WO2011040892A1

WO2011040892A1 - Combustion chamber of an internal combustion diesel engine

Info

Publication number: WO2011040892A1
Application number: PCT/TR2010/000118
Authority: WO
Inventors: Rafig Mehdiyev
Original assignee: Albayrak, Muzaffer; Ogun, Kurtulus
Priority date: 2009-10-01
Filing date: 2010-06-24
Publication date: 2011-04-07

Abstract

The present invention relates to the combustion chamber of an internal combustion diesel engine having at least one cylinder; at least one piston displacing linearly within said at least one cylinder, the upper part of said piston comprising a circular main combustion chamber with a geometry that resembles a truncated cone with rounded corners and with an inner cone apex at its base, when viewed from the vertical section; and an injector injecting fuel into this main combustion chamber. The piston according to this invention comprises a circular pre-combustion chamber provided at the upper side of the main combustion chamber, vertical symmetry axis of the pre-combustion chamber being substantially at the same direction with that of the main combustion chamber located on the piston.

Description

COMBUSTION CHAMBER OF AN INTERNAL COMBUSTION DIESEL ENGINE

The invention relates to self-ignition internal combustion engines employed in automotive and other industries (automobiles, tractors, vessels, heavy duty vehicles and stationary power engines) and provides for alterations in the combustion chamber of such engines, in order to increase their performance and efficiency, lower down hazardous chemical substances released out together with exhaust gases, and reduce noise emission.

Background of Invention

In a conventional engine according to the present invention, each cylinder is provided with one combustion chamber cavity having rotational symmetry on the piston. Mechanical or electronic fuel injection system is provided in engines, whereas the fuel-air mixture formation is carried out via two different methods of forming "pulverized mixture" and "wall film guided mixture":

In engines designated as "pulverized mixture" diesel engines, fuel is directly injected under high pressure into the volume of combustion chamber, without the fuel spray being allowed to become spread over the combustion chamber walls.

On the other hand, in engines designated as the "M-process" type or with "wall film guided mixture" formation, majority of fuel (>90-95%) injected under low pressure by means of a multi-hole injector is spread over the wall of combustion chamber prior to ignition and is evaporated by the heat transferred from piston walls.

It has been experimentally determined in diesel engines with "pulverized mixture" formation having combustion chamber with usual geometry, that the liquid phase of the fuel spray is situated just next to the injector holes, and that the vapor phase thereof is situated next to the liquid phase before fuel, which is being injected as soon as the compression process is finished, is ignited. The fuel spray's vapor phase present under an air setting with temperatures ranging between 650 - 800°C is immediately subjected to pyrolysis process, thereby generating free carbons, and is then ignited and combusted accordingly. As the fuel's injection pressure is increased, the spray's liquid phase is kept constant at a size of approximately 30 mm until injection is finished, whereas the processes of evaporation, pyrolysis and oxidation (combustion) are fairly accelerated. When injection pressure is increased from 500 up to 2200 bar, the fuel's essential combustion time is reduced (combustion is accelerated), the engine efficiency is increased and the soot emission thereof is substantially decreased. Another advantage of diesel engines with "pulverized mixture" formation are lower starting time and easy starting of engine under cold climate conditions. This feature allows to make use of relatively-lower capacity batteries.

The "common rail" electronic fuel injection system has been introduced widely for use in improved (up-to-date) diesel engines with "pulverized mixture" formation. In this system, fuel is injected into the volume of combustion chamber under a pressure of approximately 1400-2200 bar, by means of a multi-hole (7-8 holes) injector with low diameter (0.15-0.20 mm), so that the engine's performance and efficiency are increased and its soot emission is reduced considerably. Use of extremely-high injection pressures, however, renders both the production technology, and service requirements of the "common rail" system expensive. On the other hand, since the instantaneous ignition, and the combustion via diffused mechanism of fuel, accumulated within the combustion chamber as a result of high-pressure ignition, lead to an excessive increase in the pressure and temperature within the cylinder. Thus emission of nitrogen oxide (NO_x), which is more environmentally-pollutant as compared to carbon emission, as well as engine noise are increased. In this case, it becomes required to use gradual injection (pre-injection and then main injection and post-injections), exhaust gas recirculation (EGR), and additional complex systems such as urea solution injected catalysts to lower down NO_x emission and noise under the limits required by standards, but all such operations and processes reduce the engine's performance and efficiency and substantially increase the costs and service requirements.

