RU2177553C2 - High-speed direct-injection diesel engine - Google Patents

Abstract

FIELD: mechanical engineering; diesel engines. SUBSTANCE: high-speed diesel engine with direct injection of fuel through nozzle 11 into combustion chamber 9 of piston 8 has valve-actuating mechanism, consisting of cylinder head 1 with intake gas channels 2 creating swirling of air at inlet in cylinder 3, and exhaust valves 4, and also exhaust gas channels 5 and 6 with valves 7 combined in to exhaust manifold 12. Exhaust gas channels 5 and 6 are made to provide forming of swirl in cylinder 3 under action of exhaust gases with direction corresponding to direction of swirl built by intake gas channels 2, thus providing automatic change of swirl intensity in inverse dependence from engine speed and direct dependence from engine load which increases engine power output and reduces fuel consumption. EFFECT: provision of optimum swirl inside cylinder before compression without additional devices at intake. 2 cl, 2 dwg

Description

 The invention relates to the field of mechanical engineering and can be used in the engine industry in the development of the working process of diesel engines with direct fuel injection.

 In existing diesel engines with undivided combustion chambers, air inlet swirling is used to efficiently burn the fuel injected through the fuel nozzle. This ensures the creation of a stable vortex in the cylinder of the engine, which remains until the compression of fresh air charge is completed and ensures good mixing of the fuel with the oxidizing agent (air) at a moderate rate of fuel burnup. Excessively fast combustion leads to shock loads on engine parts, which increases noise, reduces the life of a diesel engine and increases harmful emissions of nitrogen oxides, and slow combustion leads to a decrease in efficiency, overheating of the engine and an increase in the proportion of unburned fuel (hydrocarbons).

 When developing an engine, an acceptable compromise is always determined on the speed of turbulence of the air flow at the inlet to the cylinder to obtain good performance in terms of power, fuel consumption and the mandatory implementation of legislative standards for harmful effects on the environment (noise, toxicity). However, the search for such a compromise for a high-speed automobile diesel engine is very time-consuming and controversial in many respects. For engines operating in stationary, or close to this modes, to find such a solution is relatively easy. Another thing when it comes to a car engine with a wide range of load changes from idle to maximum power and revolutions from 700 ... 800 to 4500 ... 5000 rpm. The required rapid change in speed in such a wide range leads to the need for a significant complication of the engine design, in particular the intake system and gas channels in the cylinder head. For low engine speeds, an increased intake vortex is required. This is also due to a decrease in the fuel injection pressure with a traditional high-pressure fuel pump, and, consequently, to a worse atomization of the fuel jet flowing out of the nozzle and to an increase in the running time (cycle), i.e., the time of heat loss to the cooling system. These components worsen engine efficiency and high-speed engine developers are striving to increase the fuel injection pressure (this problem is particularly well solved by using battery-type fuel equipment that does not have a direct dependence of the fuel pressure on engine speed) and increase the burning rate to reduce environmental losses. This can be achieved by increasing the inlet air swirl. However, with an increase in engine speed, air re-turbulence occurs in the cylinder, because the inlet tract (gas channels) goes into high air flow and its shape-forming surface intensifies the vortex component of the air flow excessively. In the ideal case, for each mode of engine speed and load, its own form of gas channels is required. Since there is no real possibility of doing this, the gas channels are projected at some average rpm value, usually this is the maximum torque mode, so under-revolutions occur at low revs, and re-vortex at high revs. To expand the speed range with an optimized vortex, inlet vortex control devices are used. A known method of tuning the inlet gas channel to a low speed range (see US patent N 4834035 from 05.30.89, MKI F 02 B 31/00). At high speeds, air is supplied through an additional channel, which reduces the vortex-forming ability of the main channel (i.e., the additional air flow counteracts the main one). To control this process, a shutter is installed in the additional channel, which is controlled by the relationship with the engine speed and load.

