Spark-ignition engine

Abstract

The present invention provides a spark-ignition engine that makes it possible to improve net thermal efficiency.　Provided is a spark-ignition engine 1 comprising a main chamber 10 that is defined by a cylinder 2 and a piston 3, and a pre-chamber 20 that has an ignition means 204, wherein: a plurality of communication holes 201a are provided and communicate the pre-chamber 20 with the main chamber 10; an air-fuel pre-mixture having an excess air ratio exceeding the flame propagation limit is supplied to the main chamber 10; and an air-fuel mixture having an excess air ratio at which flame propagation is possible is supplied to the pre-chamber 20.

Description

Spark ignition engine

[0001] The present invention relates to spark ignition engines.

[0002] Spark ignition engines (SI engines) are widely known, which are equipped with spark plugs that generate electrical sparks, and which apply high voltage between the electrodes of the spark plugs to generate spark discharge and ignite the compressed air-fuel mixture. Spark ignition engines have the advantage of being small and lightweight when used in the low-power range, but generally have inferior thermal efficiency to compression ignition engines, which use the high temperatures generated by compression to ignite the mixture.

[0003] In order to improve the thermal efficiency of a spark ignition engine, for example, the spark ignition engine of Patent Document 1 is equipped with an auxiliary chamber, and the premixed air-fuel compressed in the main chamber during the compression stroke is introduced into the auxiliary chamber.The mixture introduced into the auxiliary chamber is ignited by a spark plug, creating a jet of combustion gas from the auxiliary chamber to the main chamber, making it possible to ignite the fuel in the main chamber more powerfully than with normal ignition.

[0004] JP 2016-70270 A (pages 5 to 8, Figure 1)

[0005] However, the spark ignition engine of Patent Document 1 uses flame propagation with gasoline-based fuel as its combustion mode, and therefore not only is it unable to operate at an air excess ratio that exceeds the flame propagation limit, i.e., ultra-lean combustion, but also has the problem that heat loss essentially occurs due to wall quenching caused by the flame reaching the cylinder wall that constitutes the main chamber, so there is an upper limit to its thermal efficiency, and it is difficult to significantly increase its net thermal efficiency.

[0006] The present invention has been made in view of the above-mentioned problems, and has as its object to provide a spark ignition engine that can improve net thermal efficiency.

[0007] In order to solve the above problems, the present invention provides a spark ignition engine comprising: a main chamber partitioned by a cylinder and a piston; and an auxiliary chamber having an ignition means, wherein a plurality of communication holes are provided connecting the auxiliary chamber to the main chamber, wherein a premixed air-fuel mixture having an air excess ratio exceeding a flame propagation limit is supplied to the main chamber, and a mixture having an air excess ratio allowing flame propagation is supplied to the auxiliary chamber. According to this feature, the flame-propagating auxiliary chamber mixture ignited by the ignition means during the compression stroke undergoes flame propagation and combustion in the auxiliary chamber, and a jet of high-temperature, high-pressure combustion gas is supplied from the auxiliary chamber to the main chamber through the communication holes, and after only the portion of the premixed air reached by the jet of combustion gas is burned in the main chamber, the unburned portion of the premixed air begins to autoignite, and the remaining unburned portion also autoignites, completing the combustion of the premixed air-fuel mixture, thereby achieving ultra-lean combustion with low heat loss and improving net thermal efficiency.

[0008] The communication hole is shaped to supply a jet of combustion gas generated in the auxiliary chamber to the main chamber. With this feature, when the jet of combustion gas generated in the auxiliary chamber reaches the main chamber, only the premixed air-fuel mixture enveloped in the combustion gas burns, and flame propagation to unburned portions of an ultra-lean air-fuel mixture where flame propagation is not possible does not occur, thereby improving net thermal efficiency.

[0009] The combustion gas jet that is ejected from the auxiliary chamber through the communication hole into the main chamber does not substantially reach the wall surface of the cylinder. This feature prevents the combustion gas jet from reaching the wall surface of the cylinder that constitutes the main chamber, thereby suppressing heat loss and further improving net thermal efficiency.

[0010] A jet of combustion gas is supplied from the auxiliary combustion chamber through the communication hole to the main combustion chamber near the top dead center, and then combustion occurs in the main combustion chamber by slow autoignition. This feature further improves net thermal efficiency and prevents knocking.

[0011] The combustion mass of the premixed air-fuel mixture in the main chamber is characterized in that the ratio of the mass combusted by the jet flow to the mass combusted by the auto-ignition is 1 to 6:4 to 9. This characteristic can further increase the net thermal efficiency.

[0012] The auxiliary combustion chamber is characterized by having a fuel supply means for supplying additional fuel to the auxiliary combustion chamber during the compression stroke. According to this feature, by supplying fuel from the fuel supply means to the air-fuel mixture introduced from the main combustion chamber during the compression stroke, a mixture with an air excess ratio that allows flame propagation can be obtained at the appropriate time.

