WO2023235973A1

WO2023235973A1 - Apparatus and method for injecting and igniting fuel in an internal combustion engine

Info

Publication number: WO2023235973A1
Application number: PCT/CA2023/050782
Authority: WO
Inventors: Jian Huang
Original assignee: Westport Fuel Systems Canada Inc.
Priority date: 2022-06-07
Filing date: 2023-06-07
Publication date: 2023-12-14

Abstract

An apparatus for injecting and igniting a fuel in an internal combustion engine includes a combustion chamber defined by a cylinder in an engine block, a cylinder head capping one end of the cylinder, and a piston reciprocatable within the cylinder. The piston includes a piston bowl asymmetric about a longitudinal axis and a top land surface facing the cylinder head and extending circumferentially around the piston bowl. The top land surface is parallel to a majority of a surface of the cylinder head facing the combustion chamber. A squish volume extends between the top land surface and the cylinder head. There is an in-cylinder fuel injector configured to directly inject the fuel as a fuel jet into the combustion chamber and an igniter disposed along a trajectory of the fuel jet to ignite the fuel jet.

Description

APPARATUS AND METHOD FOR INJECTING AND IGNITING FUEL IN AN INTERNAL COMBUSTION ENGINE

Technical Field

[0001] The present application relates to an apparatus and method for injecting and igniting fuel in an internal combustion engine, and more particularly to injecting fuel and forming a fuel-air mixture, and then igniting the fuel-air mixture in a combustion chamber of the internal combustion engine.

[0002] The following discussion of the background to the invention is intended to facilitate an understanding of the present invention only. It should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge of the person skilled in the art in any jurisdiction as at the priority date of the invention.

[0003] As emission requirements become more stringent the market share of internal combustion engines fueling from gaseous fuels instead of liquid fuels increases. Gaseous fuels generate less emissions compared to liquid fuels and the engines fueling with gaseous fuels can achieve similar power density to comparable engines fueling with liquid fuels. Moreover, historically the price of gaseous fuels on an energy equivalent basis has been less than liquids fuels. As used herein, a gaseous fuel is any fuel that is in the gaseous (gas) state at standard temperature and pressure (STP), which in the context of this application is twenty degrees Celsius (20 °C) and one atmosphere (1 atm), which is also referred to as normal temperature and pressure (NTP). Similarly, a liquid fuel is any fuel that is the liquid state at standard temperature and pressure.

[0004] There are challenges associated with fueling with gaseous fuels that are not encountered in engines fueling with liquid fuels. A key challenge is the ignition problem where gaseous fuels are typically less auto-ignitable than liquid fuels. The autoignition temperature for gaseous fuels is generally above the end of compression temperature for typical diesel-cycle engines. As used herein the autoignition temperature is the temperature at which the gaseous fuel spontaneously ignites and then combusts, and this temperature is a function of the pressure environment in which the gaseous fuel is present. More particularly, it is the pressure and temperature environment that determines whether the gaseous fuel auto-ignites. Considering internal combustion engines, the auto-ignition pressure is typically the pressure in the combustion chamber near to the end of the compression stroke, although there are many different ignition strategies that are possible whereby ignition timing can be selected for a variety of crank angles during the compression stroke or even the subsequent power stroke (also referred to as an expansion stroke). Generally, the temperature required to ignite the gaseous fuel is higher earlier in the compression stroke since the pressure increases during the compression stroke. Internal combustion engines fueling with gaseous fuel typically employ a positive ignition source such as pilot fuel, glow plugs, or spark plugs to achieve reliable ignition, since the auto-ignition temperature for the gaseous fuel is higher than the end of compression (stroke) temperature in the combustion chamber.

[0005] Although using a pilot fuel, which is typically a liquid fuel such as diesel fuel, is an effective technique for igniting gaseous fuel it increases the complexity of the fuel system in the internal combustion engine since in addition to the gaseous fuel system further components are required to store, pressurize, deliver, and inject the pilot fuel into the combustion chamber. On the other hand, although glow plugs and spark plugs can effectively ignite gaseous fuels and achieve mono-fuel operation, in atypical combustion chamber configuration a single glow plug or spark plug cannot ignite all the gaseous fuel jets emanating from a gaseous fuel injector simultaneously, which leads to unreliable ignition and engine operation, high unbumed fuel emissions and reduced engine efficiency.

[0006] The state of the art is lacking in techniques for injecting and igniting fuel, and particularly gaseous fuels, in an internal combustion engine. The present apparatus and method provide a technique for injecting and igniting fuel in an internal combustion engine.

[0007] An improved apparatus for injecting and igniting a fuel in an internal combustion engine includes a combustion chamber defined by a cylinder in an engine block, a cylinder head capping one end of the cylinder, and a piston reciprocatable within the cylinder. The piston includes a piston bowl asymmetric about a longitudinal axis of the cylinder and a top land surface facing the cylinder head and extending circumferentially around the piston bowl. The top land surface is parallel to a majority of a surface of the cylinder head facing the combustion chamber. A squish volume extends between the top land surface and the surface of the cylinder head facing the combustion chamber. There is an in-cylinder fuel injector configured to directly inject the fuel as a fuel jet into the combustion chamber and an igniter disposed along a trajectory of the fuel jet to ignite the fuel jet. The top land surface can extend in a plane transverse to the longitudinal axis, and the piston bowl can be symmetrical about a mirror longitudinal plane, which can be the only longitudinal plane about which the piston bowl is symmetric.

[0008] In an exemplary embodiment, the fuel jet is a first fuel jet, and the in-cylinder injector is further configured to inject the fuel in a second fuel jet having a trajectory near the igniter. The trajectory of the first fuel jet and the trajectory of the second fuel jet are mirror images of each other in the mirror longitudinal plane, such that the first fuel jet and the second fuel jet are each ignited by the igniter. In another exemplary embodiment, the first fuel jet is a first pilot-fuel jet and the second fuel jet is a second pilot-fuel jet, and the in-cylinder fuel injector is further configured to inject the fuel in a first main-fuel jet and a second main-fuel jet. A trajectory of the first main-fuel jet and a trajectory of the second main-fuel jet are mirror images of each other in the mirror longitudinal plane, such that the first main-fuel jet and the second fuel jet are ignited by combustion of the first pilotfuel jet and the second pilot-fuel jet, respectively. Preferably, the first pilot-fuel jet and the second pilot-fuel jet inject at most 20% of the fuel. For example, the in-cylinder fuel injector can include a first pilot hole for injecting the first pilot-fuel j et, a second pilot hole for injecting the second pilotfueljet, a first main hole for injecting the first main-fuel jet, and a second main hole for injecting the second main-fuel jet, where a ratio between a sum of cross-sectional flow areas of the first main hole and the second main hole over a sum of cross-sectional flow areas of the first pilot hole and the second pilot hole is at least 5. In another exemplary embodiment, the in-cylinder fuel injector is further configured to inject a third main-fuel jet and a fourth main-fuel jet, where a trajectory of the third main-fuel jet and a trajectory of the fourth main-fuel jet are mirror images of each other in the mirror longitudinal plane, and the third main-fuel jet and the fourth main-fuel jet are ignited by combustion of the first main-fuel jet and the second main-fuel jet, respectively.

