Combustion system for internal combustion engine

Abstract

A combustion system for an internal combustion engine is provided. The combustion system comprises a cylinder extending along a longitudinal axis, a cylinder head disposed on the cylinder, and a piston configured to reciprocate within the cylinder along the longitudinal axis between a top dead center and a bottom dead center. The piston comprises a piston bowl that comprises a dome tapering to a dome tip. The dome tip comprises a protuberance, an annular protrusion spaced apart from and surrounding the protuberance, and an annular recessed surface disposed between the protuberance and the annular protrusion. Each of the protuberance and the annular protrusion extends upwardly from the annular recessed surface, such that the protuberance, the annular protrusion, and the annular recessed surface define an annular groove therebetween. The combustion system further comprises a combustion chamber defined by the cylinder, the cylinder head, and the piston.

Description

COMBUSTION SYSTEM FOR INTERNAL COMBUSTION ENGINETechnical Field

[0001] The present application relates to a combustion system for an internal combustion engine.

[0002] Gaseous fuels such as natural gas, propane, hydrogen, and blends thereof are cleaner burning fuels compared to liquid fuels such as diesel. Recent attention has been directed to developing engines that can bum gaseous fuels while matching the power and performance that engine operators are accustomed to expecting from diesel engines. However, because many gaseous fuels have high auto-ignition temperatures, ignition assistance is generally needed. In other words, gaseous fuels require positive ignition sources such as pilot fuel, glow plug or spark plug to achieve reliable ignition. In some engine systems including Diesel-cycle engine systems, a pilot injection of the pilot fuel (that is, a lower auto-ignition temperature fuel) such as diesel fuel is used to ignite gaseous fuels which do not reliably ignite from the heat of compression alone in a combustion chamber of the internal combustion engine.

[0003] The pilot fuel used for ignition of the gaseous fuel may still increase emission of particulate matter, carbon dioxide, and / or nitrogen oxide due to relatively high carbon content in the pilot fuel compared to that in the main fuel (i.e., gaseous fuel). The term “and / or” is used herein to mean “one or the other or both”. To meet the increasingly stringent emission regulations, it is desirable to further reduce the consumption of the hydrocarbon pilot fuels (i.e., diesel) so as to further limit the emission of carbon dioxide, nitrogen oxide, and particulate matter.

[0004] One of the conventional ways to reduce the consumption of pilot fuel is to reduce pulse duration of the pilot fuel during the pilot injection event. However, the pulse duration of the pilot fuel cannot be reduced below certain limit due to the risk of inconsistent pilot quantity and nonideal pilot atomization and distribution. Another conventional way to reduce the consumption of pilot fuel is to reduce the number of pilot holes for discharging the pilot fuel. However, the number of pilot holes is generally selected based on the number of main holes for discharging the mainfuel (i.e., gaseous fuel). Therefore, the reduction of the number of pilot holes implies reduction of the number of main holes, which may affect engine performance.

[0005] The state of the art is therefore lacking in effective techniques for reducing consumption of pilot fuel in a gaseous fueled engine. The present disclosure provides a technique for maximum reduction of consumption of pilot fuel in a gaseous fueled engine without compromising engine performance.

[0006] An improved combustion system for an internal combustion engine comprises a cylinder extending along a longitudinal axis. The combustion system further comprises a cylinder head disposed on the cylinder. The combustion system further comprises a piston configured to reciprocate within the cylinder along the longitudinal axis between a top dead center and a bottom dead center. The piston comprises a piston bowl that comprises a dome tapering to a dome tip. The dome tip comprises a protuberance, an annular protrusion spaced apart from and surrounding the protuberance, and an annular recessed surface disposed between the protuberance and the annular protrusion. Each of the protuberance and the annular protrusion extends upwardly from the annular recessed surface, such that the protuberance, the annular protrusion, and the annular recessed surface define an annular groove therebetween. The combustion system further comprises a combustion chamber defined by the cylinder, the cylinder head, and the piston. The combustion system further comprises a fuel injector for directly introducing a pilot fuel and a main fuel into the combustion chamber. The fuel injector is mountable in the cylinder head. The fuel injector comprises a nozzle extending at least partially into the combustion chamber. The nozzle comprises a nozzle tip facing the dome tip. Only a single pilot hole is disposed at the nozzle tip and configured to discharge a pilot jet of the pilot fuel into the combustion chamber. A plurality of main holes is angularly separated from each other and configured to discharge a corresponding plurality of main jets of the main fuel into the combustion chamber. Each main hole from the plurality of main holes is spaced apart from the nozzle tip.

