The Influence of iso-Butanol Blending on Spark-Ignition Engine Performance
Session chaired by Pr. Christine Rousselle
Bio-alcohols and other bio-derived fuels are attractive alternative fuel options for spark-ignition (SI) engines, as a means to achieve the required carbon emissions reductions from transport. Particularly for bio-alcohols, this is partly due to their similar physical and thermodynamic properties when compared with fossil fuels, as well as their viability in modern SI engine technologies and fuel distribution infrastructure, with little to no modification [1,2]. One such bio-alcohol (and the focus of this study) is iso-butanol. As SI engine technologies tend towards turbo-charged, downsized engines, the blending of bio-alcohols and gasoline may produce a further advantage over standard gasoline fuels by increasing knock resistance. This would allow engines to be operated at higher compression ratios without risking typical knock damage. However, there is also the potential to reduce the knock resistance of the fuel, which may lead to catastrophic engine damage. Therefore, it is necessary to characterise the fuels ignition behaviour over the entire range of possible fuel blends, for both engine performance and safety reasons. This study investigates the impact of iso-butanol blending on the ignition behaviour of a reference gasoline (‘PR5801’ – RON 95.4, MON 86.6). To achieve this, the study applies both fundamental ignition and full-scale research engine studies, utilising the University of Leeds Rapid Compression Machine (RCM) and Leeds University Ported Optical-access Engine (LUPOE) respectively. This equipment is described fully in previous literature [3][4]. Blending ratios of 5-70% by volume iso-butanol are investigated, as are the individual components (gasoline and iso-butanol). A 5-component surrogate is also developed to match the properties of the reference gasoline, and the ability of this surrogate to mimic the ignition behaviour of gasoline and blends with iso-butanol is investigated. From RCM experiments, the study shows that the addition of iso-butanol to gasoline does not produce a simple increase in knock resistance across all blends. At low volume percentages of iso-butanol, ignition delay times (and therefore knock resistance) are lower than those of the standard gasoline, indicating a higher reactivity. This is particularly true in the negative temperature coefficient (NTC) region. However, as iso-butanol volume percent increases beyond 10%, this behaviour changes and increasing the amount of iso-butanol in the blend increases ignition delay times, particularly at low temperatures
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