Four-stroke hydrogen-fueled internal combustion engine

Abstract

An engine casing (10), a crankshaft (20) rotatable about a crankshaft axis, a cylinder (30) disposed within said engine casing (10), a piston (35) disposed within said cylinder movably reciprocating along a reciprocating axis between a top dead center (TDC) position distal to said crankshaft (20) and a bottom dead center (BDC) position proximal to said crankshaft (20), said reciprocating piston (35) operatively connected to the crankshaft such that said reciprocating piston imparts rotational motion to the crankshaft, a combustion chamber (37) defined within said cylinder (30) between the engine casing (10) and a head of the piston (35) on the opposite side of said crankshaft (20), an intake valve (40.1), an exhaust valve (45.1), and said combustion chamber a hydrogen injector (60) configured to inject hydrogen directly into a combustion chamber (37), a water injector (70) configured to inject water directly into the combustion chamber (37); a spark or glow plug (50), and an engine control unit configured to control the timing and amount of hydrogen and water injection, wherein the engine control unit is configured to inject a first amount of hydrogen into the combustion chamber at a first time during the compression stroke from 20° before TDC to 20° after TDC, inject a second amount of water into the combustion chamber at a second time during the compression stroke from 110° before TDC to 90° after TDC, and inject a third amount of hydrogen into the combustion chamber at a third time during the compression stroke from 180° before TDC to 100° before TDC.

Description

[Technical field]

[0001] The present invention relates generally to four-stroke internal combustion engines, and more particularly to a high efficiency, low emission, high torque four-stroke hydrogen fueled internal combustion engine and method of operation thereof. [Background technology]

[0002] Four-stroke internal combustion engines are well known and typically include an engine casing, a crankshaft rotatable about a crankshaft axis, one or more cylinders disposed within the engine casing, and a piston disposed within each cylinder for movably reciprocating along a reciprocating axis between a top dead center (TDC) position distal to the crankshaft and a bottom dead center (BDC) position proximal to the crankshaft. The reciprocating pistons are operatively connected to the crankshaft to impart rotational motion to the crankshaft. The engine further includes combustion chambers defined within the cylinders between the engine casing and heads of the pistons opposite the crankshaft, at least one intake valve and one exhaust valve per cylinder, means for supplying fuel to the combustion chambers, at least one spark plug per cylinder if the engine is based on ignition of a fuel-air mixture by a spark, and typically an engine control unit for controlling operation of the engine.

[0003] A four-stroke engine with direct fuel injection operates in four successive and repeating cycles, the strokes being as follows:

[0004] Intake stroke: The piston begins to move downward from top dead center to bottom dead center, the intake valve opens, and air enters the combustion chamber.

[0005] Compression stroke: The piston returns to top dead center from bottom dead center, compressing the air in the cylinder, causing both the pressure and temperature in the combustion chamber to rise.

[0006] Combustion Stroke (Power Stroke): Generally, the fuel injector begins spraying fuel into the combustion chamber at some point between the end of the compression stroke (before the piston reaches top dead center) and very early in the combustion stroke. At some point, the fuel auto-ignites (compression ignition) or is ignited by a spark from a spark plug (spark ignition). The burning fuel-air mixture creates pressure on the piston head, forcing the piston downward, thereby transferring energy to the rotating crankshaft.

[0007] Exhaust Stroke: After the piston hits the bottom of the cylinder (bottom dead center), it begins to move upward, the exhaust valve opens and the sweep effect of the piston causes exhaust gases to leave the combustion chamber into the exhaust system and ultimately into the atmosphere.

[0008] Such engines have mainly been run on liquid or gaseous hydrocarbon fuels, but with stricter regulations regarding environmental considerations of the undesirable carbon footprint, hydrogen seems an obvious and elegant solution to completely avoid the emission of carbon oxides and unburned hydrocarbons.

[0009] However, replacing hydrocarbon fuels with hydrogen as a fuel is not straightforward: hydrogen has many properties that make it significantly different from even seemingly similar gaseous hydrocarbon fuels such as methane and propane.

[0010] First, hydrogen has the highest mass-energy ratio of any chemical fuel, with its mass energy consumption being about three times that of conventional gasoline fuel, about five to six times that of alcohol, and 2.5 times that of methane and propane.

[0011] Second, hydrogen has a very high combustion or flame speed in the engine combustion chamber, about six times that of gasoline. Hydrogen's flame speed at a stoichiometric air-fuel ratio is almost an order of magnitude higher (faster) than gasoline.

