in cost. Although the existing technology can control the regularity of fuel supply, it cannot effectively optimize the control of the combustion rate of the formed mixture. Its essential reason is caused by the single space characteristic of the open combustion chamber. In an open combustion chamber, if fuel is injected too early, the formed mixture may be combustible at the same time, and it is difficult to control the combustion rate; if fuel is injected too late, it is difficult to completely form premixed gas before ignition, and diffusion combustion is difficult to avoid. Therefore, it is necessary to develop a novel adaptive controllable thermal premixing direct injection diesel engine combustion system and method to overcome the existing problems.

Contents of the invention

The purpose of the present invention is to provide an adaptive and controllable thermal premixed direct injection diesel engine combustion method and combustion system, which solves the main problems of the current premixed direct injection diesel engine combustion, which is difficult to control the ignition point and combustion rate, and at the same time reduces the Soot, NOX and HC products in emissions.

The self-adaptive controllable thermal premixing direct injection diesel engine combustion system of the present invention comprises a multi-hole oil nozzle, a multi-communication space combustion chamber, a piston, a cylinder, a cylinder head, and an intake port; Combustion chamber, piston top surface, cylinder head, and cylinder form in communication space. The multi-communication space combustion chamber at the top of the piston of the present invention is composed of two or more than two connected combustion spaces, the bottom of the combustion chamber cross-section is composed of an approximate sine or cosine curve, and the peripheral part is composed of a semicircular arc and a straight line. Combustion chamber is composed of rounded corners. The combustion chamber space is composed of the entire bottom and the rotating body formed by the peripheral curve around the center line of the combustion chamber. The combustion chamber space on the top of the piston can also be composed of a central ω-shaped combustion chamber and a peripheral ring-shaped combustion chamber. The central combustion chamber can be divided into There are two types with or without a center boss.

The size ratio of the multi-connected space combustion chamber of the present invention is: D1/D=0.45～0.65; D0/D=0.5～0.75; H/D=0.14～0.30; H2/H=0.5～0.75; wherein, D- Piston diameter, D0-the maximum diameter of the combustion chamber section, D1-the diameter of the combustion chamber, H-the depth of the combustion chamber, H2 is the height from the top of the sine or cosine section curve of the combustion chamber to the bottom of the combustion chamber.

All fuels described in the present invention are diesel oil or a part of fuel is diesel oil, and a part of fuel is natural gas.

The fuel injection nozzle of the present invention has 6-20 oil holes with a diameter of 50-180 μm, the center line of the fuel injection nozzle coincides with the center line of the combustion chamber, and the angle between the center extension line of all the fuel injection holes and the center line of the fuel injection nozzle It is 65-80 degrees.

The fuel injector of the present invention has 8 to 20 oil holes with a diameter of 50 to 180 μm, the center line of the fuel injector coincides with the center line of the combustion chamber, and there are 3 to 4 oil holes with a diameter of 50 to 140 μm. The angle between the extension line of the center and the center line of the injector is 50-65 degrees, which matches the space of the central combustion chamber. match.

The intake swirl ratio adopted by the air intake system of the present invention is Ω=0-2, and the intake swirl ratio decreases with the increase of the number of nozzle holes.

The combustion method of the present invention is to use a multi-communication space combustion chamber to use a high-pressure injection greater than 800bar and 6-20 porous oil nozzles with a diameter of 50-180μm to form a fine spray, and form a mixed gas in a hot state in the cylinder, thereby eliminating the high pressure. The accumulation of oil jets on the walls of the combustion chamber or cylinder.

The combustion method of the present invention adopts multi-communication space combustion chambers, and uses a single injection to control the timing and regularity of fuel supply, thereby controlling the time-space distribution of fuel and air in multiple combustion chamber spaces, thereby controlling each The ignition start point of the combustion chamber space is after the top dead center and its combustion law achieves controllable thermal premixed combustion.