[0013] 1 is a schematic diagram showing a highly supercharged engine system using a spark ignition engine according to a first embodiment of the present invention; FIG. 2 is a schematic diagram showing a combustion chamber of the spark ignition engine according to the first embodiment; FIG. 3 is a partial cross-sectional view showing an auxiliary combustion chamber configuration unit according to the first embodiment; FIG. 4(a) to FIG. 4(f) are diagrams showing the progress of combustion in the main combustion chamber and the auxiliary combustion chamber of the spark ignition engine; FIG. 5 is a graph showing the results of numerical analysis of the in-cylinder pressure and heat release rate of the spark ignition engine according to the first embodiment; FIG. 6 is a graph showing the results of analysis of the in-cylinder pressure and heat release rate of the spark ignition engine according to a second embodiment of the present invention, where FIG. 6(a) shows the case of natural aspiration and FIG. 6(b) shows the case of a supercharging pressure of 280 kPa (abs.); and FIG. 7 is a graph showing the results of a comparison of combustion characteristics in the spark ignition engine according to the second embodiment, where FIG. 6(a) shows the case of natural aspiration and FIG. 7(b) shows the case of a supercharging pressure of 280 kPa (abs.). 1 is a graph showing the results of a comparison of energy balance in a spark ignition engine of Example 2, where (a) shows the case of natural aspiration and (b) shows the case of a supercharging pressure of 280 kPa (abs.). A diagram showing a comparison of the opening / closing timing and maximum lift amount of an intake valve with early closing (Early Miller) in Example 2 and an intake valve (Original) in Example 1. A graph showing the results of a comparison of analytical results of in-cylinder pressure and heat release rate according to supercharging pressure in a spark ignition engine of Example 2. A graph showing the results of a comparison of indicated thermal efficiency according to supercharging pressure in a spark ignition engine of Example 2, where (a) shows IMEP on the horizontal axis and (b) shows λ main10 is a graph showing the results of a heat balance analysis performed on the spark ignition engine of Example 2, extracting the points where the maximum indicated thermal efficiency at each supercharging pressure was recorded. 11 is a graph showing the results of a comparison of the maximum pressure rise rate and the cycle variation rate at each supercharging pressure for the spark ignition engine of Example 2, where (a) is the case where the horizontal axis is IMEP, and (b) is the case where the horizontal axis is λ main 1 shows a case where the boost pressure is 600 kPa (abs.) and the indicated thermal efficiency is 49.6%. This is a graph comparing analysis results of the in-cylinder pressure and heat release rate in a 3D-CFD combustion progress (Sim.) with one cycle of data extracted from the spark ignition engine of Example 2 (Exp. Cycle No. 352) for the boost pressure of 600 kPa (abs.). This is a graph comparing analysis results of the in-cylinder pressure when motoring under natural aspiration (atmospheric pressure) before and after repair of the spark ignition engine of Example 2. This is a graph comparing analysis results of the in-cylinder pressure and heat release rate before and after repair of the spark ignition engine of Example 2, where (a) shows the case where the boost pressure is 500 kPa (abs.) and (b) shows the case where the boost pressure is 550 kPa (abs.). 10A is a graph showing a comparison of analytical results of in-cylinder pressure and heat release rate according to boost pressure in the spark ignition engine after repair in Example 2, and FIG. 10B is a graph showing a comparison of results of heat balance analysis performed by selecting points where maximum indicated thermal efficiency was recorded at each boost pressure.

[0014] The spark ignition engine of the present invention uses gasoline, gasoline-based synthetic fuel, natural gas, or the like as fuel, and the main combustion chamber is a region defined by the cylinder and piston, and the pre-chamber is a region provided inside the cylinder head, and the main and pre-chambers are connected by a plurality of communication holes. In the spark ignition engine of the present invention, a pre-mixed air-fuel mixture with an excess air ratio exceeding the flame propagation limit is supplied to the main combustion chamber, and a pre-chamber mixture with an excess air ratio that allows flame propagation is supplied to the pre-chamber. As a result, the pre-chamber mixture that allows flame propagation is ignited by an ignition means provided in the pre-chamber during the compression stroke, and flame propagation and combustion occur within the pre-chamber. A jet of high-temperature, high-pressure combustion gas (burned gas) is supplied from the pre-chamber through the communication holes into the main combustion chamber. Only the portion of the pre-mixed air that the jet of combustion gas reaches burns within the main combustion chamber, and then the unburned portion of the high-temperature, high-pressure pre-mixed air begins to spontaneously auto-ignite, and the remaining unburned portion also spontaneously auto-ignites continuously, completing the combustion of the pre-mixed air-fuel mixture. Therefore, it is possible to realize ultra-lean combustion in the main chamber while reducing heat loss, thereby increasing net thermal efficiency.

[0015] In addition, in the spark ignition engine of the present invention, the communication hole connecting the pre-chamber and the main chamber is shaped to extinguish the flame generated in the pre-chamber and supply a jet stream of combustion gas to the main chamber, so that the flame generated in the pre-chamber is not supplied to the main chamber, and only the premixed air-fuel mixture that is enveloped in the combustion gas when the jet stream of combustion gas reaches the main chamber is combusted, and flame propagation to unburned portions does not occur, thereby improving net thermal efficiency.

[0016] Furthermore, in the spark ignition engine of the present invention, the jet of combustion gas ejected from the auxiliary combustion chamber through the communication hole into the main combustion chamber hardly reaches the wall surface of the cylinder, thereby suppressing heat loss and further improving net thermal efficiency.

