Internal combustion engine powered by gaseous fuels

Abstract

Internal combustion engine (110) fueled by gaseous fuel, with direct injection and active or passive turbulent jet ignition (TJI), having a head (130) and at least one piston (140) to form a combustion chamber (150), in which the head (130) in turn includes: - a single injector (160) suitable for gaseous fuels, which does not face directly into the combustion chamber (150), - a first duct (210) which puts the injector (160) in fluid communication with the combustion chamber (150), - a second duct (220), which branches off from the first duct (210) and flows into a seat (175) housing a spark plug (170), and - a pre-chamber (180) which puts the seat (175) in fluid communication with the combustion chamber (150).

Description

[0001] INTERNAL COMBUSTION ENGINE POWERED BY GASEOUS FUELS

[0002] D E S C R I PTI O N

[0003] Technical field of the invention

[0004] The present invention relates to an internal combustion engine having an optimized layout, powered by gaseous fuels and featuring integrated active-passive turbulent jet ignition and direct injection.

[0005] Background art

[0006] Motor vehicles typically operate by using an internal combustion engine to convert the energy of a fuel, such as gasoline or diesel, into mechanical energy to propel the motor vehicle and thereby provide motion to the vehicle's wheels. Unfortunately, fossil fuels are expensive and contribute to environmental pollution. Because of these drawbacks, attention has been paid to the problems of reducing fuel consumption and pollutants emitted by automobiles and other highway vehicles.

[0007] To alleviate some of these drawbacks, internal combustion engines fueled by gaseous fuels, such as methane, hydrogen, ammonia in the gaseous phase, have been proposed, equipped with the so-called turbulent jet ignition (TJI, hereafter). In fact, it is known to use internal combustion engines having a pre-combustion chamber, separated from a main combustion chamber, in which a portion of the fuel is ignited by a spark plug. See, for example, patent US10161296A1 and international patent application W02019 / 027800. Both of these documents are incorporated herein by reference. Although these previous turbulent jet ignition configurations constitute significant improvements in engine performance, they are ill-suited for use on standard internal combustion engine configurations because they require considerable constructional complication. In fact, such TJI engines require either an injector that injects fuel into the prechamber and not into the main combustion chamber or, preferably, two separate injectors, a first injector to inject fuel into the prechamber and a second injector to inject fuel into the main combustion chamber.

[0008] In the reference technical sector, therefore, further improvements are desirable to facilitate the assembly of components on the engine head and possibly to be able to retrofit existing engine heads. All this while obtaining better engine efficiency and, consequently, lower fuel consumption.

[0009] There is therefore a need to define an innovative internal combustion engine suitable for the use of gaseous fuels that is free from or at least minimizes the above-mentioned drawbacks.

[0010] Summary of the invention

[0011] In order to substantially solve the technical problems highlighted above, an object of the present invention is to define an internal combustion engine fueled by gaseous fuels and provided with integrated ignition, active or passive, with turbulent jet as well as with direct injection.

[0012] In particular, the invention concerns the combustion system scheme for internal combustion engines fueled by gas, for example methane, hydrogen, ammonia in gaseous phase or mixtures of such fuels, and with direct injection with active or passive TJI. Preferably, the combustion system can be derived from a diesel cycle engine.

[0013] The invention, as will be seen below, presents a considerable flexibility and is applicable to different types of fuel, engine bore, cylinder head arrangement, rotation speed and load: the different elements can be customized for the specific application, maintaining a good commonality with the design of an original Diesel engine.

[0014] Therefore, according to the present invention there is provided an internal combustion engine fueled by gaseous fuels having the characteristics set forth in the independent claim, attached to this description.

[0015] Further preferred and / or particularly advantageous embodiments of the invention are described according to the characteristics set forth in the attached dependent claims.

[0016] Brief description of the drawings

[0017] The invention will now be described with reference to the attached drawings, which illustrate some non-limiting examples of its implementation, in which:

[0018] - Figure 1 is a cross-section of a cylinder head (with parts removed for clarity) and of the relative piston of an internal combustion engine fueled by gaseous fuels according to an embodiment of the present invention,

[0019] - Figure 2 is a diagram of the operation of the injection and combustion start phases of the internal combustion engine of Figure 1, and

[0020] - Figure 3 is a cross-section of the internal combustion engine of Figure 1 illustrating some design parameters of the engine itself. Detailed description

[0021] By way of example and not limitation, the present invention will now be described with reference to the aforementioned figures.