The combustion method of the present invention adopts multi-communication space combustion chambers, and uses multiple injections to control the fuel supply timing and fuel supply rules, thereby controlling the temporal and spatial distribution of fuel and air in multiple combustion chamber spaces, thereby controlling each The ignition start point of the combustion chamber space is after the top dead center and its combustion law achieves controllable thermal premixed combustion.

The present invention is achieved through the following technical solutions. The combustion system includes a porous oil nozzle, a multi-communication space combustion chamber, and an air inlet. The multi-connected space combustion chamber is composed of two or more connected spaces, which can control the propagation path of pre-mixed combustion, and cooperate with fuel injection and fuel supply timing to effectively control the time-space distribution of the mixed gas and different working conditions. The ignition point and combustion rate under certain conditions make the system adaptive and controllable. The combustion chamber can form multiple circulations to promote the formation of a homogeneous mixture. The intake swirl ratio of the combustion system is 0-2, the aperture of the oil nozzle is 80-150 μm, and the injection pressure is greater than 800 bar. The "adaptiveness" mentioned in this article means that the diesel engine still has good combustion characteristics when the load and speed change, the "controllability" means that the ignition point and combustion rate can be effectively controlled, and the "thermal premixing" It refers to injecting fuel into the combustion chamber when the air in the cylinder is hot and strong.

For premixed combustion, if the over-rich mixture can be eliminated in the early stage of spraying, and the mixture can be distributed in different combustion spaces and effectively limit the reaction pathway, the combustion rate can be controlled. The design principle of the multi-communication space combustion chamber of the present invention is as follows.

Most of the open combustion chamber spaces of direct injection diesel engines belong to the 'single connected domain' in essence. Mathematically, a 'simply connected domain' means that the surface of a region can be reduced to a point but does not pass through a point outside the space. 'Multi-connected domain' means that if the surface of the region shrinks to a point, it must pass through points outside the space. As shown in Figure 5 and Figure 6. The property of 'multi-connected domains' has important implications in chemical reactions. If there is a reactive particle at A, in the 'simply connected domain', the reactive particle can directly affect B, but in the area of Figure 5 and Figure 6, the medium at A may not have a direct impact on B. Therefore, the medium response in the 'multi-connected domain' is more controllable than that in the 'simply connected domain', that is, the response will not be quickly spread throughout the entire 'multi-connected domain' due to a random phenomenon (such as fire), And different spaces may have different physical and chemical properties.

Using the feature of 'multi-communication area' for the design of diesel engine combustion chamber, the present invention discloses the design of 'multi-communication space' combustion chamber as shown in Figure 2, which is characterized in that the multi-communication space combustion chamber on the top of the piston consists of two or Two or more connected combustion spaces are formed. The inner bottom of the combustion chamber cross-section is composed of approximately sine or cosine curves, and the outer part is composed of semicircular arcs, straight line segments and rounded corners. The combustion chamber space is composed of the entire bottom and peripheral curves around the combustion chamber. A body of revolution formed by the centerline. When combined with oil jet and fuel supply timing, the ignition onset and combustion rate of the premixed gas are controlled because the reaction propagation of the mixture in different combustor troughs is limited by the combustor crests, and the different combustor crests With the troughs, multiple swirls can be formed to promote uniform mixing. The swirl flow formed varies with the engine speed, making the formation of the mixture adaptive. The circular flow formed in the vertical direction in the central area of the combustion chamber also helps to reduce the concentration of oil and gas near the oil nozzle. The combustion chamber space on the top of the piston can also be made of a central ω-shaped combustion chamber and a peripheral annular combustion chamber, and the central combustion chamber can be divided into two types with or without a central boss.

In recent years, high-pressure injection has become the development trend of international diesel engines. However, the ultra-fine spray (SMD<10 μm) is often limited by the traditional open combustion chamber in practical applications, that is, the ultra-fine spray may cause excessive combustion rate and coarse combustion. The multi-communication space combustion chamber of the present invention can eliminate the weakness of the traditional open combustion chamber, can obviously limit the combustion rate, and can reduce the soot by ultra-fine spray (SMD<10 μm), and control the explosion pressure at the same time.