[0017] The fact that the jet of combustion gas does not reach the cylinder wall can be confirmed by the impact marks of several millimeters wide on the cylinder wall (inner wall), i.e., the range of formation of so-called band-like deposits.The range of deposit formation in the spark ignition engine of the present invention is 20% or less of the cylinder wall, more preferably 10% or less; in other words, the total circumferential direction angle of the cylinder wall on which the deposits are formed is 72° or less, more preferably 36° or less.

[0018] In addition, in the spark ignition engine of the present invention, a jet of combustion gas is supplied from the auxiliary combustion chamber through the communication hole to the main combustion chamber near top dead center, and then combustion occurs due to auto-ignition in the main combustion chamber, thereby further improving net thermal efficiency and preventing knocking. Furthermore, the combusted mass of the premixed air-fuel mixture in the main combustion chamber is such that the ratio of the mass A combusted by the jet (hereinafter sometimes simply referred to as "mass A") to the mass B combusted by auto-ignition (hereinafter sometimes simply referred to as "mass B") is 1 to 6:4 to 9, more preferably 3 to 5:5 to 7, and even more preferably 4:6, thereby further improving net thermal efficiency.

[0019] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A spark ignition engine according to an embodiment of the present invention will be described below.

[0020] A spark ignition engine according to a first embodiment will be described with reference to FIGS. 1 to 5. FIG.

[0021] 1 and 2, the combustion chamber of the spark ignition engine 1 in this embodiment is divided into a main combustion chamber 10, which is an area defined by the cylinder 2 and the upper part of the piston 3, and an auxiliary combustion chamber 20 provided inside a cylinder head 21 that constitutes the cylinder 2, and the main combustion chamber 10 and the auxiliary combustion chamber 20 are connected via a plurality of communication holes 201a. Note that the spark ignition engine 1 in this embodiment will be described as being applied to a highly supercharged multi-cylinder engine system (see FIG. 1) equipped with a two-stage supercharging turbo 100.

[0022] The cylinder 2 is mainly composed of a cylinder head 21 and a cylinder block 22. An auxiliary chamber forming unit 200 is attached to the center of the cylinder head 21, thereby forming an auxiliary chamber 20.

[0023] 3, the auxiliary combustion chamber forming unit 200 is mainly composed of a cover 201, an adapter 202, an ignition plug 204 as ignition means, and an auxiliary combustion chamber injector 205 as fuel supply means. In this embodiment, the cylindrical cover 201 with a bottom is fixed so as to cover the adapter 202 from below, thereby forming the auxiliary combustion chamber 20 inside the cover 201.

[0024] The dome-shaped cover 201 has a plurality of communication holes 201a at its lower end. In this embodiment, the communication holes 201a are equally spaced in eight positions in the circumferential direction. The communication holes 201a are formed as linear through-holes that are inclined so that the apex angle between opposing holes is 140° to 170°, preferably 150° to 160°.

[0025] Furthermore, the diameter, length, shape, number, etc. of the communication hole 201a may be freely selected as long as it has a shape that can extinguish the flame generated in the auxiliary chamber 20 by ignition of the spark plug 204 and supply a jet stream of combustion gas (burned gas) to the main chamber 10.

[0026] The auxiliary combustion chamber 20 is configured to have a smaller volume than the main combustion chamber 10. More specifically, the ratio of the volume of the auxiliary combustion chamber 20 to the combined volume of the main combustion chamber 10 and the auxiliary combustion chamber 20 when the piston 3 is positioned at top dead center (0 degrees) is preferably 10 to 20%, and more preferably 13 to 17%.

[0027] The piston 3 is connected to one end of a connecting rod 31, the other end of which is connected to a crankshaft (not shown). The piston 3 and the crankshaft (not shown) are housed in a cylinder block 22.

[0028] 1 and 2, the spark ignition engine 1 of this embodiment has a main-chamber injector 4 that injects fuel into the intake manifold 7 as a means for introducing an ultra-lean premixture of fuel and compressed air into the main combustion chamber 10, i.e., a premixture with an excess air ratio that exceeds the flame propagation limit. That is, in this embodiment, fuel is supplied to the main combustion chamber 10 by intake manifold injection using the main-chamber injector 4. In this embodiment, the excess air ratio of the premixture in the main combustion chamber 10 is, for example, 2.5 or higher, preventing flame propagation. Although fuel is supplied to the main combustion chamber 10 by intake manifold injection using the main-chamber injector 4, the injection pressure used is the same as the injection pressure for high-pressure direct injection of the sub-chamber injector 205 in order to form a more homogeneous premixture.

[0029] The spark ignition engine 1 of this embodiment also has a pre-chamber injector 205 as an injector that injects additional fuel into the pre-chamber 20. That is, the method of supplying fuel to the pre-chamber 20 in this embodiment is direct injection into the cylinder by the pre-chamber injector 205. In this embodiment, the pre-chamber air-fuel mixture in the pre-chamber 20 has a higher fuel concentration than at least the pre-mixture in the main combustion chamber 10 due to the injection of additional fuel from the pre-chamber injector 205, and has an air excess ratio that allows flame propagation. For example, the air excess ratio in the pre-chamber 20 is 2.0 or less.

