Experimental research on effects of biodiesel fuel combustion flame temperature on NOX formation based on endoscope high-speed photography.

Biodiesel has the potential to be used as an alternative to diesel fuel, while NO X emissions from biodiesel engine are higher than those of diesel engine. According to the Zeldovich mechanism, thermal NO is the main pathway for NO X formation. Therefore, studying the temperature of biodiesel combustion flame is of great significance for understanding the formation mechanism of NO X. Hence, this paper is devoted to the investigation of effects of biodiesel combustion flame temperature on NO X formation by using Endoscope high-speed photography. The experimental work has been carried out on a diesel engine fueled with three different blending-ratios of biodiesel/diesel fuel (B0, B50, B100). The image of the engine combustion process was captured by high-speed endoscopic photography, and the flame temperature field distribution was calculated based on the brightness of the in-cylinder combustion flame image. The parameters of in-cylinder flame temperature and their changing laws with engine speed and blending-ratios were also analyzed by using six indicators, such as NO X formation flame area ( S NO ), flame area change velocity ( V NO ), mean flame area change velocity ( V NO M ), flame area duration ( ϕ NO ), flame appearance efficiency ( η NO ) and adiabatic flame temperature ( T P ). Results showed that with the increase of biodiesel fuel proportion, the positions of S NO appearance and disappearance were advanced, the peak values of S NO , V NO V NO M , η NO became greater, and ϕ NO became shorter, which indicated that more beneficial environment to NO X formation occurs as biodiesel fuel proportion increases. • Endoscope high-speed photography is used to capture the engine combustion process. • It provides a new method to calculate the in-cylinder flame temperature. • Six evaluating indicators are proposed to analyze the flame temperature characteristic. • It is found that the NO X formation environment of biodiesel is better than diesel. [ABSTRACT FROM AUTHOR]