Investigation of soot formation in laminar diesel diffusion flame by two-color laser induced incandescence

Soot emissions in the combustion process of diesel engines are greatly harmful to the environment and human health. Consequently, there is large interest and great efforts in decreasing soot emission from diesel engines to meet the increasingly stringent emission standards. The mechanisms of soot formation and oxidation so far have not been well understood. Laser induced incandescence (LII) is particularly suited to measure the instantaneous spatial distribution of the soot volume concentration, which can offer much needed detailed information of soot distribution for better understanding of soot formation and oxidation. In this paper, a two-color laser induced incandescence (2C-LII) technique was implemented for measuring absolute soot volume fraction in a laminar diesel fuel diffusion flame. Based on LII signal of the same point in the flame recorded at two wavelengths, the temperature of the laser-heated soot particles was first derived and then the soot concentration of the point could be acquired by calibration at the same time. The 2D soot concentration distribution in the flame was obtained by mapping. Measurements were performed in a laminar diesel and biodiesel/air diffusion flame by 2C-LII. It was found that with the biodiesel blended in the diesel fuel, the maximum soot concentration and the soot distribution area decrease, which are consistent with the test results of diesel engines.