Comparative Evaluation of Ethanol, n-Butanol, and Diethyl Ether Effects as Biofuel Supplements on Combustion Characteristics, Cyclic Variations, and Emissions Balance in Light-Duty Diesel Engine

Abstract

This work evaluates experimentally on a comparative basis the effects of using three customary biofuels on the cyclic variability (irregularity) of combustion and emissions balance in a single-cylinder, light-duty, direct-injection diesel engine run at three loads. Blends of fossil diesel with up to 15% (by volume) ethanol and 24% n-butanol or diethyl ether (DEE) are investigated. Related experimental study including heat release diagrams reported by the authors for these blends in the same engine disclosed the differentiation in performance and emissions of these biofuel blends from running the engine with neat fossil diesel. Given that low ignition quality fuels, as the present biofuels, mainly at high blending ratios may give rise to unstable engine functioning and hence detrimental performance, this work examines on a comparative basis the strength of combustion cycle-to-cycle variations as revealed in the measured cylinder pressure diagrams. The latter are analyzed with respect to maximum pressures, maximum rates of pressure rise, mean effective pressures (indicated), and ignition delays, by using statistical tools for mean values and coefficients of variation. Apart from the examination and interpretation of the engine stability results, this study also explores the balance of all four regulated exhaust emissions, namely the defeat of the smoke-nitrogen oxides trade-off and the interesting carbon monoxide–unburned hydrocarbons adverse coupling (trade-off) realized when alcohols or diethyl ether are used in the blends.