Hydrogen spark ignition internal combustion engine

Abstract

Described herein is a hydrogen spark ignition internal combustion engine (1) based on the configuration of prior art compression ignition diesel internal combustion engines (E). The internal combustion engine (1) according to the invention comprises at least one cylinder (2) and two intake ducts (4, 6) per cylinder, which are adapted to generate a swirling motion and to achieve effective mixing and combustion of hydrogen by, for example, arranging an ignition plug (14) in a central position and an injector (16) in a lateral position, the injector has an axis (A16) inclined with respect to a plane orthogonal to the longitudinal axis (Z2) of the cylinder (2) by an angle alpha of equal to or greater than 40 degrees.

Description

Technical Field

[0001] The present invention relates to internal combustion engines. More specifically, the present invention has been developed with reference to hydrogen spark ignition internal combustion engines, having a structure derived from compression ignition internal combustion engines. Background Art

[0002] The current trend towards a massive reduction in CO2 emissions into the atmosphere affects the production chain of the automotive industry at every level and requires the implementation of previously unconceived solutions at each stage in order to comply with increasingly stringent regulations at national and European level.

[0003] The desire to reduce CO2 emissions until they are completely eliminated requires, for example, the implementation of automotive systems that do not involve combustion (such as electric vehicles) or that employ carbon-free fuels (such as hydrogen).

[0004] Among the main characteristics of hydrogen combustion, one may mention the very high resistance to detonation and the speed of the flame front which is much higher than in the case of carbon-based fuels.

[0005] Such characteristics result in high pressure peaks during combustion and therefore require an engine having a structure suitable for withstanding the mechanical stresses thereby generated.

[0006] In this regard, reference Figure 1 The implementation of a hydrogen fuel engine having a structure derived from a diesel engine or, in general, from a compression ignition engine is particularly advantageous, since such engines are generally dimensioned so as to withstand higher mechanical stresses than an equivalent spark-ignition engine, thus making it possible to maximize the thermodynamic efficiency during the combustion of the hydrogen. Figure 1 The reference symbol E in the figure generally indicates a compression ignition internal combustion engine of the prior art; the figure shows a plan view of the intake duct 4 (tangential intake, so-called "swirl port"), 6 (so-called "filling port", introducing air in a spiral flow) and the internal volume of the cylinder 2.

[0007] However, such a choice is not without technical problems. For example, the main technical problem involves the charge flow field in the combustion chamber. As is well known, the intake duct of a diesel compression ignition engine is configured to generate a rotational motion of the air around the cylinder axis (the so-called "swirl motion"), which, although it ensures very good effects in terms of mixing and combustion when the fuel used is diesel, is ineffective or even counterproductive in the case of hydrogen combustion, and may even lead to misfire events.

[0008] The problem is closely related to the properties of hydrogen: it is an extremely light gas, especially lighter than the nitrogen and oxygen present in the combustion air.

[0009] The swirling motion induced in the combustion chamber is necessarily also imparted to the hydrogen injected into the combustion chamber, causing a rotation of the charge containing hydrogen, oxygen and nitrogen. Thus, the latter two gases are projected (and concentrated) towards the periphery of the combustion chamber by means of the centrifugal effect, since their mass is heavier than that of hydrogen, while the hydrogen is not subjected to the same projection and remains substantially around the injection point. This constitutes an obstacle to the efficient mixing of combustion air and hydrogen due to the centrifugal separation and hinders the ignition of the mixture (or at least prevents its complete combustion).

[0010] Another problem relates to the general construction of compression ignition engines; the cylinder head surface facing the cylinder is usually planar or nearly planar, and usually with the valve axis roughly perpendicular to the edge of the cylinder head (or, similarly, parallel to the longitudinal axis of the cylinder); the angle included between the valves is therefore close to zero. This is not usually a problem for the (central / coaxial) mounting of a diesel injector I, but it becomes a problem for mounting a spark plug with a hydrogen injector: if the spark plug is located centrally, it is likely to cover a volume area of ​​the combustion chamber where hydrogen is almost certainly present, since centrifugal forces are not particularly effective against hydrogen.

