Understanding of the Ignition Behavior of n-Heptane Spray in Constant Volume Combustion Bombs Focusing on Chemical Kinetics

摘要

For accurate predictions of the combustion characteristics in constant volume combustion bombs (CVCBs), the chemical kinetics mechanism is one of the most important factors because it determines the ignition timing and oxidation rate of fuels. By introducing an n-heptane oxidation mechanism for the simulation of auto-ignition in both CVCBs and shock tubes, the correlation of ignition behaviors between in CVCBs and shock tubes was investigated in this study. It was found that the combustion of CVCBs is dramatically affected by the fuel/air mixing and the heat release processes. CVCBs and shock tubes demonstrate similar reaction pathways for the occurrence of auto-ignition, and the trigger of the low-temperature heat release is a critical factor that determines the ignition delay time in CVCBs. By analyzing sensitivity coefficients of the ignition timing on reaction pathways, a similarity factor is proposed to reveal the correlation of the ignition characteristics between CVCBs and shock tubes. It is shown that operating conditions of 800-950 K in stoichiometric fuel/air mixtures in shock tubes are most relevant for auto-ignition in CVCBs.