Since the design of the 'multi-communication space' combustor can control the space-time distribution and reaction rate of the mixture, it can solve the essential problem of premixed combustion reaction rate control. The key of the present invention is to utilize fine spray (oil nozzle aperture is 50～180 μ m) to reduce soot, and simultaneously use ' multi-communication space' combustion chamber to control combustion reaction rate, reduce NOX simultaneously.

Compared with the prior art solutions, the present invention has the following advantages: 1) high-pressure injection and fine oil holes (injection pressure greater than 800 bar, nozzle aperture of 50-180 μm) are used to form a fine spray, which can significantly reduce the generation of soot; 2 ) adopts a multi-communication space combustion chamber, which can effectively control the reaction particle propagation path of thermal premixed combustion. The time and space distribution characteristics of the combustion space, so as to control the ignition point and combustion rate of the premixed combustion under different working conditions, which is controllable; 3) At the same time, the combustion chamber can form multiple rings that are beneficial to the formation and combustion of the mixture Airflow, and the strength of this compression swirl movement changes with the engine speed, so it is adaptive to different working conditions. The above advantages enable the present invention to significantly reduce flame temperature, soot, NOX and HC, and improve combustion efficiency.

Description of drawings

The present invention has eight accompanying drawings, wherein:

Accompanying drawing 1 is the overall schematic diagram of the self-adaptive controllable thermal premixing combustion system of direct-injection diesel engine;

In the figure: 1. Combustion chamber space I 2. Combustion chamber space II 3. Piston 4. Cylinder 5. Cylinder head

6. Oil nozzle 7. Oil nozzle hole 8. Intake valve 9. Exhaust valve

Accompanying drawing 2 is the scale mark schematic diagram of ' multi-communication space ' combustion chamber of Fig. 1;

Accompanying drawing 3 is the schematic diagram of the squeeze flow field of the 'multi-communication space' combustion chamber of Fig. 1;

Accompanying drawing 4 is the schematic diagram of 'simply connected domain';

Accompanying drawing 5 is a schematic diagram of 'multi-connected domain', the middle area does not belong to the area where A and B are located;

Accompanying drawing 6 is a schematic diagram of 'multi-connected domain', area II does not belong to the area where A and B are located;

Accompanying drawing 7 is the matching schematic diagram of oil beam and combustion chamber, wherein all oil beams have the same angle;

Accompanying drawing 8 is a schematic diagram of the matching of the oil beam and the combustion chamber, in which a small part of the oil beam is at a small angle, and the rest of the oil beam is at a large angle

Detailed ways

Specific embodiments of the present invention are as shown in the accompanying drawings:

For vehicle diesel engines and other small diesel engines, the combustion chamber can adopt the scheme shown in Figure 2, which is characterized in that the size ratio of the multi-communication space combustion chamber is as shown in Figure 2: D1/D=0.45～0.65; D0/D=0.5～0.75 ;H/D＝0.15～0.30; H1/H＝0.5～0.75;

H2/H=0.5-0.75; H3/H=0.3-0.6; R/H=0.28-0.4.

The combustion chamber can adopt the scheme of closing or not closing. The volume ratio of the central combustion chamber and the peripheral combustion chamber is usually 1/5 to 1/3. The whole combustion system is shown in Figure 1:

The oil nipple and the oil beam are designed according to the following two schemes. The feature of the first plan is that the fuel injector has 6-20 oil holes with a diameter of 50-180 μm, the center line of the fuel injector coincides with the center line of the combustion chamber, and the angle between the center extension line of all the fuel injection holes and the center line of the fuel injector It is 65-80 degrees. The feature of the second scheme is that the fuel injector has 8 to 20 oil holes with a diameter of 50 to 180 μm, and the center line of the fuel injector coincides with the center line of the combustion chamber, among which there are 3 to 4 oil holes with a diameter of 50 to 140 μm. The angle between the extension line of the center and the center line of the injector is 50-65 degrees, which matches the space of the central combustion chamber. match.