[0007] The accompanying drawings, which are incorporated into and constitute a part of the specification, illustrate specific embodiments of the apparatus, systems, and methods and, together with the general description above, and the detailed description of the specific embodiments, serve to explain the principles of the apparatus, systems, and methods.

[0008] FIG. 1 is a schematic view of an internal combustion engine comprising a combustion system, according to an embodiment of the present disclosure;

[0009] FIG. 2 is a perspective view of the combustion system, with some components not shown, according to an embodiment of the present disclosure;

[0010] FIG. 3A is a partial sectional side view of the combustion system of FIG. 2, wherein a piston of the combustion system is at a bottom dead center, according to an embodiment of the present disclosure;

[0011] FIG. 3B is a partial sectional side view of the combustion system of FIG. 2, wherein the piston is at a top dead center, according to an embodiment of the present disclosure;

[0012] FIG. 4 is a partial sectional view of a fuel injector of the combustion system of FIG. 2, according to an embodiment of the present disclosure;

[0013] FIG. 5A is a gray scale image of a portion of a combustion chamber of the combustion system of FIG. 2 before ignition of a main fuel, according to an embodiment of the present disclosure;

[0014] FIG. 5B is a gray scale image of the portion of the combustion chamber of FIG. 5A after ignition of the main fuel, according to an embodiment of the present disclosure;

[0015] FIG. 6A is a graph illustrating cylinder pressure versus crank angle for the combustion system of FIG. 2 and a comparative baseline combustion system, according to an embodiment of the present disclosure;

[0016] FIG. 6B is a graph illustrating heat release rate versus crank angle for the combustion system of FIG. 2 and a comparative baseline combustion system, according to an embodiment of the present disclosure;

[0017] FIG. 6C is a graph illustrating mass flow of the main fuel versus crank angle for the combustion system of FIG. 2 and a comparative baseline combustion system, according to an embodiment of the present disclosure; and

[0018] FIG. 7 is a graph illustrating cylinder pressure versus crank angle for the combustion system of FIG. 2 with normal fuel injection and with split fuel injection, according to an embodiment of the present disclosure.Detailed Description

[0019] Referring to FIG. 1, there is shown a combustion system 100 for an internal combustion engine 50, according to an embodiment of the present disclosure. FIG. 2 is a perspective view of the combustion system 100, with some components not shown, according to an embodiment of the present disclosure. FIGS. 3A and 3B are partial sectional side views of the combustion system 100, according to an embodiment of the present disclosure.

[0020] Referring to FIGS. 1 to 3B, the internal combustion engine 50 can be used for a vehicle, and can also be employed in marine, locomotive, mine haul, power generation, or stationary applications. In other words, the internal combustion engine 50 can be a light-duty engine, a medium-duty engine, a heavy-duty engine or a high horsepower (HHP) engine.

[0021] The internal combustion engine 50 is capable of being fueled by a liquid fuel and a gaseous fuel. In some embodiments, the gaseous fuel serves as a main fuel Fl (shown in FIG. 3B) for the internal combustion engine 50, and the liquid fuel serves as a pilot fuel F2 (shown in FIG. 3B) for the internal combustion engine 50. In other words, the pilot fuel F2 is a liquid fuel, and the main fuel Fl is a gaseous fuel. The main fuel Fl has a higher auto ignition temperature than the pilot fuel F2. More particularly, the autoignition temperature of the main fuel Fl is higher for a given pressure condition compared to the autoignition temperature of the pilot fuel F2. As usedherein, the gaseous fuel is any fuel in the gas state / phase at standard temperature and pressure, which in the context of this application is defined as a temperature of zero (0) degrees Celsius (°C) and an absolute pressure of one hundred (100) kilopascals (kPa). In some embodiments, the gaseous fuel is hydrogen. In some embodiments, the gaseous fuel is selected from the group consisting of natural gas, hydrogen, propane, ethane, butane, methane, ammonia, and mixtures thereof. In some other embodiments, the liquid fuel may be diesel, dimethyl ether (DME), or kerosene.

