WO2003010423A1

WO2003010423A1 - Combustion chamber

Info

Publication number: WO2003010423A1
Application number: PCT/US2002/022765
Authority: WO
Inventors: Zhengbai Liu; Xinqun Gui
Original assignee: International Engine Intellectual Property Company, Llc.
Priority date: 2001-07-23
Filing date: 2002-07-18
Publication date: 2003-02-06
Also published as: CN1556894A; JP2004536992A; EP1409858A4; BR0211398A; KR20040021645A; EP1409858A1; CN1302200C; MXPA04000642A; CA2454719A1

Abstract

A combustion chamber assembly for use in a diesel engine includes a combustion chamber (14) being defined in a crown (12) of a piston (10), the piston (10) having a central axis (16, 18, 518, 524), the combustion chamber (14) having a center portion defining a post, the center portion being defined at least in part by a portion of a sphere, the sphere having a radius, the origin of the radius lying on the piston central axis (16, 18, 518, 524) and the combustion chamber (14) further having a plurality of curved surfaces having smooth tangential transitions between adjacent smooth surfaces, the smooth surfaces including the spherical center portion and at least one annular surface, the combustion chamber (14) being symmetrical with respect to a combustion chamber longitudinal axis (16, 216, 316, 416). A piston (10) incorporating the aforementioned combustion chamber (14) and a method of forming the combustion chamber (14) are further included.

Description

COMBUSTION CHAMBER Technical Field The present invention relates to a combustion chamber designed for use in a compression ignition (diesel) internal combustion engine. More particularly, the present invention relates to a piston having a combustion chamber defined in the crown thereof.

Background of the Invention

Many attempts have been made to produce an ideal flow pattern for the charge of air and fuel within the combustion chamber of an internal combustion engine.

Considerations that must be taken into effect include, but are not limited to, providing for adequate power generation minimizing the NO_x entrained in the engine exhaust and minimizing the amount of soot particulate also entrained in the engine exhaust.

It is known that changes in any one of a variety of engine design/operating variables, such as engine compression, combustion chamber shape, fuel injection spray pattern, and other variables can have an effect on both emissions and power generated.

The amount of soot that is expelled with the engine's exhaust is unsightly and generates public pressure to clean up diesel engines. Further, the amount of soot that is entrained in the engine's lubrication oil can have a deleterious effect on engine reliability. Soot is very abrasive and can cause high engine wear.

There is additionally a great deal of pressure to reduce the NO_x emissions from the engine. Increasingly stringent regulatory demands mandate reduced levels of NO_x.

Typically, a combustion chamber design that is effective at reducing NO_x levels has been found to increase the levels of soot and vice-versa. Additionally, doing either of the aforementioned typically reduces engine torque and power outputs.

There are numerous examples of combustion chambers formed in the crown of piston. Notwithstanding all these prior art designs, there remains a need for reduction both in NO_x and entrained soot while at the same time maintaining or enhancing engine torque and power outputs.

Summary of the Invention The combustion chamber of the present invention substantially meets the aforementioned needs in the industry. The combustion chamber defined in the crown of the piston has been shown to both reduce soot entrainment and NO_x emissions while at the same time slightly increasing engine power output. The piston has been shown to function effectively with heads having two or more valves. A further advantage of the combustion chamber and of the present invention is that by being symmetrical with respect to a piston central axis, the combustion chamber is relatively easily formed in the crown of the piston. The present invention is a combustion chamber assembly for use in a diesel engine includes a combustion chamber being defined in a crown of a piston, the piston having a central axis, the combustion chamber having a center portion defining a post, the center portion being defined at least in part by a portion of a sphere, the sphere having a radius, the origin of the radius lying on the piston central axis and the combustion chamber further having a plurality of curved surfaces having smooth tangential transitions between adjacent smooth surfaces, the smooth surfaces including the spherical center portion and at least one annular surface, the combustion chamber being symmetrical with respect to a combustion chamber longitudinal axis. The present invention is further a piston having the aforementioned combustion chamber assembly and a method of forming the aforementioned combustion chamber.

Brief Description of the Drawings Fig. 1 is a sectional view of the piston of the present invention; Fig. 2 is a graphic representation of power of an existing piston and combustion chamber as compared to the piston and combustion chamber of the present invention;

Fig. 3 is a graphic representation of an NO_x generated by an existing piston and combustion chamber and the piston and combustion chamber of the present invention;

Fig. 4 is a graphic representation of the soot generated by an existing piston and combustion as compared to the piston and combustion chamber of the present invention; Fig. 5 is a sectional view of the piston of a second embodiment of the present invention;

Fig. 6 is a graphic representation of power of an existing piston and combustion chamber as compared to the piston and combustion chamber of the second embodiment of the present invention; Fig. 7 is a graphic representation of an NO_x generated by an existing piston and combustion chamber and the piston and combustion chamber of the second embodiment of the present invention;

Fig. 8 is a graphic representation of the soot generated by an existing piston and combustion as compared to the piston and combustion chamber of the second embodiment of the present invention;

Fig. 9 is a sectional view of the piston of a third embodiment of the present invention;

Fig. 10 is a graphic representation of an NO_x generated by an existing piston and combustion chamber and the piston and combustion chamber of the third embodiment of the present invention;