[0012] Third, hydrogen has wide flammability limits ranging from 4 to 75% by volume at 25° C. and 1 bar, compared with other fuels, e.g. gasoline, which has flammability limits ranging from 1.4 to 2.3% by volume in air.

[0013] Fourth, hydrogen has a very low ignition energy: a hydrogen-air mixture has a minimum ignition energy of only 0.017 mJ, compared to minimum ignition energies for other flammable gases such as gasoline, methane, and propane, which are typically on the order of 0.1 mJ.

[0014] Fifth, however, hydrogen has a relatively high auto-ignition temperature of about 585°C compared to about 350°C for gasoline. This makes it difficult to ignite a hydrogen / air mixture by heat alone without an additional ignition source, despite the low ignition energy.

[0015] Sixth, hydrogen has a very high molecular diffusivity, which means that its ability to disperse in the air is much greater than that of gasoline.

[0016] Seventh, hydrogen has a smaller quenching distance of about 0.6 mm compared to 2.0 mm for gasoline, so the distance from the cylinder wall where the combustion flame can extinguish is significantly smaller, which can adversely affect the lubricating film on the cylinder wall and increase the risk of backfiring.

[0017] Eighth, hydrogen has a well-known and undesirable effect on the mechanical properties of commonly used metals such as iron and steel, commonly referred to as the hydrogen embrittlement effect, which leads to a reduction in the metal's ductility and true stress at fracture.

[0018] At least some of these properties, while seemingly desirable and advantageous, add up to make the replacement of seemingly common hydrocarbon fuels with hydrogen clearly difficult.

[0019] This is all the more true since some of these properties, namely the first six, significantly increase the combustion temperature, which in turn increases the undesirable production of NOx during combustion. Moreover, the increased combustion temperature, combined with the shortening of the quenching distance and embrittlement effects, makes it even more difficult to replace hydrocarbon fuels with hydrogen. Technical issues

[0020] It is an object of the present invention to provide a four-stroke internal combustion engine, particularly adapted for using hydrogen as fuel, by allowing it to operate more efficiently, without compromising its high viability for environmentally clean power production, particularly with regard to NOx emissions. A further object is to provide a corresponding method for operating such an engine, in order to increase both its performance and its environmentally advantageous aspects. Summary of the Invention

[0021] To overcome at least some of the problems set forth above and to achieve its objects, the present invention provides, in a first aspect, an engine comprising an engine casing, a crankshaft rotatable about a crankshaft axis, a cylinder disposed within said engine casing, a piston disposed within said cylinder movably reciprocating along a reciprocating axis between a top dead center (TDC) position distal to said crankshaft and a bottom dead center (BDC) position proximal to said crankshaft, said reciprocating piston operatively connected to the crankshaft such that said reciprocating piston imparts rotational motion to the crankshaft, a combustion chamber defined within said cylinder between the engine casing and a head of the piston opposite the crankshaft, an intake valve, an exhaust valve, a hydrogen injector configured to inject hydrogen directly into said combustion chamber, and a combustion chamber configured to inject hydrogen directly into said combustion chamber. a water injector configured to directly inject water into the combustion chamber; a spark or glow plug; and an engine control unit configured to control the timing and amount of hydrogen and water injection, wherein the engine control unit injects a third amount of hydrogen into the combustion chamber at a third timing during the compression stroke from 180° to 100° before TDC, injects a first amount of hydrogen into the combustion chamber at a first timing during the compression stroke from 20° before TDC to 20° after TDC, and injects a second amount of water (liquid or gaseous) into the combustion chamber at a second timing during the compression stroke from 110° to 90° before TDC, preferably from less than 110° to more than 90°, for example from 107.5° to 92.5°, or even from 105° to 95°.

[0022] A preliminary note in this document is that the ordinal numbers "first", "second", "third", and "fourth" are used only to qualify the terms "amount" and "timing" and to clearly link the respective "amount" of the injected material, i.e. hydrogen or water, to its "timing" of injection. Thus, a "first amount" is injected at a "first timing", a "second amount" is injected at a "second timing", and so on. The ordinal numbers do not therefore imply any nature, magnitude, importance, chronological order, or other interrelationships. Thus, the total amount of hydrogen per cycle is the sum of the first amount of hydrogen and the third amount of hydrogen injected at the first and third timings, while the total amount of water injected per cycle is equal to the second amount of water injected at the second timing, or in some advantageous embodiments described further below, equal to the sum of the second amount of water and the fourth amount of water injected at the second and fourth timings.