 Due to the fact that in modern high-speed automobile engines, a design with four valves per cylinder (two inlet and two exhaust) is increasingly being used, one of the inlet channels is equipped with an air damper, which, depending on the engine operating mode, provides air inlet into the cylinder through one or two inlets. When the shutter is closed, air enters the cylinder through one channel, the air velocity in it increases, which makes it possible to intensify the vortex at the inlet. When the damper is open, air enters through two channels, therefore, in the channel, which is constantly open, the air speed decreases, and therefore the vortex at the inlet. This technical solution was applied on Opel Ecotek diesel engines (see MTZ N 9-97) and on a Mercedes Benz OM 611 diesel engines (see MTZ N 10-97). The above solutions require special additional control devices (actuators: shutters in special spacers, closing pneumatic chambers, pneumatic chamber control valves) and control (separate or integrated modules analyzing the engine operating mode). This increases the cost of the engine and reduces its reliability.

 The essence of the invention is the creation of the design of a high-speed automobile diesel engine, ensuring the organization of the optimal vortex inside the cylinder before compression without additional devices at the inlet.

 The specified technical result is achieved in that in order to ensure good filling of the cylinders with a fresh air charge and good purification from exhaust gases, the gas distribution phases for the engine are selected taking into account the inertial and wave phenomena occurring in the inlet and outlet ducts. This leads to the fact that the valve timing, in particular a four-stroke engine, is the so-called phase overlap, i.e. the exhaust phase of the exhaust from the cylinder has not yet been finalized, but the inlet phase is already beginning. For four-stroke engines with a valve timing, this leads to the fact that in the area where the piston is located at top dead center (TDC) with the exhaust valves not yet closed, the intake valves open. The vast majority of modern automotive diesel engines with an undivided combustion chamber have a flat lower part of the cylinder head and a piston with a flat bottom with a chamber placed in it. This design ensures the most efficient use of the air received in the cylinder for combustion (oxidation) of fuel, because between the two flat surfaces it is possible to create the smallest parasitic volume of air that did not enter directly into the combustion chamber (the best value of the so-called “k” factor), however, the flat piston surface sharply narrows the boundaries of possible phase overlap due to the probability of collision between the piston and valves however, phase overlap exists on all engines. To expand the overlap, often in the piston or in the cylinder head, tapping is performed to provide the necessary clearance between the valve plates and the piston bottom, thereby worsening the "k" factor. There are other ways to place single-cavity combustion chambers in diesel engines, however, the implementation of the overlapping of the gas distribution phases is solved in almost the same way.

 Consider the gas exchange processes that occur in the area where the piston is located at the top dead center at the end of the release and the beginning of the inlet. The completion of the release from the cylinder is accompanied by the expulsion of exhaust gases by a piston moving towards the TDC. To avoid the formation of increased pressure in the cylinder due to compression of the exhaust gases, the exhaust valves (valve) are tried to be kept open until the cylinder is completely cleaned. Since the law of movement of the valves during closing is severely limited by the physical capabilities of the valve and valve seat materials at the maximum valve seating speed to ensure the required life of this interface, the landing is relatively smooth, and the annular gap between the seat and valve also decreases smoothly. At high engine speeds (more than 2500 rpm), in order to prevent the exhaust gases from preloading in the cylinder due to the limited time for the exhaust completion process, the exhaust phase, taking into account the above-mentioned features in the smooth operation of the valve mechanism, requires completion of the piston at TDC much later . For the purpose of high filling of cylinders with a fresh charge, the intake phase must be started much earlier than the piston TDC. In this case, the position of the valves is observed when both the inlet (inlet) and outlet (outlet) valves are open. At high speeds due to the small value of the time of this state and the significant inertia of the gas flows, there is practically no gas flow between the inlet and outlet. However, what is permissible for high revolutions (the time for processes to proceed is relatively short) for low revolutions leads to a significant flow of gases between the inlet and outlet (the time for these processes to increase is a multiple of the decrease in engine revolutions). These processes significantly degrade engine performance at low engine speeds. Therefore, the valve timing is almost a compromise between the requirements of organizing work at high and low engine speeds. In many cases, to solve this problem, the range of revolutions from minimum to maximum is sharply limited. However, for high-speed diesel engines, which must operate in the range from 700 ... 800 to 4500 ... 5000 rpm, the flow of gases in the lower speed range significantly worsen their performance. This is of particular importance for turbocharged engines, where the gas distribution phases play a dominant role in the efficient operation of the turbocharger.

