WO2014011326A1

WO2014011326A1 - System and method of controlling combustion in an engine

Info

Publication number: WO2014011326A1
Application number: PCT/US2013/042995
Authority: WO
Inventors: Russell P. Zukouski; Dean Alan OPPERMANN; Grzegorz Siuchta; Jer Sheng CHEN; Michael UCHANSKI
Original assignee: International Engine Intellectual Property Company, Llc
Priority date: 2012-07-13
Filing date: 2013-05-29
Publication date: 2014-01-16

Abstract

A method of operating an internal combustion engine is provided. An air/fuel ratio of an internal combustion engine is determined. At least one of fuel injection quantity and intake air flow is adjusted to provide an air/fuel ratio between about 15 and about 18. A quantity of fuel is injected sufficient to generate a brake mean effective pressure of between about 1 1.5 and about 18.

Description

SYSTEM AND METHOD OF CONTROLLING COMBUSTION IN AN ENGINE

DESCRIPTION

TECHNICAL FIELD

[0001] The present disclosure relates to a system and method of controlling combustion within an internal combustion engine having a variety of sensors for monitoring combustion occurring within a cylinder, such that adjustments may be made to operating parameters of the internal combustion engine. The adjustments of the operating parameters allow combustion to function properly, while also allowing emissions of the engine to meet government mandates.

BACKGROUND

[0002] Many modern diesel engines have an exhaust system that features an exhaust gas recirculation ("EGR") system that routes a portion of engine exhaust gas into an air intake system, such that a mixture of fresh air and engine exhaust is supplied to a combustion chamber during engine operation. In order to reduce certain pollutants found in exhaust gas of an internal combustion engine, such as NOx and particulate matter, several approaches have been tried, including using an after-treatment chemical in conjunction with a catalytic converter, a system often referred to as a selective catalyst reduction system or an "SCR system." An SCR system adds complexity to an engine, and requires a catalyst that must be periodically replenished, which increases operating costs. If the catalyst is not replenished, the engine exhaust typically will not meet emissions standards, and the engine may be required to cease operations.

[0003] Previous attempts to reduce emissions have focused on increasing EGR levels provided to the engine, in order to reduce NO_x emissions. However, simply increasing EGR levels may not sufficiently limit emissions to meet certain standards. For instance, typical emissions control strategy would indicate that EGR rates should be raised as NO_x levels approach an unacceptably high level. However, increasing EGR rates typically results in additional particulate matter formation, or soot formation, in the exhaust. In order to reduce the particulate matter formation, typical control strategy has attempted to raise intake air boost. However, raising intake air boost results in an increase in NO_x formation. Thus, a so called "doom loop" for engine emissions is created, where an engine is unable to meet both Οχ emissions limits, and particulate matter emissions limits simultaneously, as an adjustment to limit NO_x emissions causes unacceptable levels of particulate matter emisisions, and an adjustment for particulate matter emissions causes unacceptable levels of Οχ emissions.

[0004] Therefore, a need exists for an engine capable of meeting emissions standards without the use of an after-treatment system to control parameters useful in reducing emissions of the engine to simultaneously meet NO_x emissions and particulate matter emissions.

SUMMARY

[0005] According to one process, a method of operating an internal combustion engine is provided. An air/fuel ratio of an internal combustion engine is determined. At least one of fuel injection quantity and intake air flow is adjusted to provide an air/fuel ratio between about 15 and about 18. A quantity of fuel is injected sufficient to generate a brake mean effective pressure of between about 12 and about 18.

[0006] According to another process, a method of operating an internal combustion engine is provided. An air/fuel ratio of an internal combustion engine is determined. At least one of fuel injection quantity and intake air flow is adjusted to provide an air/fuel ratio between about 15 and about 18. A quantity of fuel is injected sufficient to generate a brake mean effective pressure of between about 12 and about 18.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIG. 1 is a schematic diagram showing an engine;

[0008] FIG. 2 is a sectional view of an engine showing a cylinder having an in-cylinder pressure sensor;

[0009] FIG. 3 is block diagram showing a control system for an engine having an in- cylinder pressure sensor;

[0010] FIG. 4 is a block diagram showing an air/fuel ratio calculator. DETAILED DESCRIPTION

[0011] FIG. 1 shows an engine 10 having an exhaust system 12. The exhaust system 12 has an exhaust gas recirculation ("EGR") portion 13. The EGR portion 13 has an EGR cooler 14 and an EGR valve 16. The EGR cooler 14 reduces the temperature of exhaust gas within the EGR portion 13. The exhaust system 12 additionally is shown as having a first turbocharger turbine 18 and a second turbocharger turbine 20. The EGR valve 16 controls the flow of exhaust gas within the EGR portion 13.