Fig. 11 is a graphic representation of the soot generated by an existing piston and combustion as compared to the piston and combustion chamber of the third embodiment of the present invention; Fig. 12 is a sectional view of the piston and combustion chamber of a fourth embodiment of the of the present invention;

Fig. 13 is a graphic representation of pressure with respect to crank angle of empirical data of a prior art engine, B0, a simulation of the same engine to substantiate the validity of the simulation and a simulation of an engine with pistons and combustion chambers of the fourth embodiment of the fourth embodiment of the present invention, B44a;

Fig. 14 is a graphic representation of an NO_x generated by the prior art B0 piston and combustion chamber as compared to the piston and combustion chamber of the fourth embodiment of the of the of the present invention, B44a;

Fig. 15 is a graphic representation of the soot generated by the prior art B0 piston and combustion chamber as compared to the piston and combustion chamber of the fourth embodiment of the present invention, B44a;

Fig. 16 is a sectional view of the piston and combustion chamber of a fifth embodiment of the present invention;

Fig. 17 is a graphic representation of NO_x generated with respect to crank angle of empirical data of a prior art engine, B0, a simulation, B0, of the same engine to substantiate the validity of the simulation, substantially overlying the empirical data, and a simulation of an engine with pistons and combustion chambers of the fifth embodiment of the present invention, B27; and

Fig. 18 is a graphic representation of the soot generated by the prior art BO piston and combustion chamber as compared to the piston and combustion chamber of the fifth embodiment of the present invention, B27.

Detailed Description of the Drawings First Embodiment

The piston of the present invention is shown generally at 10 in Fig. 1. The crown 12 of the piston 10 defines in part the upper margin of the piston 10. The combustion chamber 14 of the present invention is defined in the 12. It should be noted that the combustion chamber 14 is symmetrical about the longitudinal axis 16 that is coincident with the center axis of the piston 10. The various radii (R), diameters (D), and heights (H) that will be described below are clearly indicated in the depiction of Fig. 1. The piston 10 of the present invention is designed primarily for use in heavy duty diesel engines but would also be applicable to lighter duty diesel engines. The piston 10 may be utilized with two-valve or multiple- valve heads. It is desirable that the fuel be injected proximate the center of the piston and that the injection pattern be radially - symmetrical. In a preferred embodiment, the injector injects a spray of fuel that has six subsprays that are equi-angularly displaced relative to the axis 16.

The combustion chamber 14 defined in the crown 12 of the piston 10 is comprised of curved surfaces, being both spherical and annular surfaces. The spherical surfaces are designated by a radius RS and the annular surfaces are designated by a radius R. The combustion chamber 14 has no flat surfaces. There is a smooth, tangential transition between the various curved surfaces that define the combustion chamber 14, as described in greater detail below.

Generally, the combustion chamber 14 is comprised of two spherical surfaces RSI and RS2, the spherical surface RSI defining a center post 17. The two spherical surfaces RSI and RS2 are connected by an annular surface Rl at the bottom of the combustion chamber 14. The spherical surface RS2 transits to the piston crown 12 by two annular surfaces R2, R3 having relatively small curvatures and defining a reentrant intersection with the crown 12. A diameter dimension is noted by D and a height dimension is noted by H.

There are a number of parameters that control the geometry of the combustion chamber 14 and thereby control the diesel engine combustion performance as well as NO_x and soot emissions. A portion of a spherical surface, defined by the radius RSI, is located in the central space (center portion) of the combustion chamber 14. The origin 18 of the spherical surface RSI is located on the center axis 16 of the piston 10. The distance between the origin 18 of the spherical surface RSI and the point of intersection of the axis 16 with the bottom plane 20 of the combustion chamber 14 is equal to or greater than zero and should be less than 0.25 D2. As depicted in Fig. 1, the origin 18 is at the point of intersection 22 of the axis 16 of the combustion chamber 14 and the bottom plane 20 of the combustion chamber 14. In other words, the origin 18 and the point of intersection 22 are depicted as being coincident. This is the preferred disposition of the origin 18 at the point of intersection 22 of the axis 16 of the combustion chamber 14 and the bottom plane 20 of the combustion chamber, but there could as well be a vertical height distance between the origin 18 and the point of intersection 22.

The second spherical surface, having a radius RS2, is located outside the first (center portion) spherical surface RS 1 and defines in part an outer margin of the combustion chamber 14. The outer margin spherical surface RS2 has an origin 23 that is located on the center axis 16. The distance between the respective two origins 22, 23 of the center portion spherical surface RSI and the outer margin spherical surface RS2 is equal to or greater than 0.0 and less than ±2(R1). Preferably, the distance is zero, the two origins 22, 23 being co- centric and preferably located at the intersection of the central axis 16 and the bottom plane 20 of the combustion chamber 14. It should be noted that the distance value is positive when the origin 23 is elevated with respect to the origin 22, a positive distance HI being depicted in Fig. 1. Further, the ratio of RS2/RS1 is equal to or greater than 1.0 and less than 3.0. The ratio of RS2/RS1 is preferably about 2.0 and more specifically 2.073.