[0022] The combustion system 100 comprises a cylinder 102 extending along a longitudinal axis LA. The cylinder 102 defines a cylindrical surface 104 in an engine block. The cylindrical surface 104 is an internal surface of the cylinder 102 in the engine block. The combustion system 100 further comprises a cylinder head 106 disposed on the cylinder 102. The cylinder head 106 covers a top end of the cylinder 102. The combustion system 100 further comprises a piston 108 configured to reciprocate within the cylinder 102 along the longitudinal axis LA between a top dead center (TDC) and a bottom dead center (BDC). In FIG. 3 A, the piston 108 is located at the BDC. In FIG. 3B, the piston 108 is located at the TDC. The combustion system 100 further comprises a combustion chamber 110 defined by the cylinder 102, the cylinder head 106, and the piston 108.

[0023] It should be understood that some conventional elements of the internal combustion engine 50 are not shown for simplicity and clarity purposes. Further, only a cross-section of the internal combustion engine 50 showing the combustion chamber 110 of one cylinder (i.e., the cylinder 102) is shown but those skilled in the technology will understand that the internal combustion engine 50 may comprise other components and a plurality of cylinders. In FIG. 2, some components, such as the cylinder 102 are not shown for illustrative purposes.

[0024] The combustion system 100 further comprises fuel injector 112 for directly introducing the pilot fuel F2 and the main fuel Fl into the combustion chamber 110. In an exemplary embodiment, the fuel injector 112 is hydraulically actuated. FIG. 4 is a partial sectional view of the fuel injector 112, according to an embodiment of the present disclosure. Referring to FIGS. 1 to 4, the fuel injector 112 is mountable in the cylinder head 106 for directly introducing fuel into the combustion chamber 110. The fuel injector 112 extends at least partially through the cylinder head 106 into the combustion chamber 110. The fuel injector 112 is adapted to deliver separatelyand independently the pilot fuel F2 and the main fuel Fl at their respective appropriate timings. As will be discussed in more detail below, the pilot fuel F2 is introduced towards the piston 108, as seen in FIG. 4. In some embodiments, a start of injection timing for the pilot fuel F2 allows at least 50% of the pilot fuel F2 to evaporate before impinging on the piston 108. In other embodiments, the start of injection timing for the pilot fuel F2 allows at least 40% of the pilot fuel F2 to evaporate before impinging on the piston 108.

[0025] The fuel injector 112 comprises a nozzle 114 extending at least partially into the combustion chamber 110. In FIG. 4, some parts of the fuel injector 112, such as fuel inlets, electrical connector, and valves are not shown for illustrative purposes. Referring to FIG. 4, the nozzle 114 comprises a nozzle tip 116. In the nozzle 114, only a single pilot hole H2 is disposed at the nozzle tip 116 and configured to discharge a pilot jet J2 of the pilot fuel F2 into the combustion chamber 110. Further, in the nozzle 114, a plurality of main holes Hl is angularly separated from each other and configured to discharge a corresponding plurality of main jets JI of the main fuel Fl into the combustion chamber 110. Each main hole Hl from the plurality of main holes Hl is spaced apart from the nozzle tip 116. Each main hole Hl has a main outlet 01 through which the corresponding main jet JI exits the nozzle 114.

[0026] The fuel injector 112 further comprises a main needle 118 that controls the discharge of the corresponding main jet JI through each main hole Hl. The fuel injector 112 further comprises a pilot needle 120 that controls the discharge of the pilot jet J2 through the pilot hole H2. Each of the main needle 118 and the pilot needle 120 extends along a central axis CAI of the fuel injector 112. However, in other embodiments, the main needle 118 and the pilot needle 120 may be concentrically arranged off-set from the central axis CAI of the fuel injector 112 and / or arranged adjacent to each other. In some embodiments, the central axis CAI of the fuel injector 112 is aligned with the longitudinal axis LA of the cylinder 102.

[0027] Each of the main needle 118 and the pilot needle 120 is movably received within the nozzle 114. The pilot needle 120 is concentrically guided in a bore provided inside the main needle 118. The main needle 118 is a hollow needle adapted to open or close the plurality of main holes Hl arranged at the nozzle tip 116. The pilot needle 120 is a plain needle, or inner needle, adapted to open or close the single pilot hole H2 arranged at the nozzle tip 116. In some embodiments, during each injection cycle of the fuel injector 112, the main needle 118 is configured with anopening duration from 0.5 milliseconds to 3 milliseconds to allow the discharge of the corresponding main jet JI through each main hole Hl. The fuel injector 112 also comprises valves (not shown) and fluid chambers (not shown) for controlling opening and closing movements of the main needle 118 and the pitot needle 120.

