Numerical Study of Diesel Lift-Off Flame and Soot Formation under Low-Temperature Combustion

Abstract

The effects of mixture formation on soot were studied for diesel lift-off flame under low-temperature combustion (LTC) through comprehensive numerical analysis in this work. The predicted results of lift-off length, ignition time, and soot were validated against the experimental data under various ambient conditions. The results indicated that, when the O 2 concentration decreases gradually from 21 to 12% at 14.8 kg/m 3 , the distribution ranges of both the fuel/air equivalence ratio (ϕ) and combustion temperature (T) of the mixture could be further away from the formation ranges of both high soot and high NO x . However, when the ambient density increased to 30 kg/m 3 , the effect of a decreasing O 2 concentration on lowering the combustion temperature of the dense mixture within the range of ϕ > 2.0 was not significantly the same as that at 14.8 kg/m 3 . Furthermore, the ignition time, the lift-off length, and the pressure rising rate during the initial stage after ignition changed much less with the decrease in the O 2 concentration. However, the LTC at 30 kg/m 3 could lower CO significantly and bring higher densities of OH and O 2 , contributing to soot oxidation.

An Experimental Investigation into Combustion Fitting in a Direct Injection Marine Diesel Engine

“…When modeling the turbulent flow, it is important to calculate the average chemical reaction rate and the turbulent combustion rate of fuel [10,11]. Yu et al used the characteristic time combustion model coupled with the chemical kinetic mechanism to study the mixture formation's influence on the smoke [12]. Cheng et al studied the methyl esters of soybean and coconuts formed by spray combustion and related emissions of the diesel engine and further to the effect of EGR on these biodiesel fuel combustion [13].…”