[0009] The top land surface can include a first portion and a second portion, where a surface area of the first portion is greater than a surface area of the second portion such that a predominant squish flow develops during a compression stroke in a direction away from the first portion of the top land surface towards the second portion of the top land surface. A ratio between the surface area of the first portion of the top land surface over the surface area of the second portion of the top land surface is at least 1.5. A net squish vector can be representative of the predominant squish flow and can he in the mirror longitudinal plane. During a power stroke the predominant squish flow reverses direction compared to the compression stroke and can assist with moving an ignited and combusting fuel-air mixture in the combustion chamber towards the igniter increasing mixing of the ignited and combusting fuel-air mixture. A trajectory of the fuel jet can be away from the first portion of the top land surface towards the second portion of the top land surface, particularly when the piston is at a top dead center position. The predominant squish flow supports a momentum of the fuel jet. A net fuel -jet vector can be representative of the fuel jet and includes a horizontal component and a vertical component, and the horizontal component of the net fuel -jet vector is substantially in a same direction as the net squish vector. The net fuel -jet vector can be representative of both the first fuel jet and the second fuel jet when the in-cylinder injector is configured to inject the first and second fuel jets.

[0010] In an exemplary embodiment, the piston bowl can include a protuberance that redirects the fuel jet downwards into the piston bowl. A surface of the piston bowl can include an outline in the form of a portion of an outer surface of a pear. Alternatively, the surface of the piston bowl can include a semi-spherical outline or a semi-ellipsoid outline. A space of the piston bowl can be defined between a plane of the top land surface and a surface of the piston bowl, where a center of mass of the space is offset from the longitudinal axis. The igniter can be one of a spark plug, a glow plug, a heated surface, or a pilot fuel injector. The fuel can be a gaseous fuel, where the gaseous fuel can be one of ammonia, biogas, butane, ethane, hydrogen, liquefied petroleum gas, methane, natural gas, propane. Alternatively, the fuel can be a liquid fuel, where the liquid fuel can be one of butanol, diesel, ethanol, gasoline, kerosene, and methanol.

[0011] An improved method of injecting and igniting a fuel in an internal combustion engine includes providing a combustion chamber defined by a cylinder in an engine block having a longitudinal axis and a cylinder head capping one end of the cylinder and having a surface facing the combustion chamber; providing a piston reciprocatable within the cylinder that includes a piston bowl asymmetric about the longitudinal axis and a top land surface facing the cylinder head and extending circumferentially around the piston bowl where the top land surface is substantially parallel to a majority of the surface of the cylinder head facing the combustion chamber; providing a squish volume between the top land surface and the surface of the cylinder head facing the combustion chamber; directly injecting the fuel as a fuel jet into the combustion chamber; providing an igniter disposed along a trajectory of the fuel jet; and igniting the fuel jet.

[0012] An improved method of injecting and igniting a fuel in an internal combustion engine includes injecting the fuel in a combustion chamber of the internal combustion engine as one or more fuel jets where a net fuel -jet vector can be representative of the one or more fuel jets and having a horizontal component and a vertical component; and squishing a squish volume between a top land surface of a piston and a cylinder head by moving a piston towards the cylinder head during a compression stroke whereby a predominant squish flow forms where a net squish vector can be representative of the predominant squish flow, such that a direction of the net squish vector is substantially the same as a direction of the horizontal component of the net fuel -jet vector.

[0013] 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.

[0014] FIG. 1 is a cross-sectional schematic view of a combustion chamber of an internal combustion engine according to an embodiment.

[0015] FIG. 2 is a top view of a piston of the internal combustion engine of FIG. 1.

[0016] FIG. 3 is a cross-sectional view of the piston of FIG. 2 taken along line 2-2’.

[0017] FIG. 4 is a perspective view of the piston of FIG. 2.

[0018] FIG. 5 is a cross-sectional view of the internal combustion engine of FIG. 1 illustrating a gaseous fuel jet injected into the combustion chamber.

[0019] FIG. 6 is a top view of the piston of the internal combustion engine of FIG. 5 illustrating the gaseous fuel jet injected into the combustion chamber. [0020] FIG. 7 is a top view of the piston of the internal combustion engine of FIG. 5 illustrating a plurality of squish vectors in the combustion chamber during a squish phase in a compression stroke.

[0021] FIG. 8 is a top view of the piston of the internal combustion engine of FIG. 5 illustrating a net squish vector and a horizontal component of a net gaseous fuel jet vector in the combustion chamber during the squish phase in the compression stroke.

[0022] FIG. 9 is a top view of the piston of the internal combustion engine of FIG. 5 illustrating a plurality of squish vectors in the combustion chamber during a reverse-squish phase in a power stroke.

[0023] FIG. 10 is a top view of the piston of the internal combustion engine of FIG. 5 illustrating a net reverse-squish vector during the reverse-squish phase in the power stroke.

[0024] FIG. 11 is a cross-sectional view of an internal combustion engine illustrating one fuel jet of a pair of fuel jets injected into a combustion chamber according to another embodiment.

[0025] FIG. 12 is atop view of a piston of the internal combustion engine of FIG. 11 illustrating the pair of fuel jets injected into the combustion chamber.

[0026] FIG. 13 is atop view of the piston of the internal combustion engine of FIG. 11 illustrating a net squish vector and a horizontal component of a net fuel -jet vector in the combustion chamber during the squish phase in the compression stroke.

[0027] FIG. 14 is atop view of the piston of the internal combustion engine of FIG. 11 illustrating a net reverse-squish vector during the reverse-squish phase in the power stroke.

[0028] FIG. 15 is a cross-sectional view of an internal combustion engine illustrating a fuel jet injected into a combustion chamber according to another embodiment.

[0029] FIG. 16 is atop view of a piston of the internal combustion engine of FIG. 15 illustrating the fuel jet injected into the combustion chamber. [0030] FIG. 17 is a top view of a piston in an internal combustion engine according to another embodiment illustrating a pair of fuel jets injected into a combustion chamber.

[0031] FIG. 18 is a top view of a piston of an internal combustion engine illustrating pilot fuel jets and main fuel jets injected into a combustion chamber according to another embodiment.

[0032] FIG. 19 is a top view of a piston in an internal combustion engine illustrating pilot fuel jets and main fuel jets injected into a combustion chamber according to another embodiment.

[0033] FIG. 20 is a cross-sectional view of an internal combustion engine illustrating a fuel jet injected into a combustion chamber by a side-mounted in-cylinder injector during a compression stroke according to another embodiment.

[0034] FIG. 21 is a cross-sectional view of the internal combustion engine of FIG. 20 illustrating a piston later during the compression stroke than FIG. 20.

[0035] FIG. 22 is a cross-sectional view of the internal combustion engine of FIG. 20 illustrating the piston later during the compression stroke than FIG. 21.

[0036] FIG. 23 is a cross-sectional view of an internal combustion engine illustrating a fuel jet injected into a combustion chamber by a side-mounted in-cylinder injector during a compression stroke according to another embodiment.

[0037] FIG. 24 is a top view of a piston according to another embodiment.

[0038] FIG. 25 is a cross-sectional view of the piston of FIG. 24 taken along line 24-24’.

[0039] FIG. 26 is a top view of a piston according to another embodiment.

[0040] FIG. 27 is a cross-sectional view of the piston of FIG. 26 taken along line 26-26’.

