Ignition and combustion characteristics of decanoic acid derived alkyl esters in a fuel ignition tester

This work investigated the combustion characteristics of decanoic acid derived alkyl esters in an ASTM standard Fuel Ignition Tester (FIT), with special emphasis on the influence of carbon number variation for the alkyl moiety within the alkoxy group on the autoignition delay times. The compounds of interest include methyl, ethyl, propyl, and butyl decanoate. It was found that higher carbon numbers lead to an increase in reactivity in terms of the decreased ignition delay times for methyl through propyl decanoate. However, there was a small reduction in relative reactivity for butyl decanoate. With increasing air temperature, while the ignition delay times showed a monotonic reduction for all the four fuels, the maximum rate of pressure rise exhibited a nonlinear variation. Specifically, the maximum rate of pressure rise was found to increase in the temperature range of 700-758 K and then decrease within 758-825 K. The post-combustion peak pressures also exhibited a similar trend. It is hypothesized that this reduction in reactivity with increasing temperature correlates to the negative temperature coefficient behavior. In addition, all the test fuels show a two-stage ignition response at the lowest oxidizer temperatures investigated. Therefore, the current experiments demonstrate the suitability of the FIT as a research tool that can be used to extract information on fuel reactivity other than the widely studied metric of the derived cetane number.