[0012] The engine 10 additionally has an air intake system 22. The air intake system 22 has a first turbocharger compressor 24 and a second turbocharger compressor 26. A charge air cooler 28 is additionally provided to cool intake air within the air intake system 22. A first throttle valve 30 and a second throttle valve 32 are also disposed within the air intake system 22. The first turbocharger turbine 18 and the first turbocharger compressor 24 form a first turbocharger and the second turbocharger turbine 20 and the second turbocharger compressor 26 form a second turbocharger. It is contemplated that the first turbocharger and the second turbocharger may be variable geometry turbochargers.

[0013] Turning now to FIG. 2, a cross section of a cylinder 34 of the engine 10. The cylinder 34 has a piston 36 that moves reciprocally within the cylinder 34. A cylinder head 38 is disposed above the cylinder 34, such that the movement of the piston 36 within the cylinder 34 increases a pressure within the cylinder 34. An in-cylinder pressure sensor 40 is additionally provided. The in-cylinder pressure sensor 40 is disposed within the cylinder head 38 and a portion of the in-cylinder pressure sensor 40 is exposed within the cylinder 34. The in-cylinder pressure sensor 40 monitors the pressure within the cylinder 34. In a multi- cylinder engine 10, there are multiple sensors 40 forming a sensor group 41.

[0014] Controlling combustion of fuel within the cylinder 34 requires a number of additional sensors. For instance, an oxygen sensor 42 may be provided. As shown in FIG. 1, the oxygen sensor 43 is disposed within the exhaust system 12 of the engine 10. However, it is contemplated that the oxygen sensor 43 may alternatively be placed in the air intake system 22. The oxygen sensor 43 allows a concentration of oxygen within the cylinder 34 during combustion to be calculated. Further, based on a percent of EGR being provided from the EGR portion 13 to the engine 10 for combustion, a total amount of oxygen available for combustion may be determined.

[0015] FIG. 4 shows a method of calculating an air/fuel ratio. A fuel system 44 on the engine 10 provides information to an air/fuel ratio calculator 47 regarding an amount of fuel injected into the cylinder 34 during a combustion cycle. The air/fuel ratio calculator 47 also receives an input from the oxygen sensor 43. Thus, based on the output of the oxygen sensor 43 and the fuel system 44, the air/fuel ratio calculator 47 determines the air/fuel ratio of the engine 10. The air/fuel ratio calculator 47 communicates with an electronic control module ECM 49. The ECM 49 has a memory containing prestored data relating to air/fuel ratio for various engine operating conditions, that may be an function of engine speed, engine power output, engine operating state, temperature, altitude, air pressure, and the like.

[0016] It has been found that reducing air/fuel ratio to between about 15 and about 18 has a positive effect on reducing NO_x emissions. However, such an air/fuel ratio raises particulate emissions and increases fuel consumption. In order to overcome these drawbacks, one successful approach that has been found is to increase fuel injection pressure. This is unexpected, as typically increasing fuel injection pressure increases NO_x emissions during combustion. However, it has been found that increasing fuel injection pressure above 2500 bar while simultaneously lowering air/fuel ratio to between about 15 and about 18 results in lowered output of NO_x and particulate matter, while achieving acceptable brake specific fuel consumption. This result was unexpected as prior experimentation had shown that raising fuel injection pressure would raise NO_x emissions, while lowering particulate matter emissions, while lowering air/fuel ratio would lower NO_x emissions, but raise particulate matter emissions. Thus, conventional wisdom would suggest that such adjustments to air/fuel ratio and fuel injection pressure would negate any improvement to both particulate matter emissions and NO_x emissions from combustion. However, an unexpected improvement in these emissions levels has been found by lowering air/fuel ratio and simultaneously raising fuel injection pressure.

[0017] It is contemplated that such a method of operating an engine will initially determine an air/fuel ratio of the engine. At least one of a fuel injection quantity and an intake air flow are adjusted to cause an air/fuel ratio between about 15 and about 18 to be present in the engine. Fuel is injected into the cylinder at a pressure of at least 2500 bar for combustion. It is also contemplated that the fuel injection pressure may range from about 2500 bar to about 3500 bar. It is further contemplated that fuel injection is not initiated until a piston within the cylinder has passed a top dead center (TDC) position. It is still further contemplated that the air/fuel ratio will be below about 17.