The following ratios define certain parameters of the combustion chamber 14. a. The ratio of RS1/D2 should be greater than 0.10 and should be less than 0.45 and is preferably 0.253. b. The ratio of D2 /Dl should be greater than 0.45 and should be less than 0.85 and is preferably 0.619. c. The ratio of D3/D2 should be greater than 0.75 and should be less than 0.95 and is preferably 0.849. d. The ratio of H/D2 should be greater than 0.15 and should be less than 0.45 and is preferably 0.337. e. The ratio of R1/D2 should be greater than 0.11 and should be less than

0.45 and is preferably 0.136. f. The ratio of R2/D2 should be greater than 0.0 and should be less than 0.35 and is preferably 0.11. g. The ratio of R3/D2 should be greater than 0.0 and should be less than 0.2 and is preferably 0.14.

The combustion chamber 14 as indicated above is comprised of combined spherical and annular surfaces. It is noted that the transition between RSI and Rl is smooth and tangential, the transition between Rl and RS2 is smooth and tangential, the transition between RS2 and R2 is smooth and tangential, and the transition between R2 and R3 is smooth and tangential. In this manner, there are no flat surfaces that define the combustion chamber 14. The curves and smooth transitions as previously described promote smooth flow in the combustion chamber 14 and act to reduce the thermal loading in the combustion chamber 14. Further, the combustion chamber 14 is symmetrical about the axis 16. Accordingly, it is much easier to turn the combustion chamber 14 as compared to an asymmetrical combustion chamber defined in a piston.

It should further be noted that the radii R2, R3 define a reentrant combustion chamber 14 at the intersection with the crown 12, as distinct from an open combustion chamber as depicted in some of the prior art.

Combustion performance improvement and pollutant emission reduction are depicted in Figs. 2-4. Referring to Fig. 2, power output is the area beneath each of the curves. A first actual experiment of a known combustion chamber is depicted at curve 24. Close to the peak of the curve 24, a trace of a simulation of the known combustion chamber that resulted in the curve 24 closely overlies the curve 24. The trace 26, by closely overlying the curve 24, substantiates the validity of the simulation. This same simulation was then used to simulate the performance of the combustion chamber 14. The simulation of the combustion chamber 14 is depicted by curve 28. It is noted that the area underneath the curve 28 is slightly greater than the area underneath the curve 24, indicating that the power output resulting from the combustion chamber 14 is slightly greater than the power output of the known combustion chamber.

Fig. 3 depicts the NO_x generation of a known combustion chamber as depicted by line 26 and the simulated results of NO_x generation of the combustion chamber 14 of the present invention as depicted in line 28. It is noted that the NO_x generation by the combustion chamber 14 of the present invention is significantly less than the NO_x of the known combustion chamber as depicted by line 6.

Fig 4 depicts the simulated soot generation of a known combustion chamber as depicted by line 26 in comparison with the simulated soot generation of the combustion chamber 14 of the present invention as depicted by line 28. It should be noted that soot • generation of the combustion chamber 14 is significantly less than the soot generation of the known combustion chamber. It is significant to note in reference to Figs. 2-4 that the combustion chamber 14 results in increased power output and at the same time that combustion chamber 14 decreases both the NO_x generation and soot generation as compared to a known combustion chamber.

Second Embodiment

The piston of the present invention is shown generally at 210 in Fig. 5. The crown 212 of the piston 210 defines in part the upper margin of the piston 210. The combustion chamber 214 of the present invention is defined in the crown 212. It should be noted that the combustion chamber 214 is symmetrical about the longitudinal axis 216 that is coincident with the center of the piston 210. The various radii (R), diameters (D), and heights (H) that will be described below are clearly indicated in the depiction of Fig. 5.

The piston 210 of the present invention is designed primarily for use in heavy duty diesel engines but would also be applicable to lighter duty diesel engines. The piston 210 may be utilized with two-valve or multiple- valve heads. It is desirable that the fuel be injected proximate the center of the piston and that the injection pattern be radially symmetrical. In a preferred embodiment, the injector injects a spray of fuel that has six subsprays that are equi-angularly displaced relative to the axis 216.

The combustion chamber 214 defined in the crown 212 of the piston 210 is comprised of curved surfaces, being both spherical and annular surfaces. The combustion chamber 214 has no flat surfaces. There is a smooth, tangential transition between the various curved surfaces that define the combustion chamber 214, as described in greater detail below.

There are a number of parameters that control the geometry of the combustion chamber 14 and thereby control the diesel engine combustion performance as well as NO_x and soot emissions. A portion of a spherical surface, defined by the radius Rl, is located in the central space of the combustion chamber 214 and defines a center post 217. The origin 218 of the spherical surface Rl is located on the center axis 216 of the piston 210. The distance between the origin 218 of the spherical surface Rl and the point of intersection of the axis 216 with the bottom plane 220 of the combustion chamber 214 should be equal to or greater than zero and should be less than 0.2D, the diameter of the piston. As depicted in Fig. 5, the origin 218 is at the point of intersection 222 of the axis 216 of the combustion chamber 214 and the bottom plane 220 of the combustion chamber 214. In other words, the origin 218 and the point of intersection 222 are depicted as being coincident. This is the preferred disposition of the origin 218 at the point of intersection 222 of the axis 216 of the combustion chamber 214 and the bottom plane 220 of the combustion chamber, but there could as well be a vertical distance between the origin 218 and the point of intersection 222.