[0030] Next, the combustion method of the spark ignition engine 1 of this embodiment will be described with reference to Figures 1, 2 and 4. The spark ignition engine 1 of this embodiment is a four-stroke cycle engine consisting of four strokes: intake-compression-expansion-exhaust.

[0031] 1, 2, and 4, in the spark ignition engine 1 of this embodiment, the intake valve 6 opens during the intake stroke, and fuel is injected from the main chamber injector 4 into the intake pipe 7, forming a homogeneous premixed air-fuel mixture with an excess air ratio that exceeds the flame propagation limit in the main combustion chamber 10. The premixed air-fuel mixture formed in the main combustion chamber 10 is also introduced into the auxiliary combustion chamber 20 via the communication hole 201a during the compression stroke.

[0032] Next, in the latter half of the compression stroke, specifically, fuel is directly injected from the pre-chamber injector 205 into the pre-chamber combustion chamber 20 over a predetermined injection period at a crank angle of −180° to −240°, preferably −180° to −200°, with the time after top dead center being the positive value. This supplies additional fuel to the pre-chamber combustion chamber 20, appropriately increasing the concentration of the pre-chamber air-fuel mixture in the pre-chamber combustion chamber 20 compared to the concentration of the pre-mixture in the main combustion chamber 10, resulting in a pre-chamber air-fuel mixture with an air excess ratio that allows flame propagation. The amount of fuel injected from the pre-chamber injector 205 into the pre-chamber combustion chamber 20, i.e., the pre-chamber fuel ratio (PRF), is preferably approximately 7% or less. The pre-chamber fuel ratio is calculated by the mass ratio of the pre-chamber fuel to the total fuel supply.

[0033] Next, as the compression stroke progresses further, ignition occurs in the sub-combustion chamber 20 by the spark plug 204 near top dead center (6.5 deg. BTDC) (see FIG. 4A).

[0034] Next, near top dead center (3.0 deg. BTDC), the flame generated by flame propagation combustion in the auxiliary chamber 20 attempts to eject into the main combustion chamber 10 through the multiple communication holes 201a due to the rise in pressure within the auxiliary chamber 20 (see FIG. 4B). At this time, the communication holes 201a extinguish the flame generated in the auxiliary chamber 20 and eject a jet of combustion gas into the main combustion chamber 10. Then, combustion of the premixed air occurs only in the part of the main combustion chamber 10 that is surrounded by the combustion gas ejected from the communication holes 201a.

[0035] Next, after top dead center (5.0 deg. ATDC), the jet of combustion gas ejected into the main combustion chamber 10 through the communication hole 201a combusts the premixed air and reaches a position just before the wall of the cylinder 2 (more specifically, the cylinder block 22). In other words, the jet of combustion gas ejected from the auxiliary combustion chamber 20 into the main combustion chamber 10 through the communication hole 201a does not substantially reach the wall of the cylinder 2. Furthermore, in the main combustion chamber 10, the jet of combustion gas ejected from the communication hole 201a compresses the unburned portion of the premixed air, causing so-called auto-ignition to occur.

[0036] Next, after top dead center (7.5 to 9 deg. ATDC) as shown in Figures 4(d) and (e), autoignition of the unburned portion of the premixed air-fuel mixture in the main combustion chamber 10 occurs continuously, and the autoignition region expands. Then, after top dead center (10.5 deg. ATDC) as shown in Figure 4(f), autoignition of the remaining unburned portion occurs, and combustion of the premixed air-fuel mixture in the main combustion chamber 10 is completed.

[0037] After the expansion stroke, the exhaust valve 8 opens, and the combustion gas (burned gas) in the main combustion chamber 10 and the auxiliary combustion chamber 20 is discharged from the exhaust pipe 9 .

[0038] In this way, in the spark ignition engine 1 of this embodiment, a premixed air-fuel mixture with an excess air ratio exceeding the flame propagation limit is supplied to the main combustion chamber 10, and a premixed air-fuel mixture with an excess air ratio that allows flame propagation is supplied to the auxiliary combustion chamber 20. This allows the premixed air-fuel mixture that is ignited by the spark plug 204 installed in the auxiliary combustion chamber 20 during the compression stroke to propagate and burn within the auxiliary combustion chamber 20. A jet of high-temperature, high-pressure combustion gas is supplied from the auxiliary combustion chamber 20 into the main combustion chamber 10 through the communication hole 201a. After combustion of only the portion of the main combustion chamber 10 reached by the jet of combustion gas, the unburned portion of the high-temperature, high-pressure premixed air begins to spontaneously auto-ignite. The remaining unburned portion also spontaneously auto-ignites, completing combustion of the premixed air-fuel mixture. This allows for ultra-lean combustion in the main combustion chamber 10 with low heat loss and improved net thermal efficiency.