[0041] FIG. 28 is a chart view illustrating an injection flow rate and an ignition window for the embodiments of internal combustion engines disclosed herein when operating in a partially -premixed combustion mode. [0042] FIG. 29 is a chart view illustrating an injection flow rate and an ignition window for the embodiments of internal combustion engines disclosed herein when operating in a diffusion (nonpremixed) combustion mode.

Detailed

[0043] Referring to FIG. 1, there is shown internal combustion engine 10 according to an embodiment including combustion chamber 20 defined by piston 30, cylinder 50, and cylinder head 70. Piston 30 reciprocates within cylinder 50 whereby piston rod 80 connects piston 30 with a crankshaft (not shown) and converts reciprocal motion of piston 30 into circular motion of the crankshaft. As will be described in more detail below, piston 30 includes piston bowl 160 (biased to one side of the piston) and top land surface 250 extending circumferentially around the piston bowl where both the piston bowl and the top land surface face combustion chamber 20. Surface 40 of cylinder 50 extends in engine block 60 and is characterized by longitudinal axis 55. Surface 75 of cylinder head 70 (also called fire-deck 75) faces combustion chamber 20 and extends in transverse plane 85 transverse to longitudinal axis 55. Top land surface 250 is substantially parallel to a majority of surface 75 of cylinder head 70. Although only one such combustion chamber 20 is illustrated in other embodiments there can be a plurality of combustion chambers.

[0044] Intake air is communicated through intake port 90 and selectively inducted into combustion chamber 20 through intake valve 100. In an exemplary embodiment intake port 90, intake valve 100, and combustion chamber 20 cooperate to establish a tumble flow of intake air within combustion chamber 20, and in the illustrated embodiment the tumble flow would be in a counterclockwise direction in the combustion chamber. Tumble flow can be described as bulk motion of intake air about a transverse axis with respect to longitudinal axis 55 of cylinder 50. Alternatively, intake port 90, intake valve 100, and combustion chamber 20 can cooperate to establish a swirl flow of intake air within combustion chamber 20, in other embodiments, where swirl flow can be described as bulk motion of intake air about longitudinal axis 55. It is contemplated that there can be simultaneously both tumble motion and swirl motion of intake air with combustion chamber 20 in some embodiments. In yet another exemplary embodiment, intake port 90, intake valve 100, and combustion chamber 20 cooperate to establish a quiescent combustion-chamber that can be described quantitatively as intake air motion within combustion chamber 20 having an angular momentum (including both tumble flow and swirl flow components) below a limit value, and can be described qualitatively as fuel jet induced mixing of fuel with intake air within combustion chamber 20 where the fuel-air mixing does not rely upon bulk motion of intake air within the combustion chamber (that is, the bulk motion of intake air does not substantially induce mixing). In-cylinder injector 110 receives fuel from fuel supply 125 and injects the fuel directly into combustion chamber 20 where it mixes with intake air in the combustion chamber forming a fuel-air mixture, as will be described in more detail below. The fuel-air mixture is ignited by igniter 120, which can be a positive-ignition source such as a spark plug, glow plug, or other hot surface. Exhaust from combustion of the fuel-air mixture is evacuated from combustion chamber 20 selectively through exhaust valve 130 and can be communicated by exhaust port 140 to an aftertreatment system (not shown) where it is treated before being released into the atmosphere.

[0045] Controller 150 can be an electronic controller operatively connected with in-cylinder injector 110 and igniter 120 that commands the in-cylinder injector to inject gaseous fuel and, separately and independently, commands the igniter to ignite the fuel-air mixture in combustion chamber 20. Intake valve 100 and exhaust valve 130 can be actuated by a camshaft, a variable valvetiming system, or by solenoid actuated electronically by controller 150.

[0046] Referring now to FIGS. 2, 3, and 4, piston 30 is discussed in more detail. Piston bowl 160 is a cutout or niche in end 35 of piston 30 that is asymmetrically biased to one side of longitudinal plane 170 while simultaneously being substantially symmetric about longitudinal plane 180, where longitudinal plane 170 is orthogonal to longitudinal plane 180. In this regard longitudinal plane 180 can be considered a mirror plane in relation to piston bowl 160 and is also referred to herein as a mirror longitudinal plane (180) and is the only longitudinal plane about which piston bowl 160 is symmetric. Piston bowl space 165 can be defined as the space between piston bowl 160 and transverse plane 186 at end 35 of piston 30. Center of mass Me of piston bowl space 165 is offset from longitudinal axis 190. In an exemplary embodiment, longitudinal planes 170 and 180 pass through longitudinal axis 190 of piston 30, where longitudinal axis 190 is a cylinder axis with respect to outer surface 200 of piston 30. Preferably, longitudinal axis 190 of piston 30 is coaxial with longitudinal axis 55 of cylinder 50 (seen in FIG. 1) whereby a transverse plane of piston 30 is parallel to a transverse plane of cylinder 50 and a longitudinal plane of piston 30 is parallel to a longitudinal plane of cylinder 50. In the illustrated embodiment piston bowl 160 can be described as having an outline shaped like a portion of an outer surface-of-a-pear. Piston bowl 160 includes first sloped region 210 and second sloped region 220 that each converge on deepest region 230 between the two sloped regions. First sloped region 210 can include linearly sloped regions and curved regions; second sloped region 220 can include linearly sloped regions and curved regions; and deepest region 230 can also include linearly sloped regions and curved regions. Outer circumferential region 240 flares piston bowl 160 outwardly, such as by a chamfer or fillet, to provide a transition region from first and second sloped regions 210, 220 respectively and deepest region 230 to top land surface 250 of piston 30. Each region 210, 220, and 230 extends from outer circumferential region 240 into piston bowl 160 and deepest region 230 extends to deepest point 235 of the piston bowl. There could a plurality of locations in piston bowl 160 that are at the same deepest depth with respect to transverse plane 186, and deepest point 235 can represent any of these points. In an exemplary embodiment deepest point 235 represents a mean location (that is, a central location) of a plurality of deepest points at equivalent depths with respect to transverse plane 186. Deepest point 235 lies in the mirror longitudinal plane, longitudinal plane 180. Within longitudinal plane 180, as seen in FIG. 3, an average slope of first sloped region 210 can be less than an average slope of second sloped region 220. First sloped region 210 can span both sides of longitudinal plane 170 and longitudinal axis 190 can pass through the first sloped region. Second sloped region 220 and deepest region 230 can both be on the same side of longitudinal plane 170 and longitudinal axis 190. Top land surface 250 is a circumferential region around piston bowl 160 at end 35 of piston 30 that lies and extends in transverse plane 186 and faces cylinder head 70 seen in FIG. 1. Portion 260 of top land surface 250 is adjacent first sloped region 210 and portion 270 of top land surface 250 is adjacent second sloped region 220, and portions 260 and 270 each extend circumferentially around piston bowl 160 and meet adjacent deepest region 230. In an exemplary embodiment, portions 260 and 270 of top land surface 250 meet at longitudinal plane 175 on each side of piston bowl 160, where longitudinal plane 175 extends through deepest point 235 and is transverse to longitudinal plane 180 (the mirror longitudinal plane). A surface area of portion 260 is greater than a surface area of portion 270 whereby a ratio between the surface area of portion 260 over the surface area of portion 270 can be at least 1.5.

