Three-stage auto-ignition of n-heptane and methyl-cyclohexane mixtures at lean conditions in a flat piston rapid compression machine

One approach to enhancing the thermal efficiency of combustion systems is burn fuels at ultra-lean conditions (equivalence ratio below 0.5). It has been recently reported that auto-ignition some hydrocarbon fuels, under specific temperature, pressure, and mixture conditions, releases heat in three distinctive stages. The stages can be divided as a first low-temperature stage with conventional low high-temperature separated into two sub-stages. This study presents ignition delay time measurements n-heptane methyl-cyclohexane (MCH) mixtures flat piston rapid compression machine (RCM) conditions. provides experimental evidence three-stage auto-ignition. phenomenon delayed release seldom literature this for these types fuels. experiments cover binary n-heptane/MCH 15/85 70/30 by volume, pressures 11 bar 16 bar, temperature range 700 900 K, equivalence 0.4. RCM optical access was utilized high-speed chemiluminescence imaging. Detailed chemical kinetic simulations homogenous batch reactor variable volume were conducted further interrogate phenomenon. Chemiluminescence shows occurs adiabatically compressed end-gas, which indicates chemically-driven not induced stratification experiments. model predicts features auto-ignition, experimentally observed temperatures approximately 750 K. As expected, significant discrepancies are delays experiment simulation negative coefficient (NTC) region. better agreement Positive Temperature Coefficient (PTC) region compared mixture.