WO2009074069A1

WO2009074069A1 - A compression ignition engine with a combination of features to reduce emissions

Info

Publication number: WO2009074069A1
Application number: PCT/CN2008/073228
Authority: WO
Inventors: Zhicheng Huang
Original assignee: Caterpillar Inc.
Priority date: 2007-11-30
Filing date: 2008-11-27
Publication date: 2009-06-18
Also published as: CN101451481A

Abstract

A compression ignition engine (10) has a combination of a dual spring fuel injector (17), a piston (13) with dual piston rings (15,16), a turbocharger (21), an exhaust gas recirculation system (25) and an air-to-air after cooler (20). The fuel injector (17) has two springs (50,51) in series to produce two different injection rates and two valve opening pressures. A lower injection rate is produced when only one spring (50) is compressed while a higher injection rate is produced when the second spring (51) is also compressed. Each piston in the engine housing has a groove (14), and two piston rings (15,16) are located the groove (14). In addition, two piston rings (15,16) partially define a lubricating oil accumulation cavity (60) that better seals the combustion space.

Description

A COMPRESSION IGNITION ENGINE WITH A COMBINATION OF FEATURES TO REDUCE EMISSIONS

Technical Field

[0001] The present disclosure relates generally to compression ignition engines, and relates more particularly to a combination of features to reduce emissions.

Background

[0002] Engineers are constantly seeking new ways to reduce undesirable emissions from internal combustion engines. Among the emissions of concern with regard to compression ignition engines are NOx, hydrocarbons and particulate matter. Current strategies to reduce undesirable emissions are primarily related to efforts to avoid generating undesirable emissions at the time of combustion, and thereafter relying upon aftertreatment systems to further reduce undesirable emissions before the exhaust is vented to atmosphere via a tail pipe. With regard to the former, the problem has been attacked via various combinations of compression ratio, injection timing, injection rate shapes, exhaust gas circulation, ignition techniques, and many others. Although each one of these individual strategies may be useful in reducing at least one of the types of undesirable emissions, that same strategy often may increase another emissions component. For instance, strategies to reduce NOx through a cooler combustion may conflict with more complete combustion to reduce unburnt hydrocarbons or particulate matter. A combustion strategy that results in acceptable levels in all undesirable emissions categories remains elusive, both because a more complete understanding of the combustion reactions needed, and the less than predictable nature of adjustments to a multitude of interactive variables. [0003] Various individual features are known in the art for improving performance and reducing undesirable emissions. Among these are the use of one or more turbochargers to boost intake pressure. Without need to cite to any specific reference, others have been known to recirculate exhaust gas as an additional technique in both improving emissions. Other engine manufacturers may employ an air-to-air aftercooler to cool pressure boosted air that may or may not be mixed with recirculated exhaust gas. Other individual techniques are also known. For instance, U.S. Patent 5,467,924 to Buesher et al. teaches a strategy for reducing sac volume in a fuel injector in order to reduce exhaust emissions. In another reference, U.S. Patent 4,448,356 to Nakajima et al. shows a concept for a staged fuel injector that includes a nozzle valve member biased with two springs in series. Lower pressures and shorter injection events compress only one of the springs to partially open the nozzle outlets. At higher speeds and loads, longer fuel injections at higher pressure cause the nozzle valve member to move further upwards to compress the second spring for higher injection rates. In another reference, U.S. Patent 7,044,473 to Zhu et al. shows a dual piston ring strategy that supposedly helps to prevent the combustion of engine lubricating oil and the associated elevated emissions therefrom. Various features that can assist in reducing undesirable emissions and/or improving performance are known in the art. However, engineers have continued to struggle with the problem of which combination of features will interact in a way to produce an overall acceptable level of performance and an associated overall reduction in undesirable NOx, hydrocarbon and particulate matter emissions. [0004] The present disclosure is directed to one or more of the problems or set forth above.