 In multi-cylinder engines, adjacent cylinders also act on the processes of gas flow during the period of the gas distribution overlap, since usually the intake and exhaust pipelines have inlet (outlet) volumes (pipelines) common for the engine, through which the cylinders interact. For engines with gas turbine supercharging, the turbocharger is usually located on the exhaust manifold, combining from 2 to 6 or more cylinders. In this case, the following phenomenon often occurs. A pressure impulse enters the cylinder in which the exhaust process is completed from the exhaust manifold from one of the cylinders in which the exhaust process is just beginning, and part of the exhaust gas is returned to the cylinder. This is the so-called discharge of exhaust gases from the exhaust system into the cylinders in which the exhaust valves have not yet closed. Typically, the exhaust gas channels are designed so that the cylinder can be cleaned to the fullest extent possible, that is, the gas channels must have low aerodynamic losses, especially during the initial period of release, when the pressure in the cylinder is still high and in the opening gap between the valve and the valve seat exhaust gas comes at a tremendous speed, in separate modes exceeding the speed of sound. The desire to reduce losses at the outlet in the initial phase leads to the fact that at the end of the release under the influence of a pressure pulse from the initial process of exhausting from an adjacent cylinder, the exhaust gas is thrown into the cylinder, where the exhaust ends. Particularly large emissions of exhaust gases occur at low engine speeds, when a sufficient time period appears for this process. Since the piston is near TDC during this period, the free (remaining) volume of the cylinder and the combustion chamber is additionally filled with exhaust gases, and some of the exhaust gases also enter the inlet channels due to phase overlap. To create, in the future, the necessary vortex of an air charge during the inlet to the cylinder, additional energy will be required to organize the rotation of the exhaust gases thrown into the cylinder. There will also be a loss of part of the vortex on the compression stroke when the fresh charge flows into the combustion chamber already filled with abandoned exhaust gases, and this part of the vortex losses must be compensated for by the high level of the vortex at the inlet.

 Summarizing the phenomena considered and the requirements for the operation of the inlet gas channels, the overlap of the gas distribution phases and the presence of exhaust gas throwing into the cylinder, it can be noted that for low revolutions special measures are required to ensure an intensive vortex at the inlet, i.e. application of inlet gas channels creating a more intense vortex. In the engine, this will simultaneously lead to unjustified losses at high speeds, due to the increased aerodynamic drag of such gas channels.

 To resolve the contradiction, the present invention proposes to form the outlet (outlet) gas channels (channel) so that the discharge of exhaust gases into the cylinder leads to the formation of a vortex in the cylinder with a direction corresponding to the direction of the vortex created by the inlet (inlet) gas channels. Such a process can be implemented by performing the exhaust channels in the following way: the exhaust gas channels should be directed along the turbulence of the exhaust gas stream; one of the exhaust gas channels is performed below the other exhaust gas channel by an amount determined by the required degree of turbulence, in each case selected experimentally. This will allow at a low engine speed to significantly intensify the vortex of gases in the cylinder and in the combustion chamber, thereby improving the flow of this process in the initial intake period. At high speeds, due to the smaller time effect of phase overlap on reverse casting, this will not lead to re-turbulence of the air charge in the cylinder and in the combustion chamber. Since the value of the reverse charge of the exhaust gases in the cylinder is directly related to the load (i.e., the cyclic supply of fuel and the resulting gas volume as a result of combustion), this will automatically increase the turbulence in the engine load. Inlet gas channels with relatively moderate vortex formation, which can be used in this case, will improve their aerodynamic characteristics, i.e. increase the filling ratio at high speeds and, as a result, increase engine power and reduce fuel consumption.

In FIG. 1 shows a device of a high-speed diesel engine with the proposed solution for organizing the working process and gas turbulence in the cylinder, front view; in FIG. 2 - the same, top view. The high-speed diesel engine device shown in the drawing consists of the following elements:
- a cylinder head 1 with inlet gas channels 2, creating a swirl of air at the inlet to the cylinder 3, inlet valves 4, as well as exhaust gas channels 5 and 6 with exhaust valves 7;
- a piston 8 with a combustion chamber 9 in the piston bottom 10;
- a fuel injector 11 through which fuel is injected into the combustion chamber 9;
- exhaust manifold 12, combining the exhaust channels of the cylinders of a multi-cylinder engine.

