The impact of EGR components on ozone decomposition under engine relevant conditions in a rapid compression machine

Abstract In this work, with the addition of 90 ppm ozone, the influence of the main EGR components, namely nitrogen, carbon dioxide, steam, and methane, along with the gasoline surrogate iso-octane, on ozone oxidation were investigated at 30 bar, 800 K using a rapid compression machine (RCM). Taking the case diluted with nitrogen as a reference, it was found that the chemical effects of CO2 on ozone decomposition accelerated with the increase in the carbon dioxide concentration. The promoting effect of steam on ozone decomposition remained constant regardless of the steam mole fraction added. The mutual effect of methane and ozone was detectable, but the enhancement of ozone decomposition was lower than when iso-octane was added. A comprehensive detailed kinetic model was employed to interpret the experimental data. The model performance was improved by replacing the rate coefficients of O3 + O = 2O2. Analysis of the rate of production showed that the IC8H18 + O = CC8H17 + OH reaction predominated over the chain terminating reaction O3 + O = 2O2, which can explain the significant promoting effect in the presence of iso-octane. When steam is added, two OH radicals are derived from the chain branching reaction H2O + O = 2OH. When methane is added, only one OH radical, originating from the O radical attacking methane, is formed. Consequently, the promoting effect of methane addition is the lowest.