Summary of the Invention

[0005] In one aspect, the present disclosure provides an engine having a housing with at least one cylinder disposed therein, an intake port and an exhaust port. A piston is positioned in each of the cylinders, and each of the pistons has an outer cylindrical surface with at least one groove. An upper piston ring and a lower piston ring are located in the groove. The upper piston ring and the lower piston ring partially define a lubricating oil accumulation cavity. A fuel injector is positioned to inject fuel into each cylinder. Each fuel injector includes a fuel nozzle outlet and a fuel nozzle member. The fuel nozzle member is movable to open and close the fuel nozzle outlet. A first spring and a second spring in series bias the fuel nozzle member toward a closed position. The engine also includes a turbocharger having a turbine, a turbine inlet, a compressor, and a compressor outlet. The turbine inlet is fluidly connected to the exhaust port, and the compressor outlet is fluidly connected to the intake port. The engine further includes an exhaust gas recirculation system (EGR) having an EGR passage, an EGR valve, an EGR inlet and an EGR outlet. The EGR valve is inside the EGR passage. The EGR inlet is fluidly connected to the exhaust port, and the EGR outlet is fluidly connected to the intake port. Lastly, the engine includes an air- to-air after cooler (ATAAC) that is fluidly connected to the intake port. [0006] In another aspect, the present disclosure provides a method of operating an engine. The method includes a step of injecting fuel into a cylinder at a low rate by compressing a first spring of two springs in series and then injecting fuel at a higher rate by also compressing a second spring. In addition, the method includes the step of accumulating oil in a cavity between an upper piston ring and a lower piston ring that are located in a groove in a piston. A mixture of fresh air and recirculated exhaust are cooled in an air-to-air aftercooler and then supplied to each cylinder. At least one of the fresh air and recirculated exhaust boosted in pressure via a compressor of a turbocharger.

Brief Description of the Drawings

[0007] Figure 1 is a schematic view of an engine according to one embodiment of the present disclosure;

[0008] Figure 2 is a schematic view of a fuel injector of the engine of Figure 1 according to one aspect of the present disclosure; -A-

[0009] Figure 3 is an enlarged sectioned view of a fuel nozzle of the fuel injector of Figure 2.

[0010] Figure 4 is a partial enlarged sectioned view of upper and lower piston rings of the engine of Figure 1 according to another aspect of the present disclosure; and

[0011] Figure 5 is a graph of the relationship between PM and NOx emissions.

Detailed Description

[0012] Referring to Figure 1, there is shown an engine 10. In one embodiment, a housing 11 has cylinders 12 disposed therein. A piston 13 is positioned to reciprocate inside each cylinder. A groove 14 in each piston 13 includes an upper piston ring 15 and a lower piston ring 16 located in the groove. A fuel injector 17 is placed so as to inject fuel into the cylinder 12. Each fuel injector 17 may include a spill valve 18 to control the timing of the injection. An intake port 32 brings air into the cylinder 12, and an exhaust port 33 removes exhaust out of the cylinders 12. An air-to-air after cooler (ATAAC) 20 is fluidly connected to the intake port 32 to cool air before entering the cylinder 12. The ATAAC 20 may be constructed with stainless steel, or another corrosive resistant material. A turbocharger 21 is fluidly connected to the exhaust port 33. The exhaust enters a turbocharger intake port 22 and turns a turbine of the turbocharger, which spins a compressor 23. A compressor outlet port 24 is fluidly connected to intake port 32, and the compressor 23 compresses the intake air. In addition, an exhaust gas recirculation (EGR) system 25 is used to adjust the concentration of exhaust gas that mixes with the intake air. An EGR intake port 27 is fluidly connected to the exhaust port 33. An EGR passage 34 connects the EGR inlet port 22 with an EGR outlet 28. An EGR valve 26 in the EGR passage controls the amount of exhaust that passes through the EGR outlet 28. The ATAAC 20, the compressor 23 and the EGR outlet 28 are all fluidly connected to the intake port 32. [0013] These components can be organized in any suitable order; however, the order presented in Figure 1 in the illustrated embodiment shows intake air mixing with exhaust gas, then the mixture enters the compressor, passes through the ATAAC 20, and the cooled boosted mixture enters the intake port 32 of engine 10. Similarly, the turbocharger 21 and the EGR inlet 22 can be in any suitable order; however, the illustrated embodiment allows the exhaust gas to pass though the turbocharger 21 followed by a low pressure EGR sys tern 25. A reduction catalytic converter 29 and a particulate filter 30 may also be fluidly connected to the exhaust port 33. An electronic controller 31 electronically communicates with the EGR valve 26 and the spill valve 18 to control the amount of exhaust gas that flows though the EGR passage and to control the injection timing, respectively.

