Effect of exhaust gas recirculation and hydrogen direct injection on combustion and emission characteristics of a n-butanol SI engine

Abstract

The n-butanol as a clear and renewable biofuel is considered an ideal alternative fuel for SI engines. Hydrogen as a partial alternative fuel can improve the combustion and emissions of SI engine because of its advantages of low ignition energy, fast flame propagation and so no. In order to decrease the additional NOx caused by hydrogen addition, the cooperative effect of EGR and hydrogen direct injection on combustion and emission in an SI n-butanol engine was investigated in this paper. Experiments are conducted at five hydrogen addition ratios (0%, 5%, 10%, 15%, 20%), five EGR ratios (0%, 5%, 10%, 15%, 20%) and three excess air ratios (1, 1.1, 1.2) with 1500 rpm of engine speed. The results indicate that Ttq, Pmax, dQmax and Tmax decrease with the increasing ηEGR and increase with the increasing φH2, while the APmax, AdQmax, θ0–10 and θ10–90 show the contrary tendency. The 15% EGR rate cooperate with 10%~15% hydrogen addition ratio can keep emissions (HC, CO, NOx) better than the original engine. Compared to the original pure butanol engine, the n-butanol engine with hydrogen direct injection and EGR could obtain better comprehensive performance through the coordinated control of φH2 and ηEGR. More specifically, 15% EGR rate cooperated with 10% hydrogen addition ratio can obtain better comprehensive performance of combustion and emission, but there is a little expense on combustion parameters compared to the original engine under λ = 1. So the 15% EGR ratio is considered a superior EGR ratio cooperated with hydrogen addition.