# Autoignition of Methyl Valerate at Low to Intermediate Temperatures and Elevated Pressures in a Rapid Compression Machine

## TL;DR

This study measures ignition delays of methyl valerate under various conditions relevant to engines, compares them with existing models, and develops a new chemical kinetic model to improve predictive accuracy.

## Contribution

The paper provides new experimental ignition delay data for methyl valerate and introduces a new RMG-based kinetic model to better match observed data.

## Key findings

- Negative temperature coefficient observed between 720 K-800 K.
- Existing models under-predict ignition delays by factors of 2 to 10.
- RMG-based model shows improved but still imperfect agreement.

## Abstract

Methyl valerate (C$_6$H$_{12}$O$_2$, 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 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 K-800 K for both $\phi$=2.0, 15 bar and $\phi$=1.0, 30 bar, with two-stage ignition apparent over the narrower temperature ranges of 720 K-760 K for the lower pressure and 740 K-800 K at the higher pressure. 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. To help determine the possible reasons for the discrepancy between simulations and experiments, 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 improved but still not satisfactory. Directions for future improvement of the methyl valerate model are discussed.