[0011] Due to such installation difficulties, solutions are known for hydrogen-fueled engines based on compression-ignition engines, which envisage mounting the spark plug in an eccentric position relative to the cylinder axis, which generally coincides with the position originally envisaged for mounting the glow plug GP of the compression-ignition engine, from which its construction was borrowed. This inevitably leads to a compromise solution: the spark plug is located in a zone where, regardless of possible hydrogen starvation, the charge velocity due to the swirl motion is so high as to hinder optimal ignition of the mixture in any case. Summary of the invention

[0012] The present invention aims to solve the technical problems outlined above. Specifically, the object of the present invention is to provide a hydrogen spark ignition internal combustion engine which borrows its structure from the compression ignition internal combustion engine but which does not have the aforementioned technical problems.

[0013] The objects of the invention are achieved by means of an internal combustion engine having the characteristics set out in the appended claims, which form an integral part of the technical disclosure provided herein in relation to the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The figure shows the outline of the cylinder head of the internal combustion engine of the prior art and the charge flow field therein.

[0015] Figure 2 shows the intake and exhaust volumes and the volumes of the cylinders in an internal combustion engine according to the invention,

[0016] Figure 3 is similar to Figure 1 but refers to an engine according to the invention, and

[0017] Figure 4 is a cross-sectional view along the cylinder axis of an engine according to the present invention. DETAILED DESCRIPTION

[0018] Figure 2 Reference numeral 1 in the drawing generally designates a hydrogen spark ignition internal combustion engine according to the present invention. Figure 2 The reference numerals used in Figure 1 The reference numerals adopted in the description of the known solution are consistent, mainly to illustrate that the internal combustion engine according to the invention borrows its construction from the engines of the prior art, while introducing the modifications that will be described hereinafter.

[0019] The engine 1 comprises at least one cylinder 2 having a longitudinal axis Z2 along which a piston P can reciprocate ( Figure 4 ). Each cylinder 2 is closed at the top by a cylinder head surface 3, which is part of a cylinder head (which is not shown because it is known per se) and which faces the cylinder 2 so as to define, together with the piston P, and in particular its crown, a combustion chamber. The engine 1 comprises a first intake duct 4 and a second intake duct 6 associated with each cylinder, and at least one exhaust duct 8, which in this case is bifurcated and comprises a first section 8A and a second section 8B, which are substantially facing the ducts 4 and 6 and are positioned opposite them (in particular, at the location where the ducts connect to the cylinder head surface 3). Reference Figure 2 and Figure 3 , the first intake duct 4 and the second intake duct 6 are arranged side by side, and refer to Figure 2 and Figure 3 With the geometry of the cylinder head shown, if the cylinder head surface were ideally divided into pseudo quadrants ("pseudo" because normally the diameter of the intake valves and the diameter of the exhaust valves are not the same), the ducts 4 and 6 would open into adjacent and consecutive quadrants.

[0020] Similar to the engine E, the duct 4 is a so-called “swirl port” configured to admit air at a position peripheral to the axis Z2 and in a tangential direction so as to induce and maintain a swirl motion of the air (and of the filling in general) inside the cylinder 2. The duct 6 has a spiral geometry (a so-called “filling port”) and is configured to admit air at a position peripheral to the axis Z2 with a spiral motion (and with the axis of the spiral motion parallel or substantially parallel to the same axis Z2) so as to introduce the admitted air (whose velocity is lower than the admitted velocity of the air moving through the duct 4) into the main swirl motion induced by the duct 4.

[0021] In combination with the aforementioned features, the first intake duct 4 is configured to introduce air into the cylinder 2 at a first radial distance D4 from the longitudinal axis Z2 of the cylinder 2, and the second intake duct 6 is configured to introduce air into the cylinder 2 at a second radial distance D6 from the axis Z2 of the cylinder 2, wherein the second radial distance D6 is smaller than the first radial distance D4.

