COMBUSTION CHAMBER FOR INTERNAL COMBUSTION ENGINES

Abstract: Described herein is a combustion chamber (3, 103) for internal combustion engines, including a protuberance (12, 112) projecting radially inward from a peripheral wall surface (3a, 103a) of a combustion chamber (3, 103) which is formed by hollowing the top of a piston (1) in the axial direction thereof. The protuberance (12, 112) induces rolling streams turning in the same direction as the swirl, thereby collecting air and atomized fuel in a region on the upstream side of the protuberance (12, 112). The rolling stream serves to improve the ignition quality by enriching the concentration of fuel vapors in that locality. The flames generated in the vicinity of the protuberance (12, 112) are propagated to the atomized fuel which is supplied to other regions of the combustion chamber (3, 103), permitting to provide an internal combustion engine with improved ignition and combus­ tion qualities.

Description: Field of the Invention This invention relates to a combustion chamber for internal combustion engines, and more particularly to a combustion chamber for an internal combustion engine employing a spark plug for igniting a volatile fuel of low cetane number such as alcohol, gasoline or the like. Description of the Prior Art Generally, a Diesel engine spark assisting device as shown in Fig. 6 (proposed in Japanese Laid-Open Utility Model Application No. 58-178419) has been known as a spark plug ignition means ensuring high thermal efficiency and good mileage. According to this proposal, in a combustion chamber b which is hollowed out of a piston top a , a spark plug f is located to have a spark position upstream of a sprayed zone d of a fuel injected toward the inner wall c of the combustion chamber b when seen in the direction of a swirl S, and in the vicinity of the inner wall c . With this arrangement, the time which is taken for reaching a spark position from an injection point by the sprayed fuel zone d which is carried away from the upstream side to the downstream side by the swirl S is utilized as a volatilization period for evaporating the fuel by contact with compressed air, thereby improving the degree of air-fuel mixing for attaining higher ignition and starting qualities. However, the arrangement of this proposal is incapable of igniting and burning a volatile fuel of low cetane number such as alcohol, gasoline or the like. Namely, a volatile fuel is instantly volatilized and dispersed upon injection into the combustion chamber due to its high volatility, so that it is necessary to increase the amount of fuel injection or to adjust the air-fuel ratio by throttling intake air to enrich the air-fuel mixture to a concentration suitable for sparking ignition and flame propagation. The throttling of intake air, however, increases the pumping work of the internal combustion engine and is therefore undesirable from a standpoint of mileage and output qualities. Under the circumstances, there has been a demand for new proposals which can distribute an air-fuel mixture of a suitable concentration in terms of ignition and combustion qualities to the neighborhood of the sparking terminal of a spark plug. From the US-A-2 457 652 an internal combustion engine is known, comprising: a combustion chamber for an internal combustion engine, especially for burning volatile fuel of low cetane number, comprising a combustion chamber formed by hollowing the top of a piston in the axial direction thereof; a protuberance projecting radially inward from a peripheral wall surface of said combustion chamber; a fuel injection nozzle means adapted to supply atomized fuel toward a peripheral wall in the neighborhood and on the upstream side of said protuberance in the direction of swirl and toward other peripheral walls of said combustion chamber; and a spark plug means located in the neighborhood of said protuberance to accelerate ignition of atomized fuel supplied thereto. Preferably two deflectors are provided, but the above mentioned drawbacks are not eliminated. A further improvement can not be achieved by a device known from JP 59-81775, where auxiliary jets are injected in the direction of the ignition means and main jets are injected to the front of the ignition means. The present invention contemplates to eliminate the above-mentioned problems or drawbacks. More specifically, it is an object of the present invention to provide a combustion chamber for internal combustion engines, which can produce an air-fuel mixture of suitable richness in the vicinity of a spark plug, which is located in the combustion chamber for burning a volatile fuel of low cetane number such as light oil, alcohol, gasoline or the like, thereby ensuring satisfactory starting characteristics as well as stable combustion quality in all