Chemical Kinetic Influences of Alkyl Chain Structure on the High Pressure and Temperature Oxidation of a Representative Unsaturated Biodiesel: Methyl Nonenoate

The
high pressure and temperature oxidation of methyl trans-2-nonenoate, methyl trans-3-nonenoate, 1-octene,
and trans-2-octene are investigated experimentally
to probe the influence of the double bond position on the chemical
kinetics of long esters and alkenes. Single pulse shock tube experiments
are performed in the ranges p = 3.8–6.2 MPa
and T = 850–1500 K, with an average reaction
time of 2 ms. Gas chromatographic measurements indicate increased
reactivity for trans-2-octene compared to 1-octene,
whereas both methyl nonenoate isomers have reactivities similar to
that of 1-octene. A difference in the yield of stable intermediates
is observed for the octenes when compared to the methyl nonenoates.
Chemical kinetic models are developed with the aid of the Reaction
Mechanism Generator to interpret the experimental results. The models
are created using two different base chemistry submodels to investigate
the influence of the foundational chemistry (i.e., C0–C4),
whereas Monte Carlo simulations are performed to examine the quality
of agreement with the experimental results. Significant uncertainties
are found in the chemistry of unsaturated esters with the double bonds
located close to the ester groups. This work highlights the importance
of the foundational chemistry in predictive chemical kinetics of biodiesel
combustion at engine relevant conditions.