[0022] Reference numerals 10 and 12 denote a pair of holes, the position of which corresponds to the position of the holes that house the injector 1 and the glow plug GP. However, in the engine 1, the hole 10, which has a central position (coaxial with the axis Z2 or with a minimum eccentricity relative to this axis, which depends mainly on the diameter of the valve), provides a seat for the ignition spark plug, while the hole 12 provides a seat for the injector 16 configured to inject hydrogen into the cylinder 2. In this way, the injector 16 is arranged between the intake ducts 4 and 6, and therefore in an eccentric position relative to the axis Z2, while the spark plug 14 is arranged in the center, that is, coaxial with the axis Z2 or with a minimum eccentricity relative to this axis, which depends mainly on the diameter of the valve. If there is an eccentricity, it is usually equal to or less than 10 mm.

[0023] According to the invention, the injector 16 comprises a respective longitudinal axis A16 which, when mounted, is inclined at an angle α equal to or greater than 40° relative to a reference plane P3 orthogonal to the axis Z2. The plane P3 is preferably chosen (but it will be understood that any plane parallel thereto will produce the same result) to be a plane tangential to the surface of the cylinder head (that is to say to the connection surface between the cylinder head and the cylinder block housing the cylinder 2).

[0024] In an embodiment, the centres of the holes 10 and 12 are aligned along the radial direction so that the axis A16 intersects the axis Z2 incidentally, ie they are not skewed.

[0025] In such embodiments, the projection of the longitudinal axis A16 defining an angle α with the plane P3 intersects the axis Z2 of the cylinder 2 and the spark plug 14 at the point P16, i.e., in other words, the axis A16 and the axis Z2 may be incident and intersecting rather than oblique. In such cases, when the piston P is at top dead center, the longitudinal axis A16 of the injector 16 intersects the longitudinal axis Z2 at the point P16 below the bottom of the bowl-shaped recess 20 (see Figure 4 ).

[0026] However, embodiments are generally preferred in which the axis A16 and the axis Z2 are skewed, i.e., in which the hole 12 and the hole 10 are not aligned in a radial direction (the hole 10 is arranged in the center or with minimal eccentricity, as previously described). The skewed arrangement of the axis A16 relative to the axis Z2 results in the introduction of hydrogen in a direction that is generally oriented along a chord of the circumference of the bowl-shaped recess 20 and that does not generally intersect or pass through the center or any central region of incidence.

[0027] Even if the axis is tilted, Figure 4 The condition is always valid, so when the piston P is at the top dead center, the point P16 is located below the bottom of the bowl-shaped recess 20, but the point P16 should be understood as the intersection of the projection of the axis A16 onto the axis Z2 (and vice versa).

[0028] refer to Figure 4 , the injector 16 comprises a terminal end 16T configured to deliver hydrogen into the cylinder 2 and thus facing the cylinder 2 itself (thus implementing direct fuel injection), and the spark plug 14 comprises a terminal end 14T comprising a discharge section configured to ignite the mixture of air and hydrogen entering the cylinder 2 (thus, the end 14T also faces the cylinder 2). Solutions that do not envisage direct injection of hydrogen into the cylinder 2 are generally not adopted, because the low density of hydrogen makes injection upstream of the intake valve very likely to cause hydrogen to flow back towards the manifold, thus causing backfire.

[0029] refer to Figure 4 , reference numeral 18 generally denotes the combustion chamber of the engine 1, which is located in the position where the piston P is at top dead center. The combustion chamber 18 is defined by the cylinder head surface 3 (including the surfaces facing the intake and exhaust valves of the cylinder 2), to a lesser or negligible extent by the wall of the cylinder 2 (in the portion exposed at the moment of ignition, which portion however varies along the range of crank degrees where combustion occurs), and to a greater extent by a bowl-shaped recess (the so-called "bowl") 20 provided at the top of the piston P. The bowl-shaped recess 20 preferably has an Ω-shaped profile.

[0030] As is known, the piston P including the bowl-shaped recess 20 thus also includes, at the crown, an annular space 22 defining a squeezing area which is equal to the area of ​​the annular space itself and which causes an annular squeezing movement of the charge in the cylinder 2 when the piston P approaches the top dead center, as shown in FIG. Figure 4 The vortex S22 in FIG.

[0031] As is well known, the squish motion originates from the variation of the local compression ratio near top dead center and, in particular, from the local variation of the compression ratio existing between the squish area 22 and the bowl 20. The gas compressed by the piston P during the compression stroke radially discharges from the squish area 22 (where the local compression ratio is relatively large) towards the bowl-shaped recess 20 (where the local compression ratio is relatively small) near top dead center, thus generating an annular swirling motion represented by the vortex S22, which is supported and defined by the contour of the bowl-shaped recess 20.

