A Comparison of Two Injectors in Mixture Preparation for a High Tumble GDI Engine - A CFD Study

Of late direct injection engines are replacing carbureted and port-injected engines due to their high thermal efficiency and fuel economy. One of the reasons for the increased fuel economy is the ultra-lean mixture with which the engine operates under low loads. Under the low load conditions, the air-fuel ratio of the mixture near the spark plug is near stoichiometric values while the overall mixture is lean, which is called stratified mixture. In order to achieve this, proper air motion during the late stages of compression is a must. Quality of the mixture depends on the time of injection as well as the type of fuel injector and mixture preparation concept used. Engines employing air-guided mixture preparation are considered as the second-generation engines. The air-guided mixture preparation method uses either swirl or tumble in preparing the mixture. The swirl injector which has traditionally dominated the GDI engine is currently being replaced by high-pressure multi-hole injectors, which is an evolving technology. Hence a study is conducted on a high-tumble GDI engine with swirl and multi-hole injectors to find out the equivalence ratio of air-fuel mixture near the spark plug gap for different injection timings (90°, 180° and 270°). The results reveal that multi-hole injector with late injection provides a better mixture distribution and combustion compared to swirl injector.