Chemical kinetic investigation on NOx emission of SI engine fueled with gasoline-ethanol fuel blends

Understanding the nitrogen oxide (NOx) formation chemical kinetic mechanism and analyzing the effect of relevant influence parameters are the effective strategy for NOx emission control. Based on the essential role of ethanol-gasoline blends among oxygenate alternative fuel, the experiments in a GDI (gasoline direct injection) SI (spark ignition) engine and the chemical kinetic simulation were carried out. According to the validated model, seven NO contributing reactions and three reaction pathways were observed. Besides the thermal NO formation pathway, two other pathways with N2O and NNH through NH-HNO-NO have nonnegligible places in the high engine speed condition. As for the parameters, initial temperature aggravates NO emission, initial pressure and ethanol fraction inhibit NO, which influence it through thermal NO pathway and have slight impact on the other two pathways. While with the increase of equivalence ratio (ER) from 0.5 to 1.0, ER promotes first and then resists NO formation, getting highest emission when ER equals to 0.85. In a lean burn condition, the thermal pathway is highly inhibited and the N2O pathway is sharply accelerated. Through current work, NOx producing mechanism under high-speed condition is investigated comprehensively, which not only completes the total NO formation pathways from atmospheric N2 but also provides reference for the designing and modification of low harmful NOx emitting gasoline-ethanol engines. [Display omitted] •Experimentally and numerically study NOx of gasoline/ethanol engine at high speed.•NOx formation mechanism and the effect of dominant parameters are studied.•Seven dominant reactions for NO go reverse direction in late combustion stage.•Three NO pathways including N2O and NNH through NO-HNO-NO are observed.•ER promotes first and then resists NO from lean burn to mildly lean burn condition.