[0022] An internal combustion engine 110, as illustrated schematically in figure 1 (in this figure, many components of a known type have been omitted to lighten the figure itself which illustrates a detail of the combustion system), includes an engine block which defines at least one cylinder 125, having a piston coupled to rotate a crankshaft. The cylinder head 130 cooperates with the piston 140 to define a combustion chamber 150. A mixture of fuel and air is disposed in the combustion chamber and is ignited, causing combustion and expansion of the exhaust gases which causes the reciprocating motion of the piston. The fuel is supplied by at least one fuel injector 160 and the air through at least one intake port. The ignition of the air / fuel mixture is controlled at the required time by an ignition device (spark plug). Each of the cylinders 125 has at least two valves, operated by a camshaft rotating in synchrony with the crankshaft. The valves selectively allow air to enter the combustion chamber from the intake port and alternately allow exhaust gases to exit through an exhaust port.

[0023] The air may be distributed to the air intake port(s) via an intake manifold. An air intake duct may supply air from the ambient environment to the intake manifold. In other embodiments, a throttle body may be provided to regulate the air flow into the manifold. In still other embodiments, a forced air system may be provided such as a turbocharger, having a compressor rotationally coupled to a turbine. Rotation of the compressor increases the pressure and temperature of the air in the manifold. An intercooler, disposed in the intake duct, may reduce the temperature of the air. The turbine rotates by receiving exhaust gases from an exhaust manifold that directs the exhaust gases from the exhaust ports and through a series of vanes before expanding through the turbine. The exhaust gases exit the turbine and are directed into an exhaust system.

[0024] The exhaust system may include an exhaust pipe having one or more exhaust gas aftertreatment devices. The aftertreatment devices may be any device configured to change the composition of the exhaust gases. Some examples of aftertreatment devices include, but are not limited to, catalytic oxidation converters. Other aftertreatment devices include selective catalytic reduction (SCR) systems. Other embodiments may include an exhaust gas recirculation (EGR) system coupled between the exhaust manifold and the intake manifold. The EGR system may include an EGR cooler to reduce the temperature of the exhaust gases in the EGR system. An EGR valve regulates a flow of exhaust gases into the EGR system.

[0025] According to the invention, the internal combustion engine is fueled with gaseous fuel, such as methane, hydrogen, ammonia in gaseous phase or mixtures of such fuels, and is a direct injection engine with active or passive TJI integrated into the combustion system. The box referred to under the reference TJI includes all the elements that contribute to the realization of the turbulent jet ignition.

[0026] For this purpose, the engine 110 is therefore also provided with a spark plug 170 for TJI systems (in other words, a spark plug that produces multiple and distributed ignition points) and a combustion pre-chamber 180. The invention has as its first objective that of defining the layout for the fuel supply to the pre-chamber 180 and as its second objective the characteristics of the pre-chamber 180.

[0027] More specifically, the cylinder head 130 comprises:

[0028] - an injector 160 suitable for gaseous fuels, which does not directly face the combustion chamber 150,

[0029] - a first duct 210 which puts the injector 160 in fluid communication with the combustion chamber 150,

[0030] - a second duct 220, which branches off from the first duct 210 and flows into a seat 175 housing the spark plug 170, and

[0031] - a pre-chamber 180 which puts the seat 175 in fluid communication with the combustion chamber 150.

[0032] Preferably, the second duct 220 is provided with a non-return valve 240 upstream of the housing seat 175 of the spark plug.

[0033] Advantageously, the second duct 220 is isolated from the outside by means of a sealing element 230, for example a spring pin.

[0034] According to the invention, therefore, it is possible to enable the active TJI using a single injector. The injected fuel is divided, by means of the previously illustrated ducts, between the combustion chamber 150 (main combustion chamber) and the active pre-chamber. The active TJI can be optimized, as better explained below, by defining specific injection times, sizing the length and diameter of the second duct 220 and possibly using the non-return valve 240.

[0035] Furthermore, since the injector 160 is not in direct contact with the combustion chamber 150, it will have less stringent requirements for resistance to high temperatures. Therefore, direct injection injectors derived from PFI (port fuel injector) applications on gasoline and / or gaseous fuel engines can be used.

[0036] Evidently a passive TJI, without specific fuel supply but with only fuel supply from the main combustion chamber 150, can be installed by sealing the second duct 220 at the fuel inlet and using a standard spark plug by specific machining of the cylinder head, instead of a spark plug 170 for TJI systems.

[0037] A possible mode of operation is illustrated in figure 2.

[0038] The start of injection can occur during the air compression phase in the cylinder, for example around -150° from the top dead center (TDC).