The following ratios define certain parameters of the combustion chamber 214. a. The ratio of Dl to D should be greater than 0.49 and should be less than 0.81 and is preferably 0.6065. b. The ratio of D2 to Dl should be greater than 0.81 and should be less than 0.99 and is preferably 0.908. c. The ratio of HI to Dl should be greater than 0.17 and should be less than 0.47 and is preferably 0.344. d. The ratio of H2 to HI should be greater than 0.05 and should be less than 0.45 and is preferably 0.253. e. The ratio of Rl to Dl should be greater than 0.13 and should be less than 0.43 and is preferably 0.257. f. The ratio of R2 to Dl should be greater than 0.09 and should be less than 0.25 and is preferably 0.133. g. The ratio of R3 to Dl should be greater than 0.17 and should be less than 0.55 and is preferably 0.36. h. The ratio of R4 to Dl should be greater than 0.08 and should be less than 0.33 and is preferably 0.142. i. The ratio of R5 to Dl should be greater than 0.01 and should be less than 0.02 and is preferably 0.14. The combustion chamber 214 as indicated above is comprised of combined spherical and annular surfaces. The spherical surface Rl is defined by the radius Rl. The annular surfaces are defined by the radiuses R2-R5. It is noted that the transition between spherical surface Rl and annular surface R2 is smooth and tangential, the transition between annular surface R2 and annular surface R3 is smooth and tangential, the transition between annular surface R3 and annular surface R4 is smooth and tangential, and the transition between annular surface R4 and annular surface R5 is smooth and tangential. In this manner, there are no flat surfaces that define the combustion chamber 214. The curves and smooth transitions as previously described promote smooth flow in the combustion chamber 214 and reduce the thermal loading in the combustion chamber 214. Further, the combustion chamber 214 is symmetrical about the axis 216. Accordingly, it is much easier to turn the combustion chamber 214 as compared to an asymmetrical combustion chamber defined in a piston.

It should further be noted that the surfaces R3-R5 define a reentrant combustion chamber 214 as distinct from an open combustion chamber as depicted in the prior art. Combustion performance improvement and pollutant emission reduction are depicted in Figs. 6-8. Referring to Fig. 6, power output is the area beneath each of the curves. A first actual experiment of a known combustion chamber is depicted at curve 224. Close to the peak of the curve 224, a trace of a simulation of the known combustion chamber that resulted in the curve 224 closely overlies the curve 224. The trace 226, by closely overlying the curve 224, substantiates the validity of the simulation. This same simulation was then used to simulate the performance of the combustion chamber 214. The simulation of the combustion chamber 214 is depicted by curve 228. It is noted that the area underneath the curve 228 is slightly greater than the area underneath the curve 224, indicating that the power output resulting from the combustion chamber 214 is slightly greater than the power output of the known combustion chamber.

Fig. 7 depicts the NO_x generation of a known combustion chamber as depicted by line 226 and the simulated results of NO_x generation of the combustion chamber 214 of the present invention as depicted in line 228. It is noted that the NO_x generation by the combustion chamber 214 of the present invention is significantly less than the NO_x of the known combustion chamber as depicted by line 226.

Fig 8 depicts the simulated soot generation of a known combustion chamber as depicted by line 226 in comparison with the simulated soot generation of the combustion chamber 214 of the present invention as depicted by line 228. It should be noted that soot generation of the combustion chamber 214 is significantly less than the soot generation of the known combustion chamber. It is significant to note in reference to Figs. 6-8 that the combustion chamber 214 results in increased power output and at the same time decreases both the NO_x generation and soot generation as compared to a known combustion chamber. Third Embodiment

The piston of the present invention is shown generally at 310 and the combustion chamber of the present invention at 314 in Fig. 9. Generally, the piston 310 has a centrally located symmetrical upward directed cavity for forming a major portion of a combustion bowl within a cylinder of a diesel engine, the engine having a fuel injector for forming a fuel injection plume. The piston 310 may be utilized with two-valve or multiple- valve heads. It is desirable that the fuel be injected proximate the center of the piston 310 and that the injection pattern be radially symmetrical. In a preferred embodiment, the injector injects a spray of fuel that has six subsprays that are equi-angularly displaced relative to the axis 316. The piston 310 with combustion chamber 314 is effective at reducing diesel engine pollutant emissions, such as NOx and soot. The piston 310 is preferably applicable to heavy- duty and medium duty diesel engines.

The crown 312 of the piston 310 defines in part the upper margin of the piston 310. The combustion chamber 314 of the present invention is defined in the crown 312. It should be noted that the combustion chamber 314 is symmetrical about the chamber longitudinal axis 316 and that longitudinal axis 316 is coincident with the center axis of the piston 310. The various radii (R), diameters (D), and heights (H) that will be described below are clearly indicated in the depiction of Fig. 9.

The combustion chamber 314 defined in the crown 312 of the piston 310 is comprised of curved surfaces, including spherical surfaces. The spherical surfaces are designated by a radius RS and the curved surfaces are designated by a radius R and may be annular surfaces. The combustion chamber 314 has no flat surfaces. There is a smooth, generally tangential\ transition between the various curved surfaces that define the combustion chamber 314, as described in greater detail below.

