Experiments and modeling of the autoignition of methyl pentanoate at low to intermediate temperatures and elevated pressures in a rapid compression machine

Methyl valerate (C6H12O2, methyl pentanoate) is a methyl ester and a relevant surrogate component for biodiesel. In this work, we present ignition delays of methyl valerate measured using a rapid compression machine at a range of engine-relevant temperature, pressure, and equivalence ratio conditions. The conditions we have studied include equivalence ratios (ϕ) from 0.25 to 2.0, temperatures between 680 K and 1050 K, and pressures of 15 bar and 30 bar. The ignition delay data demonstrate a negative temperature coefficient region in the temperature range of 720-800 K for both ϕ=2.0, 15 bar and ϕ=1.0, 30 bar, with two-stage ignition apparent over the narrower temperature ranges of 720-760 K for 15 bar and 740-760 K at 30 bar. In addition, the experimental ignition delay data are compared with simulations using an existing chemical kinetic model from the literature. The simulations with the literature model under-predict the data by factors between 2 and 10 over the entire range of the experimental data. In addition, a new chemical kinetic model is developed using the Reaction Mechanism Generator (RMG) software. The agreement between the experimental data and the RMG model is also not satisfactory. To help determine the possible reasons for the disagreement, a path analysis of both models is completed. It is found that improvements to both the reaction pathways and thermodynamic properties are required. Further directions for future improvement of the methyl valerate model are discussed.