Validation of a large-molecular weight five-component diesel surrogate: Emphasizing on NTC behavior

The reliability of diesel combustion mechanisms depends heavily on the validation of combustion characteristics of surrogates. This study performed an experimental investigation of the autoignition of a large-molecular weight five-component diesel surrogate and verified it with that of a commercial diesel. The ignition delay times (IDTs) of the five-component surrogate (21.6 % n-cetane, 15.5 % n-octadecane, 26.0 % isocetane, 20.7 % 1-methylnaphthalene, 16.2 % decalin, by mole) were determined in a heated rapid compression machine under 10–20 bar, 670–880 K and equivalence ratios of 0.5–1.25. The surrogate shows excellent agreement with the target diesel in matching IDTs, particularly the first-stage IDTs and negative-temperature coefficient (NTC) behavior, and is greatly superior to a three-component surrogate. A combustion kinetic model of the five-component surrogate was employed to successfully predict the IDTs of the target diesel. Special attention was paid to discussing the NTC behavior. The improvement of the surrogate was attributed to the introduction of cycloalkane decalin, and the inherent mechanism was revealed. Finally, compositional adjustment and optimization strategies for diesel surrogate based on combustion characteristics were proposed. The study correlated autoignition, including NTC behavior, with surrogate composition and provided reference for actively adjusting surrogates to better match the combustion characteristics of target diesel.