[0032] As can be observed, the axis A16 of the injector 16 (which defines the initial introduction direction of hydrogen) intersects the volumetric area that forms the vortex S22 and the overall squish motion of the charge, thus facilitating the mixing of hydrogen due to the intense mixing caused by the vortex S22.

[0033] The operation of the engine 1 according to the present invention is as follows.

[0034] In the engine 1, when the intake valve is open, air enters the cylinder 2 through the swirling motion generated by the ducts 4 and 6. In this regard, the ducts 4 and 6 are preferably shaped and sized such that a swirling motion can be caused, which is less pronounced than the swirling motion typically obtained in internal combustion engines from which this configuration is borrowed; specifically, the duct 4, which is the main duct, generates a swirling motion with a tangential introduction and a velocity V4, which is suitable for generating a vortex with a clockwise rotation direction around the axis Z2, while the duct 6 is configured to generate an air introduction into the cylinder 2 with a tangential direction and a velocity V6, which is suitable for generating a vortex with an opposite (counterclockwise) rotation direction around the axis Z2. Assuming that the resulting velocities V4 and V6 at the radial distances D4 and D6 from the axis Z2 are different from each other because D6 < D4 (due to the arrangement of the ducts 4 and 6 across the axis Z2 and due to the asymmetry of the ducts 4 and 6 themselves), the vortex generated by the duct 6 weakens the vortex generated by the duct 4, thus obtaining a swirling motion that is less pronounced than in the case of engines of the prior art (such as the engine E), and this swirling motion is generally more favorable for hydrogen combustion.

[0035] Reference Figure 3 will be made, and it will be observed that, for this purpose, the duct 6 can preferably be shaped such that it can have a less pronounced helical geometry than the duct 6 in the engine E, or it can be shaped such that the helical geometry can be eliminated and the so-called "plunger" geometry can be adopted, thus enhancing the effect of reducing the swirling motion, which is useful for hydrogen combustion.

[0036] Such a swirling motion is typically characterized by a total swirl ratio equal to or less than 1.5, which is composed of the swirling motion caused by the duct 4 (with an average swirl ratio of 2) and the swirling motion caused by the duct 6 (with an average swirl ratio equal to or less than 1 unit).

[0037] Hydrogen injection via injector 16 begins after (and usually close to) intake valve closing and has two main purposes:

[0038] - avoid leakage of hydrogen towards the intake manifold, thereby avoiding the risk of so-called backfire events which could damage the engine 1,

[0039] - Concentrate the injection as close as possible to the crank angle degree range where squash and swirl S22 are present, since swirl facilitates the mixing of hydrogen with the combustion air.

[0040] In any case, it should be remembered that, in a given scenario (which depends largely on the operating point of the engine), it is conceivable to start the injection of hydrogen through the injector 16 slightly earlier, before the closing of the intake valve. In particular, when the air enters the cylinder 2 at a high speed, the dynamic effect of the introduced air entraining the hydrogen flow introduced into the cylinder 2 takes precedence over possible backflow events during intake.

[0041] By way of example only, the start timing of hydrogen injection by injector 16 covers a crank angle degree range between 110 crank angle degrees (injection starts after intake valve closing) and 300 crank angle degrees (injection starts before intake valve closing) of combustion top dead center.

[0042] In the internal combustion engine 1 according to the invention, the movement in the cylinder 2 that favors the mixing of hydrogen with the combustion air develops only during the last few tens of crank angle degrees before the top dead center, and therefore the injection during such a stroke period of the piston P, i.e., approximately when the intake valve closes (slightly earlier or slightly later depending on the load), ensures the best combustion performance. In addition, the squeezing movement that occurs near the top dead center concentrates the mixture of air and hydrogen at the terminal end 14T of the spark plug 14, where the ignition electrode is arranged, thus creating the best conditions not only for mixing but also for igniting the mixture of air and hydrogen.