[0039] That is, in the spark ignition engine 1 of this embodiment, a premixed air-fuel mixture with an excess air ratio exceeding the flame propagation limit in the main combustion chamber 10 cannot be burned by flame propagation, so it is burned by a jet of high-temperature, high-pressure combustion gas that is ejected from the auxiliary combustion chamber 20 through the communication hole 201a into the main combustion chamber 10, and further, the unburned portion of the premixed air-fuel mixture that has been compressed in the main combustion chamber 10 and has become high-temperature and high-pressure as a result of this combustion is caused to self-ignite, thereby completing the combustion of the premixed air-fuel in the main combustion chamber 10, and achieving ultra-lean combustion in the main combustion chamber 10.

[0040] Furthermore, in the spark ignition engine 1 of this embodiment, the communication hole 201a connecting the auxiliary combustion chamber 20 and the main combustion chamber 10 is shaped to extinguish the flame generated in the auxiliary combustion chamber 20 and supply a jet stream of combustion gas to the main combustion chamber 10. As a result, the flame generated in the auxiliary combustion chamber 20 is not supplied to the main combustion chamber 10, and only the premixed air-fuel mixture that is enveloped in the combustion gas that reaches the main combustion chamber 10 is combusted, and flame propagation to unburned portions does not occur, thereby improving net thermal efficiency.

[0041] Furthermore, in the spark ignition engine 1 of this embodiment, the jet of combustion gas ejected from the auxiliary combustion chamber 20 through the communication hole 201a into the main combustion chamber 10 does not substantially reach the wall surface of the cylinder 2, thereby suppressing heat loss due to cooling caused by contact with the wall surface of the cylinder 2, thereby further improving net thermal efficiency.

[0042] Furthermore, in the spark ignition engine 1 of this embodiment, a jet of combustion gas is supplied from the auxiliary combustion chamber 20 through the communication hole 201a to the main combustion chamber 10 near top dead center, and then combustion occurs due to autoignition in the main combustion chamber 10. This allows combustion of the premixed air-fuel mixture in the main combustion chamber 10 by the jet of combustion gas and subsequent combustion due to autoignition to occur in a stepwise manner over a relatively long period of time, further improving net thermal efficiency. In addition, since autoignition can be caused to occur continuously in the main combustion chamber 10 over a certain amount of time, and combustion of the premixed air-fuel mixture can be completed, knocking can be prevented.

[0043] Furthermore, in the spark ignition engine 1 of this embodiment, the auxiliary combustion chamber 20 has an auxiliary combustion chamber injector 205 that supplies additional fuel to the auxiliary combustion chamber 20 during the compression stroke, thereby making it possible to timely obtain a mixture with an air excess ratio that allows flame propagation.

[0044] Furthermore, the spark ignition engine 1 of this embodiment is applied to a highly supercharged multi-cylinder engine system (see FIG. 1) equipped with a two-stage turbocharger 100, and by achieving high supercharging with a supercharging pressure of 500 kPa and a turbocharging efficiency of 60% or more, the pumping work can also be made positive work, thereby maximizing the net thermal efficiency.

[0045] Next, combustion calculations are performed using 3D-CFD (CONVERGE v3.0) for the spark ignition engine 1 of this embodiment to examine the net thermal efficiency at high supercharging.

[0046] The results of a comparison of the numerical analysis results of the in-cylinder pressure and heat release rate in the spark ignition engine 1 of this embodiment are shown in FIG. 5. main : Main chamber excess air ratio, λ pre @ignition: Pre-chamber excess air ratio, T in : intake air temperature, P in : intake air pressure, IMEP: indicated mean effective pressure, η i_gross : Gross indicated thermal efficiency.

[0047] The specifications of the spark ignition engine 1 of this embodiment are shown in Table 1.

[0048]

[0049] The compression ratio (CR) and the volume ratio (VR) of the auxiliary chamber are defined by the following equations 1 and 2. swept is the total displacement, V large is the volume of the main chamber at the top dead center, V small is the volume of the antechamber.

[0050]

[0051]

[0052] Table 2 shows the calculation conditions for the numerical analysis.

[0053]

[0054] The heat release rate of the spark ignition engine 1 of this embodiment was calculated using the following formula 3: where κ is the specific heat ratio, P large is the pressure in the main chamber, P small is the pressure in the antechamber.

[0055]

[0056]

[0057] As shown in Figure 5, it was confirmed that in the spark ignition engine 1 of this embodiment, the ratio of mass A burned by the jet flow (see area A in Figure 5) to mass B burned by auto-ignition (see area B in Figure 5) was 4:6, with the boundary (see dash-dot line) being the crank angle of 5 degrees (see Figure 4(c)), at which auto-ignition of the premixed mixture in the main chamber begins. Note that the ratio of the burned masses of the premixed mixture is approximately equal to the ratio of the areas calculated from the integrals of areas A and B in the heat release rate graph shown in Figure 5.

[0058] Furthermore, the IMEP of 3.16 MPa in the spark ignition engine 1 of this embodiment is higher than the maximum IMEP of 2.7 MPa in a conventional spark ignition engine, and it was confirmed that the operating range can be expanded to higher loads.

[0059] Furthermore, the spark ignition engine 1 of this embodiment, assuming a turbocharging efficiency equivalent to 65% and a mechanical efficiency of 95%, has a BMEP (break mean effective pressure) of 3.0 MPa, which is higher than the maximum BMEP of 2.57 MPa in conventional spark ignition engines, confirming that the break mean effective pressure (BMEP) has been improved.