[0018] In addition to lowering air/fuel ratio and utilizing high injection pressure, it has also been found that combustion with a break mean effective pressure (BMEP) of from about 11.5 to about 18 may be present while reducing NO_x emissions below 0.2 g/hp-hr. In order to generate a BMEP in the desired range, an amount of fuel is calculated to generate a power output for the engine to raise the BMEP to the desired range. Previous attempts to reduce NO_x emissions to the 0.2 h/hp-hr level have been limited to engines with lower BMEP levels, where far less fuel is required. [0019] Such a method of operating an engine determines an air/fuel ratio of the engine, as descr4ibved above. Once the air/fuel ratio is determined, at least one of the fuel injection quantity and the intake air flow is adjusted to provide an air fuel ratio of between 15 and about 18. A quantity of fuel is injected into the cylinder of the engine to generate a BMEP of between about 1 1.5 and about 18. It is additionally contemplated that an air/fuel ratio of less than about 17 is provided.

[0020] An alternative manner that has been found to lower formation of both NO_x emissions and particulate matter is to lower the air/fuel ratio to between about 15 and about 18, and to utilize a variable compression ratio on the cylinder of the engine. The variable compression ratio of the cylinder may use one of several designs. For instance, valve closing timing may be adjusted to reduce compression within the cylinder at higher loads, and increase compression ratio at light loading conditions and during engine startup. It is contemplated that the compression ratio of the engine 10 may be varied from about 14: 1 to 18: 1. More preferably, the compression ratio will be lower than 15.5: 1. The lower compression ratio allows lower EGR rates to be utilized, and also allows for higher boost to be utilized. In addition to utilizing a lower air/fuel ratio, it is contemplated that an engine with variable compression ratio would also increase EGR rates at lower engine power outputs, as less oxygen is required to combust the smaller amount of fuel injected. Similarly, a high EGR rate during lower power operations may also be beneficial, as the higher EGR rates increase the volume of gas being compressed within the cylinder, thereby maintaining a temperature within the cylinder to allow for complete combustion of the fuel injected, reducing the quenching effects of the fuel injection.

[0021] Thus, it has been found that the use of variable compression ratios and low air/fuel ratios may reduce NO_x emissions and particulate matter emissions to allowable levels, without the use of selective catalyst reduction systems. In order to operate an engine according to such a process, an air/fuel ratio of the engine is determined. For instance, data from the fuel system, and from an oxygen sensor allow the air/fuel ratio to be calculated. Once, the air/fuel ratio is calculated, at least one of a fuel injection quantity and an intake air flow are adjusted to provide an air/fuel ratio between about 15 and about 18. Engine operating conditions, such as torque output, and engine speed are also monitored. The compression ratio is adjusted based upon the engine operating conditions. For instance, if the engine torque output is below a threshold value, the compression ratio may be reduced.

[0022] FIG. 3 depicts a block diagram for a control system 42 for the engine 10, while FIGs. 6a and 6b depict a flow chart of a method of controlling the engine 10. The control system 42 has a fuel system control component 44 and an air system control component 46. The fuel system control component 44 has an accelerator position sensor 48 and an engine speed sensor 50. The accelerator position sensor 48 and the engine speed sensor 50 are in electrical communication with a fuel system controller 52.

[0023] The fuel system controller 52 has a memory that stores fuel injection quantity data 54, fuel injection pressure data 55 as well as fuel injection timing data 56, wherein both data 54, 56 are graphically represented with curves. The fuel injection pressure data 55 is variable, and is dependent at least in part on the in-cylinder pressure data from the group 41 of in-cylinder pressure sensors 40. For instance, the fuel injection pressure data 55 may vary proportionally with the in-cylinder pressure observed by the in-cylinder pressure sensors 40. For instance, as in-cylinder pressure increases, fuel injection pressure may also increase. The increased fuel injection pressure allows fuel injected into the cylinder 34 with a high in- cylinder pressure to penetrate to locations proximate walls of the cylinder 34 , thereby utilizing oxygen disposed within areas of the cylinder 34 not previously used for combustion. Similarly, when in-cylinder pressure is low, fuel injection pressure may be lowered to prevent an excess amount of fuel from contacting walls of the cylinder 34.

[0024] Based upon the input received from the accelerator position sensor 48 and the engine speed sensor 50, the fuel system controller 52 retrieves a fuel injection quantity output from the fuel injection quantity data 54, retrieves a fuel injection pressure output 55, and also retrieves a fuel injection timing output from the fuel injection timing data 56. The fuel injection quantity output is communicated to a fuel injection quantity comparator 58, the fuel injection pressure output is communicated to a fuel injection pressure comparator 59, while the fuel injection timing output is communicated to a fuel injection timing comparator 60.

