Effect of Ambient Temperature and Oxygen Concentration on Ignition and Combustion Process of Diesel Spray

The mixture formation prior to the ignition process plays as a key element in the diesel combustion. Parametric studies of ignition process in a low oxygen concentration and low ambient temperature have received considerable attention in potential for reducing emissions. Purpose of this study was to clarify the effects of ambient temperature and oxygen concentration parameters during ignition delay period which have to be significantly influences throughout the combustion process that strongly affects the exhaust emissions. This study investigated the effects of ambient temperature and oxygen concentration on diesel combustion fundamentally using rapid compression machine. The detail behavior of mixture formation during ignition delay period was investigated using the schlieren photography system with a high speed camera. This method can capture spray evaporation, spray interference, mixture formation and flame development clearly with real images. Ignition process and flame development were investigated by direct photography method using a light sensitive high-speed color digital video camera. The sensitive camera can capture flame development clearly with the mixture of dark, bright and blue flames. The oxygen availability and ambient temperature are important variable that strongly affect to the fuel evaporation, endothermic and pyrolysis process during ignition delay. Decreased ambient temperatures, the ignition delay period is extended and enhanced fuel-air premixing which promotes the initial heat release. However, lowering oxygen concentration in volume slightly increases the ignition delay and generates low-luminosity flames at ignition. The flames develop very slowly to the combustion chamber. This type of flame development produces two-stage history of heat release rate after ignition. Further, initial heat generation after ignition is strongly dependent on oxygen mass concentration.