Effects of Blending C3-C4 Alcohols on Motor Gasoline Properties and Performance of Spark Ignition Engines: A Review: Article No. 106194

Supplementing petroleum fuels with sustainable and renewable alternatives is a good option for increasing the sustainability of transportation fuels. Alcohols are particularly attractive blendstocks for spark ignition (SI) engines, mainly due to their desirable fuel properties such as high octane, good charge cooling and reduced sooting propensity. Although the use of SI engines is widespread around the world, predominately for light duty vehicles due to sustainability concerns such as air and CO2 emissions, the consensus is that SI engines need to be more efficient and lower emitting, and the intelligent blending of C2-C4 alcohols into motor gasoline is a viable method for achieving that goal. There are a multitude of ways to produce renewable alcohols such as through fermentation from first-generation feedstocks (sugar and corn) and second-generation feedstocks (lignocellulosic biomass), or by gasification and mixed alcohol fuel synthesis routes from lignocellulosic biomass. Currently ethanol is extensively used in motor gasoline fuels worldwide and although many have proposed the use of C3 and C4 alcohols in motor gasoline as an improvement over ethanol, the higher cost of production and lack of clear definition as to their benefit over ethanol when blended into motor gasoline have led to slow acceptance into the market. In this review, special emphasis is placed on C3 and C4 alcohols blending effects on motor gasoline in terms of physicochemical properties, volatility behavior, and engine performance when compared to ethanol blends. Furthermore, the C3, C4 alcohol blending effect on emission (particulate matter, nitrogen oxides, carbon monoxide, hydrocarbons, and unregulated oxygenates) and combustion (volumetric efficiency, thermal efficiency, fuel consumption, and cold performance) characteristics is discussed. Although there are some disagreements in the literature over the effect of alcohols predominately around the type of SI engine, i.e., port fuel injected versus direct fuel injected and engine operating mode, generally it is stated that alcohols can potentially reduce soot, unburned hydrocarbons and CO emissions while increasing thermal efficiency. Thus, further research must be conducted to find the optimum combination of alcohol blends and engine configurations and this review will explore this concept in depth.