Effect of increased fuel volatility on CDC operation in a light-duty CIDI engine

Alternative diesel fuels derived from biomass can vary significantly in volatility compared to their petroleum-derived counterparts, and their appropriate utilization is contingent on their compatibility with existing engine infrastructure. To investigate this compatibility, experiments were carried out to study the effect of fuel volatility on conventional diesel combustion (CDC) performance under a wide range of in-cylinder thermodynamic conditions at start of injection (SOI). Fuels of matched reactivity (i.e., cetane number (CN)) and varying volatility were produced by blending binary mixtures of 2,6,10-trimethyldodecane (farnesane) and 2,2,4,4,6,8,8-heptamethylnonane, octane number primary reference fuels (PRF), and cetane number secondary reference fuels (SRF). Nine fuel blends were tested in total, consisting of 3 volatility characteristics at 3 reactivity levels. Five engine operating conditions were utilized, ranging from 14.7-29 kg/m3 and 980-1120 K in-cylinder density and temperature at SOI. Testing was performed in a single-cylinder GM 1.9 L diesel engine. Only small differences in ignition delay (ID), in-cylinder pressure, and heat release rate (HRR) were observed between fuels of matched CN, regardless of their volatility. An analysis of the spray breakup and mixture formation process indicated that there were only small variations in ambient air entrainment and jet temperature between fuel blends, in agreement with the observed combustion behavior.