[0028] The pitot hole H2 has a pitot hole diameter D2 (shown in FIG. 4) and a pitot cross- sectional area A2. Each main hole Hl has a main cross-sectional area Al . In some embodiments, the pitot cross-sectional area A2 is less than 2% of the main cross-sectional area Al. In other embodiments, the pitot cross-sectional area A2 is less than 5% of the main cross-sectional area Al. In other embodiments, the pitot cross-sectional area A2 is less than 10% of the main cross- sectional area Al.

[0029] The pitot hole H2 extends along a pitot axis PA. Each main hole Hl extends along a main axis MA inclined to the pitot axis PA by a main inclination angle bl . In some embodiments, the main inclination angle bl is between 40 degrees and 80 degrees. In some embodiments, the pitot axis PA is aligned with the central axis CAI of the fuel injector 112. In some embodiments, the pitot axis PA is aligned with the longitudinal axis LA of the cylinder 102. In some embodiments, the pitot axis PA is aligned with a central axis CA2 (shown in FIG. 3A) of the piston 108. In some embodiments, the central axis CA2 of the piston 108 is aligned with the longitudinal axis LA of the cylinder 102.

[0030] In some embodiments, the nozzle 114 further comprises a plurality of bridge holes H3 angularly spaced apart from each other and angularly disposed between the pitot hole H2 and the plurality of main holes Hl with respect to the central axis CAI of the fuel injector 112. The plurality of bridge holes H3 is configured to discharge a corresponding plurality of bridge jets J3 of the main fuel FL In some embodiments, a number of the plurality of bridge holes H3 is equal to a number of the plurality of main holes HL In other embodiments, a number of the plurality of bridge holes H3 is different than a number of the plurality of main holes Hl .

[0031] Each bridge hole H3 from the plurality of bridge holes H3 extends along a bridge axis BA. The bridge axis BA is inclined to the pitot axis PA by a bridge inclination angle b2 that is less than the main inclination angle bl. In some embodiments, the bridge inclination angle b2 isbetween 20% of the main inclination angle bl and 90% of the main inclination angle bl. In some embodiments, the bridge inclination angle b2 is about 50% of the main inclination angle bl.

[0032] Each bridge hole has a bridge cross-sectional area A3. In some embodiments, the bridge cross-sectional area A3 is between 5% and 100% of the main cross-sectional area Al. In some embodiments, the bridge cross-sectional area A3 is between 40% and 60% of the main cross- sectional area Al. Each bridge hole H3 from the plurality of bridge holes H3 has a bridge outlet 03 through which the corresponding bridge jet J3 exits the nozzle 114. The bridge outlet 03 of each bridge hole H3 is disposed between the nozzle tip 116 and the main outlet 01 of each main hole Hl with respect to the central axis CAI of the fuel injector 112.

[0033] Referring again to FIGS. 2 to 4, the piston 108 comprises a piston bowl 122 that comprises a dome 124 tapering to a dome tip 126. In some embodiments, the piston bowl 122 further comprises a toroidal surface 128 surrounding the dome 124. The dome tip 126 comprises a protuberance 130 (shown in FIG. 3 A), an annular protrusion 132 spaced apart from and surrounding the protuberance 130, and an annular recessed surface 134 disposed between the protuberance 130 and the annular protrusion 132. Each of the protuberance 130 and the annular protrusion 132 extends upwardly from the annular recessed surface 134, such that the protuberance 130, the annular protrusion 132, and the annular recessed surface 134 define an annular groove 136 therebetween.

[0034] In some embodiments, the protuberance 130 is centrally disposed on the dome tip 126 and aligned with the central axis CA2 of the piston 108. In other embodiments, the protuberance 130 may not be aligned with the central axis CA2 of the piston 108. In some embodiments, the dome tip 126 is axisymmetric with respect to the central axis CA2 of the piston 108. In other embodiments, the dome tip 126 may not be axisymmetric with respect to the central axis CA2 of the piston 108. In some embodiments, the protuberance 130 is convex with respect to the annular recessed surface 134. In some embodiments, the annular protrusion 132 is disposed along a perimeter Pl of the dome tip 126.