[0025] The fuel system control component 44 additionally utilizes the group 41 of in- cylinder pressure sensors 40 that communicate with a combustion monitoring processor 64 that contains a fuel system memory 66 containing fuel injection timing correction data, fuel injection pressure correction data, and fuel injection quantity correction data based upon the output of the group 41 of in-cylinder pressure sensors 40. Outputs of the fuel system memory 66 is electronically communicated to the fuel injection quantity comparator 58, the fuel injection pressure comparator 59, and the fuel injection timing comparator 60. The fuel injection quantity comparator 58 compares the output of the fuel injection quantity data 54 with the output from the fuel system memory 66 of the combustion monitoring processor 64 to generate a corrected fuel injection quantity communicated to a fuel injector 70. The fuel injection pressure comparator 59 compares the output of the fuel injection pressure data 55 with the output from the fuel system memory 66 of the combustion monitoring processor 64 to generate a corrected fuel injection pressure communicated to a fuel injector 70. Similarly, the fuel injection timing comparator 60 compares the output of the fuel injection timing data 56 with the output from the fuel system memory 66 of the combustion monitoring processor 64 to generate a corrected fuel injection timing communicated to a fuel injector 70.

[0026] The air system control component 44 of the control system 42 for the engine 10 additionally utilizes the group 41 of in-cylinder pressure sensors 40 that communicate with the combustion monitoring processor 64 that has an air intake system memory 68. An air intake system controller 72 has a memory that stores turbocharger data 74 as well as EGR system data 76. The air intake system controller 72 retrieves a turbocharger setting from the turbocharger data 74 based upon engine operating conditions. The air intake system controller 72 additionally retrieves an EGR valve setting from the EGR system data 76. Output of the turbocharger data 74 and the air intake system memory 68 is transmitted to a turbocharger comparator 78 which compares the turbocharger data 74 with the output of the air intake system memory 68 and may adjust the turbocharger setting output using the turbocharger data 74 to generate a corrected turbocharger setting to a turbocharger 82.

[0027] The EGR system data 76 from the air intake system controller 72 is transmitted to an EGR system comparator 80 where the EGR system comparator 80 compares it to the output of the air intake system memory 68 and may adjust the EGR setting output using the EGR system data 76 to generate a corrected EGR system setting to an EGR valve 84.

[0028] A variety of approaches may be utilized to adjust fuel injection pressure. For instance, in a common-rail fuel system, a pressure relief valve may be provided at an outlet of the common-rail in order to reduce the pressure of the fuel injection. Similarly, a pressure relief valve may be provided at each injector, or in a fluid line in fluid communication with a fuel injector, so that fuel pressure at the injector is reduced. In a unit injector, a length of travel of a piston may be adjusted to vary the pressure of fuel injected by the injector. Such an variable piston travel may be implemented by a variable profile cam surface. Similarly, a piston-type fuel pump may have a variable cam surface to modify the length of travel of the piston used to pressurize the fuel that is fed to injectors to vary the injection pressure.

[0029] Additionally, it is contemplated that adjustments can be made to diameters of flow paths within fuel injectors to modify the pressure of fuel leaving the injector. For instance, the diameter of the flow path may be reduced in order to increase pressure, or the diameter of the flow path may be increased to reduce the pressure of fuel injected into the cylinder. [0030] Further, in addition to adjusting the diameter of the flow path within a fuel injector, it is also contemplated that relief valves may be provided on each injector to reduce the injection pressure below its maximum value. The pressure relief valve could be electronically actuated to allow a portion of the fuel passing through the injector to drain back to a fuel tank of a vehicle.

[0031] Balancing the ratio between fuel injection pressure and in-cylinder pressure is beneficial in obtaining atomization of fuel within the cylinder 34. Proper atomization of the fuel allows more of the oxygen available within the cylinder to be utilized, thereby allowing higher rates of EGR to be used during combustion to reduce the formation of NO_x during combustion. Controlling fuel injection pressure also allows more accurate control of the timing of combustion of fuel, allowing the temperature generated by combustion of fuel to be more accurately controlled.

Claims

CLAIMS What is claimed is:

1. A method of operating an internal combustion engine comprising:

determining an air/fuel ratio of an internal combustion engine;

adjusting at least one of fuel injection quantity and intake air flow to provide an air/fuel ratio between about 15 and about 18; and

injecting a quantity of fuel sufficient to generate a brake mean effective pressure of between about 11.5 and about 18.

2. A method of operating an internal combustion engine comprising:

determining an air/fuel ratio of an internal combustion engine;

adjusting at least one of fuel injection quantity and intake air flow to provide an air/fuel ratio less than 17; and