Experimental and modeling validation of a large diesel surrogate: Autoignition in heated rapid compression machine and oxidation in flow reactor

Abstract

Autoignition and oxidation characteristics of a three-component diesel surrogate fuel were studied in a heated rapid compression machine (RCM) and a flow reactor (FR) over a wide range of conditions. The surrogate components, n-cetane, 2,2,4,4,6,8,8-heptamethylnonane (HMN), and 1-methylnaphthalene (1-MN), all fall within the C10–C20 range of real diesel fuel. The RCM-measured ignition delay times (IDTs) and FR oxidation data of the surrogate fuel were then compared with those of the target diesel. It is found that the diesel surrogate fuel is in good agreement with the target diesel in total ignition delay time and FR speciation data over the whole temperature range, reflecting the success of the surrogate fuel construction. A semi-detailed kinetic model was used to predict the autoignition and oxidation behavior of the surrogate fuel in RCM and FR experiments. Results show that the kinetic model captures well the measured total IDTs and the mole fractions of O2, H2, CO2, and small hydrocarbons under all investigated conditions. To deepen the understanding of low-temperature reaction scheme, rate of production (ROP) analysis of OH and HO2 radicals was carried out during the first-stage ignition to explore the causes of low-temperature and negative temperature coefficient (NTC) reactivity. A brute force sensitivity analysis of first-stage ignition delay time was also conducted to further identify the controlling reactions in the first-stage ignition of the surrogate fuel.