[0047] Referring now to FIGS. 5 to 8, and first to FIGS. 5 and 6 the formation of the fuel-air mixture in combustion chamber 20 is discussed in more detail. Fuel jet 300 is injected into combustion chamber 20 by in-cylinder injector 110 through nozzle hole 116 along a trajectory (or path) in longitudinal plane 180 (the symmetrical plane of piston 30 best seen in FIG. 2) towards and adjacent to igniter 120 whereby the fuel jet 300 can be ignited by the igniter. The trajectory of fuel jet 300 is also away from portion 260 of top land surface 250 towards second portion 270 of top land surface 250, particularly away from a part of portion 260 and towards a part of portion 270 along longitudinal plane 180 and when piston 30 is at a top dead center position. As fuel jet 300 travels it mixes with intake air along the trajectory such that an ignitable fuel-air mixture forms when the fuel jet passes by igniter 120. In the absence of charge air motion with combustion chamber 20 the trajectory of fuel jet 300 remains along longitudinal plane 180. However, the trajectory of fuel jet 300 may deviate from along longitudinal plane 180 due to charge air motion within combustion chamber 20, and particularly swirl motion where a bulk motion of intake air can cause fuel jet 300 to deviate in a clockwise or counter-clockwise motion (depending on the direction of swirl) with respect to longitudinal plane 180. It is possible that nozzle hole 116 can be offset with respect to longitudinal plane 180 such that a swirl motion will cause fuel jet 300 to move towards longitudinal plane 180. Fuel jet 300 is injected into combustion chamber 20 towards and redirected by second sloped region 220 of piston bowl 160 back into combustion chamber 20 towards igniter 120 and in-cylinder injector 110. When the bulk air motion of intake air in combustion chamber 20 is tumble flow the tumble flow of intake air can aid in redirecting the fuel jet downwards into piston bowl 160 and back towards igniter 120. That portion of fuel jet 300 that emanates from in-cylinder injector 110 and before it is redirected by second sloped region 220 forms net fuel -jet vector 320 (seen in FIG. 5), such as a velocity vector, including horizontal component 330 (also known as a transverse component) directed across a transverse plane of cylinder 50 and vertical component 340 (also known as a longitudinal component) directed away from cylinder head 70 into piston bowl 160 along a longitudinal plane of cylinder 50. Net fuel -jet vector 320 is generally directed away from first portion 260 of top land surface 250 towards second portion 270 of top land surface 250 (although not directly towards). Horizontal component 330 and vertical component 340 are substantially parallel to longitudinal plane 180 due to the symmetry of fuel jet 300 about longitudinal plane 180. That is, components of fuel jet 300 that extend parallel to longitudinal plane 170 cancel each other out, at least when effects of air motion on fuel jet 300 are ignored.

[0048] A volume between top land surface 250 and cylinder head 70 extending circumferentially around piston bowl 160 is referred to as squish volume 360 (seen in FIG. 1). A high pressure develops in squish volume 360 as piston 30 moves towards cylinder head 70 during a compression stroke reducing the squish volume and creating a squish flow of intake air (or intake charge) out of the squish volume to evacuate the intake air into that portion of combustion chamber 20 above piston bowl 160. With reference to FIG. 7, this squish flow is represented as a plurality of squish jets 400 circumferentially around piston bowl 160 and directed inwardly towards piston bowl 160. Due to the symmetry of piston 30 about longitudinal plane 180 the plurality of squish jets 400 forms a predominant squish flow that can be represented by net squish vector 410 (seen in FIG. 8), such as a velocity vector that is directed away from portion 260 towards portion 270 of top land surface 250. Preferably, net squish vector 410 lies in longitudinal plane 180 (the mirror longitudinal plane); and generally parallel to transverse plane 185 (seen in FIG. 3) (although the squish flow can induce a tumble flow as will be described in more detail below and net squish vector 410 is not representative of the squish induced tumble flow). Net squish vector 410 can be substantially parallel to and in the same direction as horizontal component 330 of net fuel-jet vector 320 that can be described as a horizontal sheet of air (or charge) moving atop of combustion chamber 20 that interacts with fuel jet 300 and with intake air motion within the combustion chamber. Net squish vector 410 and net fueljet vector 320 are both directed towards a same side of piston bowl 160 furthest away from longitudinal plane 170 and away from first portion 260 of top land surface 250 towards second portion 270 of top land surface 250. The predominant squish flow (represented by net squish vector 410) helps to support a momentum of fuel jet 300, particularly a magnitude of the momentum of fuel jet 300 and particularly when an injection pressure of the fuel decreases, which helps with mixing of the fuel in fuel jet 300 with the intake air in combustion chamber 20. Before the present invention, the direction of squish air motion opposed the direction of fuel jets, which reduced momentum of the fuel jets. When the bulk air motion of intake air in combustion chamber 20 is a tumble flow, net squish vector 410 shears the tumble flow of the bulk motion of the intake air at the top of combustion chamber 20, which improves the tumble flow of the entire fuel-air charge, and the squish flow can itself induce a tumble motion as it reaches second sloped region 220 of piston bowl 160 and begins to descend into the piston bowl. The squish induced tumble flow is in the same direction as the intake air induced tumble flow. It is advantageous that injection timing for in-cylinder injector 110 corresponds to when net squish vector 410 forms, and fuel jet 300 can either lead or lag net squish vector 410. It is noteworthy that top land surface 250 is parallel to fire-deck 75 of cylinder head 70 such that the predominant squish flow (represented by net squish vector 410) has enough momentum to improve fuel jet momentum and tumble flow within combustion chamber 20. Squish jets 400 can be employed to define a boundary condition between portions 260 and 270 of top land surface 250. Each jet 400 includes a horizontal component directed either to the left or the right with respect to FIG. 7 and a vertical component directed either upwards or downwards with respect to FIG. 7. When top land surface 250 is divided circumferentially into infinitesimal radial regions, portion 260 of top land surface 250 includes those radial regions where local jet 400 includes a horizontal component directed to the left with respect to FIG. 7, and portion 270 includes those radial portions where local jet 400 includes a horizontal component directed to the right. That is, portion 260 includes regions of top land surface 250 where horizontal components (with respect to FIG. 7) of jets 400 are in the same direction and opposite to the direction of the horizontal components of jets 400 in portion 270.

[0049] The squish flow changes direction as piston 30 reaches a top dead center position (the closest position piston 30 gets to cylinder head 70) during the compression stroke and begins to move away from cylinder head 70 during a power stroke. A low pressure develops in squish volume 360 as piston 30 moves away from cylinder head 70 increasing squish volume 360. With reference to FIGS. 9 and 10, the reverse-squish flow during the power stroke is represented as a plurality of rev erse-squish jets 420 circumferentially around piston bowl 160 and directed outwardly into squish volume 360. Due to the symmetry of piston 30 about longitudinal plane 180 the plurality of reverse- squish jets 420 form net reverse-squish vector 430 that is directed substantially parallel to longitudinal plane 180 and transverse plane 185 (best seen in FIG. 3) away from portion 270 towards portion 260 of top land surface 250. This reverse-squish flow causes the charge within combustion chamber 20, including ignited and combusting fuel, to move in the direction of net reverse-squish vector 430 (that is, to the right in the illustrated embodiment of FIG. 10) towards igniter 120, which is another mixing mechanism for later phase mixing and combustion.