[0023] The inventors have found that by injecting liquid water at a timing of about 110° to about 90° before TDC during the compression stroke, some of the above-mentioned problems arising from the use of hydrogen and its specific properties can be overcome. In fact, the introduction of a large amount of water into the combustion chamber not only reduces the temperature in the combustion chamber during compression, but also further reduces the temperature during combustion, thereby reducing the production of undesirable NOx. In fact, it seems possible to at least partially control the effects of the high mass-to-energy ratio and very high combustion rate of hydrogen by injecting water, even well before combustion is triggered by a spark or glow plug, and even before the first amount of hydrogen is injected. However, such relatively early injection of water into the combustion chamber is not only beneficial in terms of keeping the combustion of hydrogen at least partially under control, but also does so in an energetically favorable manner. In fact, at a timing of about 110° to about 90° before TDC, the pressure (and temperature) in the cylinder is still relatively low, which means that neither high-pressure injectors nor expensive and energy-intensive high-pressure pumps are required for the injection of water at this stage. Thus, the water is generally injected in liquid form at a temperature well below 150° C., preferably below about 100° C., such as below 70° C., below 50° C., or even at about room temperature.

[0024] Generally speaking, when water is injected into the combustion chamber of an internal combustion engine, there is a risk that the water will not evaporate fast enough and will deposit on the cylinder walls, thereby impairing the integrity of the lubricating film on the cylinder walls and leading to dilution of the lubricant, which is even more harmful in a hydrogen-fueled engine due to the embrittlement effects and short quenching distances mentioned above. The inventors have found that it is possible to largely control or even prevent the adverse effects of this water deposition by injecting a (third) relatively small amount of hydrogen at a time point prior to the injection of liquid water (second amount). This positive effect is believed to be due to the fact that hydrogen, due to the very high molecular diffusivity mentioned above, promotes the dispersion of water, thereby promoting the evaporation of water and thus reducing the risk of harmful deposits on the cylinder walls. To achieve said effect, the (third amount) of hydrogen may be injected at a (third) time point between 180° and 100° before TDC during the compression stroke, most preferably at the latest before the start of the injection of the second amount of water.

[0025] It has also been found that an advantageous dispersal effect of hydrogen on the water injection is obtained with a relatively small amount of hydrogen as the third quantity. Indeed, advantageously, said engine control unit is configured to control the third quantity of hydrogen to be 5 to 50% by weight, preferably 10 to 45% by weight, in particular 15 to 40% by weight of the total hydrogen quantity, said total hydrogen quantity (per cycle) being the sum of the third quantity and the first quantity of hydrogen.

[0026] Although early injection of an effective amount of water would most likely lead to destruction of the lubricant film or dilution of the lubricant, since the temperature in the cylinder at that time would be too low to ensure evaporation of the water, the inventors have surprisingly established that, working according to the invention, this does not preclude the injection of water at these early times. Indeed, the early injection of the third amount of hydrogen, and its dispersive effect resulting from its very high molecular diffusivity, allows relatively small amounts of water to be injected even very early during the compression stroke, thereby introducing an additional amount of water into the combustion chamber without risking lubrication. Thus, in an advantageous embodiment, the engine control unit is configured to further inject a fourth amount of water into the combustion chamber at a fourth time point between 180° and 110° before TDC during the compression stroke. The third amount of hydrogen can start at or before or after the injection of the fourth amount of water, which means that the injection of the fourth amount of water and the third amount of hydrogen can be well timed overlapped. Advantageously, the fourth amount of water is injected at the earliest fourth time point, which is simultaneous with the injection of the third amount of hydrogen.

[0027] Preferably, the engine control unit is configured to control the fourth amount of water to be 0.5 to 5% by weight of the total water amount, preferably 0.75 to 4% by weight, in particular 0.85 to 3.0% by weight, and the total water amount per cycle is the sum of the second amount of water and the fourth amount of water.

[0028] In addition to the above-mentioned advantages and effects of the present invention, a further major advantage is the fact that the presence of added water reduces knocking, and as a result, the internal combustion engine can be operated at lambda values ​​(i.e., air-fuel equivalence ratios) that are significantly lower than those typically useful for hydrogen-fueled internal combustion engines. Indeed, hydrogen-fueled engines must generally be operated at very lean conditions, both for engine temperature control and NOx reduction reasons, especially considering hydrogen's high mass-to-energy ratio and very high combustion rate. As a result, conventional hydrogen-fueled engines cannot be operated with the same high brake thermal efficiency as known from, for example, diesel engines.

