As a result of the increase in the compression ratio, the pressure in the cylinder will be too high, so that gasoline cannot be injected into the combustion chamber smoothly. At this time, a high-pressure gasoline pump and a high-pressure spiral injector must be used to cope with it. Generally, the pressure of the fuel supply system of a GDI engine can be It reaches above 50.Okg/cm, which is much higher than that of a general engine with fuel injection from the general intake port. The GDI engine is also different from the general engine in the intake duct. In order to control the flow path of the intake air flow, the GDI engine uses vertical intake ducts and concave bowl-top pistons. This combination is mainly to achieve laminar lean combustion to save The basic principle of fuel is to use the special shape of the concave bowl-top piston to match the high-pressure spiral injector to control the richer oil and gas around the ignition point of the spark plug. Therefore, even if the air-fuel ratio of the mixture is as low as 40:1, GDI The engine can still operate smoothly and produce the same power. Because of the large increase in fuel supply pressure and compression ratio of GDI engines, the materials used for the various parts of the engine need to be more robust and durable. Because GDI in-cylinder direct injection only performs fuel injection when the engine compression stroke is not due, the ignition timing needs to be more accurate than the intake port injection, so the high-precision computer ECU is also very important when designing the engine. One ring. The stratified lean combustion technology is derived to overcome the slow combustion rate and incomplete combustion of the port injection engine. After years of research and development, the current in-cylinder direct injection system can only be achieved around the spark plug. With mixed oil and gas, the other parts of the combustion chamber are entirely air, so the limit of lean combustion can be greatly increased to below 40:1, so the fuel consumption must be much lower than that of ordinary engines.
How does the GDI engine output high horsepower? We know that a naturally aspirated engine modification must be done to increase the compression ratio and intake and exhaust. This is why the GDI engine can provide high output, because the high compression ratio is originally the GDI engine and Naturally, the high-inertia airflow caused by the vertical high-efficiency air intake can also promote the air to flow into the combustion chamber more quickly. The piston reaches the bottom dead center, and the air forms a rolling airflow in the cylinder. When the piston is in the compression stroke. The fuel is sprayed into the curved groove above the bowl top piston in a cylindrical shape, causing high concentration of oil and gas to collect around the spark plug. When the piston reaches the top dead center. The spark plug ignites the mixed gas. High-inertia airflow caused by vertical high-efficiency intake ducts. When the GDI engine is operating, it usually uses the ultra-lean burn mode at low speeds and the high output mode at high speeds. The fuel injection time of high output mode is completely different from the fuel injection time of ultra-lean combustion. When the GDI engine is in ultra-lean combustion mode, the fuel injection action is in the compression stroke, and the fuel injector directly injects the high-density fuel. To the surface of the groove on the top of the bowl, so that there is a thicker gas surrounding the ignition point of the spark plug to achieve the purpose of stratified combustion; while the high output mode is to inject fuel during the intake stroke, which is the same as the normal intake engine. , In a homogeneous state to improve combustion efficiency, and use oil and gas to reduce cylinder temperature.
Usually the ultra-lean combustion mode is used at low speeds, and the high output mode is used at high speeds. As long as it is internal combustion, increasing the volumetric efficiency and lowering the engine temperature can improve its performance. GDI engines have both. Since gasoline is not mixed with air before entering the cylinder, the air intake density can be improved. From another point of view, the GDI engine can absorb a lot of heat after the gasoline is sprayed in the cylinder, so it can effectively reduce the temperature in the cylinder, suppress the occurrence of knocking and increase the density of the mixture; therefore, in the above Under the two-pronged approach of two advantages for engine operation, the GDI engine can easily achieve the goal of high output. Experiments have shown that the direct injection engine is about 10% higher in torque and 10% higher in horsepower than the port injection engine.
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