[0050] Referring now to FIGS. 11 to 14 there is shown internal combustion engine 11 according to another embodiment that is similar to internal combustion engine 10 and like parts in this and other embodiments have like reference numerals and at least differences between the embodiments are discussed. In-cylinder injector 111 includes nozzle holes 117 and 118 (best seen in FIG. 12) through which fuel jets 310 and 312, respectively are injected into combustion chamber 20. Fuel jet 310 is injected into combustion chamber 20 on one side of longitudinal plane 180 adjacent igniter 120 and fuel jet 312 is injected into combustion chamber 20 on an opposite side of longitudinal plane 180 adjacent igniter 120. Preferably, in the absence of charge air motion with combustion chamber 20 fuel jets 310 and 312 are symmetrical with respect to longitudinal plane 180 and can be described as mirror images of each other. However, jets 310 and 312 may deviate from their mirror images due to charge air motion within combustion chamber 20, and particularly due to bulk swirl motion of the intake air where the swirl will cause one of fuel jets 310 and 312 to move towards igniter 120 and the other fuel jet to move away from igniter 120. In the presence of bulk swirl motion nozzle holes 117 and 118 can be offset with respect to longitudinal plane 180 such that the bulk swirl motion will cause fuel jets 310 and 312 to move towards mirror image alignment with respect to longitudinal plane 180. Each jet 310 and 312 is injected into combustion chamber 20 towards and redirected by second sloped region 220 of piston bowl 160 back into combustion chamber 20 towards in-cylinder inj ector 111. Those portions of fuel j ets 310 and 312 that emanate from in-cylinder inj ector 111 and before they are redirected by second sloped region 220 together form net fuel-jet vector 321 (seen in FIG. 11), such as a velocity vector, including horizontal component 331 directed across a transverse plane of cylinder 50 and vertical component 341 directed away from cylinder head 70 into piston bowl 160 along a longitudinal plane. Horizontal component 331 and vertical component 341 are substantially parallel to longitudinal plane 180 due to the symmetry of fuel jets 310 and 312 about longitudinal plane 180 (that is, they are mirror images of each other). Components of each fuel jet 310 and 312 (not shown) that extend parallel to longitudinal plane 170 are equal in magnitude and opposite in direction and accordingly cancel each other out with respect to net fuel-jet vector 321.

[0051] During a compression stroke of piston 30, net squish vector 410 (seen in FIG. 13) is substantially parallel to and in the same direction as horizontal component 331 of net fuel-jet vector 321 and can be described as a horizontal sheet of air (or charge) moving atop of combustion chamber 20 that interacts with fuel j ets 310 and 312 and with intake air motion within the combustion chamber. Net squish vector 410 helps to maintain the momentum of fuel jets 310 and 312, particularly when an injection pressure of the fuel decreases, which helps with mixing of the fuel in jets 310 and 312 with the intake air within combustion chamber 20. Net squish vector 410 can also induce a tumble flow when it reaches second sloped region 220 that supports the intake air induced tumble flow in combustion chamber 20, which further improves mixing of fuel with intake air.

[0052] During a power stroke of piston 30, net reverse-squish vector 430 (seen in FIG. 14) is directed substantially parallel to longitudinal plane 180 and transverse plane 185 (best seen in FIG. 3) away from portion 270 towards portion 260 of top land surface 250. Reverse-squish flow of net reverse-squish vector 430 causes the charge within combustion chamber 20, including ignited and combusting fuel, to move in the direction of net reverse-squish vector 430 (that is, to the right in the illustrated embodiment of FIG. 14) towards igniter 120, which is another mixing mechanism for later phase mixing and combustion.

[0053] Referring now to FIGS. 15 and 16 there is shown internal combustion engine 12 that is similar to internal combustion engine 10 of FIG. 1 and differences between the embodiments are discussed. Protuberance 500 in piston bowl 162 of piston 32 operates to guide and induce (or enhance) a tumble flow in fuel jet 300 within combustion chamber 22 compared to piston bowl 160 shown in FIG. 5. Preferably, protuberance 500 prevents stagnation of fuel jet 300 at a surface of piston bowl 162. Protuberance 500 is part of second sloped region 222 and increases an average slope of second sloped region 222 compared to the average slope of second sloped region 220 shown in FIG. 5. Fuel jet 300 is redirected by protuberance 500 downwards towards deepest region 230 and back towards igniter 120 and first sloped region 210. With reference to FIG. 17, protuberance 502 guides fuel jets 310 and 312 by redirecting them downwards (into piston bowl 163) and circumferentially in opposite directions, respectively along piston bowl 163 of piston 33, back towards regions of unmixed intake air (for example those regions around or near igniter 120) for a better utilization of air within combustion chamber 20 for mixing, which improves combustion. More particularly, fuel jet 310 is directed downwards (into the piston bowl) and circumferentially along piston bowl 163 in a counter-clockwise direction and fuel jet 312 is directed downwards (into the piston bowl) and circumferentially along piston bowl 163 in a clockwise direction, both travelling back towards igniter 120. From the fuel jets perspective, protuberance 502 causes fuel jets 310 and 312 to rotate to the left and to the right, respectively, in addition to the downward rotation into the piston bowl. That is, protuberance 502 induces both a tumble flow and a swirl flow in fuel jets 310 and 312, where the tumble flow is in the same direction from each jet and the swirl flows are in the opposite directions.