[0029] Here, the efficient water injection of the present invention allows operation at significantly reduced lambda values ​​compared to those of conventional hydrogen fueled internal combustion engines by only injecting the second amount of water at the second time point, or by injecting an additional and early fourth amount of water at the fourth time point, thereby allowing operation at higher efficiency. As a result, the engine control unit is typically configured to control the total amount of hydrogen per cycle and the total amount of liquid water per cycle (the latter being only the second amount of water in the absence of injection of the fourth amount of water, or the sum of the second and fourth amounts of water) to obtain a lambda value between 1.5 and 2.5, preferably between 1.6 and 2.4, and more preferably between 1.7 and 2.3.

[0030] Thus, the efficient water injection of the present invention also eliminates or at least reduces the need for expensive and complex additional equipment such as exhaust gas recirculation (EGR) valves and advanced turbo compressors.

[0031] Furthermore, it has been found that the water to hydrogen mass ratio is surprisingly insensitive to the engine speed, and the advantages of the invention, such as more efficient operation, lower NOx production, lower engine stress, etc., are not only obtainable in stationary engines operating at only a certain number of revolutions per minute, such as in generators, but are also applicable to any other type of application, in particular vehicle engines. Advantageously, the engine control unit is arranged to control the total hydrogen amount and the total water amount to obtain a water to hydrogen mass ratio of between 1.0 and 2.0, preferably between 1.3 and 1.9, more preferably between 1.5 and 1.7, for example about 1.6.

[0032] In a particularly advantageous embodiment of the reciprocating four-stroke hydrogen fuelled internal combustion engine with spark according to the invention, the first timing is from 15° before TDC to 15° after TDC during the compression stroke, and / or the second timing is from 105° to 95°, preferably about 100°, before top dead centre (TDC) during the compression stroke, and / or the third timing for injecting hydrogen is from 175° to 120° before TDC during the compression stroke, and / or if applicable the fourth timing is from 175° to 120° before TDC during the compression stroke.

[0033] Adding liquid water, which changes to a gas, can reduce the temperature and therefore increase the actual compression ratio, i.e., the ratio of the cylinder and combustion chamber volumes of the internal combustion engine at their maximum and minimum values. In the preferred spark reciprocating four-stroke hydrogen fueled internal combustion engine, the actual compression ratio of the engine is between 12.9:1 and 17:1, preferably between 13.4:1 and 16.5:1, and more preferably between 13.9:1 and 16.

[0034] In a second aspect, the present invention also proposes a method of operating a spark-assisted reciprocating four-stroke hydrogen-fuelled internal combustion engine, preferably comprising an engine according to the first aspect, the engine comprising an engine casing, a crankshaft rotatable about a crankshaft axis, a cylinder arranged within the engine casing, a piston arranged within the cylinder for movably reciprocating along a reciprocating axis between a Top Dead Centre (TDC) position distal to the crankshaft and a Bottom Dead Centre (BDC) position proximal to the crankshaft and operatively connected to the crankshaft such that the reciprocating piston imparts rotational motion to the crankshaft, a combustion chamber defined within the cylinder between the engine casing and a head of the piston opposite the crankshaft, an intake valve, an exhaust valve, a hydrogen injector configured to inject hydrogen directly into the combustion chamber, a water injector configured to inject water directly into the combustion chamber; a spark or glow plug, and an engine control unit configured to perform the steps of the method, the method comprising the steps of: a) injecting a third amount of hydrogen into the combustion chamber via the hydrogen injector at a third timing during the compression stroke from 180° to 100° before TDC; b) injecting a first amount of hydrogen into the combustion chamber through a hydrogen injector at a first timing during the compression stroke from 20° before TDC to 20° after TDC; and c) injecting a second amount of water into the combustion chamber through the water injector at a second timing during the compression stroke from 110° to 90° before TDC, preferably from less than 110° to more than 90°, such as from 107.5° to 92.5°, or even from 105° to 95°; Each step is included.

[0035] In the method of operating a spark-driven reciprocating four-stroke hydrogen-fuelled internal combustion engine, the third amount of hydrogen in step a) is preferably controlled to be 5 to 50 wt. % of the total amount of hydrogen, said total amount of hydrogen being the sum of the third amount of hydrogen and the first amount of hydrogen.