Generally, the combustion chamber 314 is comprised of two spherical surfaces RSI and RS2, spherical surface RSI defining a convex spherical surface and spherical surface RS2 defining a concave spherical surface. The spherical surface RSI is formed at the center of the combustion chamber 314 defining a center post 317 with the spherical surface RS2 being formed radially outward of the spherical surface RS 1 The two spherical surfaces RS 1 and RS2 are connected by a small annular surface having a radius R2 at the bottom of the combustion chamber 314. The combustion chamber sidewall is defined by a curved annular surface with a radius of Rl. The sidewall curved surface Rl is connected to spherical surface RS2 by a curved surface having a radius of R3. The sidewall curved surface Rl transitions to a point of intersection with the crown 312 by means of a small curved surface(s), such as R4.

There are a number of parameters that control the geometry of the combustion chamber 314 and thereby control the diesel engine combustion performance as well as NO_x and soot emissions. The convex spherical surface RSI, defined by the radius RSI, is located in the central bottom space (center portion) of the combustion chamber 14. The origin 318 of the spherical surface RSI is located on the chamber longitudinal axis 316 preferably coincident with the longitudinal axis of the piston 310. The distance between the origin 318 of the spherical surface RSI and the point of intersection of the axis 316 with the bottom plane 320 of the combustion chamber 314 is equal to or greater than zero (a distance measured upward from the origin as depicted in Fig. 9 being positive) and should be less than 0.3D1, Dl being the piston 310 diameter. Said distance is preferably zero wherein the origin 318 is coincident with the point of intersection 322 of the bottom plane 320 and the axis 316. The concave spherical surface having the diameter RS2 has its point of origin

324 is on the axis 316 and is depicted in Fig. 9 well above the piston 310. The distance between the origin 324 of the spherical surface RS2 and the point of intersection 322 of the bottom plane 320 and the axis 316 is equal to or greater than 1.0D1 and less than 8.0D1 and is preferably 2.5D1 (a distance measured upward from the point of intersection 22 of the bottom plane 320 and the axis 316 as depicted in Fig. 9 being positive).

The following ratios define certain parameters of the combustion chamber 314, D2 being the maximum diameter of the combustion chamber 314, D3 being the diameter of the combustion chamber 314 at the point of intersection with the crown 312, HI being the maximum height of the combustion chamber 314, and H2 being the height from the peak of convex spherical surface RSI to the crown 312. a. The ratio of RS1/D2 is greater than 0.11 and is less than 0.44, and is preferably 0.245. b. The ratio of RS2/D2 is greater than 1.5 and is less than 30.0, and is preferably 3.432. c. The ratio of D2/D1 is greater than 0.42 and is less than 0.88, and is preferably 0.635. d. The ratio of D3/D2 is greater than 0.7 and is less than 0.995, and is preferably 0.832. e. The ratio of H1/D2 is greater than 0.13 and is less than 0.49, and is preferably 0.318. f. The ratio of H2/D2 is greater than 0.005 and is less than 0.49, and is preferably 0.073. g- The ratio of R1/D2 is greater than 0.11 and is less than 0.65, and is preferably 0.412. h. The ratio of R2 D2 is greater than 0.01 and is less than 0.33, and is preferably 0.068. i. The ratio of R3/D2 is greater than 0.01 and is less than 0.33, and is preferably 0.068.

The curves and smooth transitions of the combustion chamber 314 as previously described promote smooth flow in the combustion chamber 314 and act to reduce the thermal loading in the combustion chamber 314. Further, the combustion chamber 314 is symmetrical about the axis 316. Accordingly, it is much easier to turn the combustion chamber 314 as compared to an asymmetrical combustion chamber defined in a piston.

Combustion performance improvement and pollutant emission reduction are depicted in Figs. 10 and 11. Fig. 10 depicts the NO_x generation of a known combustion chamber as depicted by line 328 and the simulated results of NO_x generation of the combustion chamber 314 of the present invention as depicted in line 330. It is noted that the NO_x generation by the combustion chamber 314 of the present invention (line 330) is significantly less than the NO_x of the known combustion chamber as depicted by line 328. Fig 11 depicts the simulated soot generation of a known combustion chamber as depicted by line 328 in comparison with the simulated soot generation of the combustion chamber 314 of the present invention as depicted by line 330. It should be noted that soot generation of the combustion chamber 314 (line 330) is significantly less than the soot generation of the known combustion chamber (line 328). Fourth Embodiment

The piston and combustion chamber of the present invention are shown generally at 410 and 414, respectively, in Fig. 12. Generally, the piston 410 has a centrally located symmetrical upward directed combustion chamber 414 for forming a portion of a complete combustion chamber within a cylinder of a diesel engine. The combustion chamber 414 is defined in the crown 412 of the piston 410. The engine has a fuel injector for forming a fuel injection plume relative to the combustion chamber 414. The piston 410 may be utilized with two-valve or multiple-valve heads. It is desirable that the fuel be injected proximate the center of the piston 410 and that the injection pattern be radially symmetrical relative to the axis 416. The piston 410 is effective at reducing diesel engine pollutant emissions, such as NOx and soot, as depicted in the graphic representations of Figs. 14 and 15. The piston 410 is preferably applicable to heavy-duty and medium duty diesel engines.

