Review on bioethanol as alternative fuel for spark ignition engines

Bioethanol fuel obtained from biomass and bioenergy crops has been proclaimed as one of the feasible alternative to gasoline fuel, as it is considered to be clean, renewable and green. In this review, the bioethanol production techniques from different lignocellulosic biomass, and its potential ethanol yield are studied. Moreover, this paper has reviewed the effects of bioethanol fuel blends on spark ignition engine combustion characteristics (i.e. cylinder pressure, cylinder temperature, flame speed, combustion efficiency, combustion duration, heat release rate, knocking and cold start); engine performance parameters (i.e. torque, brake power, brake specific fuel consumption, brake mean effective pressure, brake thermal efficiency and volumetric efficiency); and emission characteristics (i.e. carbon monoxide, oxides of nitrogen, carbon dioxide, unburned hydrocarbon and other unregulated emissions). Recently, many researchers produced bioethanol from herbaceous, industrial and municipal solid wastes (MSW) instead of agriculture and woody biomass. Most of the engine test results showed a remarkable improvement in engine performance and enhanced combustion characteristics for bioethanol fuel. In addition, the carbon monoxide and unburned hydrocarbon emissions decreased. Conversely, carbon dioxide and oxides of nitrogen emissions were not significantly reduced. Furthermore, there was no significant reduction of unregulated emissions, such as aromatics, acetaldehyde, and carbonyls. Abbreviations 1C, single cylinder; 4C, four cylinders; BMEP, brake mean effective pressure; BP, brake power; BSFC, brake specific fuel consumption; BTE, brake thermal efficiency; CO, carbon monoxide; CO2, carbon dioxide; CR, compression ratio; DOHC, double overhead camshaft; E0, 0% ethanol & 100% gasoline; E100, 100% ethanol & 0% gasoline; E85, 85% ethanol & 15% gasoline; GHG, greenhouse gas emission; HC, unburned hydrocarbon; MPFI, multi-port fuel injection; NOx, oxides of nitrogen; PFI, port fuel injection; SHF, separate hydrolysis and fermentation; SI, spark ignition; SOHC, single overhead camshaft; SSF, simultaneous saccharification and fermentation; VE, volumetric efficiency; WOT, wide open throttl