load ranges of the engine operation. In accordance with the present invention, the above-mentioned object is achieved by provision of a combustion chamber construction, which is characterized in that the spark plug means is located on the upstream side of said protuberance in the direction of said swirl, the protuberance is located and formed in that way that a rolling stream in the direction of rotation of swirl is created by said protuberance in the vicinity of said spark plug means, the fuel injection nozzle means is provided with main nozzle holes for supplying said atomized fuel toward a number of equidistantly spaced segmental areas on the inner peripheral wall of said combustion chamber and with an auxiliary nozzle for supplying atomized fuel such that the fuel is sprayed just upstream of or toward an electrode of said spark plug means such that the fuel and the fuel from the auxiliary nozzle hole is not accelerated by the swirl in the direction in which the swirl flows and such that said rolling stream confines the fuel to create relatively fuel-rich mixture around the electrode of said spark plug means whereas said atomized fuel supplied toward the other peripheral walls in the direction in which the swirl flows creates relatively fuel-lean mixture outside the fuel-rich mixture area created by said fuel, whereby the flame built upon the combustion of said relatively fuel-rich mixture propagates to combust said relatively fuel-lean mixture. In operation, a vortical flow of air which is supplied to the combustion chamber in the piston top forms a swirl turning about the center axis of the combustion chamber. The velocity of this swirl is increased by the radial protuberance, with the radial projection thereof inducing rolling streams turning in the same direction as the swirl on the upstream side thereof, entraining and stirring the atomized fuel, which is supplied through the fuel injections means, as well as air in the center portion of the combustion chamber and air in the neighborhood of the radial projection. These rolling streams stir the trapped fuel and volatilize same by hot compressed air in the streams, mixing the volatilized fuel with air to produce an air-fuel mixture of good ignition and combustion qualities. In this way, an enriched air-fuel mixture is locally produced. On the other hand, the atomized fuel which is supplied toward other peripheral wall portions of the combustion chamber is stirred by the swirl and volatilized by the heat of compressed air, so that an air-fuel mixture of suitable concentration is evenly dispersed and distributed in the combustion chamber. Consequently, as soon as the air-fuel mixture which is formed by the rolling streams is ignited by a spark of the spark plug means, flame propagation takes place promptly in the combustion chamber. Therefore, the combustion is effected stably in any load condition, supressing HC, NOx and smoke. The above and other objects, features and advantages of the invention will become more apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings which show by way of example preferred embodiments of the invention. In the accompanying drawings: Fig. 1 is a schematic sectional view of a combustion chamber for internal combustion engines according to the present invention; Fig. 2 is a plan view of the combustion chamber of Fig. 1; Fig. 3 is a schematic illustration of rolling streams induced by a protuberance; Fig. 4 is a fragmentary sectional view of an injection nozzle; Fig. 5 is a schematic plan view of another embodiment of the invention; and Fig. 6 is a schematic plan view of a conventional spark assisting device for Diesel engines. Referring to Figs. 1 and 2, there is shown a combustion chamber for internal combustion engines according to the present invention, in which indicated at 1 is a piston, at 2 a piston top, at 3 a combustion chamber, and at 4 a cylinder head. As shown in Fig. 1, the combustion chamber 3 is formed in the piston 1 by hollowing an open cavity deeply in the axial direction from a piston top 2a. In this particular embodiment, the combustion chamber 3 has a circular shape in cross section taken perpendicularly across the axis of the piston 1. The combustion chamber is supplied with intake air through a swirl port (not shown) forming a swirl S1 turning along the peripheral wall 3a of the combustion chamber 3. A feature of the internal combustion engine according to the invention resides in that a volatile fuel of low cetane number can be burned without ignition failures in the engine operations of any load range including the engine-starting stage. Now, the shape of the combustion engine is explained in relation with the fuel injection nozzle means and the spark plug means which are provided therein. The fuel injection nozzle means 5 is arranged as