The crown 412 of the piston 410 defines in part the upper margin of the piston 410. The combustion chamber 414 of the present invention is defined in the crown 412. It should be noted that the combustion chamber 414 is symmetrical about the chamber longitudinal axis 416 and that the chamber longitudinal axis 416 is preferably coincident with the center axis of the piston 410. The various radii (R), diameters (D), and heights (H) that will be described below are clearly indicated in the depiction of Fig. 12. RS indicates a spherical radius and annular surfaces are indicated by R. The combustion chamber 414 of the piston 10 is comprised of curved surfaces, including spherical surfaces and annular surfaces. The combustion chamber 414 has no flat surfaces. There is a smooth, generally tangential transition between the various curved surfaces that define the combustion chamber 414, as described in greater detail below.

Generally, the combustion chamber 414 is comprised of four groups of triple parameters, as depicted in Fig. 12, including

(1) the diameter group;

(2) the sphere group; (3) the height group; and

(4) the annulus group.

The diameter group is comprised of three diameter parameters, in which Dl is the piston 410 diameter, D2 is the combustion chamber 414 diameter, and D3 is the diameter of the reentrancy of the combustion chamber 414 where the combustion chamber 414 intersects the crown 412. The sphere group includes three spherical surfaces with radii of RSI, RS2, and RS3 respectively. The height group is comprised of three height parameters in which HI is the depth of the combustion chamber 414, H2 is the distance between the piston crown 412 and the top point of the convex spherical surface RSI, and H3 is the thickness of the reentrancy of the combustion chamber 414. The annulus group includes three annular surfaces Rl, R2, and R3 respectively.

The convex spherical surface RSI is located at the center of the bottom of the combustion chamber 414 defining a center post 417. The two spherical surfaces RS2 and RS3 respectively form the side wall of the combustion chamber 414. The two spherical surfaces RS2 and RS3 are connected by the annular surface Rl. The annular surface Rl forms the bottom portion of the combustion chamber 414. The two spherical surfaces RS2 and RS3 are connected by a small annular surface R2, thereby defining a smooth transition between the two spherical surfaces RS2 and RS3. The spherical surface RS3 transitions to the crown 412 by means of the small annular surface R3. The centers of the three spherical surfaces RSI, RS2, and RS3 are all located on the chamber longitudinal axis 416, defining the centerline of the combustion chamber 414.

The following relationship of parameters controls the geometry of the combustion chamber 414 and the resultant emissions in diesel engines employing the piston 410 and combustion chamber 414. a. The ratio of D2:D1 is greater than 0.43 and is less than 0.83, and is preferably 0.631. b. The ratio of D3:D2 is greater than 0.68 and is less than .998, and is preferably .883. c. The ratio of RS1:D1 is greater than 0.08 and is less than 0.38, and is preferably 0.181. d. The ratio of RS2:D2 is greater than 0.16 and is less than 0.56, and is preferably 0.364. e. The ratio of RS3:D1 is greater than 0.18 and is less than 0.48, and is preferably 0.282. f. The ratio of H1:D2 is greater than 0.12 and is less than 0.52, and is preferably 0.321. g. The ratio of H2:D1 is greater than 0.006 and is less than 0.256, and is preferably 0.056. h. The ratio of H3:D1 is greater than 0.01 and is less than 0.45, and is preferably 0.05. i. The ratio of R1:D1 is greater than 0.02 and is less than 0.28, and is preferably 0.081. j. The ratio of R2:D1 is equal to or greater than zero and less than 0.31, and is preferably 0.017. k. The ratio of R3:D1 is equal to or greater than zero and less than 0.31, and is preferably 0.009. The curves and smooth transitions of the combustion chamber 414 as previously described promote smooth flow in the combustion chamber 414 and act to reduce the thermal loading in the combustion chamber 414. Further, the combustion chamber 414 is symmetrical about the axis 416. Accordingly, it is much easier to turn the combustion chamber 414 as compared to an asymmetrical combustion chamber defined in a piston. Fig. 13 shows the comparison of the combustion performance as indicated by the in-cylinder pressure, where the area under a pressure curve represents the power output of a diesel engine. It should be noted in Figs. 13, 14, and 15 that the simulations for prior art engine and the experimental results for the prior art engine are in substantial agreement as an indication of the validity of the simulation. Again in Fig. 13, the pressure curve of the present invention, B44a is slightly greater than that of the prior art engine, B0, which indicates that the performance of the present invention is somewhat better than the prior art engine. The power output of the present invention is slightly greater than the prior art engine.

Combustion performance improvement and pollutant emission reduction are depicted in Figs. 14 and 15. Fig. 14 depicts the NO_x generation of a known combustion chamber as depicted by line B0 and the simulated results of NO_x generation of the combustion chamber 414 of the present invention as depicted in line B44a. It is noted that the NO_x generation by the combustion chamber 414 of the present invention is significantly less than the NO_x of the known combustion chamber as depicted by line BO.