[0036] Advantageously, the method further comprises: d) injecting a fourth amount of water into the combustion chamber via the water injector at a fourth timing during the compression stroke from 180° to 110° before TDC.

[0037] The fourth amount of water is preferably controlled to be 0.5 to 5% by weight of the total amount of water, said total amount of water being the sum of the second amount of water and the fourth amount of water.

[0038] In particularly advantageous embodiments, the total hydrogen amount and the second amount of water or the total water amount are controlled to obtain a lambda value that is an air to fuel equivalence ratio between 1.5 and 2.5, preferably between 1.6 and 2.4, and more preferably between 1.7 and 2.3.

[0039] In a method of operating a reciprocating four-stroke hydrogen fuelled internal combustion engine with spark, preferably the total hydrogen and water amounts are controlled to obtain a water to hydrogen mass ratio of between 1.0 and 2.0, more preferably between 1.3 and 1.9, most preferably between 1.5 and 1.7, especially about 1.6.

[0040] The method of operating a reciprocating four-stroke hydrogen fuelled internal combustion engine with spark is controlled such that in step a) the third timing of hydrogen injection is set at 180° to 100°, preferably 175° to 120° before TDC during the compression stroke, and / or in step b) the first timing is set at 15° before TDC to 15° after TDC during the compression stroke, and / or in step c) the second timing is set at 105° to 95°, preferably about 100° before top dead centre (TDC) during the compression stroke, and / or, if applicable, the fourth timing is set at 180° to 110°, preferably 175° to 120° before TDC during the compression stroke.

[0041] Timing of an internal combustion engine, generally, and more specifically, the timing of injections herein, is indicated in terms of crankshaft angles expressed relative to the position of a reciprocating piston in a cylinder of the engine, and where appropriate, relative to the relevant stroke of the working cycle. The expressions "top dead centre" or "TDC" and "bottom dead centre" or "BDC" are expressions commonly known in the art of internal combustion engines and refer to the extreme positions along a reciprocating axis of a reciprocating piston, or more specifically, the top of the piston, in a cylinder. Top dead centre is the position of the piston when it is distal from the crankshaft, and bottom dead centre is the position proximal to the crankshaft. Thus, positions along a reciprocating axis are generally given in degrees (°) from either dead centre relative thereto in the sense of rotation of the crankshaft. Often, the above expressions are preceded by the prepositions "after" or "before". For example, "110° before top dead center" (shortened to 110° before TDC or 110° BTDC) means that the top of the piston is at a position along the reciprocating axis that corresponds to -110° of crankshaft rotation relative to top dead center. The designation of the range "-20° to +20° from top dead center" is synonymous with "20° before top dead center to 20° after top dead center" or "20° before TDC to 20° after TDC."

[0042] Also, the indications of injection timing in the text refer to the start of the corresponding injection. In practice, the duration of the injection is necessarily short, but it is unavoidable that a certain period of time is required during which the piston continues its path within the cylinder.

[0043] The intake and exhaust valves can be any suitable type of valve, driven by the engine itself, such as a camshaft (hence the engine is the actuator), or by another actuator, such as a pneumatic, hydraulic, electric actuator, etc., preferably they are poppet, sliding or rotating disc valves, which are used independently on almost all four-stroke engines. For example, a valve system designed as a sliding or spinning disc advantageously allows for the timing of opening and closing of the exhaust valve at bottom dead centre, and the intake valve opening prior to the exhaust valve closing.

[0044] The internal combustion engine of the invention may advantageously further comprise a water tank as a water supply for the water injector(s) together with a condenser unit downstream of the exhaust valve(s). A condenser unit, e.g. a heat exchanger, may be provided to condense steam from the exhaust gases into water, which is then fed to the water tank via a conduit. Such recycling of water used for steam production is particularly important in mobile applications, where the amount of water to be transported is usually limited. Furthermore, recycling of water reduces the number of water refills. Filter means may also be provided to filter the exhausted steam. The water tank is preferably designed both for water filling with the normal filling cap and for filling with condensed exhausted water.

[0045] The internal combustion engine of the present invention may of course be constructed with a number of cylinders, each of which may further include a number of water injectors preferably distributed around the circumference of the combustion chamber, the water injectors being positioned at any suitable location of the cylinder within the combustion chamber.