[0043] In this respect, the skewed arrangement of axes Z16 and Z2 is particularly effective for mixing because, within the crank degree range within which the annular whirling motion of vortex S22 occurs, there is also the influence of eddy current motion which does not weaken as compression proceeds (unlike what would happen, for example, with a tumbling motion).

[0044] In principle, this means that the streamlines of the flow field of the fluid undergoing the circular swirling motion do not develop along radial planes, but along planes that are "deflected" relative to the radial direction of the tangential component brought about by the vortex motion. In general, the vortices S22 form their spirals along the chordal plane, and therefore the deflected arrangement of the axis A16 in the chordal plane rather than the diametrical plane is very effective in introducing hydrogen and mixing it with the combustion air, because by doing so, the hydrogen is mixed along the natural flow path of the combustion air, thereby avoiding local over-leaning or insufficient mixing due to undesirable interaction on the incident intersection path of hydrogen and combustion air.

[0045] In general, the present invention provides a method for burning hydrogen and air in an internal combustion engine 1, comprising the following steps:

[0046] - controlling the opening of the first and second intake valves associated with the first and second intake ducts 4, 6, respectively,

[0047] - by means of the movement of the piston P towards the bottom dead center, the combustion air is sucked into the cylinder 2 through the first intake duct 4 and the second intake duct 6,

[0048] - controlling the closing of the first intake valve and the second intake valve,

[0049] - compressing the combustion air in the cylinder 2 by means of a movement of the piston P towards the top dead center, wherein compressing the combustion air also comprises forcing the combustion air to move radially towards the bowl-shaped recess 20 (squeezing movement) so as to generate a circular swirling movement of the combustion air, the axis of which is oriented according to the longitudinal axis Z2 of the cylinder 2 (and is therefore parallel or substantially coincident), and the axis of the vortex S22 is substantially orthogonal to the longitudinal axis Z2 of the cylinder 2, the vortex S22 developing in the bowl-shaped recess 20,

[0050] - introducing hydrogen into the cylinder 2 by means of the injector 16 corresponding to the circular swirling movement of the bowl-shaped recess 20 and the combustion air, in order to mix the hydrogen with the combustion air,

[0051] The ignition of the mixture of combustion air and hydrogen is controlled by means of the spark plug 14 .

[0052] Taking into account the timing information provided above, the step of introducing hydrogen into the cylinder 2 does not necessarily define the start of injection, but simply indicates that injection is ongoing. In other words, at least a portion of the hydrogen flow is introduced into the cylinder 2 at the location of the bowl-shaped recess 20 and the circular swirling motion of the combustion air so as to mix the hydrogen with the combustion air, while the other portion of the hydrogen flow delivered by the injector 16 can (and usually is) be introduced into the cylinder 2 under different conditions of the flow field of the fluid.

[0053] More specifically, if the injection start time is very early, and if it occurs before closing the intake valve, a portion of the hydrogen flow enters the cylinder 2 at the moment when the swirling motion (such motion originates from the squeezing motion of the mixture in the cylinder, which occurs near the end of compression) has not yet developed. If the injection start time occurs after closing the intake valve, a larger portion of the hydrogen flow is introduced into the cylinder 2 when the swirling motion has already started or has developed.

[0054] The arrangement of the point P16 below the bottom of the bowl-shaped recess 20 (together with the choice of the angle α) makes it possible to effectively introduce the hydrogen flow into the circular gyration developed in the bowl-shaped recess (20) when the piston P is at top dead center. For the reasons previously described, by adding the skewed arrangement of the axes Z2 and A16, a solution is obtained that is preferred in terms of its effectiveness.

[0055] This constitutes a solution to the problem of mixing and igniting a mixture of air and hydrogen, a problem that affects engines of prior art with a construction similar to that of engine E, while requiring very minor modifications to the cylinder head of internal combustion engine E in order to accommodate injector 16 and spark plug 14. Such modifications consist essentially of a slight reshaping (widening) of the seat of glow plug GP in order to enable the introduction of injector 16, and of a likewise slight widening of the seat that normally accommodates injector I, by adopting, for example, a spark plug 14 with a long protrusion and a small diameter, similar to those already used in small-bore spark-ignition internal combustion engines.

[0056] Of course, the implementation details and the embodiments may vary widely with respect to what has been described and illustrated herein, without departing from the scope of the present invention as set forth in the appended claims.