Fig 15 depicts the simulated soot generation of a known combustion chamber as depicted by line BO in comparison with the simulated soot generation of the combustion chamber 414 of the present invention as depicted by line B44a. It should be noted that soot generation of the combustion chamber 414 (line B44a) is significantly less than the soot generation of the known combustion chamber (line BO). Fifth Embodiment

The piston and combustion chamber of the present invention is shown generally at 510 and 512, respectively, in Fig. 16. Generally, the piston 510 has a centrally located symmetrical upward directed cavity for forming a portion of a combustion chamber 512 within a cylinder of a diesel engine. The combustion chamber 512 is defined in the crown 514 of the piston 510. The engine has a fuel injector for forming a fuel injection plume relative to the combustion chamber 512. The piston 510 may be utilized with two- valve or multiple-valve heads. The piston 510 is effective at reducing diesel engine pollutant emissions, such as NOx and soot, as depicted in the graphic representations of Figs. 17 and 18. The piston 510 is preferably applicable to heavy-duty and medium duty diesel engines.

The piston 510 has a symmetrical upwardly opening combustion chamber 512 for forming a major part of a complete combustion chamber within a cylinder of a diesel engine having a fuel injector for forming a fuel injection plume in order to reduce diesel engine pollutant emissions such as NOx and soot without hurting the fuel economy and power output.

The combustion chamber 512 located in the piston crown 514 of diesel engines and mainly comprises a portfolio of spherical surfaces, as shown in Figure 16. Two spherical surfaces, RSI and RS2, with a co-center 516 lying on the chamber axis 518 form the major part of the combustion chamber 512. The inner spherical surface RSI is located at the central bottom of the combustion chamber 512 to form a post 520 and has a radius of RSI. The outer spherical surface RS2 forms the lower part of the sidewall of the combustion chamber 512 and has a radius of RS2. A third spherical surface RS3, having a radius of RS3, forms the outer bottom margin of the combustion chamber 512. A fourth spherical surface RS4 has a radius of RS4 and forms the higher part of the sidewall of the combustion chamber 512. Four small annular surfaces R1-R4 function as connection and transition surfaces between adjacent spherical surfaces and with the crown 514. The inner spherical surface RSI and the outer bottom spherical surface RS3 are connected by an annular surface that has a radius of Rl. The lower sidewall spherical surface RS2 and the outer bottom spherical surface RS3 are connected by an annular surface that has a radius of R2. The lower sidewall spherical surface RS2 and the higher sidewall spherical surface RS4 are connected by an annular surface that has a radius of R3. The higher sidewall spherical surface RS4 transits to or reenters the piston crown 514 through a small annular surface R4 that has a radius of R4. The origins of spherical surfaces RSI and RS2 are in coincidence with each other, that is, they have a co-center 516, and the co-center 516 is located on the central axis 518 of the combustion chamber 512. The distance between the co-center 516 of spherical surfaces RSI and RS2 and the point of intersection of the combustion chamber axis 518 with the bottom plane 522 of the combustion chamber is equal to or greater than zero and is less than 0.28 Dl, Dl being the piston diameter, and is preferably 0.073 Dl. The origin of the spherical surface RS3 is on the central axis 518 of the combustion chamber, and the distance between the origin of spherical surface RS3 and the point of intersection of the combustion chamber axis 518 with the bottom of the plane 522 of the combustion chamber 512 is greater than 0.75 Dl and less than 3.0 Dl, and is preferably 2.178 Dl. The origin of the spherical surface RS4 is on the central axis 518 of the combustion chamber 512, and the distance between the origin of spherical surface RS4 and the point of intersection of the combustion chamber axis 518 with the crown 514 of the piston 510 is equal to H3. The ratio of H3/D1 is greater than 0.02 and is less than 0.42, and is preferably 0.051.

The central axis 518 of the combustion chamber 512 can coincide with the central axis 524 of the piston 510 or has an offset, that is the distance H4 between the central axis 18 of the combustion chamber 512 and the central axis 524 of the piston 510 is equal to or greater than zero and is less than 0.1D1, and is preferably zero. Preferably then, the axes 518 and 524 are coincident.

The other relationship of parameters also controls the combustion chamber geometry, and the combustion performance and emissions in diesel engines, as are listed below: 1. The ratio of D2/D1 is greater than 0.43 and is less than 0.83, and is preferably 0.637, D2 being the maximum diameter of the combustion chamber.

2. The ratio of D3/D1 is greater than 0.33 and is less than 0.83 and is preferably 0.548, D3 being the minimum diameter of the combustion chamber. 3. The ratio of RS1/D1 is greater than 0.05 and is less than 0.35, and is preferably 0.18.

4. The ratio of RS2/D1 is greater than 0.23 and is less than 0.53, and is preferably 0.334.

5. The ratio of RS3/D1 is greater than 1.18 and is less than 4.18, and is preferably 2.18.

6. The ratio of RS4/D1 is greater than 0.18 and is less than 0.38, and is preferably 0.28.

7. The ratio of Hl/Dl is greater than 0.1 and is less than 0.4 and is preferably 0.2, HI being the depth of the combustion chamber. 8. The ratio of H2/D1 is greater than 0.04 and is less than 0.24, and is preferably

0.144, H2 being the height of the post.

