Constant volume spray ignition of C9-C10 biodiesel surrogates: Methyl decanoate, ethyl nonanoate, and methyl decenoates

Ignition delay times were measured in a constant volume spray combustion chamber for four compounds considered as surrogates for fatty-acid methyl/ethyl ester biodiesel fuels. Experiments were performed for methyl decanoate, ethyl nonanoate, methyl 9-decenoate, and methyl 5-decenoate for characterization of the derived cetane number (DCN) and temperature-dependent spray ignition delay of these compounds under conditions relevant to low-temperature combustion engines (625-820 K and 2.14 and 4.0 MPa). The low-temperature reactivity of these compounds, from least reactive to most reactive at the DCN condition (818 K and 2.14 MPa), was determined to be: methyl 5-deceonate (DCN = 33.6), methyl 9-decenoate (DCN = 40.0), ethyl nonanoate (DCN = 50.2), and methyl decanoate (DCN = 52.5). Experimental results for temperature dependent ignition delay are compared to prior shock tube results and show the same order of reactivity with quantitatively similar differences in ignition delay for the C10 methyl esters, illustrating that spray ignition delay and DCN correlate to homogenous chemical kinetic reactivity for fuels with similar physical properties. Comparisons of measured DCNs with the statistical group contribution model of Dahmen and Marquardt (Energy and Fuels 2015, 29, 5781-5801) show good agreement for the influence of double bonds on reactivity for the C10 methyl esters studied.