[0035] In some embodiments, the annular recessed surface 134 is planar. In other embodiments, the annular recessed surface 134 may be curved. In some embodiments, the dome 124 has a conical side surface 138 extending angularly from the dome tip 126. In someembodiments, when the piston 108 is in the top dead center (as shown in FIG. 3B), a distance DI between the nozzle tip 116 and the protuberance 130 along the longitudinal axis LA of the cylinder 102 is greater than 30 times the pilot hole diameter D2. In other embodiments, when the piston 108 is in the top dead center, the distance DI may be greater than 20 times the pilot hole diameter D2.

[0036] In some embodiments, the annular protrusion 132 comprises an angled surface 140 extending from the annular recessed surface 134. The angled surface 140 forms an inclination angle b3 with a horizontal plane HP that is normal to the central axis CA2 of the piston 108. In some embodiments, the inclination angle b3 is between -30 degrees and 45 degrees. In some embodiments, the inclination angle b3 is about 35 degrees.

[0037] Further, in some embodiments, the dome tip 126 is configured to receive the pilot jet J2 from the nozzle tip 116 and deflect the pilot jet J2 into a conical sheet 142. The conical sheet 142 depicts a direction of a deflected spray that can be continuous along a circumferential direction around the longitudinal axis LA of the cylinder 102. The dome tip 126 is configured to receive the pilot jet J2 from the nozzle tip 116 and guide the pilot jet J2 towards the plurality of main jets JI discharged by the plurality of main holes HL

[0038] The protuberance 130, the annular protrusion 132, and the annular recessed surface 134 together provide the dome tip 126 a desirable geometry so as to guide the pilot jet J2 towards the plurality of main jets JI discharged by the plurality of main holes HL Such geometrical design of the dome tip 126 may bring the pilot jet J2 to closer proximity of the plurality of main jets JI discharged by the plurality of main holes HL In other words, the design of the dome tip 126 directs the pilot jet J2 of the pilot fuel F2 to deflect or guide towards the plurality of main jets JI of the main fuel Fl in order to improve mixing quality of the main fuel Fl (gaseous fuel) and the pilot fuel F2 (liquid fuel) in the combustion chamber 110.

[0039] In some embodiments, inclusion of the plurality of bridge holes H3 in the nozzle 114 between the pilot hole H2 and the plurality of main holes Hl may enhance ignition of the main fuel Fl in the combustion chamber 110. In other words, the plurality of bridge jets J3 of the main fuel Fl between the pilot jet J2 and the plurality of main jets JI may provide robust ignition of the main fuel Fl in the combustion chamber 110. Therefore, the disclosed geometrical design of thedome tip 126 of the piston 108 and the inclusion of plurality of bridge holes J3 may lead to improved mixing quality of the main fuel Fl and the pilot fuel F2 as well as achieving robust ignition of the main fuel Fl in the combustion chamber 110.

[0040] Due to disclosed geometrical design of the dome tip 126 of the piston 108 and the inclusion of plurality of bridge holes J3, only the single pilot hole H2 may be enough to achieve robust ignition of the main fuel Fl in the combustion chamber 110. Therefore, there is no need for plurality of pilot jets (as provided in conventional injectors) in the fuel injector 112 to meet ignition requirements of the main fuel Fl. Hence, as compared to conventional combustion systems, the combustion system 100 may consume less pilot fuel F2 because of the single pilot hole H2, geometry of dome tip 126 of the piston 108, and the plurality of bridge holes H3. The reduced consumption of the pilot fuel F2 may cause less emission of carbon dioxide, nitrogen oxide, and particulate matter, thereby meeting stringent emission regulations without compromising the performance of the internal combustion engine 50.

[0041] Further, due to disclosed geometrical design of the dome tip 126 of the piston 108, inclusion of plurality of bridge holes J3, and the single pilot hole H2, a pilot fraction of the combustion system 100 may be reduced by at least 5 times in comparison to conventional combustion systems. In some embodiments, the pilot fraction of the combustion system 100 may be reduced from 5% of the total fuel consumed (including pilot fuel and main fuel) to 1% of the total fuel consumed.

[0042] FIG. 5 A is a gray scale image of a portion of the combustion chamber 110 of the combustion system 100 before ignition of the main fuel Fl, according to an embodiment of the present disclosure. As shown in the gray scale image of FIG. 5A, the pilot fuel F2 is guided towards the main jet JI of the main fuel Fl after impinging on the dome tip 126 of the piston 108. The bridge jet J3 discharged by the bridge hole H3 enhances the ignition of the main fuel Fl.