In "M-Process" type of diesel engines, around 95% of fuel is tangentially-injected under low pressure (150-250 bar) at the direction of air cycle by means of an injector with no more than two holes, so that fuel is spread over the wall of combustion chamber and evaporated there with the heat transferred from wall. Since the temperature at the wall is twice lower (300 - 400°C) than that of air compressed at a ratio from 16:1 to 20:1 in the volume of combustion chamber, the rate of pressure increase during the pyrolysis process (C generation) and combustion is fairly restrained. For this reason, even if improvements are made in respect of C and NO_x emissions, the facts that the combustion rate is lowered excessively and that the flame front can die down near the cold walls reduce the efficiency of combustion process and increase the engine's fuel consumption. Therefore, "M-Process" type engines are not preferred nowadays.

Another example of diesel engines with "wall film guided mixture" formation is protected under the Utility Model Certificate N° TR 2004/01674 on behalf of MOTOSAN & R.MEHDiYEV. The cavity of combustion chamber situated on the piston of this engine provides a rotationally-symmetric volume of a frusto-conical geometry with the cone angle being 2a=80...100°. There is provided an inner cone apex with a cone angle kept in the range of 2β=130...180° at the base of cavity, and the walls and base of cavity are joined to each other at a radius determined from the combustion chamber's volume, depending on the engine's compression ratio. The orientation angle (δ) of holes of injector with at least three holes situated over the symmetry axis of the combustion chamber cavity is selected from such values, that almost all of fuel injected is spread over the combustion chamber wall, and that a "wall film guided mixture" is formed at a percentage of approximately 100%. Since injectors with three or more holes can be used in such combustion chambers, it is possible to accelerate the mixture formation and combustion processes by 100% as compared to " M-Process " type of engines, and thus to obtain an optimum combustion process, which is advantageous with respect to both performance and efficiency, and exhaust gas and noise emissions (see. Rafig Mehdiyev, Cem Soru§bay, Levent Ozgur, Hikmet Arslan, Akin Kutlar, "Dizel Motorlann Geli§tirilmesinin Alternatif Bir Yolu" ("An Alternative Way of Improving Diesel Engines") 3rd Automotive Technologies Congress", ΟΤΕΚΟΝΌ6, 26 - 28 June 2006, BURSA, Congress Book, page 57-66).

In experimental works, however, a drawback of this combustion chamber was found in that the cranking time of engine is lengthened and that the first cranking becomes difficult at cold winter seasons and particularly when air temperature is below -5°C. It has been further found that a while after cranking (until the engine temperature reaches normal limits), the engine exhaust is released in the form of "white smoke", which is rich with respect to unburned fuel or hydrocarbon compounds (HC), thereby both polluting the environment and increasing fuel consumption. The reason of this drawback is the temporary insufficiency of heat required to evaporate the fuel spread over the cold walls of combustion chamber.

In order to eliminate this drawback in current diesel engines, a combustion chamber with a novel geometry is proposed according to the present application, capable of combining advantageous features of both "pulverized mixture" formation and "wall film guided mixture" formation for use in internal-combustion diesel engines.

In order to achieve this object, this invention provides a combustion chamber for internal-combustion diesel engines having at least one cylinder; at least one piston displacing linearly within said at least one cylinder, the upper part of said piston comprising a circular main combustion chamber with a geometry that resembles a truncated cone with rounded corners and with an inner cone apex at its base, when viewed from the vertical section; and an injector, injecting fuel into this main combustion chamber. The piston according to this invention comprises a circular pre-combustion chamber provided at the upper side of the main combustion chamber, vertical symmetry axis of the pre-combustion chamber being substantially at the same direction with that of the main combustion chamber located on the piston.