[0039] At the middle of injection, for example, around -120° TDC, a first portion of fuel has reached, through the first duct 210, the combustion chamber 150, while a second portion of fuel has reached, through the second duct 220, the pre-chamber 180.

[0040] At the end of injection, for example between -90° TDC and -60° TDC, the fuel that has passed through the pre-chamber 180 also reaches the combustion chamber 150, stratifying with the fuel coming directly from the injector 160.

[0041] Finally, with a certain advance with respect to the TDC, for example between -30° TDC and -15° TDC, combustion will begin, where the fuel will be very well stratified inside the combustion chamber 150.

[0042] The correct sizing (both in absolute and relative terms) of the second duct 220, i.e. the duct that puts injector 160 in fluid communication with the pre-chamber 180 of the TJI and of the first duct 210, the duct that creates fluid communication between the injector 160 and the combustion chamber 150, is the critical parameter for trapping the correct quantity of fuel inside the pre-chamber 180 of the TJI.

[0043] Below and also with reference to figure 3, the following definitions are introduced:

[0044] - fluid dynamic resistances Rl, R2, RA, RB having as unit of measurement [bar / (kg / s)]. In particular:

[0045] Rl is the resistance of the first duct 210,

[0046] R2 is the resistance of the complete TJI supply channel which can in turn be divided into RA, resistance of the upstream TJI supply channel, i.e. resistance of the second duct 220, and RB, resistance of the downstream TJI supply channel, i.e. resistance of the pre-chamber 180;

[0047] - fuel flow rates expressed in [kg / s]. In particular:

[0048] MTOT: total fuel flow rate,

[0049] MMAIN : fuel flow rate that flows in the first duct 210 and reaches the combustion chamber 150 directly,

[0050] MTJI : fuel flow rate that flows in the second duct 220 and reaches the pre-chamber 180 of the TJI;

[0051] - pressures expressed in [bar]. In particular APINJ, injection pressure, or the difference between the pressure in the injector 160 and the pressure in the combustion chamber 150.

[0052] Once these quantities have been defined, it is possible, using the analogy of an electrical circuit, to write the following equations to calculate the respective fuel flow rates: and finally also the total amount of mass [kg] of the MTJI fuel that reaches the pre-chamber 180 of the TJI:

[0053] It is also appropriate to provide design rules for the sizing of the entire combustion system according to the present invention. Conveniently:

[0054] - the diameter of a single injection hole of the injector 160 is a function of the bore of the internal combustion engine, the air / fuel ratio, the type of fuel and the injection pressure. In this case, the diameter of the hole must be proportionate to the engine bore until it reaches a maximum plateau value corresponding to approximately twice the flame-quenching layer on the wall;

[0055] - the number of injection holes is a function of the swirl motion in the supply ducts and of the diameter of the single injection hole. In particular, the number of holes tends to be inversely proportional to the intensity of the swirl motion;

[0056] - the resistance RB of the downstream TJI supply channel, i.e. resistance of the pre-chamber 180 is a function of the diameter of the single injection hole and of the number of injection holes;

[0057] - the internal volume of the TJI, in other words the volume of the pre-chamber 180 is a function of the diameter of the single injection hole, of the number of injection holes and finally proportionate to the displacement of the internal combustion engine;

[0058] - the mass of fuel MT I retained in the TJI, is a function of the internal volume of the TJI, of the fuel injection pressure, of the injection start time, of the injection duration and of the ignition advance of the spark plug 170. For example, to maximize this mass it is possible to appropriately calibrate the fuel injection by delaying it as much as possible in correspondence with the ignition advance;

[0059] - the resistance RA of the upstream TJI supply channel, i.e. resistance of the second duct 220, is a function of the mass of fuel MTJI in the TJI and of the resistance RB of the downstream TJI supply channel. If it turns out:

[0060] RA, actual < RA, objective it is appropriate to introduce the non-return valve 240 to avoid the backflow of fuel upstream of the spark plug 170, where it would not be effective in promoting combustion;

[0061] - the resistance R1 of the first duct 210 is a function of the total mass of fuel, of the resistance R2, sum of the resistances RA and RB, of the injection pressure and of the injection duration.