[0043] FIG. 5B is a gray scale image of the portion of the combustion chamber 110 after ignition of the main fuel Fl, according to an embodiment of the present disclosure. As shown in the gray scale image of FIG. 5B, the ignition of the main fuel Fl is denoted by a shaded region 144. The shaded region 144 indicates robust and desirable ignition of the main fuel Flin the combustion chamber 110.

[0044] FIG. 6A is a graph 146 illustrating cylinder pressure versus crank angle for the combustion system 100 of FIG. 2 and a comparative baseline combustion system (not shown), according to an embodiment of the present disclosure. The combustion system 100 and the comparative baseline combustion system have the same construction except that in the comparative baseline combustion system, the fuel injector 100 (shown in FIGS. 1 to 4) does not comprise any bridge hole (i.e., the bridge holes H3). Further, in the comparative baseline combustion system, the dome tip 126 does not comprise an annular protrusion and an annular recessed surface. In other words, in the comparative baseline combustion system, the piston has a conventional design. The cylinder pressure is the pressure in the combustion chamber 110 in the interior of the cylinder 102 (shown in FIG. 1). Further, for plotting the graph 146, natural gas is taken as the main fuel Fl and diesel is taken as the pilot fuel F2.

[0045] In the graph 146, crank angle is shown in the abscissa in arbitrary units and cylinder pressure is shown in the ordinate in arbitrary units. The graph 146 comprises curves 148, 150, 152. The curve 148 depicts cylinder pressure versus crank angle for the comparative baseline combustion system. The curve 150 depicts cylinder pressure versus crank angle for the combustion system 100, wherein during each injection cycle of the fuel injector 112, the main needle 118 (shown in FIG. 4) opens to allow the discharge of the corresponding main j et JI through each main hole Hl. The curve 152 depicts cylinder pressure versus crank angle for the combustion system 100, wherein during each injection cycle of the fuel injector 112, the main needle 118 transitions from a closed position to a fully open position in a time duration (the opening time of the fuel injector 112) that is twice of that with the case of the curve 150 to allow the slower discharge of the corresponding main jet JI through each main hole Hl. In other words, the fuel injector 112 in the curve 152 opens more slowly than the fuel injector 112 in curve 150.

[0046] Referring to the curves 148, 150, 152, it is apparent that the peak cylinder pressure is relatively lower in the case of the combustion system 100 when the main needle 118 has an opening time duration that is twice of that with the case of curve 150. Therefore, such slow opening of the main needle 118 may help in mitigating the peak cylinder pressure thereby leading to better performance of the internal combustion engine 50.

[0047] FIG. 6B is a graph 154 illustrating heat release rate versus crank angle for the combustion system 100 of FIG. 2 and the comparative baseline combustion system, according toan embodiment of the present disclosure. For plotting the graph 154, natural gas is taken as the main fuel Fl and diesel is taken as the pilot fuel F2.

[0048] In the graph 154, crank angle is shown in the abscissa in arbitrary units and heat release rate is shown in the ordinate in arbitrary units. The graph 154 comprises curves 156, 158, 160. The curve 156 depicts heat release rate versus crank angle for the comparative baseline combustion system. The curve 158 depicts heat release rate versus crank angle for the combustion system 100, wherein during each injection cycle of the fuel injector 112, the main needle 118 (shown in FIG. 4) opens to allow the discharge of the corresponding main jet JI through each main hole Hl. The curve 160 depicts heat release rate versus crank angle for the combustion system 100, wherein during each injection cycle of the fuel injector 112, the main needle 118 transitions from a closed position to a fully open position in a time duration that is twice of that with the case of the curve 158 to allow the slower discharge of the corresponding main jet JI through each main hole Hl.

[0049] Referring to the curves 158, 160, for the combustion system 100, it is apparent that the peak rate of heat release is relatively lower when the main needle 118 has an opening time duration that is twice of that with the case of the curve 158. Therefore, such slow opening of the main needle 118 may help in mitigating the peak rate of heat release thereby leading to reduced combustion harshness and improved durability of the internal combustion engine 50.

