A focus on the first-stage ignition of n-pentane

Abstract

It is important to investigate the first-stage ignition of alkane fuels as it is responsible for the cool flame heat release in combustors, particularly engines. In the present study, a new set of ignition delay time (IDT) data of n-pentane is measured in a rapid compression machine (RCM) at φ = 1.0, p = 30 atm, and T = 685–994 K. Moreover, the species concentration profiles of major intermediate species, including alkenes, cyclic ethers, and aldehydes are measured in an RCM at a two-stage ignition condition (T = 730 K) using an updated 2 × fast-acting-valves sampling system. A new kinetic model has been developed to simulate this data. Both the core chemistry and thermochemistry of the low-temperature species associated with n-pentane have been systematically updated. It is found that updating the HȮ₂ + HȮ₂ reaction, which leadstwo ȮH radicals and O_2, has no obvious influence on the 1st-stage ignition but significantly affects the prediction of the total IDT. This is because ȮH radicals are mainly produced from the formation and consumption of carbonyl-hydroperoxide species before the 1st-stage ignition; HȮ₂ radical recombination and the reaction H₂O₂ (+M) ↔ ȮH + ȮH (+M) become the main source of ȮH radical production only at/after the 1st-stage ignition. The updated thermochemistry data inhibit both the 1st-stage and total IDTs due to the shift towards reactant in the equilibrium of the RȮ₂ ⇌ $\dot{Q}$OOH reaction. The key reactions involved in the low-temperature chemistry are optimized using the Optima++ code within the uncertainty limits of reviewed rate constants in the literature. The present model can predict the experimentally measured data well and shows an improvement compared to previous models.