Patent Application
20200116088
This application claims priority to and the benefit of Korean Patent Application No. 10-2018-0122593, filed on Oct. 15, 2018, the entire contents of which are incorporated herein by reference.
The present disclosure relates to a method for controlling combustion in a diesel engine.
The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
A diesel engine injects a fuel into a combustion chamber with high pressure and high temperature at around the top dead center of the compression stroke of the cylinder, so that the fuel is burned by its self-ignition.
Generally, the combustion of the diesel engine is divided into diffusion combustion, premixed combustion, or homogeneous charge compression ignition (HCCI).
In the diffusion combustion of the diesel engine, when air and EGR (Exhaust Gas Recirculation) gas are sucked into the cylinder of the engine in the intake stroke, the fuel is injected into the cylinder during the initial part of the compression stroke, and the injected fuel is atomized into small droplets and vaporized to form an air-fuel mixture. As a piston continues to rise and move closer to a cylinder head, the mixture temperature increases so that auto-ignition occurs. At this time, the diffusion combustion, in which the air-fuel mixing and combustion simultaneously occur, takes place. Emissions are produced as a byproduct of the diffusion combustion process. In the diffusion combustion process, chemical energy of the fuel is converted into thermal energy so that heat is released. Then, in a process that converts it into mechanical energy, engine performance is calculated, and fuel consumption is calculated by the quantity of fuel consumed and the engine performance.
The diffusion combustion of the diesel engine has disadvantages of lowering purification efficiency of soot, reducing fuel efficiency, and increasing combustion noise.
In the premixed combustion of the diesel engine, after air and EGR gas are sucked into the cylinder of the engine in the intake stroke, the fuel is injected into the cylinder at the end of the compression stroke, and the injected fuel is atomized into small droplets and vaporized to form an air-fuel mixture. As the piston continues to rise and move closer to the cylinder head, the mixture temperature increases so that auto-ignition occurs. At this time, the premixed combustion, in which the combustion occurs after the air-fuel mixing, takes place. Emissions are produced as a byproduct of the premixed combustion process, and the premixed combustion process has the effect of reducing soot formation as the combustion occurs after the air-fuel mixing. During the premixed combustion process, chemical energy of the fuel is converted into thermal energy and heat is released. Then, in a process that converts it into mechanical energy, engine performance is calculated, and fuel consumption is calculated based on the quantity of fuel consumed and the engine performance.
We have discovered that the premixed combustion of the diesel engine has the advantage of mitigating soot formation, but has disadvantages of causing unstable combustion since it is difficult to control combustion, and increasing combustion noise due to rapid combustion.
The above information described in this background section is provided to assist in understanding the background of the inventive concept, and may include any technical concept which is not considered as the prior art that is already known to those skilled in the art.
The present disclosure has been made to solve the above-mentioned problems occurring in the prior art while advantages achieved by the prior art are maintained intact.
An aspect of the present disclosure provides a method for controlling combustion in a diesel engine by allowing premixed combustion and diffusion combustion to take place simultaneously, thereby achieving premixed and diffusion harmonized combustion.
According to an aspect of the present disclosure, a method for controlling combustion in a diesel engine may include: premixing ambient air, exhaust gas recirculation (EGR) gas, and vaporized diesel fuel in a combustion chamber of the diesel engine during an intake stroke of each cylinder of the diesel engine; and sequentially performing, by an injector, pilot injection, main injection, and post injection during a compression stroke which occurs after the intake stroke.
The main injection may be performed at the end of the compression stroke.
The main injection may be performed in a range from approximately 1.0° degree before top dead center (BTDC) to 1.0° degree after top dead center (ATDC).
A premixed quantity of diesel fuel introduced into the combustion chamber during the intake stroke may account for approximately from 25% to 35% of a total fuel quantity which is supplied per cycle of each cylinder.
A premixed quantity of diesel fuel introduced into the combustion chamber during the intake stroke may account for approximately 30% of a total fuel quantity which is supplied per cycle of each cylinder.
The pilot injection may be performed in a range of from 1100 μs to 1200 μs before starting the main injection, and a pilot injection quantity in the pilot injection may be 1-2 mg.
The post injection may be performed in a range of 300-400 μs after the end of the main injection, and a post injection quantity in the post injection may be from approximately 1 mg to 2 mg.
Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which:
The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.
The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.
In addition, a detailed description of well-known techniques associated with the present disclosure will be ruled out in order not to unnecessarily obscure the gist of the present disclosure.
Terms such as first, second, A, B, (a), and (b) may be used to describe the elements in exemplary forms of the present disclosure. These terms are only used to distinguish one element from another element, and the intrinsic features, sequence or order, and the like of the corresponding elements are not limited by the terms. Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meanings as those generally understood by those with ordinary knowledge in the field of art to which the present disclosure belongs. Such terms as those defined in a generally used dictionary are to be interpreted as having meanings equal to the contextual meanings in the relevant field of art, and are not to be interpreted as having ideal or excessively formal meanings unless clearly defined as having such in the present application.
Referring to
A piston 3 may be arranged to reciprocally move in a vertical direction within each cylinder 2. The piston 3 may define a combustion chamber 4 within each cylinder 2. A fuel injector 15 may be mounted to inject a liquid diesel fuel such as light oil into the combustion chamber 4 of each cylinder 2. The fuel injector 15 may be connected to a fuel supply system 19, and the fuel supply system 19 may supply the high-pressure diesel fuel to the fuel injector 15.
Each cylinder 2 may have an intake port 5 and an exhaust port 6 communicating with the combustion chamber 4. The intake port 5 may communicate with an intake pipe 11, and the exhaust port 6 may communicate with an exhaust pipe 12. An inlet of an EGR pipe 13 may be connected to the exhaust pipe 12, and an outlet of the EGR pipe 13 may be connected to the intake pipe 11. An EGR valve, an EGR cooler, and the like may be provided on the EGR pipe 13. EGR gas may be recirculated to the intake port 5 of each cylinder 2.