 The engine operates as follows. When the piston 8 approaches the TDC position on the exhaust stroke, the cylinder 3 is cleaned of exhaust gases through the exhaust channels 5 and 6 with valves 7. Valves 7 are in the process of moving towards closing, but are still not completely closed. This is done to ensure good cleaning of cylinder 3 at high engine speeds. Inlet valves 4 are already open at this time. This is done to well fill cylinder 3 with a fresh charge of air at high engine speeds. The delay in closing the exhaust valves 7 and the timing of the opening of the intake valves 4 are necessary to coordinate the inertial and wave processes of the intake and exhaust and the operation of the valve mechanism with low wear. In a multi-cylinder engine, the exhaust system usually combines several (in groups of cylinders) or all cylinders into a common line (system) for supplying exhaust gases to the exhaust silencer, and in a turbocharged engine to a turbine. In this regard, pulsating flows of exhaust gases flow in the exhaust manifold 12, creating pressure waves from each cylinder. With a uniform cylinder operation, which all ICE developers strive for, for smooth and low noise engine operation, it usually turns out that the completion of the exhaust process in one of the cylinders coincides with the start of the exhaust process in the other cylinder. This leads to the fact that in the final phase of the exhaust for the cylinder 3 from the manifold 12 through the exhaust channels 5 and 6, a portion of the exhaust gases is thrown again into the cylinder 3 and the combustion chamber 9. The exhaust process is accompanied by high turbulence of gas flows. This is especially evident at the time of exhaust gas injection into cylinder 3, because in this case, the gas flows change in the opposite direction. In order to not create conditions at the same time in the cylinder 3 and in the combustion chamber 9 for counteracting the vortex from the gas inlet channels 2, the shape of the exhaust channels 5 and 6 is performed so that during this period they create a vortex in the cylinder and in the combustion chamber in the same direction as the inlet gas channels 2. For this, the exhaust gas channels 5 and 6 should be directed along the turbulence of the exhaust gas stream (see Fig. 2); the exhaust gas channel 6 is lower than the exhaust channel 5 by an amount determined by the desired degree of turbulence, in each case selected experimentally (see Fig. 1). During the casting period, the intake valves 4 are already ajar, and some of the exhaust gases rush into them. Since the movement of gases coincides with the direction of the vortex that these channels form, in the neck of the inlet channels 2 the direction of swirl of the gas flows does not change, thereby creating favorable conditions for the formation of an intense vortex during the inlet. In addition, this vortex at the outlet is superimposed on the already formed vortex in the cylinder 3 and the combustion chamber 9, thereby strengthening it. The greater the intensity of the discharge of exhaust gases into the cylinder 3 and into the combustion chamber 9 (in proportion to the load on the engine), the more intense is the total vortex during the intake process. A similar amplification of the vortex occurs with an increase in the time of casting of exhaust gases, which is typical for low engine speeds. At high engine speeds, the gas flow processes under consideration change in the direction of reducing the exhaust gas discharge intensity due to a decrease in the length of time for these processes and a significant increase in the inertia of gas flows.

 Thus, due to reflux of the exhaust gases, the change in the intensity of the vortex of the fresh charge is automatically controlled inversely with the engine speed and directly dependent on the load, i.e., the cyclic fuel supply through the nozzle 11 and, accordingly, from the exhaust gas flow from the engine cylinders.

 The considered processes occur only during the period of exhaust emissions, i.e. with small valve openings, this especially applies to exhaust valves. Therefore, the shape of the exhaust gas channels is carried out taking into account that in the process of cleaning the cylinder of exhaust gases, the channels would have low resistance for the flow of gases from the cylinder to the exhaust manifold, and when throwing exhaust gases, i.e. when gases flow from the exhaust manifold into the cylinder, the directional gas flow in the cylinder and the combustion chamber with the organization of the vortex coincides with the direction of the vortex in the gas inlet channels. The above applies to the execution of the engine with one inlet and one outlet channels and valves.

Claims (1)

 A high-speed diesel engine with direct injection of fuel into a single-cavity combustion chamber having a valve gas distribution mechanism with overlapping valve phases and with inlet gas channels creating a directed vortex of fresh gas charge in the engine cylinder, characterized in that the exhaust gas channels are made such that when the exhaust of gases from the exhaust manifold to the engine cylinder, the directional movement of gases created a vortex in the same direction as in the intake channels, providing m the most automatic change in vortex intensity at the inlet is inversely dependent on engine speed and directly dependent on engine load.

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