[0054] Referring to FIG. 18 there is shown internal combustion engine 14 according to another embodiment that employs piston 33 from the embodiment of FIG. 17, including protuberance 502. In-cylinder injector 114 includes nozzle holes 510 and 520 for injecting pilot fuel jets 530 and 540, respectively, and nozzle holes 550 and 560 for injecting main fuel jets 570 and 580, respectively. In the illustrated embodiment all fuel jets 530, 540, 570, and 580 are injected simultaneously although this is not a requirement and in other embodiments pilot fuel jets 530 and 540 can be injected separately and independently of main fuel jets 570 and 580. A ratio of a sum of cross-sectional flow areas through each main nozzle hole 550 and 560 over a sum of cross-sectional flow areas through each pilot nozzle hole 510 and 520 can be at least 5. That is, at most 20% of the overall fuel injected can be through pilot nozzle holes 510 and 520. However, preferably total pilot fuel consumption is limited to at most 10% of total fuel consumption. In the absence of air motion within the combustion chamber, pilot fuel jets 530 and 540 are mirror images of each other with respect to longitudinal plane 180 (that is, the mirror longitudinal plane) where pilot fuel jet 530 is adjacent igniter 120 on one side of longitudinal plane 180 and pilot fuel jet 540 is adjacent an opposite side of igniter 120 on an opposite side of longitudinal plane 180. Main fuel jets 570 and 580 are mirror images of each other with respect to longitudinal plane 180, in the absence of air motion within the combustion chamber, where main fuel jet 570 is adjacent pilot fuel jet 530 on an opposite side of igniter 120, and main fuel jet 580 is adjacent pilot fuel jet 540 on an opposite side of igniter 120. Pilot fuel jets 530 and 540 form a local fuel-air mixture around igniter 120 that can have increased ignitability compared a local fuel-air mixture around igniter 120 in previous discussed embodiments. The momentum and velocity of pilot fuel jets 530 and 540 is substantially less than the momentum and velocity of main fuel jets 570 and 580, and the momentum of pilot fuel jets 530 and 540 spreads out more widely and they lose momentum more rapidly than main fuel jets 570 and 580 as they mix with air. Accordingly, when portions of the fuel in pilot fuel jets 530 and 540 are ignited there is less likelihood that the unignited trailing portions of pilot fuel jets 530 and 540 will blowout the ignited pilot fuel thereby allowing formation of a large and robust ignition kernel capable of igniting the main fuel jets. Main fuel jets 570 and 580 are ignited by the combustion of pilot fuel jets 530 and 540, respectively and not directly by igniter 120. The combustion of pilot fuel jets 530 and 540 provides a much more robust positive ignition source for main fuel jets 570 and 580 compared to igniter 120. With reference to FIG. 19, there is shown internal combustion engine 15 according to another embodiment that is similar to engine 14 and where in-cylinder injector 115 further includes another pair of main nozzle holes 555 and 565 through which main fuel jets 575 and 585 are injected. Main fuel jets 575 and 585 are mirror images of each other with respect to longitudinal plane 180, in the absence of air motion within the combustion chamber, and are adjacent main fuel jets 570 and 580, respectively, and further away from igniter 120. Piston bowl 164 can have a different geometry compared to piston bowls 160, 162, and 163 to accommodate the larger number of fuel jets. In some embodiments the cross-sectional profde of piston bowl 164 illustrated in FIG. 19 can resemble a kidney bean shape, whereby space is opened up for main fuels jets 575 and 585. The amount of space opened up can be limited by a reduction in the compression ratio within cylinder 50. In some embodiments the shape of piston bowl 164 encourages or directs a common rotational direction of main fuel jets 530, 570, and 575 about longitudinal axis 55 of cylinder 50, as well as a common rotational direction of main fuel jets 540, 580, and 585 about longitudinal axis 55 of cylinder 50. Although internal combustion engines 14 and 15 are illustrated with pistons 33 and 34 having protuberance 502, this is not a requirement and in other embodiments piston 30 (without a protuberance) can be employed in those embodiments employing a pair of pilot fuel jets and one or more pairs of main fuel jets. Protuberance 502 can be employed to redirect either all the main fuel jets or a portion of the main fuel jets. In the illustrated embodiment of FIG. 19, main fuel jets 575 and 585 are not redirected by protuberance 502, although in other embodiments another protuberance can be employed that also redirects main fuel jets 575 and 585. A cascading ignition sequence takes place in combustion chamber 24, where combustion of pilot fuel jets 530, and 540 ignites main fuel jets 570 and 580, respectively, and combustion of main fuel jets 570 and 580 ignites main fuel jets 575 and 585, respectively. Pilot fuel jets 530 and 540 typically do not require guidance from protuberance 502 since the momentum of the pilot fuel jets substantially dissipates before they reach protuberance 502 (that is, protuberance 502 can be a point of stagnation for pilot fuel jets 530 and 540), unlike main fuel jets 570, 575, 580, and 585 that have substantially higher momentum when they reach the surface of the respective piston bowl 163 or 164.

[0055] Referring now to FIGS. 20, 21, and 22 there is shown internal combustion engine 16 according to another embodiment. In-cylinder injector 119 is a side mounted injector disposed in engine block 66 instead of in cylinder head 72 and is configured to inject at least one fuel jet 300 having a trajectory through combustion chamber 26 laterally from one side to another side that can be inclined away from cylinder head 72. In-cylinder injector 119 is actuated by controller 150 during the compression stroke, for example, such that piston 32 travels sufficiently towards cylinder head 72 whereby tip 600 of fuel jet 300 impinges on lower surface 505 of protuberance 500 (as seen in FIG. 21, which is further into the compression stroke than FIG. 20) and gets redirected downwards and back towards igniter 120 (as seen in FIG. 22, which is further into the compression stroke than FIG. 21). Most and preferably all of fuel jet 300 clears top land surface 250 and is above or in piston bowl 162 before piston 32 has traveled enough during the compression stroke for top land surface to contact fuel jet 300. Alternatively, in other embodiments internal combustion engine 17 illustrated in FIG. 23 can be employed where channel 610 in piston 37 allows fuel jet 300 to be injected from side- mounted in-cylinder injector 119 while the piston is at the TDC position after the compression stroke. Channel 610 extends from outer surface 206 of piston 37 to piston bowl 167, which is like piston bowl 162 (seen in FIG. 15) except for the cutout of channel 610. Piston 37 allows fuel injection later in the compression stroke and earlier in the power stroke compared to piston 32 of internal combustion engine 16 seen in FIGS. 20-22. In other embodiments in-cylinder injector 119 can inject a pair of pilot fuel jets and one or more pairs of main fuel jets (like pilot fuel jets 530 and 540 and main fuel jets 570, 575, 580, and 585, respectively, in FIG. 18 or 19), and pistons 36 and 37 can employ a protuberance like protuberance 502 to guide these fuel jets into leaner regions of the combustion chamber.

[0056] Different shapes to the piston bowl (other than the portion of the outer-surface-of-a-pear) can be employed in alternative pistons in other embodiments. For example, with reference to FIGS. 24 and 25, piston bowl 168 in piston 38 has a semi-spherical outline or shape, and in FIGS. 26 and 27, piston bowl 169 in piston 39 has a semi-ellipsoid outline or shape. Longitudinal plane 180 in the illustrated embodiments of FIGS. 24 through 27 is not the only longitudinal plane about which piston bowls 168 and 169 are symmetric due to the symmetrical nature of spheres and ellipsoids. That is, there are a plurality of longitudinal planes about which piston bowl 168 is symmetric, and piston bowl 169 is symmetric about longitudinal planes 175 and 180. Regarding piston bowl 169, in other embodiments the semi-ellipsoid outline of piston bowl 169 can be rotated about an axis transverse to longitudinal plane 180 (and moved up or down with respect to longitudinal axis 190) such that longitudinal plane 180 is the only longitudinal plane about which piston bowl 169 is symmetric. First sloped regions 218, 219 of pistons 38, 39 respectively, particularly in longitudinal plane 180 have an average slope equal to second sloped regions 228, 229. The portion of the outer-surface-of-a-pear shape seen in piston bowls 160, 162, 163, 164, and 167 has advantages compared to the semi- spherical or semi-ellipsoid shapes, such as favoring an asymmetric, biased configuration allowing for a greater squish flow. That is, the portion of the outer-surface-of-a-pear shaped piston bowl allows for portion 260 of top land surface 250 (for example, seen in FIGS. 2 and 3) to have a greater percentage of the overall surface area of top land surface 250 than portion 270, compared to when the piston bowl is semi-spherical or semi-ellipsoid. For example, a ratio of a surface area of portion 260 over a surface area of portion 270 (seen in FIG. 2) can typically be greater than a ratio of surface area of portion 268 over a surface area of portion 278 of top land surface 258 (seen in FIG. 24) and greater than a ratio of surface area of portion 269 over a surface area of portion 279 of top land surface 259 (seen in FIG. 26). Moreover, the portion of the outer-surface-of-a-pear shaped piston bowl typically fits the shape of fuel jets better, for example, as the fuel jet travels away from the in-cylinder injector it expands forming a cone shape, and in this regard the average slope of first sloped region 210 compared to the average slope of second sloped region 220 results in piston bowl space 165 expanding in congruence with the fuel jet(s) as the fuel jet(s) travels from the first sloped region 210 towards the second sloped region 220. The portion of the outer-surface-of-a-pear shaped piston bowl can reduce the likelihood of the redirected fuel jet (due to protuberances 500 or 502) impinging firedeck 75 since with the portion of the outer-surface-of-a-pear shaped piston bowl the fuel jet can be deeper in the piston bowl when it is redirected thereby requiring it to travel a greater distance to reach the fire-deck compared to the semi-spherical or semi-ellipsoid piston shaped bowls.