Using a diesel engine with this combustion chamber provides easiness in cranking the engine and prevents "white smoke" formation, increases performance and efficiency, reduces engine costs and service requirements, and improves exhaust gas and noise emission facts on behalf of the environment. Brief Description of Figures

The combustion chamber proposed to achieve the objects of the present invention under this application is schematically illustrated in Figure 1. Figure 2 illustrates the position of piston illustrated in Figure 1 , while it is more close to the top dead center.

Figure 3 illustrates the position in which the piston is at the top dead center. List of Reference Numbers in Figures

1. Cylinder

2. Piston

3. Main combustion chamber

4. Inner cone apex

5. Pre-combustion chamber

6. Fuel spray injected

7. Injector Detailed Description of Invention In diesel engines with single or multiple cylinders, the combustion chamber situated on the piston (2) in each cylinder is composed of two rotationally- symmetric volumes, i.e. a main combustion chamber (3), which when viewed from the vertical section has a geometry resembling a truncated cone with rounded corners, and with an inner conic apex (4) at the base of the cone, and a pre- combustion chamber (5), of which the symmetry axis is substantially the same with that of the former (3). The pre-combustion chamber (5) is provided at the upper side of the main combustion chamber (3) on the piston. The diameter of the inlet (di) of the main combustion chamber (3), while the piston comes to its 1^st position relative to the top dead center (T.D.C.) at the maximum of the fuel injection advance angle (i.e. when engine is cranking or running idly), is sized so that the fuel spray (6), comprising approximately 15-20% of fuel injected per cycle under full load and having a determined cone angle (2γ=~10...15°) does not enter into this space and that the inlet diameter (di) of the main combustion chamber is preferably larger than approximately 20% of and smaller than approximately 25% of the piston diameter (D). The pre-combustion chamber (5) is larger than approximately 15% of and smaller than approximately 20% of the entire volume of combustion chamber and the formation of air-fuel mixture here during cranking and idly-running regimens of the engine is carried out via pulverization. The angular position of the base of the pre-combustion chamber (5) with respect to the horizontal axis is approximately the same with the orientation angle (a) of injector (5) holes; as for its inner limit diameter (d₂), it is sized approximately at d₂ > 2l__d, depending on the length ( ) of the fuel spray containing approximately 25% of fuel injected per cycle under full load.

At the 2^nd position, at which the piston makes an aperture with respect to the T.D.C. with the fuel injection advance becoming lowered under partial loads of the engine, some part of the fuel spray (6) is spread over the base of the pre- combustion chamber (5) and the other part thereof over the wall of the main combustion chamber (3), such that a fuel-air mixture is formed via the wall film guided method. Since the fuel injection advance gains its minimum under the full load of engine and causes the piston to come to its 3 position which is close to T.D.C., the fuel spray (6) is spread over the wall of the main combustion chamber (3) only, so that a wall film guided fuel-air mixture is formed. Filling the cylinder with fresh air during the suction process and compressing the fresh air sucked by a ratio from 16:1 to 20:1 during the compression process are carried out as with customary engines. At a time point close to the end of the compression process, fuel is injected towards the combustion chamber cavity provided on the piston (2), in the form of a fuel spray (6) with a determined cone angle (2v=~10..,15°) by means of an injector having at least three holes. The combustion chamber is composed of two rotationally-symmetric volumes, i.e. the main combustion chamber (3) and pre-combustion chamber (5) with symmetry axes substantially at the same direction. Fuel injection advance into the combustion chamber during the engine's cranking and idly-running regimens is adjusted to its maximum (0_maximum ^s 20-25° KMA), as is it case of customary diesel engines. According to this adjustment, at the 1^st position of the piston which it assumes with respect to T.D.C., S_x=f(9_max), as illustrated in Figure 1 , the fuel spray (6) injected at a determined orientation angle (a) is included entirely in the volume of the pre-combustion chamber (5) so as to form a pulverized fuel-air mixture; and under an air temperature of around 650-800°C, it is rapidly ignited even in cold winter seasons and burns without forming any "white smoke". In order to avoid the injected fuel spray (6) from entering into the main combustion chamber (3) according to these working regimens, the diameter of the inlet (di) of the main combustion chamber is sized so as to be larger than approximately 20% of and smaller than approximately 25% of the piston diameter (D).