[0014] Referring to Figure 2, the fuel injector 17 includes a fuel injector body 40 with a nozzle valve member 41 that resides inside the fuel injector body. Rotation of a cam 36 actuates fuel injector piston 37 to displace fuel from fuel chamber 38 either into fuel supply passage 47, or to drain 39 via spill valve 18 in a conventional manner. The fuel supply passage 47 brings fuel to a fuel nozzle outlet 48. A fuel nozzle member comprises two separate sections, a lower fuel nozzle member 41a and an upper fuel nozzle member 41b, that are separated by a lift gap 46. A first spring 50 is located between a first stationary spring seat 44 and a first moveable spring seat 42. The first spring biases the lower fuel nozzle member 41a to close fuel nozzle outlet 48. A second spring 51 is located between a second stationary spring seat 45 and a second moveable spring seat 43. The second spring 51 is in series with the first spring. The second spring biases the upper fuel nozzle member 41b toward the lower fuel nozzle member 41a. The fuel nozzle outlet 48 is in a partially open position when the first spring 50 is compressed, and the fuel nozzle outlet 48 is in a fully open position when the lift gap 46 is closed and the second spring 51 is also compressed. Thus first spring has a lower preload defining a low valve opening pressure, while the greater preload of the second spring produces a higher valve opening pressure. [0015] Referring to Figure 3, an enlarged view of the fuel nozzle outlet section of fuel injector 17 is shown. The fuel nozzle outlet 48 is shown in a closed position where the nozzle valve member 41 is in contact with a fuel nozzle seat 53, wherein the fuel nozzle seat is part of the fuel injector body 40. A sac 49 is formed by the space between the nozzle valve member 41 and the fuel injector body 40. Fuel injector orifices 52 fluidly connect the sac 49 and the cylinder 12 (Fig. 1). One embodiment may include six injector orifices in a typical spray pattern. Each injector orifice 52 may have a diameter of about 0.25 mm with an injection spray pattern angle of about 153°. A corresponding sac volume of about 0.8 mm³ has dimensions of about 1.0 mm in diameter and about 1.0 mm in length. The term "about" means that when the number is rounded to the number of significant digits, they are equal. For instance, 0.75 is about 0.8. Another embodiment may be shaped so that each injector orifice 52 has a diameter of about 0.23 mm with a sac volume of about 0.4 mm³ and dimensions of about 0.8 mm diameter and about 0.8 mm length. Reduction in the injector orifice diameter may improve fuel atomization at a given fuel pressure, but reduction in injector orifice diameter reduces the total injector orifice area and hence injection rate. More orifices may be needed to maintain the total injector orifice area as the injector orifice diameter is decreased. A reasonably small sac volume is generally preferred. Fuel often remains in the sac after injection and may not burn until a subsequent injection event. Unburned fuel may leave the sac at low pressure into the cylinder and be expelled along with the exhaust gas resulting in an increase in emissions when the sac 49 is too large.

[0016] Referring to Figure 4, a cross section view of the upper piston ring 15 and the lower piston ring 16 are shown located in the groove 14 of the piston 13. A lubricating oil accumulation cavity 60 is partially defined by the upper piston ring 15 and the lower piston ring 16. The housing 11 or a cylinder liner completes the defined area of the lubricating oil accumulation cavity 60. The upper piston ring 15 may have an outer cross section thickness 61 and an inner cross section thickness 62. Likewise, the lower piston ring 16 may have an outer cross section thickness 63 and an inner cross section thickness 64. At least one of the upper piston ring 15 and the lower piston ring 16 are may have a frustoconical surface. In the illustrated embodiment, rings 15 and 16 have two frustoconical surfaces with different cone angles. In addition, the outer cross section thickness 63 may be greater than the inner cross section thickness 64 of the lower piston ring 16. The inner cross section thickness 62 may be greater than the outer cross section thickness 61 of the upper piston ring 15. And, an average cross section thickness of the upper piston ring 15 may be greater than the lower piston ring 16. In some applications, upper piston ring 15 and the lower piston ring 16 may be constructed or coated to have superior wear and corrosion resistance. For instance, a protective coating such as chromyl can be used that has superior wear and corrosion resistance compared to the base material, which may be steel.

Industrial Applicability

[0017] The present disclosure is applicable for compression ignition engines. More particularly, the disclosure is applicable to a combination of features to reduce undesirable emissions from such an engine.