[0062] From these considerations it follows that:

[0063] - the diameter of the second duct 220, feeding the pre-chamber 180 must be between 20% and 40% of the diameter of the first duct 210, feeding the combustion chamber 150, depending on the relative length of the two ducts 210, 220;

[0064] - the angle a between the first duct 210 and the second duct 220 feeding TJI must preferably be between 120° and 150°: a larger angle, and therefore a greater efflux coefficient in the second duct 220, corresponds to the lower ratio (20%) reported above between the diameters of the two ducts 210, 220 and vice versa;

[0065] - a greater length of the second duct 220 upstream of the TJI must preferably be coupled with small TJI exit holes, to increase the resistance ratios and vice versa;

[0066] - a delayed injection can be combined with the above design guidelines in order to maximize the fuel entrapment ratio in the TJI, avoiding excessive dilution in the combustion chamber 150 and improving compression; the same rule applies to reduce excessive fuel stratification;

[0067] - injection timing should be advanced as load increases, since it is synergistic with good entrapment efficiency and less stringent requirements for ignition energy and air / fuel ratio in the TJI.

[0068] In conclusion, the internal combustion engine according to the present invention has several advantages:

[0069] - it is flexible in terms of retrofitting on existing engines: the required processes can be adapted to the dimensions of the engine, the available space and the properties of the fuel. In particular, the machining of a standard head is simple and efficient in existing Diesel engines so that they can use other fuels such as hydrogen, methane, ammonia in gaseous state, etc., - it can be used for high pressure and low-pressure direct injection,

[0070] - the combined injection design and control strategies described above allow further flexibility in the combustion system sizing,

[0071] - the use of a single injector per cylinder allows advantages in terms of costs and assembly possibilities: in a prior art layout, the coexistence of the main injector and the TJI injector is generally not feasible or is very expensive from a design, manufacturing and control point of view,

[0072] - it is effective in improving combustion performance (stability, emission, efficiency, knock, anomalous combustions), exploiting known technologies combined in a synergistic way,

[0073] - it allows an optimized regulation based on the different fuels, in other words, the engine is "agnostic" with respect to the fuel used.

[0074] In addition to the embodiment of the invention, as described above, it is to be understood that numerous other variations exist. It is also to be understood that such embodiments are exemplary only and do not limit the scope of the invention, its applications, or its possible configurations. Conversely, while the above description enables the skilled craftsman to carry out the present invention at least according to one exemplary embodiment thereof, it should be understood that many variations of the described components are possible without departing from the scope of the invention, as defined in the appended claims, which are construed literally and / or according to their legal equivalents.

Claims

C LA I M S1. Internal combustion engine (110) fueled by gaseous fuel, with direct injection and active or passive turbulent jet ignition (TJI), comprising a head (130) and at least one piston (140) to form a combustion chamber (150), in which the head (130) in turn includes:- a single injector (160) suitable for gaseous fuels, which does not face directly into the combustion chamber (150),- a first duct (210) which puts the injector (160) in fluid communication with the combustion chamber (150),- a second duct (220), which branches off from the first duct (210) and flows into a seat (175) housing a spark plug (170), and- a pre-chamber (180) which puts the seat (175) in fluid communication with the combustion chamber (150).

2. Internal combustion engine (110), according to claim 1, in which the second duct (220) is provided with a non-return valve (240) upstream of the seat (175) housing the spark plug (170).

3. Internal combustion engine (110), according to claim 1 or 2, wherein the second duct (220) is isolated from the outside by means of a sealing element (230).

4. Internal combustion engine (110), according to any of the previous claims, wherein the diameter of a single injection hole of the injector (160) is a function of bore of the internal combustion engine (110), air / fuel ratio, fuel type and injection pressure.

5. Internal combustion engine (110), according to claim 4, in which the number of injection holes is a function of the swirl motion in the fuel ducts and the diameter of the single injection hole.

6. Internal combustion engine (110), according to claim 5, in which the fluid dynamic resistance (RB) of the pre-chamber (180) is a function of the diameter of the single injection hole and the number of injection holes.

7. Internal combustion engine (110), according to claim 5 or 6, wherein the internal volume of the pre-chamber (180) is a function of the diameter of the single injection hole, the number of injection holes and the internal combustion engine (110) displacement.

8. Internal combustion engine (110), according to claim 7, wherein the mass of fuel in the pre-chamber (180) is a function of the internal volume of the pre-chamber (180), the injection pressure, the start of the injection, the duration of the injection and the spark plug ignition (170) timing.

9. Internal combustion engine (110), according to claim 8, wherein the fluid dynamic resistance (RA) of the second duct (220) is a function of the mass of fuel in the pre-chamber (180) and of the resistance (RB) of the pre-chamber (180).

10. Internal combustion engine (110), according to claim 9, wherein the fluid dynamic resistance (Rl) of the first duct (210) is a function of the total mass of fuel, the sum of the resistance (RA) of the second duct (220) with the resistance (RB) of the pre-chamber (180), the injection pressure and the injection duration.

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