Exploring the chemistry behind low temperature auto-ignition of isopropyl nitrate in an RCM: An experimental and kinetic modeling study

The low-temperature auto-ignition chemistry of isopropyl nitrate (iPN) was experimentally and numerically investigated in the present study. The ignition delay times (IDTs) of iPN were measured stoichiometrically over a temperature range of 560–600 K at effective pressures of 5 and 10 bar in a rapid compression machine. A two-stage ignition phenomenon of iPN was observed. Both the first-stage IDTs and total IDTs vary rapidly within the narrow temperature range investigated (∼40 K). A recent iPN kinetic mechanism proposed by Fuller and Goldsmith for pyrolysis studies was extended. The reaction kinetics of CH3CHO + NO2 has been theoretically calculated at 500–1500 K and 0.01–100 atm. The rate information of CH3 + NO2 was updated based on previous theoretical results. The O2-addition channel of acetyl radical (CH3CO), which accounts for the first-stage IDT, was also considered in the present work. The extended iPN kinetic model predicts the two-stage IDTs well. Simulation results suggest that the IDTs are most sensitive to the following two reactions: (1) CH3 + NO2 = CH3O + NO; (2) CH3 + NO2 = CH3NO2. The former promotes the overall reactivity by yielding the reactive methoxy radical, while the latter forms a relatively stable product (i.e., CH3NO2). The reaction of CH3CHO + NO2 = CH3CO + HONO supplements the formation of CH3CO. The different consumption channels of CH3CO radicals (the O2-addition reaction and the decomposition reaction) lead to different chain reactions yielding OH radicals with increasing temperature in the ignition process. The “NONO2 loop” is the main route for OH formation in the studied conditions, which is mainly responsible for the iPN ignition.