shown particularly in Fig. 4. A nozzle casing 7 which movably receives therein a needle valve 6 is formed with a valve seat 8 at its front end for engagement with a throttle portion 6a of the needle valve 6. Formed in the front end portion of the nozzle casing 7 is a fuel injection chamber 9 which is axially extended from the value seat 8 and opened and closed by the throttle portion 6a which forms the front end portion of the needle valve 6. The valve seat 8 contains one auxiliary nozzle hole 10, while the fuel injection chamber 9 has a plurality of main nozzle holes 11 in its peripheral wall at predetermined intervals. The auxiliary nozzle hole 10 of the fuel injection nozzle means 5 has a smaller diameter than the main nozzle holes 11. The auxiliary nozzle hole 10 is opened when the lift of the needle valve 6 is in a certain range below a predetermined value, and the main nozzle holes 11 are also opened when the lift exceeds the predetermined value. Thus, the fuel injection nozzle means 5 which is employed in this embodiment constitutes the so-called pintaux type. On the other hand, as shown particularly in Figs. 1 to 3, the combustion chamber 3 is formed with a protuberance 12 Which is projecting radially inward from the surface of a peripheral wall 3a of the combustion chamber 3. As illustrated in Figure 2, the protuberance 12 protrudes radially inward from the peripheral wall surface of the combustion chamber 3 and the sectional configuration of the protuberance 12 transversal to the axis of the piston is like a ball, more specifically the projection 12 is gradually increased in the circumferential direction of the combustion chamber 3 and then gradually reduced after reaching a maximum point. As shown in Fig. 3, this protuberance 12 functions to increase the velocity of the swirl S1 in the neighboring regions, and locally generates rolling streams turning in the same direction as the swirl S1 on the upstream side of the protuberance 12 in the flow direction of the swirl S1, rolling thereinto compressed air which is distributed to the center portions of the combustion chamber 3 as well as compressed air which is distributed to the vicinity of the protuberance 12. Accordingly, an enriched air-fuel mixture can be distributed locally in the combustion chamber 3 by entraining a suitable amount of injected fuel into the rolling streams R and volatilizing same acceleratedly. For this purpose, as shown in Figs. 1 and 2, the fuel injection nozzle means 5 is located substantially in a center position of the combustion chamber 3. The auxiliary nozzle hole 10 of the fuel injection means 5 is opened toward a peripheral wall 3a in the vicinity of the upstream side of the protuberance 12 in the flow direction of the swirl S1. The spark plug means 13 ist fixedly fitted in the cylinder head and a notched groove in an upper marginal edge portion of the combustion chamber 3, and its sparking end 13a is disposed in the vicinity of the protuberance of the combustion chamber 3 when the piston is moved to a position in the vicinity of its upper top dead center. On the other hand, the main nozzle holes 11 of the fuel injection nozzle means 5, the four main nozzle noles 11 in this particular embodiment, are directed toward equidistant segmental areas on the peripheral wall of the combustion chamber 3. In the present embodiment, the fuel injection nozzle means 5 is provided with only one auxiliary nozzle hole for ensuring satisfactory qualities in both ignitability and combustibility, imparting a predetermined penetrating force to the atomized fuel from the auxiliary nozzle hole relative to the intensity of the rolling streams R. Namely, in a case where only one auxiliary nozzle hole is provided, it is possible to entrap part of the injected fuel in the rolling streams R to enrich the air-fuel mixture in the rolling streams R to a suitable concentration, while letting the remainder of the injected fuel penetrate the rolling streams R and deposite in the form of a uniform thin film F1 (a liquid film) on a peripheral wall portion 3a on the upstream side of the protuberance 12 in the flow direction of the swirl S1. Thus, the rolling streams R have the function of generating a fuel vapor layer G1 of a concentration suitable for ignition and simultaneously accelerating volatilization of the fuel film F1 on the wall surface, in addition to a function of rolling in and collecting the volatilized part of the fuel. In order to disperse the injected fuel uniformly in the combustion chamber for flame propagation, the fuel injection nozzle means is provided with four main nozzle holes 11. The diameter and directions of these main nozzle holes 11 are determined such that part of the atomized fuel which is supplied to the combustion chamber is entrained on the swirl S1 and instantly