The matching between the oil beam and the combustion chamber can adopt two kinds as shown in Fig. 7 or Fig. 8 . In the matching shown in Figure 7, the crest of the combustion chamber space should be lower than the centerline of the fuel jet, but higher than the boundary line of the fuel jet. Usually, the crest extends into 1/4 to 1/2 of the section of the fuel jet, so that the fuel oil The distribution of the central combustion chamber and the peripheral combustion chamber is directly proportional to the amount of air in it, and is matched by experiment according to the specific diesel engine. In the matching of Figure 8, the crest of the combustion chamber space should be lower than the boundary line of the large-angle oil beam or slightly tangent.

High-pressure injection is adopted, and the injection pressure is greater than 800bar (usually 800-2000bar). The fuel supply advance angle of a single injection is 10°CA or later before top dead center (BTDC). The fuel supply advance angle of multiple pilot injections varies with the number of injections, but they should all be after BTDC 100°CA, and the main injection start point is 5-10°CA after top dead center (ATDC). Both single injection and multiple injection control the ignition onset after top dead center (TDC).

The combustion system adopts an intake swirl ratio of Ω=0-2, and the intake swirl ratio decreases as the number of nozzle holes increases.

For medium and large diesel engines, the non-stop scheme can be adopted, and the depth of the combustion chamber is shallow (H/D=0.14～0.28), the diameter of the oil nozzle increases with the cylinder diameter (100～180μm), and the cross section of the combustion chamber can form two or more Combustion chamber space, other parameters can adopt the scheme similar to the above small diesel engine.

Claims (4)

1, a kind of self adaption, controlled, heat premixing direct jet type diesel engine combustion system comprise perforated plate type atomizer, multiply connected space firing chamber, piston, cylinder, cylinder head, intake duct; The multiply connected space firing chamber is made of central combustion chamber and peripheral ring-like firing chamber; It is characterized in that:

(1) above-mentioned multiply connected space firing chamber dimension scale is: D1/D=0.45～0.65, D0/D=0.5～0.75, H/D=0.14～0.30, H2/H=0.5～0.75; D1-firing chamber bore wherein; D0-section of combustion chamber maximum diameter; The D-piston diameter; The H-combustion-chamber depth; H2-sine or cosine cross section curve top height at the bottom of the firing chamber;

(2) the above-mentioned central combustion chamber and the volume ratio of peripheral firing chamber are 1/5～1/3;

(3) above-mentioned oil nozzle center line and firing chamber central lines, oil nozzle has 8～20, it is the oilhole of 50～140 μ m that 3～4 diameters are wherein arranged, its center line stretcher and oil nozzle center line angle are 50～65 degree, with central combustion chamber's space coupling, the diameter of all the other oilholes is 50～180 μ m, and its center line stretcher and oil nozzle center line angle are 65～80 degree, with peripheral bags coupling;

(4) induction swirl ratio that adopts of described combustion system is Ω=0～2, and induction swirl ratio increasing and reduce with the oil nozzle hole count.

2, a kind of method of utilizing the described combustion system of claim 1 to burn, it is characterized in that: adopt high-pressure injection greater than 800bar with the oil nozzle of multiply connected space firing chamber coupling, and utilize the single injection event or the multi-injection mode of oil nozzle, fuel feeding timing and fuel supply rate curve are controlled, thereby control fuel oil and air are in the spatial and temporal distributions of a plurality of bagss, and the initial point that catches fire of controlling each bags reaches the controlled thermal pre-mixing combustion at after top dead center and combustion law.

3, self adaption according to claim 2, controlled, method that the heat premixing direct jet type diesel engine combustion system is burnt; It is characterized in that: above-mentioned oil nozzle adopts the single injection event mode, and its fuel supply advance angle should be after 10 ° of CA of before top dead center.

4, self adaption according to claim 2, controlled, method that the heat premixing direct jet type diesel engine combustion system is burnt; It is characterized in that: above-mentioned oil nozzle adopts the multi-injection mode, and its pilot injection fuel supply advance angle should be after 100 ° of CA of before top dead center, and the main injection initial point should be at 5～10 ° of CA of after top dead center.

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