Claims

1. A hydrogen spark ignition internal combustion engine (1), comprising: - at least one cylinder (2), each cylinder (2) having a longitudinal axis (Z2) along which a piston (P) can reciprocate, said piston (P) comprising a top portion at which a bowl-shaped recess (20) is formed, - a cylinder head, comprising: a cylinder head surface (3) facing each cylinder (2), the cylinder head surface defining a combustion chamber together with the piston (P); and a plurality of inlet ducts including a first inlet duct (4) and a second inlet duct (6); and at least one exhaust duct, the first inlet duct (4) being arranged side by side with the second inlet duct (6), wherein the first inlet duct is configured to introduce air into the cylinder (2) in a tangential direction and at a position located at a first radial distance (D4) from the longitudinal axis (Z2) of the cylinder (2), the second inlet duct being configured to introduce air into the cylinder (2) according to a spiral path, its axis being substantially parallel to the longitudinal axis (Z2) of the cylinder (2) and its inlet being located at a second radial distance (D6) from the longitudinal axis (Z2) of the cylinder, the second radial distance (D6) being smaller than the first radial distance (D4), - an injector (16) for hydrogen, arranged between the first intake duct (4) and the second intake duct (6), said injector comprising a respective longitudinal axis (A16) inclined at an angle (α) equal to or greater than 40° with respect to a plane orthogonal to the longitudinal axis (Z2) of the cylinder (2), - a spark plug (14) which is arranged centrally with respect to the cylinder (2).

2. The internal combustion engine (1) according to claim 1, wherein: The spark plug is arranged coaxially with the longitudinal axis (Z2) of the cylinder (2).

3. The internal combustion engine (1) according to claim 1, wherein: The spark plug (14) is arranged eccentrically relative to the longitudinal axis of the cylinder, and the eccentricity is equal to or less than 10 mm.

4. The internal combustion engine (1) according to claim 1, wherein: The injector (16) includes a terminal end (16T) configured to deliver hydrogen to the cylinder (2), and the spark plug (14) includes a terminal end (14T) including a spark gap configured to ignite a mixture of air and hydrogen in the cylinder, wherein the terminal ends (16T, 14T) of the injector and the spark plug face into a bowl-shaped recess (20) of the piston (P).

5. The internal combustion engine according to claim 1, wherein: The longitudinal axis (A16) of the injector (16) is offset relative to the longitudinal axis (Z2) of the cylinder (2).

6. The internal combustion engine according to claim 5, wherein: When the piston (P) is at top dead center, the projection of the longitudinal axis (A16) of the injector (16) on the longitudinal axis of the cylinder (2) intersects with the longitudinal axis (Z2) of the cylinder (2) at a point (P16) below the bottom of the bowl-shaped recess (20).

7. A method for combusting hydrogen and air in an internal combustion engine according to any one of claims 1 to 6, comprising: - controlling the opening of a first intake valve and a second intake valve associated with said first intake duct (4) and said second intake duct (6), respectively, - by means of the movement of the piston (P) towards the bottom dead center, combustion air is sucked into the cylinder (2) through the first and second intake ducts (4, 6), - controlling the closing of the first intake valve and the second intake valve, - compressing the combustion air in the cylinder (2) by means of the movement of the piston (P) towards the top dead center, said compressing the combustion air further comprising forcing the combustion air to move radially towards the bowl-shaped recess (20) so as to generate a circular swirling motion of the combustion air, the axis of which is oriented according to the longitudinal axis (Z2) of the cylinder (2) and the axis of a vortex (S22) is substantially orthogonal to the longitudinal axis (Z2) of the cylinder (2), said vortex (S22) developing in the bowl-shaped recess (20), - introducing hydrogen into the cylinder (2) by means of the injector (16) corresponding to the circular swirling movement of the bowl-shaped recess (20) and the combustion air, so as to mix the hydrogen with the combustion air, - Controlling the ignition of the mixture of combustion air and hydrogen by means of the spark plug.

8. The method according to claim 7, wherein: The introduction of hydrogen into the cylinder (2) is performed within a crank angle range between 110 crank angle degrees and 330 crank angle degrees before combustion top dead center.

Images