A kinetic modelling study of alcohols operating regimes in a HCCI engine

Abstract

Pursuing a sustainable energy scenario for transportation requires the blending of renewable oxygenated fuels such as alcohols into commercial hydrocarbon fuels. From a chemical kinetic perspective, this requires the accurate description of both hydrocarbon reference fuels (n-heptane, iso-octane, toluene, etc.) and oxygenated fuels chemistry. A recent systematic investigation of linear C-2-C-5 alcohols ignition in a rapid compression machine at p = 10-30 bar and T = 650-900 K has extended the scarcity of fundamental data at such conditions, allowing for a revision of the low temperature chemistry for alcohol fuels in the POLIMI mechanism. Heavier alcohols such as n-butanol and n-pentanol present ignition characteristic of interest for application in HCCI engines, due to the presence of the hydroxyl moiety reducing their low temperature reactivity compared to the parent linear alkanes (i.e. higher octane number). The promising performances of ethanol in a HCCI engine have been recently discussed by Bissoli et al. (Energy & Fuels, 2017, Submitted), observing wider stable operability conditions in terms of fuel/air load (lambda) and exhaust gas recirculation (EGR) extent compared to PRF80 and PRF100. The aim of this study is to present briefly the reliability of the updated POLIMI mechanism for heavier alcohols and to investigate the fundamental role of chemical kinetics on the performance maps of HCCI engines fueled with n-butanol and n-pentanol, in terms of operability limits and engine efficiency.