9. The radius of the annular surface Rl is equal to the radius of the annular surface R2. The ratio of Rl/Dl and R2/D1 are each greater than 0.03 and less than 0.25, and is preferably 0.051. 10. The radii of the annular surfaces R3 and R4 are very small. Therefore, ratio of

R3/D1 and R4/D1 are each greater than zero and less than 0.1.

The curves and smooth transitions of the combustion chamber 512 as previously described promote smooth flow in the combustion chamber 512 and act to reduce the thermal loading in the combustion chamber 512. Further, the combustion chamber 512 is preferably symmetrical about the piston axis 524, but may be offset the distance H4 as noted in Fig. 16. Accordingly, it is much easier to turn (form) the combustion chamber 512 as compared to an asymmetrical combustion chamber defined in a piston.

It should be noted in Figs. 17 and 18 that the simulations for prior art engine and the experimental results for the prior art engine are in substantial agreement (the empirical and simulation traces, B0 and B0, are substantially coincident) as an indication of the validity of the simulation. Combustion performance improvement and pollutant emission reduction are depicted in Figs. 17 and 18. Fig. 17 depicts the NO_x generation of a known combustion chamber as depicted by line BO and the simulated results of NO_x generation of the combustion chamber 512 of the present invention as depicted in line B27. It is noted that the NO_x generation by the combustion chamber 512 of the present invention is significantly less than the NO_x of the known combustion chamber as depicted by line BO. Fig 18 depicts the simulated soot generation of a known combustion chamber as depicted by line BO in comparison with the simulated soot generation of the combustion chamber 512 of the present invention as depicted by line B27. It should be noted that soot generation of the combustion chamber 512 (line B27) is significantly less than the soot generation of the known combustion chamber (line BO). It will be obvious to those skilled in the art that other embodiments in addition to the ones described herein are indicated to be within the scope and breadth of the present application. Accordingly, the applicant intends to be limited only by the claims appended hereto.

Claims

What is claimed is:

1. A combustion chamber assembly for use in a diesel engine, comprising: a combustion chamber being defined in a crown of a piston, the piston having a central axis, the combustion chamber having a center portion defining a post, the center portion being defined at least in part by a portion of a sphere, the sphere having a radius, the origin of the radius lying on the piston central axis and the combustion chamber further having a plurality of curved surfaces having smooth tangential transitions between adjacent smooth surfaces, the smooth surfaces including the spherical center portion and at least one annular surface, the combustion chamber being symmetrical with respect to a combustion chamber longitudinal axis.

2. The combustion chamber assembly of claim 1 wherein the origin of the center portion spherical surface lies in a bottom plane of the combustion chamber or lies below the bottom plane of the combustion chamber.

3. The combustion chamber assembly of claim 2 wherein the origin of the center portion spherical surface lies coincident with a point of intersection of the bottom plane with a piston central axis.

4. The combustion chamber assembly of claims 1, 2, and 3 being free of flat surfaces.

5. The combustion chamber assembly of claim 1 wherein a curved surface defines a reentrant interface with the crown of the piston.

6. The combustion chamber assembly of claim 1 wherein a bottom surface of the combustion chamber is defined by a spherical surface coupled to the post.

7. The combustion chamber assembly of claim 1 wherein a bottom surface of the combustion chamber is defined by an annular surface coupled to the post.

8. The combustion chamber assembly of claims 6 and 7 wherein a sidewall surface of the combustion chamber is defined by a spherical surface coupled to the bottom surface.

9. The combustion chamber assembly of claims 6 and 7 wherein a sidewall surface of the combustion chamber is defined by an annular surface coupled to the bottom surface.

10. A piston for use in a diesel engine, the piston having the combustion chamber assembly of claim 1.

11. A method of forming a combustion chamber assembly for use in a diesel engine, comprising: defining a combustion chamber in a crown of a piston, the piston having a central axis; defining a post with a combustion chamber center portion; defining the center portion at least in part by a portion of a sphere, the sphere having a radius; disposing the origin of the radius on the piston central axis; defining the combustion chamber further with a plurality of curved surfaces having smooth tangential transitions between adjacent smooth surfaces, the smooth surfaces including the spherical center portion and at least one annular surface; and symmetrically disposing the combustion chamber with respect to a combustion chamber longitudinal axis.

12. The method of claim 11 including disposing the origin of the center portion spherical surface in a bottom plane of the combustion chamber or below the bottom plane of the combustion chamber.

13. The method of claim 22 including disposing the origin of the center portion spherical surface coincident with a point of intersection of the bottom plane with a piston central axis.

14. The method of claims 11, 12, and 13 including forming the combustion chamber free of flat surfaces.

15. The method of claim 11 including defining a reentrant interface with the crown of the piston with a curved surface.

16. The method of claim 11 including defining a bottom surface of the combustion chamber by a spherical surface coupled to the post.

17. The method of claim 11 including defining a bottom surface of the combustion chamber by an annular surface coupled to the post.

18. The method of claims 16 and 17 including defining a sidewall surface of the combustion chamber by a spherical surface coupled to the bottom surface.

19. The method of claims 16 and 17 including defining a sidewall surface of the combustion chamber by an annular surface coupled to the bottom surface.