volatilized by the heat of compressed air to generate fuel vapor layers G2 to G4, while the remainder of the atomized fuel deposits on the opposing peripheral wall portions 3a to form fuel films F2 to F4 thereon. The above-described combustion chamber for internal combustion engines according to the invention operates in the following manner. As illustrated in Fig. 4, in a light load condition including an engine-starting stage, the needle valve 6 of the fuel injection nozzle means 5 is lifted to a certain extent, disengaging the throttle portion 6a of the valve 6 from the valve seat 8. Since the stem portion 15 which is formed coaxially at the front end of the throttle portion 6a holds the fuel injection chamber 9 in a closed state until the valve lift reaches a predetermined value, only the auxiliary nozzle hole 10 is opened as shown in Figs. 1 and 2 to supply atomized fuel to the upstream side of the protuberance 12. Part of the atomized fuel which is supplied from the auxiliary nozzle hole 10 is enclosed by the rolling streams R and volatilized acceleratedly therein. Accordingly, a volatilized fuel layer G1 with good ignitability is distributed to the neighborhood of the sparking end 13a of the spark plug means 13, and, if a spark is produced at this time point, the volatilized fuel layer G1 undergoes rapid combustion, suppressing generation of HC. On the other hand, volatilization of the fuel film F1 is accelerated by the resulting flame energy. As a result, the volatilized part of the fuel film is entrained and confined in the rolling streams R, so that flame propagation takes place adequately on the upstream side of the protuberance 12 in the flow direction of the swirl S1, thereby effecting combustion of good quality. In medium and high load operations, the needle valve 6 is lifted in excess of the predetermined lift value to open the main nozzle holes 11. The fuel which is supplied in atomized state from a plurality of main nozzle holes 11 is partly volatilized upon contact with hot air, and carried away toward the downstream side with the swirl S1 turning in the combustion chamber 3. The remainder of the atomized fuel is deposited on the peripheral wall 3a in the form of fuel films F2 to F4, and volatilized by the heat of compressed air and the wall heat. The amount of fuel injection through the respective main nozzle holes 11 is greater than that of the auxiliary nozzle hole 10, and increased according to the load condition, supplying to the combustion an air-fuel mixture of uniform and desired concentration. At this time, the atomized fuel supplied from the auxiliary nozzle hole 10 has already been ignited and burned, so that the air-fuel mixture undergoes rapid combustion by flame propagation. As mentioned hereinbefore, the rapid combustion suppresses production of HC. In this manner, a volatile fuel of low cetane number can be burned without misfiring in a light load operating range, while achieving combustion which is satisfactory in mileage and output qualities in medium and high load operating ranges. Referring now to Fig. 5, there is shown a second embodiment of the invention. In this embodiment, a combustion chamber 103 is formed into the piston top, the combustion chamber 103 having substantially a rectangular shape in section perpendicularly across the axis of the piston. In this case, a protuberance 112 corresponding to the protuberance 12 of the first embodiment is provided, when seen in the flow direction of a swirl S2, on the downstream side of a corner portion 17 which connects adjacent peripheral walls 103a to each other. The fuel injection nozzle means and spark plug means employed in this embodiment are of the same constructions as in the foregoing embodiment. The auxiliary nozzle hole 10 of the fuel injection nozzle means 5 is directed toward the corner portion 17, while the main nozzle holes 11 are directed toward the peripheral walls 103a of the combustion chamber 103 in the same manner as in the first embodiment. The spark plug means 13 is located in the neighborhood of the corner portion on the upstream side of the protuberance 112 in the flow direction of the swirl S2. Thus, in this embodiment, the compressed air which is distributed to the corner portion 17 by fluid inertia of the swirl S2 is hardly stirred, and therefore forms rolling streams R2 which turn in the same direction as the swirl S2. Due to the existence of the rolling stream R2, the atomized fuel supplied from the auxiliary nozzle hole 10 is distributed to the corner portion 17 on the upstream side of the protuberance 112 in the direction of the swirl S2. Consequently, a volatilized fuel layer G5 is distributed to the neighborhood of the sparking end 13a by the rolling stream R1. This improves the degree of stability in ignition and combustion characteristics.