[0057] The embodiments disclosed herein can be operated in a variety of different operating modes that take into consideration, for example, whether the internal combustion engine is operating under a high load or low load condition. With reference to FIG. 28, injection flow rate 700 is illustrated where the fuel is introduced with an injection timing allowing the fuel to mix with intake air to form a partially-premixed fuel-air mixture within the combustion chambers of internal combustion engines 10, 11, 12, 13, 14, 15, 16, and 17 disclosed herein. Preferably, the fuel is injected during the compression stroke after the intake valve has closed, such that the fuel (particularly gaseous fuel) does not displace intake air, although this is not a requirement. Injection flow rate 700 includes ramping up region 702 and ramping down region 704, where these ramping regions reduce a local strain, and substantially constant-flow region 706. The local strain refers to a strain rate in the local flow field near the ignition source, where strain refers to the local gradient in the velocity field. High strain in the flow field stretches the flame and enhances the species transport. A moderate strain can increase the rate of combustion, but a very high strain can quench the flame. The ramping regions in the flow field can be controlled to facilitate ignition and prevent quench due to high strain rate. Ignition window 710 is a range of crank angle degrees during a later phase of the compression stroke, for example after the partially- premixed fuel-air mixture forms, where ignition can occur, and as is illustrated ignition occurs before the top dead center (TDC) position. Different types of positive ignition sources require different amounts of time to ignite fuel, for example, a spark plug is a type of instantaneous ignition source at the time of spark (provided there is an ignitable fuel-air mixture around the spark), and a heated surface ignites fuel near the heated surface when the fuel reaches an auto-ignition temperature (that is dependent on the pressure near the heated surface), and the point in time of ignition can occur anywhere within window 710, preferably. Referring now to FIG. 29, injection flow rate 750 is illustrated where fuel is introduced with an injection timing starting later during the compression stroke compared to the partially-premixed condition (seen in FIG. 28) such that a stratified fuel-air mixture is formed within the combustion chambers of internal combustion engines 10, 11, 12, 13, 14, 15, 16, and 17 disclosed herein. Injection flow rate 750 also includes ramping up region 752 and ramping down region 754, where these ramping regions reduce local strain, and substantially constant-flow region 756. In an exemplary embodiment a start of injection timing of injection flow rate 750 (that is, the beginning of ramping up region 752) can begin at the earliest 30 degrees before top dead center during the compression stroke and an end of injection timing (that is, the ending of ramping down region 754) can end at most 20 degrees after top dead center during the power stroke. To bum the fuel in a diffusion combustion mode, ignition window 760 (where ignition can occur) begins at the start of injection instead of occurring near to the end of the injection as in the partially-premixed condition in FIG. 28.

[0058] A pressure ratio between jets 300, 310, 312, 570, 575, 580, 585 over the pressure in the combustion chamber when the fuel is injected into the combustion chamber is preferably within a range whereby the momentum of the jets does not cause significant fire deck impingement when the jets are redirected back towards igniter 120 and traveling upwards towards the fire-deck 75 (seen in FIG. 1). One reason why significant fire deck impingement is to be avoided is that it causes energy loss through increased heat transfer. It is desirable that with proper selection of pressure ratio in conjunction with sufficient bowl depth and bowl shape, the extent of fire deck impingement can be reduced such that heat transfer loss is also reduced.

[0059] The present invention as disclosed in the embodiments herein is particularly advantageous for igniting and combusting gaseous fuels such as ammonia, biogas, butane, ethane, hydrogen, liquefied petroleum gas, methane, natural gas, propane, and combinations of these fuels. Liquefied petroleum gas is in a gas state at standard temperature and pressure, and since it is typically stored at pressures above standard pressure it is typically stored in a liquefied state. The present invention as disclosed in the exemplary embodiments herein can also be employed to ignite liquid fuels (and particularly but not exclusively those that are difficult to auto-ignite) such as bunker fuel, butanol, diesel, dimethyl ether (DME), ethanol, gasoline, kerosene, methanol, and combinations of these fuels. Although diesel fuel is relatively an easily ignitable fuel that can be auto-ignited, there are applications contemplated where diesel fuel and other fuels with comparable cetane numbers (for example a cetane number of 40 or higher) can be employed as the main fuel in the embodiments herein, particularly when the compression ratio employed does not create a pressure and temperature environment within the combustion chamber suitable for auto-ignition. Other hydrocarbon fuels that are difficult to auto-ignite are contemplated as well. The conditions required to ignite a fuel are specific for each fuel, whereby different fuels having unique ignition energies require different igniter characteristics. Pressure and temperature conditions in the combustion chamber, the surface temperature of a hot surface igniter, and the energy in the discharge of a spark igniter are some characteristics that influence ignition. The compression ratio of the engine, the inlet manifold temperature, and the use of exhaust gas recirculation can influence the pressure and temperature conditions in the combustion chamber around the time of ignition. In the circumstance where liquid fuel is employed, the liquid fuel is preferably injected at a high pressure to enhance and accelerate atomization and vaporization of the liquid fuel in the combustion chamber such that the liquid fuel behaves more like a gas even though it’s a liquid, and to reduce and preferably eliminate the wetting of igniter 120. However, high pressure injection of liquid fuel for atomization purposes can result in fuel jet velocity that hinders ignition by blowing out ignited fuel from a spark or heated surface, and in this regard the spacing between the fuel injector and the igniter can be configured to reduce this effect. Igniter 120 is spaced from injector 110 by at least a distance required to atomize the fuel when the fuel is a liquid fuel. Whether the fuel is a gaseous fuel or a liquid fuel, an ignitable fuel air mixture has formed near igniter 120 (particularly in an ignition zone of the igniter) at the time of ignition.

[0060] Although igniter 120 is preferably a positive ignition source other than a pilot fuel, since there is a desire to eliminate a secondary fuel (and associated fuel system) that is employed as the pilot fuel, there are no technical reasons preventing this arrangement such that the igniter in other embodiments can be a fuel injector that directly injects a pilot fuel.

[0061] 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

We claim:

1. An internal combustion engine for injecting and igniting a fuel comprising: a combustion chamber defined by: a cylinder in an engine block having a longitudinal axis; a cylinder head capping one end of the cylinder and having a surface facing the combustion chamber; and a piston reciprocatable within the cylinder and comprising: a piston bowl asymmetric about the longitudinal axis; and a top land surface facing the cylinder head and extending circumferentially around the piston bowl, wherein the top land surface is substantially parallel to a majority of the surface of the cylinder head facing the combustion chamber; a squish volume between the top land surface and the surface of the cylinder head facing the combustion chamber; an in-cylinder fuel injector configured to directly inject the fuel as a fuel jet into the combustion chamber; and an igniter disposed along a trajectory of the fuel jet to ignite the fuel jet.