Since the pre-combustion chamber (5) is active while the engine is under 0-20% load, its volume is larger than approximately 15% and smaller than approximately 20% of the entire volume of the combustion chamber. In order to form a volumetric mixture in this space (5), the angular position of the base of combustion chamber with respect to the horizontal axis is made the same with the orientation angle (a) of injector (7) holes; and its inner limit diameter (d₂) is sized approximately at d₂ > 21_d, depending on the length (l_d) of the fuel spray containing approximately 20% of fuel injected per cycle.

When the engine runs under partial load regimens, the fuel injection advance is reduced by one so as to come to an intermediary level ^intermediary⁵^ 0-1 5° KMA). In this case, in which the piston takes its 2^nd position with respect to the T.D.C., as illustrated in Figure 2,

some part of the fuel spray (6) is spread over the base of the pre-combustion chamber (5) and the other part thereof over the wall of the main combustion chamber (3), such that a wall film guided fuel-air mixture is formed.

Since the fuel injection advance gains its minimum under the engine's full load regimen and causes the piston to come to its 3^rd position close to T.D.C. (Figure 3), the fuel spray (6) is spread over the wall of the main combustion chamber (3) only, so that a wall film guided fuel-air mixture is formed.

Thus, the engine, having reached to the normal temperature regimen without any "white smoke" formation, starts running substantially via wall film guided -mixture formation and combustion mechanism and demonstrates a more advantageous work regimen with respect to performance, efficiency, exhaust gas and noise emissions.

After completion of the combustion process, the activated expansion and exhaust processes take place as they occur in customary engines. Thus, even in current mechanical fuel injection systems, not making use of very special and complex emission-reduction systems, inexpensive, and requiring less service as compared to the "common rail" electronic fuel injection system, the proposed novel size of the combustion chamber cavity provides for substantially-complete combustion of fuel, thereby minimizing energy losses, generation of pollutants and noise.

In result, running a diesel engine with this proposed combustion chamber provides easiness in cranking the engine and prevents "white smoke" formation, increases performance and efficiency, reduces engine costs and service requirements, and improves exhaust gas and noise emission facts on behalf of the environment.

Claims

1. A combustion chamber of an internal-combustion diesel engine having at least one cylinder (1); at least one piston (2) moving linearly within the at least one cylinder (1), the upper part of said piston (2) comprising a circular main combustion chamber (3) of a geometry that resembles a truncated cone with rounded corners and with an inner cone apex (4) at its base, when viewed from the vertical section; and an injector (7) injecting fuel into this main combustion chamber (3), characterized by further comprising a circular pre-combustion chamber (5), provided at the upper side of the main combustion chamber (3), vertical symmetry axis of the pre-combustion chamber (5) being substantially at the same direction with that of the main combustion chamber (3) located on the piston (3).

2. A combustion chamber according to Claim 1 , characterized in that the diameter of the inlet (di) of the main combustion chamber is larger than approximately 20% of and smaller than approximately 25% of the piston diameter (D).

3. A combustion chamber according to Claim 1 , characterized in that the pre- combustion chamber (5) is larger than approximately 15% of and smaller than approximately 20% of the total volume of combustion chamber.

4. A combustion chamber according to Claim 1 , characterized in that the angle which the base of the pre-combustion chamber (5) makes with the horizontal axis is approximately the same with the orientation angle (a) of the injector (7) holes.

5. A combustion chamber according to Claim 1 , characterized in that the inner limit diameter (d₂) of the pre-combustion chamber is correlated to the length (l__d) of the fuel spray, including approximately 20% of fuel injected per cycle under full length, by d₂≥ 2