Abstract
Nitrogen dioxide (NO(2)) is an active species of exhaust gas recirculation gas, and it has a significant impact on the autoignition and combustion processes of fuels. This study presented a comprehensive investigation of the effect of NO(2) on the combustion characteristics of the n-butanol/biodiesel dual fuel. Experiments were conducted on a single-cylinder engine with 0, 100, 200, and 400 v/v ppm NO(2) addition at two fuel injection ratios. The findings of the experiments indicated that adding NO(2) resulted in an earlier start of heat release and an increase in peak in-cylinder pressure as compared to experiments where no NO(2) was added. The evolutions of n-butanol, biodiesel, and OH radicals were evaluated using the computational fluid dynamics software coupled with the n-butanol-biodiesel-NO(2) mechanism. The results revealed that when 400 v/v ppm NO(2) was added, the consumption of n-butanol and biodiesel occurred earlier, and the formation of OH radicals was approximately an order of magnitude higher before the biodiesel was injected. Furthermore, reaction rate and flux analyses were performed to understand the effect of NO(2) addition on the reaction process. When NO(2) was added, 35% of the HO(2) radicals reacted with NO which converted from NO(2) via the reaction NO + HO(2) ⇌ NO(2) + OH, promoting the formation of OH radicals in the reaction system. The addition of NO(2) can also enhance the consumption of CH(3) radicals via the reaction CH(3) + HO(2) ⇌ CH(3)O + OH.