[0060] As described above, in the spark ignition engine 1 of this embodiment, a jet of combustion gas is supplied from the auxiliary combustion chamber 20 through the communication hole 201a to the main combustion chamber 10 near top dead center, and then combustion occurs due to autoignition in the main combustion chamber 10. This allows combustion of the premixed air-fuel mixture in the main combustion chamber 10 by the jet of combustion gas and subsequent combustion by autoignition to occur in stages over a relatively long period of time, thereby improving net thermal efficiency. Furthermore, by adjusting the ratio of the mass A of the premixed air-fuel mixture in the main combustion chamber 10 combusted by the jet of combustion gas (see area A in Figure 5) to the mass B of the premixed air-fuel mixture combusted by autoignition (see area B in Figure 5) to be 4:6, net thermal efficiency can be maximized.

[0061] A spark ignition engine according to a second embodiment will be described with reference to FIGS.

[0062] In this embodiment, the results of a demonstration experiment using a spark ignition engine different from that of the first embodiment will be described. The specifications of the spark ignition engine of this embodiment are shown in Table 3. The compression ratio (CR) of the spark ignition engine of this embodiment is the same as that of the spark ignition engine 1 of the first embodiment.

[0063]

[0064] FIG. 6 shows the results of a comparison of the analysis results of the in-cylinder pressure and heat release rate in the spark ignition engine of this embodiment.

[0065] As shown in FIG. 6(b), the spark ignition engine of this embodiment has a higher λ at a boost pressure of 280 kPa compared to the naturally aspirated engine (see FIG. 6(a)). main It was confirmed that this enabled operation at low pressure, i.e., lean burn in the main chamber, and that this resulted in improved in-cylinder pressure and heat release rate.

[0066] FIG. 7 shows the results of a comparison of combustion characteristics in the spark ignition engine of this embodiment.

[0067] As shown in FIG. 7(b), the spark ignition engine of this embodiment has a significantly improved IMEP and indicated thermal efficiency η at a boost pressure of 280 kPa compared to the naturally aspirated engine (see FIG. 7(a)). ｉ（ｇ） It was confirmed that the lean mixture combustion was possible due to the increased combustion efficiency. It was also confirmed that the NOx emission concentration was reduced to approximately 65 to 75 ppm (see the dashed box in Figure 7).

[0068] The results of a comparison of the energy balance in the spark ignition engine of this embodiment are shown in FIG. ｕｎｂｕｒｎｔ is the unburned loss ratio, φ ｅｘ is the exhaust loss ratio, φ ｃｏｏｌ is the cooling loss rate, η ｂ is the net thermal efficiency (when the mechanical efficiency is 95%).

[0069] As shown in Figure 8(b), the spark ignition engine of this embodiment has a slightly improved indicated thermal efficiency at a boost pressure of 280 kPa compared to the naturally aspirated case (see Figure 8(a)). However, the cooling loss is still large at 20% or more, so the boost pressure is insufficient at 280 kPa, and it is presumed that auto-ignition of the unburned portion of the pre-mixture in the main chamber after top dead center, as explained in Example 1 above, does not occur, and operation with ultra-lean burn in the main chamber cannot be achieved.

[0070] Therefore, the results of a demonstration experiment conducted on the spark ignition engine of this embodiment by increasing the compression ratio and closing the intake valve earlier will be described. The specifications of the spark ignition engine of this embodiment are shown in Table 4.

[0071]

[0072] The experimental conditions for the demonstration experiment are shown in Table 5.

[0073]

[0074] 9, in the spark ignition engine of this embodiment, the intake valves are closed early (Early Miller) with opening and closing timings of -1 deg. ATDC and 132 deg. ATDC, whereas the intake valves of the first embodiment (Original), which do not employ early closing, are opened at -10 deg. ATDC and closed at 240 deg. ATDC. Furthermore, in the spark ignition engine of this embodiment, the maximum lift of the intake valves during early closing is less than half of the maximum lift of the intake valves of the first embodiment. The lift amounts at both opening and closing timings are 0.1 mm.

[0075] FIG. 10 shows a comparison of analytical results of the in-cylinder pressure and heat release rate according to the boost pressure (400 kPa, 450 kPa, 500 kPa, 550 kPa, 600 kPa) in the spark ignition engine of this embodiment.

[0076] As shown in FIG. 10, when the boost pressure exceeds 450 kPa, the heat release rate after the top dead center becomes active, and therefore a higher λ mainIt was confirmed that operation at this temperature, i.e., auto-ignition of the unburned portion of the premixture in the main chamber after top dead center, can occur, and operation with ultra-lean burn in the main chamber can be achieved.

[0077] FIG. 11 shows the results of a comparison of the indicated thermal efficiency according to the supercharging pressure in the spark ignition engine of this embodiment.

[0078] As shown in FIG. 11, as the boost pressure increases, the IMEP and λ increase. main It was confirmed that operation at an ultra-lean fuel mixture became possible, and an indicated thermal efficiency of up to 49.6% could be achieved.

[0079] FIG. 12 shows the results of a heat balance analysis performed on the points where the maximum indicated thermal efficiency was recorded at each boost pressure.