[0046] All explicit values ​​set forth herein should be understood as approximations unless specifically stated otherwise. Thus, each of the above explicit values ​​should be understood to include a range of values ​​from less than 10% to more than 10% of the above-mentioned value. Express values ​​preceded by terms such as "about," "approximately," or the like should be understood to include a range of values ​​from less than 20% to more than 20% of the above-mentioned value. [Brief description of the drawings]

[0047] Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Figure 1] FIG. 1 is a schematic partial cross-sectional view of an embodiment of a reciprocating four-stroke hydrogen fueled internal combustion engine with sparks at different times during the compression stroke, showing the engine 180° before TDC (i.e., BDC). [Diagram 2] FIG. 1 is a schematic partial cross-sectional view of an embodiment of a reciprocating four-stroke hydrogen fueled internal combustion engine with sparks at different times during the compression stroke, showing the engine at timings from approximately 110° to 90° before TDC. [Diagram 3] 1 is a schematic partial cross-sectional view of an embodiment of a reciprocating four-stroke hydrogen fueled internal combustion engine with differently timed sparks during the compression stroke, showing the engine at a timing of about 20° before TDC. Further details and advantages of the invention will become apparent from the following detailed description of several non-limiting embodiments, with reference to the accompanying drawings. Description of the Preferred Embodiments

[0048] 1 to 3 are schematic diagrams of an embodiment of a spark-assisted reciprocating four-stroke hydrogen-fueled internal combustion engine of the present invention, with reference numbers in these figures representing like features.

[0049] The internal combustion engine includes an engine casing 10, a crankshaft 20 rotatable about a crankshaft axis, a cylinder 30 disposed within the engine casing 10, and a piston 35 with a piston head 35.1 disposed within the cylinder, movably reciprocating along a reciprocating axis between a top dead center (TDC) position distal to the crankshaft 20 and a bottom dead center (BDC) position proximal to the crankshaft 20, and operatively connected to the crankshaft by a rod 25 such that the reciprocating piston 35 imparts rotational motion to the crankshaft. A combustion chamber 37 is defined within the cylinder 30 between the engine casing 10 and the piston head 35.1 opposite the crankshaft 20. A spark or glow plug 50 is disposed such that its glow or spark tip is located within the combustion chamber 37. The air intake 40 is in fluid communication with the combustion chamber 37 when the intake valve 40.1 is open (not shown) during the intake stroke and is disconnected from said fluid connection when the intake valve 40.1 is closed (i.e. essentially during the compression, combustion and exhaust strokes). The exhaust 45 is in fluid communication with the combustion chamber when the exhaust valve 45.1 is open (not shown) during the exhaust stroke and is disconnected from said fluid connection when the exhaust valve 45.1 is closed (i.e. essentially during the intake, compression and combustion strokes). A hydrogen injector 60 is configured to inject hydrogen directly into the combustion chamber 37 and a water injector 70 is configured to inject water (liquid) directly into the combustion chamber 37.

[0050] FIG. 1 shows the engine at a timing of 180° before TDC, i.e., the beginning of the compression stroke at BDC. At a third timing between 180° and 100° before TDC, such as 180° before TDC, a third amount of hydrogen is injected into the combustion chamber 37 through the hydrogen injector 60. At a fourth timing between 180° and 110° before TDC, such as 180° before TDC, a fourth amount of water is injected into the combustion chamber 37 through the water injector 70. Although both injections are simultaneous at 180° before TDC in FIG. 1, both injections can be separated in time or overlap within the third and fourth timings. The third amount of hydrogen is a small to medium amount, typically 5 to 50% by weight, compared to the overall amount of hydrogen required for efficient operation, and typically helps to better distribute the injected fourth amount of water due to the very high molecular diffusivity of hydrogen. The fourth amount of water is only a small fraction of the total water injected per cycle, e.g., 0.5 to 5 wt. % of the total water. Water is injected as a liquid, preferably at a temperature below 100° C., typically at room temperature to 70° C. Injection of water (and hydrogen) at this stage does not require high pressure injection, since the pressure in the combustion chamber is near atmospheric (in the absence of a compressor or turbocharger) or slightly higher (in the presence of a compressor or turbocharger).

