The small enhanced technology that synergizes in-cylinder direct injection and turbocharging has good power and fuel economy, and has become a trend in the development of gasoline direct injection engines. However, the enhanced technology has sharply increased the thermal load in the cylinder. It is easy to cause engine knocks, which is currently one of the main limiting factors in improving the performance of direct injection gasoline engines. This paper discusses the influence of direct injection of water into the cylinder on the combustion of gasoline direct injection engines through numerical simulation. The gasoline engine is induced to knock by increasing the compression ratio and advancing the ignition timing. The influence of the water injector (six nozzle holes) layouts (direct water injection in the cylinder) and the water temperatures on the water movement in the cylinder and on the combustion and knock is explored. The in-cylinder water injector and the fuel injector are injected with two nozzles. Results show that when the water injector is arranged in the center of the cylinder head, the water evaporation in the cylinder before ignition is faster. Most of the water is located near the cylinder wall surface, which can reduce the temperature near the wall surface as much as possible and suppress the knock. Therefore, the effect of suppressing knocks is better. The injecting water is advantageous to make the mixed gas distribution uniform and the turbulent kinetic energy high when its temperature is low.
Response surface method is used to build models for predicting an octane number and determining the component proportions of a gasoline surrogate fuel. The fuel is synthesized using toluene, iso-octane, and n-heptane and is referred to as toluene reference fuel. The built models include second-order model and third-order model. Both models can excellently predict the octane number of the toluene reference fuel with known component proportions. Moreover, the third-order model is more accurate than second-order model in determining the component proportions of the toluene reference fuel, and the relative error is less than 8%. Therefore, the third-order model can accurately predict the octane number and determine the component proportions of the toluene reference fuel. Moreover, a new reduced mechanism of the toluene reference fuel is proposed and validated by using shock tube ignition delay and in-cylinder pressure in a homogeneous charge compression ignition engine. The toluene reference fuel mechanism coupled with third-order model is used to simulate the ignition delay of American gasoline (RD387) and the homogeneous charge compression ignition combustion behaviors of European gasoline (ULG95). Both cases are simulated thoroughly.
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