[0080] As shown in FIG. 12, the higher the boost pressure, the higher the λ main It was confirmed that this enables operation at a low pressure, i.e., operation with ultra-lean burn in the main chamber, and that it is possible to achieve both reduced cooling loss and high indicated thermal efficiency. Although not shown in the figures for the sake of convenience, it was also confirmed that as the boost pressure increases, NOx and THC (total hydrocarbon) emissions are reduced.

[0081] FIG. 13 shows the results of a comparison of the maximum pressure rise rate and cycle variation rate at each supercharging pressure.

[0082] As shown in Figure 13(a), the maximum pressure rise rate at each boost pressure was 0.8 MPa / deg or less, confirming that the combustion noise during operation was relatively quiet. Also, as shown in Figure 13(b), the cycle variation rate at each boost pressure was 3% or less, confirming that operation was possible and that this value was low even at a practical level.

[0083] Next, for the spark ignition engine of this embodiment, one cycle of data showing an indicated thermal efficiency of 49.6% at a boost pressure of 600 kPa was extracted, and combustion calculations were performed using 3D-CFD (CONVERGE v3.0) to examine the net thermal efficiency at high boost pressure.

[0084] One cycle of data for an indicated thermal efficiency of 49.6% (Exp. Cycle No. 352) is extracted, along with the 3D-CFD combustion progress (Sim.) shown in Figure 14. As shown in Figure 14, the 3D-CFD combustion progress is able to largely reproduce the demonstration experiment, and therefore combustion will be considered through numerical analysis based on these results.

[0085] 14, it was confirmed that the graph showing the results of numerical analysis of the in-cylinder pressure and heat release rate in the spark ignition engine of this embodiment has a shape with similar characteristics to the graph (see FIG. 5) showing the results of numerical analysis of the in-cylinder pressure and heat release rate in the spark ignition engine 1 of Example 1. That is, in the spark ignition engine of this embodiment, the jet stream of high-temperature, high-pressure combustion gas ejected from the auxiliary combustion chamber through the communication hole into the main combustion chamber hardly reaches the wall surface of the cylinder, and the unburned portion of the premixed air that has been compressed in the main combustion chamber due to combustion by the jet stream of high-temperature, high-pressure combustion gas moves from the exhaust side to the intake side and self-ignites, thereby completing combustion of the premixed air.

[0086] In the spark ignition engine of this embodiment, the temperature near the cylinder wall is approximately 1600 K at 20 deg. ATDC, and it has been confirmed that the jet of high-temperature, high-pressure combustion gas ejected into the main combustion chamber does not substantially reach the cylinder wall, thereby contributing to a reduction in cooling loss.

[0087] Furthermore, it was confirmed that the turbulent kinetic energy decreases rapidly after top dead center, and the jet of high-temperature, high-pressure combustion gas ejected into the main chamber does not reach the cylinder wall at all, and the unburned portion of the premixed air-fuel mixture, which has been compressed in the main chamber due to combustion by the jet of high-temperature, high-pressure combustion gas and has become high-temperature and high-pressure, migrates from the exhaust side to the intake side and self-ignites, thereby realizing ultra-lean combustion in the main chamber while reducing heat loss and improving net thermal efficiency.

[0088] As explained above, in the spark ignition engine of this embodiment, the lean limit is expanded by increasing the supercharging pressure, and λ main Specifically, the indicated thermal efficiency is 49.6% at a boost pressure of 600 kPa, and λ mainIt was confirmed that a tensile strength of 3.0 and an IMEP of 2364 kPa could be achieved.

[0089] Furthermore, it is presumed that the early closing (Early Miller) of the intake valve in the spark ignition engine of this embodiment facilitates the realization of ultra-lean combustion in the main combustion chamber. Note that the opening and closing pattern of the intake valve is not limited to the Early Miller Cycle of this embodiment, and it goes without saying that ultra-lean combustion in the main combustion chamber can be achieved by any opening and closing pattern.

[0090] In the graphs of Fig. 10 and Fig. 14 for a boost pressure of 600 kPa, afterburning becomes noticeable after 20 deg. ATDC, but when the spark ignition engine of this example was disassembled after the demonstration experiment, damage to the pin supporting the connecting rod was confirmed. This suggests that the above-mentioned afterburning may be influenced by a decrease in the degree of constant volume (DCV) due to a malfunction of the pin before it breaks.

[0091] Therefore, the pin supporting the connecting rod of the spark ignition engine of this example was replaced, and motoring was performed under natural aspiration (atmospheric pressure) before and after the engine was repaired. As a result, it was confirmed that the internal pressure of the pipe in the spark ignition engine after repair increased by 0.34 MPa compared to before repair, as shown in Figure 15. The data before repair used for comparison was data before the pin was broken.

[0092] Next, a comparison of the analysis results of the in-cylinder pressure and heat release rate before and after repair of the spark ignition engine of this embodiment is shown in Figure 16. Note that the results shown here are from test runs of the spark ignition engine after repair at boost pressures of 500 kPa and 550 kPa.

[0093] As shown in FIG. 16, it was confirmed that in the repaired spark ignition engine, the DCV was improved and afterburning was suppressed in both cases where the boost pressure was 500 kPa and 550 kPa.