[0050] FIG. 6C is a graph 162 illustrating mass flow of the main fuel Fl versus crank angle for the combustion system 100 of FIG. 2 and the comparative baseline combustion system, according to an embodiment of the present disclosure. For plotting the graph 162, natural gas is taken as the main fuel Fl and diesel is taken as the pilot fuel F2. The mass flow of the main fuel Fl is the flow rate of the main fuel Fl out of the nozzle 114.

[0051] In the graph 162, crank angle is shown in the abscissa in arbitrary units and mass flow is shown in the ordinate in arbitrary units. The graph 162 comprises curves 164, 166, 168. The curve 164 depicts mass flow versus crank angle for the comparative baseline combustion system. The curve 166 depicts mass flow versus crank angle for the combustion system 100, wherein during each injection cycle of the fuel injector 112, the main needle 118 (shown in FIG. 4) opens to allow the discharge of the corresponding main jet JI through each main hole Hl. The curve 168 depicts mass flow versus crank angle for the combustion system 100, wherein during eachinjection cycle of the fuel injector 112, the main needle 118 opens for a time duration, which is twice of that with the case of the curve 150 to allow the slower discharge of the corresponding main jet JI through each main hole Hl.

[0052] Referring to the curves 164, 166, 168, it is apparent that the peak mass flow of the main fuel Fl is relatively higher in the case of the combustion engine 100 (depicted as curves 166 and 168) as compared to the comparative baseline combustion engine (curve 164). This may improve combustion process along with lower emission levels of the greenhouse gases.

[0053] FIG. 7 is a graph 170 illustrating cylinder pressure versus crank angle for the combustion system 100 of FIG. 2 with normal fuel injection and with split fuel injection, according to an embodiment of the present disclosure. For plotting the graph 170, hydrogen is taken as the main fuel Fl and diesel is taken as the pilot fuel F2. Split injection is a known variation of direct injection. With split injection, two pulses of main fuel Fl are directly injected into the cylinder 102 during a given working cycle. In some applications, split injection is employed with a first portion of the main fuel Fl injected into the combustion chamber 110 before an intake valve closes and a second portion of the main fuel Fl injected after the intake valve is closed.

[0054] In the graph 170, crank angle is shown in the abscissa in arbitrary units and cylinder pressure is shown in the ordinate in arbitrary units. The graph 170 comprises curves 172, 174. The curve 172 depicts cylinder pressure versus crank angle for the combustion system 100 when there is normal inj ection of the main fuel F 1. The curve 174 depicts cylinder pressure versus crank angle for the combustion system 100 when there is split injection of the main fuel Fl. Referring to the curves 172, 174, it is apparent that use of split injection strategy may help in mitigating the peak cylinder pressure in the cylinder 102. Peak cylinder pressure is relatively lower in the case of split injection, thereby leading to improved performance of the internal combustion engine 50.

[0055] While particular elements, embodiments, and applications of the present invention have been shown and described, it will be understood, that the invention is not limited thereto since modifications can be made by those skilled in the art without departing from the scope of the present disclosure, particularly in light of the foregoing teachings.

Claims

What is claimed is:

1. A combustion system for an internal combustion engine, the combustion system comprising: a cylinder extending along a longitudinal axis; a cylinder head disposed on the cylinder; a piston configured to reciprocate within the cylinder along the longitudinal axis between a top dead center and a bottom dead center, the piston comprising a piston bowl that comprises a dome tapering to a dome tip, the dome tip comprising a protuberance, an annular protrusion spaced apart from and surrounding the protuberance, and an annular recessed surface disposed between the protuberance and the annular protrusion, wherein each of the protuberance and the annular protrusion extends upwardly from the annular recessed surface, such that the protuberance, the annular protrusion, and the annular recessed surface define an annular groove therebetween; a combustion chamber defined by the cylinder, the cylinder head, and the piston; and a fuel injector for directly introducing a pilot fuel and a main fuel into the combustion chamber, the fuel injector mountable in the cylinder head, the fuel injector comprising a nozzle extending at least partially into the combustion chamber, the nozzle comprising a nozzle tip facing the dome tip, only a single pilot hole disposed at the nozzle tip and configured to discharge a pilot jet of the pilot fuel into the combustion chamber, and a plurality of main holes angularly separated from each other and configured to discharge a corresponding plurality of main jets of the main fuel into the combustion chamber, wherein each main hole from the plurality of main holes is spaced apart from the nozzle tip.

