Experimental Research Of In-cylinder Mixture Formation Of An Air-assist Direct Injection Engine

Enviormental and energy problems are important guidelines of the internal combustion engine's development. Car emission and the specific fuel consumption must be lowered to meet the strigent regulations and high fuel price. GDI engines can realize low BSFC and CO2 emission, due to which this technology has become an important research direction.One of the most important aspects about GDI is the match between fuel injection system and the engine's combustion system, through simulation or experimental instrumentalities an ideal mixture formation can be obtained, as a result combustion and emission performance will be promoted .In-cylinder mixture formation is a key problem of GDI engine. By means of optic instrument the mixture formation can be filmed. In this paper, in-cylinder mixture formation was obtained using high-speed camera.First, experiment of spray characteristic of low pressure air-assist injection was carried out; and then a transparent optic engine based on the prototype engine was developed; finally, in-cylinder mixture formation was shoot by high-speed camera. The results showed that:First, spray penetration and the cone angle droped when back pressure rose. Fuel injection pressure increased in proportion with penetration, but cone angle didn't chang. Incrament of fuel injection pulse width made the automization worse, antithetically air injection pulse width and fuel injection pressure were in proportional to the automization quality.Augemnt of injection interval between fuel and air can increase the automization qulity when it was below 5ms.Secend, based on the parameters of proto-entgine a transparent optical engine was developed, and the in-cylinder mixture formation process was filmed by means of high-speed camera. The research results showed that: guiedence of the combustion chamber with decentralized cavity piston was better than that of the proto-engine's combustion chamber; fuel injection timing played a key role in forming the mixture formation, a good one can be obtained if choosing the injectiong timing when intake flow was not that strong and the piston moved in the middle position of the cylinder, 60°CA ATDC was chosen to be the optimized result; when the intake flow is strong, an increased engine speed can accelerate the evaporation of the fuel droplets, and at the same time the combustion chamber geometry had an effect on the development and distribution of the fuel spray. On the contrary, when the intake flow was weak, higher engine speed can promote the effect of combustion chamber's guidance to the fuel plume.