Experimental study of the effects of different exhaust gas recirculation ratios on the flame temperature and soot formation when using diesel fuels with different T90 distillation temperatures

In this paper the diesel in-cylinder control of nitrogen oxide (NOx) and soot formation was tested. Carbon dioxide (CO₂) was used as a diluent to simulate the exhaust-gas recirculation (EGR) process at ratios of 4.3%, 9.5% and 14.3%, thus making oxygen (O₂) concentrations of 20%, 19% and 18% respectively. In addition, three diesel fuels with different T90 distillation temperatures were used. The fuel parameters were isolated from the influence of the aromatics content, sulfur content, and cetane number. A single-cylinder rapid compression machine (RCM) was used to simulate the diesel-type combustion. The ignition and combustion processes of the diesel-fuel spray were observed using high-speed direct photography. The flame temperature (an indication of NO formation) and KL factor (an indication of the soot concentration inside the diesel-fuel spray) were analyzed using the two-color method. The study demonstrated that with an increase of the CO₂ concentration in the intake charge, the maximum flame temperature and the soot formation decrease. Also, when there was a CO₂ =4.3% concentration in the intake charge, the results showed no significant influence of the diesel-fuel T90 distillation temperature on the maximum flame temperature and the soot formation.