[0051] FIG. 2 shows the same engine at an early stage of the compression stroke, approximately 110° to 90° before TDC. At a second timing between 110° and 90° before TDC, a second amount of water is injected through the water injector 70 into the combustion chamber 37. At this point, the fourth timing for injecting a fourth amount of water has ended, but the third timing for injecting a third amount of hydrogen could still be ongoing if the second timing had begun at 100° before TDC. Thus, in FIG. 2, both injections occur simultaneously at approximately 110° to 100° before TDC, but the larger second amount of water could be the only injection at this point. Again, because hydrogen has a very high molecular diffusivity, the third amount of hydrogen helps to better distribute the second amount of water injected. The second amount of water constitutes a large proportion of the total amount of water injected per cycle, e.g., 95 to 99.5% by weight of the total amount of water. Again, since the pressure in the combustion chamber is still relatively low at this stage, high pressure injection is still not required for water injection at this stage.

[0052] 3 again shows the same engine approximately 20° before TDC, i.e., at the end of the compression stroke. At this point during the compression stroke, from 20° before TDC to 20° after TDC, a primary first quantity of hydrogen is injected under high pressure into the combustion chamber for ignition by a spark or glow plug 50 at or after the end of injection of the first quantity of hydrogen, thereby initiating combustion of the air-water-hydrogen mixture. [Explanation of symbols]

[0053] 10 engine casing, 20 crankshaft, 25 rod, 30 cylinder (wall), 35 (reciprocating) piston, 35.1 piston head, 37 combustion chamber, 40 air intake, 40.1 intake valve, 45 exhaust port, 45.1 exhaust valve, 50 spark or glow plug, 60 hydrogen injector, 70 water injector.

Claims

1. An engine casing (10), a crankshaft (20) rotatable about a crankshaft axis, a cylinder (30) disposed within said engine casing (10), a piston (35) disposed within said cylinder movably reciprocating along a reciprocating axis between a top dead center (TDC) position distal to said crankshaft (20) and a bottom dead center (BDC) position proximal to said crankshaft (20), said reciprocating piston (35) operatively connected to the crankshaft such that it imparts rotational motion to the crankshaft, a combustion chamber (37) defined within said cylinder (30) between the engine casing (10) and a head of the piston (35) on the opposite side of the crankshaft (20), an intake valve (40.1), an exhaust valve (45.1), and said combustion chamber.

1. A reciprocating four-stroke hydrogen fueled internal combustion engine with spark, comprising: a hydrogen injector (60) configured to inject hydrogen directly into a combustion chamber (37); a water injector (70) configured to inject water directly into the combustion chamber (37); a spark or glow plug (50); and an engine control unit configured to control the timing and amount of hydrogen and water injection, wherein the engine control unit is configured to inject a first amount of hydrogen into the combustion chamber at a first timing during the compression stroke from 20° before TDC to 20° after TDC, inject a second amount of water into the combustion chamber at a second timing during the compression stroke from 110° before TDC to 90° before TDC, and inject a third amount of hydrogen into the combustion chamber at a third timing during the compression stroke from 180° before TDC to 100° before TDC.

2. 2. The spark-assisted reciprocating four-stroke hydrogen fueled internal combustion engine of claim 1, wherein the engine control unit is configured to control the third amount of hydrogen to be between 5 and 50 wt. % of a total amount of hydrogen, the total amount of hydrogen being a sum of the third amount of hydrogen and the first amount of hydrogen.

3. 3. The spark-operated reciprocating four-stroke hydrogen fueled internal combustion engine of claim 1 or 2, wherein the engine control unit is configured to further inject a fourth amount of water into the combustion chamber at a fourth time during the compression stroke that is between 180° and 110° before TDC.

4. 4. The spark-operated reciprocating four-stroke hydrogen-fueled internal combustion engine of claim 3, wherein the engine control unit is configured to control the fourth amount of water to be 0.5 to 5% by weight of a total amount of water, the total amount of water being the sum of the second amount of water and the fourth amount of water.

5. 5. The reciprocating four-stroke hydrogen fuelled internal combustion engine with spark according to claim 1, wherein the engine control unit is configured to control the total hydrogen amount and the second amount of water or the total water amount to obtain a lambda value that is an air / fuel equivalence ratio between 1.5 and 2.5, preferably between 1.6 and 2.4, more preferably between 1.7 and 2.

3.

6. 6. The reciprocating four-stroke hydrogen fuelled internal combustion engine with spark according to claim 1, wherein the engine control unit is configured to control the total hydrogen and water amounts to obtain a water to hydrogen mass ratio between 1.0 and 2.0, preferably between 1.3 and 1.9, more preferably between 1.5 and 1.

7.