[0018] Referring to the drawing generally, the operation of a compression ignition engine 10 of the present disclosure comprises continuous cycles, and each cycle contains a series of steps. First the piston 13 in the cylinder 12 moves downward in an intake stroke, and air is drawn into the cylinder from the intake port 32. The intake port is closed, and the piston 13 is then raised during a compression stroke. When the piston 13 is at a desired engine angle in a vicinity of top dead center, fuel is injected into the cylinder from the fuel injector 17 by electronically closing spill valve 18 via command from electronic controller 31. Fuel is injected by the fuel injector by first sending pressurized fuel into the fuel supply passage 47. Once the fuel pressure is great enough to compress the first spring 50 and move the lower nozzle member 41a up, fuel is injected into the cylinder at a first low injection rate. As fuel pressure increases, the lower nozzle member moves up further, it closes the lift gap 46. The fuel pressure will continue to increase until fuel pressure is great enough to also compress the second spring 51 and close lift gap 46. The upper and lower nozzle members 41a and b move up together resulting in a second higher injection rate. The resulting second injection rate is greater than the first injection rate because a flow area past seat 53 increases. In addition to the fuel injector controlling the injection rate, the spill valve 18, electronically controlled by the electronic controller, can open and close to stop and start the injection, respectively, at selected timings somewhat independent of engine crank angle.

[0019] Once fuel is injected into the cylinder, combustion of the air and fuel mixture occurs and forces the piston 13 back down for the power stroke. The exhaust port 32 is opened and the piston 13 is raised back up to expel exhaust out the exhaust port for the exhaust stroke. As the piston 13 moves up and down, oil is accumulated in the oil accumulation cavity 60 between the upper piston ring 15 and the lower piston ring 16. The upper piston ring 15, the lower piston ring 16 and the oil accumulation cavity 60 may block combustion air from escaping the cylinder and also block lubricating oil from entering the cylinder. The first of these effects can improve the overall combustion and avoid unburned hydrocarbons from occurring, and the latter may reduce emissions by avoiding combustion of lubricating oil.

[0020] Exhaust gas enters a turbocharger 21 though the turbocharger intake 22 where the exhaust gas turns a turbine. The turbine of the turbocharger then spins a compressor 23. The compressor boosts intake pressure by compressing intake air prior to entering the cylinder 13. The exhaust gas then goes though the EGR system 25 where some of the exhaust gas is recirculated and enters the EGR intake port 27, passes though the EGR passage 34, exits out the EGR outlet port 28, and mixes with the intake air. The EGR valve 26, which may be electronically controlled by the electronic controller 31 to control the amount of exhaust gas that passes though the EGR passage, thereby adjusting a portion of exhaust gas in an intake mixture. The exhaust gas then passes though a reduction catalytic converter 29 and particulate filter 30 to further reduce undesired emissions and trap particulate matter before being vented to atmosphere. [0021] The present disclosure offers numerous advantages over previous compression ignition engines. Referring to Figure 5, PM and NOx are generally inversely related. As the combustion becomes more perfected, the amount of NOx increases while PM decreases. Therefore, other components of the compression ignition engine need to be improved upon in order to decrease PM and NOx at the same time. Each line of the graph of Figure 5 moving from right to left illustrates one individual additional improvement to the engine. The illustration demonstrates that the addition of all the features described above can have the combined result of significant decrease in both PM and NOx. [0022] The first emissions improvement feature is the injector 17 with the first spring 50 and the second spring 51 that produce an injection with two different rates. With the first injection rate lower than the second injection rate, there may be a reduction in the amount of NOx and PM in the exhaust. In addition, small injections that occur at idle and low load may be more easily controlled. In addition, the dual spring construction of fuel injector 17 inherently produces front end rate shaping (ramp or boot shape) to reduce emissions at higher loads and speeds. . The second feature is the inclusion of the upper piston ring 15 and the lower piston ring 16. The two piston rings along with the lubricating oil accumulation cavity 60 may improve the ability to seal the combustion air from the lubricant oil, which in turn reduces the exhaust pollutants by promoting more complete combustion. In addition, there are other features such as the EGR system 25, the ATAAC 20, the turbocharger 21, the reduction catalytic converter 29 and particulate filter 30 that decrease the amount of PM, hydrocarbons and NOx in the exhaust. The combination of these improvements reduces PM and NOx emissions more than any individual improvement is able to alone. [0023] The present description is for illustrative purposes only, and should not be construed to narrow the breadth of the present disclosure in any way. Thus, those skilled in the art will appreciate that various modification might be made to the presently disclosed embodiments without departing from the full and fair and scope and spirit of the present disclosure. For example, the order of components attached to the exhaust port 33, such as the turbocharger 21, the EGR 25, the reduction catalytic converter 29 and the particulate filter 30, can be arranged into any configuration including not using all the components. Similarly, the components attached to the intake port 32, such as the ATAAC 20, compressor 23, and EGR outlet 28, can be arranged into any configuration including not using all the components. For another example, the geometry of the groove, the upper piston ring and the lower piston ring can vary. Those skilled in the art would appreciate that the space between the upper piston ring and the lower piston ring forming the oil accumulation cavity can be achieved with other geometries. Other aspects, features and advantages will be apparent from an examination of the attached drawings and appended claims.

