Optical diagnostics of the combustion process in a PFI SI boosted engine fueled with butanol–gasoline blend

Alcohol blends with hydrocarbon fuels for spark-ignition engine increase fuel octane rating and power for a given engine displacement and compression ratio. In this work, the influence of butanol addition to gasoline was investigated. The experiments were performed in a ported fuel injection single cylinder SI engine with an external boosting device. The optically accessible engine was equipped with the head of a commercial SI turbocharged engine with the same geometrical specifications. The effect on the spark ignition combustion process of 40% of n-butanol blended in volume with 60% pure gasoline (BU40) was investigated by cycle resolved visualization. The engine worked at low speed, medium boosting and WOT. Changes in the spark timing and fuel injection phasing were considered. Comparisons between flame luminosity and combustion pressure data were performed. The fuel was injected at closed (CV) and open intake valves (OV). Butanol blend allowed working in more advanced spark timing without occurrence of abnormal combustion. For the blend BU40, the duration of injection (DOI) was increased to obtain a stoichiometric mixture. BU40 granted performance levels similar to gasoline and in open valve injection allowed to minimize the abnormal combustion effects including the emission of ultrafine carbonaceous particles, NOx and HC.