To analyze the combustion phenomena of DI diesel engines in detail, the “cross-correlation method” and the “two-color method” have been applied to measure the combustion flame motion and the flame temperature, respectively by processing the high speed photographs. The purpose of this investigation is to study the effects of engine parameters such as pumping rate, injector nozzle hole size, and injection timing on combustion processes; particularly on flame motion and flame temperature.
The results showed that the flame motion was more active during the injection period; and after the end of injection, the motion of flame was largely governed by the air swirl. Increasing fuel pumping rate and using a small hole area injector nozzle, caused the flame motion to become more active, especially during the injection period.
The flame temperature was higher with both increased pumping rate and advanced injection timing. Using a small hole area injector nozzle, the results showed that the flame temperature was lowered in the premixed combustion stage and increased in the diffusion combustion stage.
Experimental results concering flame motion and flame temperature under different operating conditions are shown to correlate well with engine data such as heat release rate and changes in engine exhaust gas emissions of NOx, black smoke, etc.