Claims: A combustion chamber for an internal combustion engine, especially for burning volatile fuel of low cetane number, comprising: a combustion chamber (3) formed by hollowing the top (2) of a piston (1) in the axial direction thereof; a protuberance (12) projecting radially inward from a peripheral wall surface (3a) of said combustion chamber (3); a fuel injection nozzle means (5) adapted to supply atomized fuel toward a peripheral wall (3a) in the neighborhood and on the upstream side of said protuberance (12) in the direction of swirl (S1) and toward other peripheral walls of said combustion chamber (3); and a spark plug means (13) located in the neighborhood of said protuberance (12) to accelerate ignition of atomized fuel supplied thereto, characterized in that the spark plug means (13) is located on the upstream side of said protuberance (12) in the direction of said swirl (S1), the protuberance (12) is located and formed in that way that a rolling stream (R) in the direction of rotation of swirl (S1) is created by said protuberance (12) in the vicinity of said spark plug means (13), the fuel injection nozzle means (5) is provided with main nozzle holes (11) for supplying said atomized fuel (F1-F4) toward a number of equidistantly spaced segmental areas on the inner peripheral wall (3a) of said combustion chamber (3) and with an auxiliary nozzle hole (10) for supplying atomized fuel (F5) such that the fuel (F1, F1) is sprayed just upstream of or toward an electrode (13a) of said spark plug means (13), such that the fuel (F1) and the fuel from auxiliary nozzle hole (10) the is not accelerated by the swirl (S1) in the direction in which the swirl (S1) flows and such that said rolling stream (R) confines the fuel (F1, F5) to create relatively fuel-rich mixture around the electrode (13a) of said spark plug means (13) whereas said atomized fuel (F2-F4) supplied toward the other peripheral walls in the direction in which the swirl flows creates relatively fuel-lean mixture outside the fuel-rich mixture area created by said fuel (F1, F5) whereby the flame built upon the combustion of said relatively fuel-rich mixture (F1, F5) propagates to combust said relatively fuel-lean mixture (F2-F4). The combustion chamber of claim 1, wherein said fuel injection nozzle means (5) is adapted to open said auxiliary nozzle hole (10) before said main nozzle holes (11). The combustion chamber of claim 1 or 2, wherein said auxiliary nozzle hole (10) of said fuel injection nozzle means (5) has a smaller open area than said main nozzle holes (11). The combustion chamber of any of claims 1 to 3, wherein said fuel injection nozzle means (5) is fixedly fitted in a cylinder head (4) and located substantially in a center position of said combustion chamber (3). The combustion chamber of claim 1, wherein said spark plug means (13) is fixedly fitted in the cylinder head (4). The combustion chamber of claim 1, wherein said protuberance (12) projecting radially inward from the peripheral wall surface (3a) of said combustion chamber (3) is extended toward the bottom thereof. The combustion chamber of claim 1 or 6, wherein the projecting protuberance (12) is gradually increased in the circumferential direction of said combustion chamber (3) and then gradually reduced after reaching a maximum point. The combustion chamber of claim 1 or 6, wherein said protuberance (12) has a bell-like shape in section taken perpendicularly across the axis of said piston (1). The combustion chamber of claim 1, wherein said combustion chamber (3) has a circular shape in section taken perpendicularly across the axis of said piston (1). The combustion chamber of claim 1, wherein said combustion chamber (3, 103) has a polygonal shape in section taken perpendicularly across the axis of said piston (1), said spark plug means (13) is located in a corner portion (17) of said polygonal shape, said protuberance (12, 112) is formed on the downstream side of said corner portion (17) in the direction of said swirl, and said fuel injection nozzle means (5) is adapted to supply atomized fuel toward said corner portion (17) and toward peripheral wall portions (3a, 103a) of said combustion chamber (3, 103). The combustion chamber of claim 10, wherein said polygonal combustion chamber (3, 103) has a square shape in section. The combustion chamber of claim 10, wherein said polygonal combustion chamber (3, 103) has a pentagonal shape in section. The combustion chamber of claim 10, wherein said polygonal combustion chamber (3, 103) has a hexagonal shape in section.

Inventors: ISHIDA, SHIRO FUJISAWA FACTORY
Applicants: ISUZU MOTORS LIMITED
Application year: 1986
Main classification: F02B23
IPC codes: F02M61, F02B23, F02B3, F02B1, F02B75