The spray behavior of direct-injection spark-ignition (DISI) engines is crucial for obtaining the required mixture distribution for optimal engine combustion. The spray characteristics of DISI engines are affected by many factors. In this study, the effect of injector temperature was particularly investigated.
Spray images from slit injectors using Mie scattering and shadowgraph techniques showed that spray penetration decreases and spray width increases at higher injector temperature. However, opposite trend has been observed for the spray structure from swirl injector. Phase Doppler Anemometry (PDA) results showed, for both injectors, a reduction in droplet sizes at higher injector temperatures.
The effect of injector temperature using the slit injector on engine combustion during cold start and warming-up operating conditions was also investigated. Successive flame images using high speed camera, engine-out emissions and performance data have been analyzed. During the homogeneous mode of combustion, results showed that, it is always beneficial to increase the injector temperature to achieve faster stable combustion, lower total hydrocarbon (THC) emissions and higher indicated mean effective pressure (IMEP). However, during the stratified mode of combustion, an optimum injector temperature exists. In cold start engine mode, increasing the injector temperature causes fast burning rate during the early stage of combustion. However, in warming up engine conditions, a very low combustion rate is observed. In the late stage of combustion process, the trend becomes different depending on engine operating conditions.