An intake valve 7 may open or close the intake port 5, and an exhaust valve 8 may open or close the exhaust port 6.
The intake valve 7 and the exhaust valve 8 may be controlled by a variable valve timing mechanism 10 so that the opening/closing timing, opening/closing rate, opening/closing duration, and the like thereof may be adjusted.
An electronic control unit or engine control unit (ECU) 20 may be configured to control the fuel supply system 19, the fuel injector 15, and the variable valve timing mechanism 10. The ECU 20 may include a processor 21 and a memory 22. The processor 21 may be programmed to receive instructions stored in the memory 22 and to send instructions to the fuel supply system 19, the fuel injector 15, and the variable valve timing mechanism 10. The memory 22 may be a data store, such as a hard disk drive, a solid state drive, a server, a volatile storage medium, or a non-volatile storage medium.
As illustrated in
According to an exemplary form, as illustrated in
According to another exemplary form, as illustrated in
The quantity of diesel fuel introduced into the combustion chamber 4 during the intake stroke, that is, the quantity of diesel fuel premixed with the ambient air and EGR gas in the combustion chamber 4 during the intake stroke may account for from 25% to 35% (diesel fuel premixed ratio) of the total fuel quantity which is supplied per cycle of each cylinder 2, and the quantity of diesel fuel directly injected into the combustion chamber 4 during the compression stroke may account for from 65% to 75% of the total fuel quantity which is supplied per cycle of each cylinder 2. In other words, a ratio of the premixed quantity of diesel fuel introduced during the intake stroke and the quantity of diesel fuel injected during the compression stroke may be in a range from 25:75 to 35:65. As illustrated in
As the piston 3 rises after the intake stroke, the compression stroke may occur as illustrated in
The pilot injection S2 may be performed during the initial part of the compression stroke, and the fuel injector 15 may inject a predetermined pilot injection quantity of diesel fuel into the combustion chamber 4. For example, the pilot injection S2 may be performed in a range of 1100-1200 μs before the start of the main injection S3, and the pilot injection quantity in the pilot injection S2 may be in a range of approximately 1-2 mg.
The pilot injection S2, also called as ignition injection or pre-injection, may inject a small amount of fuel before the main injection. By providing a short non-injection period before the main injection, the pilot injection S2 may help to improve air-fuel mixing and reduce noise and vibration of the diesel engine due to ignition delay of the main injection, contributing to combustion. Due to the pilot injection, the combustion pressure may moderately increase so that vibration and noise may be reduced, and the air-fuel mixing period may increase so that the emissions may be reduced.
The main injection S3 may be performed at the end of the compression stroke, and the fuel injector 15 may inject a predetermined main injection quantity of diesel fuel into the combustion chamber 4. For example, the main injection S3 may be performed in a range of a crank angle of 1.0° degree before top dead center (TDC) to a crank angle of 1.0° degree after TDC (i.e., 1.0° BTDC, −1.0° ATDC), and the main injection quantity in the main injection S3 may be approximately between 7.3 mg and 15.3 mg.
The post injection S4 may be performed after the main injection S3 and before the exhaust stroke, and the fuel injector 15 may inject a predetermined post injection quantity of diesel fuel into the combustion chamber 4. For example, the post injection S4 may be performed in a range of 300-400 μs after the end of the main injection, and the post injection quantity in the post injection S4 may be approximately between 1 mg and 2 mg. By performing the post injection S4 after the main injection S3, the liquid diesel fuel may be supplied to a catalytic converter, lowering the combustion temperature in the combustion chamber to reduce NON.
As illustrated in
After the power stroke, as illustrated in
As described above, the vaporized diesel fuel, together with the ambient air and EGR gas, may be introduced into the combustion chamber 4 during the intake stroke so that the vaporized diesel fuel may be premixed with the ambient air and EGR gas during the intake stroke, and thus the premixed combustion may take place until the start of the main injection S3. As the premixed combustion takes place before the main injection S3, the diffusion combustion after the main injection S3 may be relatively reduced so that soot formation may be reduced.
Table 1 below indicates variations in main injection quantity in cases in which the premixed quantity of diesel fuel is 0 mg, 2 mg, 4 mg, 6 mg, 8 mg, and 10 mg.
Referring to
Referring to
Referring to
Referring to
Referring to
As indicated in table 2 below, in the case in which the premixed quantity of diesel fuel is 6 mg (approximately 30% of the total fuel quantity), BSFC is improved by approximately 3%, and CNL is improved by approximately 5%. In particular, when the diesel fuel premixed ratio (the premixed quantity of diesel fuel/the total fuel quantity) is 30%, and the start of main injection occurs at a crank angle of 0.3° degree before TDC (0.3° BTDC), an optimum effect may be achieved.
Referring to
Referring to
Referring to
As set forth above, according to exemplary forms of the present disclosure, the premixed combustion and the diffusion combustion may take place simultaneously, thereby improving fuel efficiency, reducing combustion noise, and significantly reducing emissions.
In addition, according to exemplary forms of the present disclosure, as the vaporized diesel fuel is premixed with the ambient air and EGR gas in the intake stroke, the premixed combustion may take place before the start of the main injection, and the diffusion combustion may be relatively reduced after the main injection, thereby reducing soot formation.
Hereinabove, although the present disclosure has been described with reference to exemplary forms and the accompanying drawings, the present disclosure is not limited thereto, but may be variously modified and altered by those skilled in the art to which the present disclosure pertains without departing from the spirit and scope of the present disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2018-0122593 | Oct 2018 | KR | national |
