A fundamental investigation into chemical effects of carbon dioxide on intermediate temperature oxidation of biodiesel surrogate with laminar flow reactor

The chemical effects of carbon dioxide on the oxidation of biodiesel surrogate, methyl butanoate (MB) were investigated experimentally in the SJTU laminar flow reactor at equivalence ratios of 1.5, 1 and 0.5, at atmospheric pressure. Generally, there are three kinds of effects from carbon dioxide (CO2): thermal, dilution and chemical effects. In this study, argon was replaced by CO2 as the dilute gas as a way to isolate the chemical effects by keeping the factors of temperature profile and dilution ratio constant. Therefore, the differences in concentrations of species at the exit from the flow reactor could be attributed to the chemical effects of CO2. Good agreement was found between the experimental and the computational results. The chemical effects were classified into two types. First, there was the radical factor, by which the reaction CO2 + H = OH + CO played a significant role in the oxidation of MB. In CO2 atmosphere, radical factors led to the reduction in reactivity and suppressed the decomposition of MB. The second effect was the collision factor, which derived from the high frequency of third-body collisions of CO2. This collision factor contributed to the formation of carbon monoxide and ethane. Moreover, in the combustion of biodiesel engine with EGR, pure chemical effects of CO2 addition decreased the concentration of acetylene as well as suppressed formation of larger PAHs.