2. The combustion system of claim 1, wherein the protuberance is centrally disposed on the dome tip and aligned with a central axis of the piston.

3. The combustion system of claim 2, wherein the pilot hole extends along a pilot axis that is aligned with the central axis of the piston.

4. The combustion system of claim 2, wherein the dome tip is axisymmetric with respect to the central axis of the piston.

5. The combustion system of claim 1, wherein the protuberance is convex with respect to the annular recessed surface.

6. The combustion system of claim 1, wherein the annular protrusion is disposed along a perimeter of the dome tip.

7. The combustion system of claim 1, wherein the annular protrusion comprises an angled surface extending from the annular recessed surface, the angled surface forming an inclination angle with a horizontal plane that is normal to a central axis of the piston.

8. The combustion system of claim 7, wherein the inclination angle is between -30 degrees and 45 degrees.

9. The combustion system of claim 1, wherein the annular recessed surface is planar.

10. The combustion system of claim 1, wherein the dome has a conical side surface extending angularly from the dome tip.

11. The combustion system of claim 1, wherein the piston bowl further comprises a toroidal surface surrounding the dome.

12. The combustion system of claim 1, wherein the dome tip is configured to receive the pilot jet from the nozzle tip and guide the pilot jet towards the plurality of main jets discharged by the plurality of main holes.

13. The combustion system of claim 1, wherein the dome tip is configured to receive the pilot jet from the nozzle tip and deflect the pilot jet into a conical sheet.

14. The combustion system of claim 1, wherein pilot hole has a pilot hole diameter, and wherein, when the piston is in the top dead center, a distance between the nozzle tip andthe protuberance along the longitudinal axis of the cylinder is greater than 30 times the pilot hole diameter.

15. The combustion system of claim 1, wherein the pilot hole has a pilot cross-sectional area, wherein each main hole has a main cross-sectional area, and wherein the pilot cross- sectional area is less than 2% of the main cross-sectional area.

16. The combustion system of claim 1, wherein the nozzle further comprises a plurality of bridge holes angularly spaced apart from each other and angularly disposed between the pilot hole and the plurality of main holes with respect to a central axis of the fuel injector, and wherein the plurality of bridge holes is configured to discharge a corresponding plurality of bridge jets of the main fuel.

17. The combustion system of claim 16, wherein each main hole has a main outlet through which the corresponding main jet exits the nozzle, wherein each bridge hole from the plurality of bridge holes has a bridge outlet through which the corresponding bridge jet exits the nozzle, and wherein the bridge outlet of each bridge hole is disposed between the nozzle tip and the main outlet of each main hole with respect to the central axis of the fuel injector.

18. The combustion system of claim 16, wherein the pilot hole extends along a pilot axis, wherein each main hole extends along a main axis inclined to the pilot axis by a main inclination angle, wherein each bridge hole from the plurality of bridge holes extends along a bridge axis, and wherein the bridge axis is inclined to the pilot axis by a bridge inclination angle that is less than the main inclination angle.

19. The combustion system of claim 18, wherein the bridge inclination angle is between 20% of the main inclination angle and 90% of the main inclination angle.

20. The combustion system of claim 18, wherein the pilot axis is aligned with the central axis of the fuel injector.

21. The combustion system of claim 16, wherein each main hole has a main cross-sectional area, wherein each bridge hole has a bridge cross-sectional area, and wherein the bridge cross-sectional area is between 5% and 100% of the main cross-sectional area.

22. The combustion system of claim 16, wherein a number of the plurality of bridge holes is equal to a number of the plurality of main holes.

23. The combustion system of claim 1, wherein the fuel injector further comprises a pilot needle that controls the discharge of the pilot jet through the pilot hole.

24. The combustion system of claim 1, wherein the fuel injector further comprises a main needle that controls the discharge of the corresponding main jet through each main hole.

25. The combustion system of claim 24, wherein, during each injection cycle of the fuel injector, the main needle is configured -with an opening duration from 0.5 milliseconds to 3 milliseconds to allow the discharge of the corresponding main jet through each main hole.

26. The combustion system of claim 1, wherein the pilot fuel is a liquid fuel.

27. The combustion system of claim 1, wherein a start of injection timing for the pilot fuel allows at least 50% of the pilot fuel to evaporate before impinging on the piston.

28. The combustion system of claim 1, wherein the main fuel is a gaseous fuel.

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