Evaluation of reaction scheme at high initial temperature condition bypassing low-temperature reaction

Abstract

Abstract

By using ‘contribution matrices’, the authors had clarified that a major reaction path during the thermal ignition preparation phase of dimethyl ether and n-heptane was a set of reactions named the ‘H₂O₂ reaction loop’, and suggested it may be a universal rule that the heat accumulated by this loop plays a dominant role in preparing a thermal ignition. In the present study, this suggestion was verified by using a fuel with a higher octane number, iso-octane, and by changing the initial temperature. It was verified in all cases that the ignition delay, a period of the thermal ignition preparation phase, depends on the H₂O₂ concentration at the beginning of this phase. Reaction path analyses showed that higher initial temperature conditions and skipping reactions in the low-temperature oxidation (LTO or cool flame) and negative temperature coefficient (NTC) range result in lower H₂O₂ concentrations and lower heat release during the thermal ignition preparation phase. Fuels with low and high octane number show similar ignition characteristics when the initial temperature is higher than NTC range temperatures. When a low-octane-number fuel reacts at a lower initial temperature than NTC range temperatures, the fuel is given an ‘H₂O₂ bonus by LTO’.