2. The internal combustion engine as claimed in claim 1, wherein the top land surface extends in a plane transverse to the longitudinal axis.

3. The internal combustion engine as claimed in claim 1, wherein the piston bowl is symmetrical about a mirror longitudinal plane.

4. The internal combustion engine as claimed in claim 3, wherein the mirror longitudinal plane of the piston is the only longitudinal plane about which the piston bowl is symmetric.

5. The internal combustion engine as claimed in claim 3, wherein the fuel jet is a first fuel jet and the in-cylinder inj ector is further configured to inj ect the fuel in a second fuel j et having a traj ectory near the igniter, the trajectory of the first fuel jet and the trajectory of the second fuel jet are mirror images of each other in the mirror longitudinal plane, wherein the first fuel jet and the second fuel jet are each ignited by the igniter.

6. The internal combustion engine as claimed in claim 5, wherein the first fuel jet is a first pilot-fuel jet and the second fuel jet is a second pilot-fuel jet, and the in-cylinder fuel injector is further configured to inject the fuel in a first main-fuel jet and a second main-fuel jet, a trajectory of the first main-fuel jet and a traj ectory of the second main-fuel jet are mirror images of each other in the mirror longitudinal plane, wherein the first main-fuel jet and the second main-fuel jet are ignited by combustion of the first pilot-fuel jet and the second pilot-fuel jet, respectively.

7. The internal combustion engine as claimed in claim 6, wherein the first pilot-fuel jet and the second pilot-fuel jet inject at most 20% of the fuel.

8. The internal combustion engine as claimed in claim 6, wherein the in-cylinder fuel injector includes a first pilot hole for injecting the first pilot-fuel jet, a second pilot hole for injecting the second pilot-fuel j et, a first main hole for inj ecting the first main-fuel j et, and a second main hole for injecting the second main-fuel jet, a ratio between a sum of cross-sectional flow areas of the first main hole and the second main hole over a sum of cross-sectional flow areas of the first pilot hole and the second pilot hole is at least 5.

9. The internal combustion engine as claimed in claim 6, wherein the in-cylinder fuel injector is further configured to inject a third main-fuel jet and a fourth main-fuel jet, a trajectory of the third main-fuel j et and a traj ectory of the fourth main-fuel j et are mirror images of each other in the mirror longitudinal plane, wherein the third main-fuel jet and the fourth main-fuel jet are ignited by combustion of the first main-fuel jet and the second main-fuel jet, respectively.

10. The internal combustion engine as claimed in claim 1, wherein the top land surface includes a first portion and a second portion, a surface area of the first portion is greater than a surface area of the second portion such that a predominant squish flow develops during a compression stroke in a direction away from the first portion of the top land surface and towards the second portion of the top land surface.

11. The internal combustion engine as claimed in claim 10, wherein a ratio between the surface area of the first portion of the top land surface over the surface area of the second portion of the top land surface is at least 1.5.

12. The internal combustion engine as claimed in claim 10, wherein a net squish vector is representative of the predominant squish flow and lies in a mirror longitudinal plane.

13. The internal combustion engine as claimed in claim 10, wherein during a power stroke the predominant squish flow reverses direction compared to the compression stroke and assists with moving an ignited and combusting fuel-air mixture in the combustion chamber towards the igniter increasing mixing of the ignited and combusting fuel-air mixture.

14. The internal combustion engine as claimed in claim 10, wherein a trajectory of the fuel jet is away from the first portion of the top land surface towards the second portion of the top land surface when the piston is at a top dead center position.

15. The internal combustion engine as claimed in claim 14, wherein the predominant squish flow supports a momentum of the fuel jet.

16. The internal combustion engine as claimed in claim 14, wherein a net fuel-jet vector is representative of the fuel jet and includes a horizontal component and a vertical component, and a net squish vector is representative of the predominant squish flow, the horizontal component of the net fuel -jet vector is substantially in a same direction as the net squish vector.

17. The internal combustion engine as claimed in claim 16, wherein the fuel jet is a first fuel jet and the in-cylinder injector is further configured to inject a second fuel jet having a trajectory near the igniter, wherein the net fuel -jet vector is representative of both the first fuel jet and the second fuel jet, and the first fuel jet and the second fuel jet are each ignited by the igniter.

18. The internal combustion engine as claimed in claim 1, wherein the piston bowl includes a protuberance that redirects the fuel jet downwards into the piston bowl.

19. The internal combustion engine as claimed in claim 1, wherein a surface of the piston bowl comprises an outline in the form of a portion of an outer surface of a pear.

20. The internal combustion engine as claimed in claim 1, wherein a surface of the piston bowl comprises a semi-spherical outline or a semi-ellipsoid outline.

21. The internal combustion engine as claimed in claim 1, wherein a space of the piston bowl is between a plane of the top land surface and a surface of the piston bowl, wherein a center of mass of the space is offset from the longitudinal axis.

22. The internal combustion engine as claimed in claim 1, wherein the igniter is one of a spark plug, a glow plug, a heated surface, or a pilot fuel injector.

23. The internal combustion engine as claimed in claim 1, wherein the fuel is a gaseous fuel.

24. The internal combustion engine as claimed in claim 23, wherein the gaseous fuel is one of ammonia, biogas, butane, ethane, hydrogen, liquefied petroleum gas, methane, natural gas, propane, and combinations of these fuels.

25. The internal combustion engine as claimed in claim 1, wherein the fuel is a liquid fuel.

26. The internal combustion engine as claimed in claim 25, wherein the liquid fuel is one of bunker fuel, butanol, diesel, dimethyl ether, ethanol, gasoline, kerosene, methanol, and combinations of these fuels.

27. A method of injecting and igniting a fuel in an internal combustion engine comprising: providing a combustion chamber defined by: a cylinder in an engine block having a longitudinal axis; a cylinder head capping one end of the cylinder and having a surface facing the combustion chamber; and a piston reciprocatable within the cylinder and comprising: a piston bowl asymmetric about the longitudinal axis; and a top land surface facing the cylinder head and extending circumferentially around the piston bowl, wherein the top land surface is substantially parallel to a majority of the surface of the cylinder head facing the combustion chamber; providing a squish volume between the top land surface and the surface of the cylinder head facing the combustion chamber; directly injecting the fuel as a fuel jet into the combustion chamber; providing an igniter disposed along a trajectory of the fuel jet; and igniting the fuel jet. ethod of injecting and igniting a fuel in an internal combustion engine comprising: injecting the fuel in a combustion chamber of the internal combustion engine as one or more fuel jets, a net fuel -jet vector is representative of the one or more fuel jets and having a horizontal component and a vertical component; and squishing a squish volume between a top land surface of a piston and a cylinder head by moving a piston towards the cylinder head during a compression stroke whereby a predominant squish flow forms, a net squish vector is representative of the predominant squish flow, wherein a direction of the net squish vector is substantially the same as a direction of the horizontal component of the net fuel -jet vector.