Claims

Claims What is claimed is:

1. An engine comprising: a housing with at least one cylinder disposed therein, an intake port, and an exhaust port; a piston positioned in each of the cylinders, and each of the pistons has an outer cylindrical surface with at least one groove; an upper piston ring and a lower piston ring located in the groove, wherein the upper piston ring and the lower piston ring partially define a lubricating oil accumulation cavity; a fuel injector positioned for injection of fuel into each cylinder, each fuel injector includes a fuel nozzle outlet, a fuel nozzle member wherein the fuel nozzle member is movable to open and close the fuel nozzle outlet, and a first spring and a second spring in series to bias the fuel nozzle member toward a closed position; a turbocharger having a turbine, a turbine inlet, a compressor, and a compressor outlet, the turbine inlet is fluidly connected to the exhaust port, and the compressor outlet is fluidly connected to the intake port; an exhaust gas recirculation (EGR) system having an EGR passage, an EGR valve, an EGR inlet and an EGR outlet, wherein the EGR valve is inside the EGR passage, the EGR inlet is fluidly connected to the exhaust port, and the EGR outlet is fluidly connected to the intake port; an air-to-air after cooler (ATAAC) fluidly connected to the intake port.

2. The engine of claim 1 wherein the fuel injector includes a spill valve and an electronic controller that electronically communicates with the spill valve.

3. The engine of claim 2 including: a particulate filter and a reduction catalytic converter that are fluidly connected to the exhaust port.

4. The engine of claim 1 wherein the fuel nozzle member includes: a lower fuel nozzle member and an upper fuel nozzle member; wherein a volume between the lower fuel nozzle member and the upper fuel nozzle member define a fuel nozzle member gap; wherein the fuel nozzle outlet is in a partially open position when the first spring is compressed, and the fuel nozzle outlet is in a fully open position when the gap is closed and the second spring is also compressed.

5. The engine of claim 4 includes: a fuel injector body that encompasses the nozzle valve member; wherein the fuel injector body and the fuel nozzle outlet define a sac, the sac includes a hemispherical portion and a cylindrical portion, and the radius of the hemispherical portion is about equal to the radius of the cylindrical portion.

6. The engine of claim 5 wherein the length of the sac is about equal to the diameter of the hemispherical portion.

7. The engine of claim 6 including: six injector orifices on the fuel nozzle outlet.

8. The engine of claim 1 wherein at least one of the upper piston ring and the lower piston ring has at least one surface that is a frustoconical surface.

9. The engine of claim 8 wherein at least one frustoconical surfaces have at least two frustoconical surfaces with different cone angles.

10. The engine of claim 9 wherein an outer cross section thickness is greater than the inner cross section thickness of the lower piston ring, an outer cross section thickness is less than the inner cross section thickness of the upper piston ring, and an average cross section thickness of the upper piston ring is greater than the lower piston ring.

11. The engine of claim 10 wherein the upper piston ring and lower piston ring include a base material and a coating material, and the coating material has greater wear resistance and corrosion resistance than the base material.

12. The engine of claim 11 wherein the upper piston ring and the lower piston ring have a chromyl coating.

13. A method of operating an engine, comprising the steps of: injecting fuel into a cylinder at a low rate by compressing a first spring of two springs in series and then injecting fuel at a higher rate by also compressing a second spring; accumulating oil in a cavity between an upper piston ring and a lower piston ring that are located in a groove in a piston; boasting intake pressure by spinning a compressor with a turbine of a turbocharger; recirculating exhaust gas from an exhaust port to an intake port; adjusting a portion of exhaust gas in an intake mixture. cooling an intake mixture prior to the intake mixture entering the cylinder.

14. The method of claim 13 including a step of controlling an injection timing with a spill valve.

15. The method of claim 13 including a step of trapping particulate matter in an exhaust passage and passing exhaust gas through a reduction catalytic converter.

16. The method of claim 13 wherein the injecting fuel step includes partially opening a fuel nozzle outlet when the first spring is compressed and fully opening the fuel nozzle outlet when the second spring is compressed.