Alcohol Fuels in Spark Ignition Engines

Carbon dioxide (CO2), nitrogen oxides (NOx) and soot emissions are primary concerns and the most investigated topics in the automotive sector. Indeed, recent governments directives push toward carbon-neutral mobility by 2050. In this framework, zero-carbon fuels, as hydrogen, or renewable low carbon alcohol fuels, play a fundamental role. To this aim, in this chapter, the main results on largely used alcohol fuels application in spark-ignition (SI) engines are discussed. Aspects inherent ethanol and methanol production processes, chemical-physical properties and their application in SI engines are presented. Different engine fuelling strategies, dual fuel and blend are analysed. Alcohols have higher enthalpies of vaporisation and research octane number (RON) values as well as excellent anti-knock ability compared to gasoline. This effect enhances in dual fuel mode. Ethanol and methanol have higher thermodynamic conversion efficiencies than gasoline combustion. Cycle to cycle variation is in line with gasoline values. In general, NOx decreases with alcohol fuels, and the best results are achieved in blend mode with a reduction of up to 30% with methanol compared to gasoline. Independently of the fuelling mode, significant benefits on particle number emissions are observed by using alcohol fuels. Carbon monoxide (CO) and hydrocarbons (HC) emission trends strongly depend on fuelling mode and engine operating conditions. Additionally, the lower carbon content of alcohol fuels reduces the CO2 emissions up to 10% compared to reference gasoline.