Assessment of Physical and Chemical Effects of Ethanol Enrichment on the Autoignition of Biodiesel Surrogates

This study employed detailed chemistry in conjunction with a zero-dimentional model (senkin code) to numerically investigate the ignition delay times of ternary biodiesel surrogate fuels (comprising n-heptane/methyl-decanoate/methyl-9-decenoate in an 80/10/10% molar ratio) blended with ethanol at ratios of 5, 10, 15 and 20%. Equivalence ratios covered the lean (Φ = 0.5), stoichiometric (Φ = 1.0) and rich (Φ = 1.5) mixtures with temperatures ranging from 700 to 1000 K and pressures from 20 to 40 bar. The primary objective of this work was to assess and quantify the role of chemical and physical (dilution and thermal) effects resulting from ethanol enrichment on the ignition delay times of these blended fuels. The modeling results indicated that ethanol addition had a distinctly different effect on the biodiesel reactivity in the low- and intermediate-temperature regimes. Below 900 K, ethanol addition decreased reactivity, whereas the opposite trend was observed in the temperature range of 900–1000 K. Irrespective of the ethanol ratio, a significant reduction in ignition delay times occurred upon increasing chamber pressure and equivalence ratio, with this phenomenon being more pronounced at higher chamber temperatures. Finally, it was found that under all modeling conditions, the physical effect of ethanol enrichment was less pronounced than the chemical one.