7. 7. The reciprocating four-stroke hydrogen fuelled internal combustion engine with spark of claim 1, wherein the first timing for injecting hydrogen is from 15° before TDC to 15° after TDC during the compression stroke, and / or the second timing is from 105° to 95°, preferably about 100° before Top Dead Centre (TDC) during the compression stroke, and / or the third timing is from 175° to 120° before TDC during the compression stroke, and / or if applicable, the fourth timing is from 175° to 120° before TDC during the compression stroke.

8. 8. A spark-operated reciprocating four-stroke hydrogen fuelled internal combustion engine as claimed in any one of claims 1 to 7, wherein the compression ratio of the engine is between 12.9:1 and 17:1, preferably between 13.4:1 and 16.5:1, more preferably between 13.9 and 16:

1.

9. The engine comprises an engine casing (10), a crankshaft (20) rotatable about a crankshaft axis, a cylinder (30) disposed within the engine casing (10), and a reciprocating piston (35) movably reciprocating along a reciprocating axis between a top dead center (TDC) position distal to the crankshaft (20) and a bottom dead center (BDC) position proximal to the crankshaft (20), the reciprocating piston (35) being disposed within the cylinder (30) operatively connected to the crankshaft to impart rotational motion to the crankshaft (20). a combustion chamber (37) defined in said cylinder (30) between an engine casing (10) and a head of the piston (35) opposite said crankshaft (20), an intake valve (40.1), an exhaust valve (45.1), a hydrogen injector (60) configured to inject hydrogen directly into said combustion chamber (37), a water injector (70) configured to inject water directly into said combustion chamber (37); a spark or glow plug (50), and an engine control unit configured to perform each of the steps of the method, The method includes, for each four-stroke cycle: a) injecting a third amount of hydrogen into the combustion chamber (37) through a hydrogen injector (60) at a third time during the compression stroke from 180° to 100° before TDC; b) injecting a second amount of water through said water injector (70) into the combustion chamber (37) at a second time during the compression stroke from 110° to 90° before TDC; and c) injecting a first amount of hydrogen into the combustion chamber (37) through a hydrogen injector (60) at a first time during the compression stroke from 20° before TDC to 20° after TDC; A method for operating a spark-powered reciprocating four-stroke hydrogen-fueled internal combustion engine, comprising the steps of:

10. 10. The method of operating a reciprocating four-stroke hydrogen fueled internal combustion engine with spark as described in claim 9, wherein in step a) the third amount of hydrogen is controlled to be 5 to 50 wt. % of the total amount of hydrogen, said total amount of hydrogen being the sum of the third amount of hydrogen and the first amount of hydrogen.

11. d) injecting a fourth amount of water into the combustion chamber (37) via the water injector (70) at a fourth time during the compression stroke from 180° to 110° before TDC:

11. A method of operating a reciprocating four-stroke hydrogen fuelled internal combustion engine with a spark as claimed in claim 9 or 10, further comprising the steps of:

12. 12. The method of operating a reciprocating four-stroke hydrogen fueled internal combustion engine with spark as described in any one of claims 9 to 11, wherein the fourth amount of water is controlled to be 0.5 to 5 wt. % of the total water amount, said total water amount being the sum of the second amount of water and the fourth amount of water.

13. 13. A method of operating a reciprocating four-stroke hydrogen fuelled internal combustion engine with spark as claimed in any one of claims 9 to 12, wherein the total hydrogen amount and the second amount of water or the total water amount are controlled to obtain a lambda value that is an air / fuel equivalence ratio between 1.5 and 2.5, preferably between 1.6 and 2.4, more preferably between 1.7 and 2.

3.

14. 14. A method of operating a reciprocating four-stroke hydrogen fuelled internal combustion engine with spark as claimed in any one of claims 9 to 13, wherein the total hydrogen and water amounts are controlled to obtain a water to hydrogen mass ratio between 1.0 and 2.0, preferably between 1.3 and 1.9, more preferably between 1.5 and 1.

7.

15. 15. The method of operating a reciprocating four-stroke hydrogen fuelled internal combustion engine with spark according to any one of claims 9 to 14, wherein the third timing of injecting hydrogen in step a) is set at 175° to 120° before TDC during the compression stroke, and / or the first timing in step b) is set at 15° before TDC to 15° after TDC during the compression stroke, and / or the second timing in step c) is set at 105° to 95°, preferably about 100° before Top Dead Centre (TDC) during the compression stroke, and / or, if applicable, the fourth timing is set at 175° to 120° before TDC during the compression stroke.

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