[0094] Figure 17(a) shows a comparison of the analysis results of the in-cylinder pressure and heat release rate according to the boost pressure (400 kPa, 450 kPa, 500 kPa, 550 kPa) of the repaired spark ignition engine. Figure 17(b) shows the results of a heat balance analysis performed on the points where the maximum indicated thermal efficiency was recorded at each boost pressure.

[0095] As shown in Figures 17(a) and 17(b), in the spark ignition engine after repair, as in the spark ignition engine before repair (see Figure 10), when the boost pressure exceeds 450 kPa, the heat release rate that occurs after top dead center becomes active, and therefore a higher λ main In other words, auto-ignition of the unburned portion of the pre-mixture in the main chamber after top dead center occurred, and the reproducibility of operation with ultra-lean burn in the main chamber was confirmed. Furthermore, as described above, in the spark ignition engine after repair, DCV was improved and afterburning was suppressed, so that a higher λ main Specifically, the indicated thermal efficiency is 53.8% at a boost pressure of 550 kPa, and λ main It was confirmed that a value of 3.06 could be achieved.

[0096] Although the embodiments of the present invention have been described above with reference to the drawings, the specific configuration is not limited to these embodiments, and the present invention also includes modifications and additions that do not deviate from the gist of the present invention.

[0097] For example, in the above embodiment, the spark ignition engine 1 is described as being applied to a highly supercharged multi-cylinder engine system equipped with a two-stage turbocharger 100, but the invention is not limited to this and may also be applied to, for example, a highly supercharged single-cylinder engine system equipped with a supercharger. Furthermore, the spark ignition engine of the present invention may be applied to a naturally aspirated engine system as long as it can realize the combustion method described in the above embodiment.

[0098] Furthermore, in the above embodiment, the spark ignition engine 1 has been described as being configured to increase the concentration of the pre-chamber air-fuel mixture in the pre-chamber 20 by directly injecting additional fuel from the pre-chamber injector 205 into the pre-chamber 20, but this is not limiting, and the pre-chamber does not need to be equipped with an injector as long as it is possible to supply a pre-chamber air-fuel mixture with an air excess ratio that allows flame propagation to the pre-chamber.

[0099] In the above embodiment, the auxiliary injector 205 injects additional fuel into the auxiliary combustion chamber 20 during the compression stroke at a crank angle of −120°. However, the present invention is not limited to this, and the timing of fuel injection by the injector may be freely set as long as the concentration of the mixture in the auxiliary combustion chamber 20 can be appropriately increased before top dead center.

[0100] Furthermore, in the above embodiment, the method of supplying fuel to the main combustion chamber 10 was described as an intake manifold injection type in which fuel is injected from the main combustion chamber injector 4 into the intake manifold 7, but this is not limiting, and the method of supplying fuel to the main combustion chamber may be a direct injection type into the cylinder using a main combustion chamber injector or a center injector.

[0101] In the above embodiment, the communication hole 201a connecting the auxiliary chamber 20 and the main chamber 10 is described as having a shape that extinguishes the flame generated in the auxiliary chamber 20 and supplies a jet of combustion gas to the main chamber 10, but this is not limiting, and the flame generated in the auxiliary chamber may be slightly ejected into the main chamber through the communication hole. In this case, from the viewpoint of thermal efficiency, it is preferable that the flame does not substantially reach the wall surface of the main chamber.

[0102] REFERENCE SIGNS LIST 1 Spark ignition engine 2 Cylinder 3 Piston 4 Main chamber injector 6 Intake valve 7 Intake pipe 8 Exhaust valve 9 Exhaust pipe 10 Main chamber 20 Pre-chamber 21 Cylinder head 22 Cylinder block 31 Connecting rod 200 Pre-chamber forming unit 201 Cover 201a Communication hole 202 Adapter 204 Spark plug (ignition means) 205 Pre-chamber injector (fuel supply means)

Claims

1. A spark ignition engine comprising a main chamber separated by a cylinder and a piston, and an auxiliary chamber having an ignition means, wherein a plurality of communication holes are provided connecting the auxiliary chamber to the main chamber, and wherein a premixed air-fuel mixture with an air excess ratio exceeding the flame propagation limit is supplied to the main chamber, and a mixture with an air excess ratio that allows flame propagation is supplied to the auxiliary chamber.

2. A spark ignition engine according to claim 1, characterized in that the communication hole is shaped to supply a jet of combustion gas generated in the auxiliary chamber to the main chamber.

3. A spark ignition engine according to claim 2, characterized in that the jet of combustion gas ejected from said auxiliary chamber through said communication hole into said main chamber does not substantially reach the wall surface of said cylinder.

4. A spark ignition engine as described in claim 2 or 3, characterized in that a jet of combustion gas is supplied from the auxiliary chamber through the communication hole to the main chamber near top dead center, and then combustion occurs in the main chamber by spontaneous ignition.

5. A spark ignition engine as described in claim 4, characterized in that the ratio of the mass of premixed air burned in the main chamber by the jet flow to the mass burned by the self-ignition is 1 to 6:4 to 9.

6. A spark ignition engine according to claim 1, characterized in that said pre-chamber has a fuel supply means for supplying additional fuel to said pre-chamber during the compression stroke.

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