Optical Investigation of the Effect on the Combustion Process of Butanol-Gasoline Blend in a PFI SI Boosted Engine 2011-24-0057

The addition of alcohol to conventional hydrocarbon fuels for a spark-ignition engine can increase the fuel octane rating and the 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 an optical ported fuel injection single-cylinder SI engine with an external boosting device. The engine was equipped with the head of a commercial SI turbocharged engine having the same geometrical specifications (bore, stroke and compression ratio). The effect of a blend of 20% of n-butanol and 80% of gasoline (BU20) on in-cylinder combustion process was investigated by cycle-resolved visualization. The engine worked at low speed, medium boosting and wide open throttle. Changes in spark timing and fuel injection phasing were considered. Comparisons between the flame luminosity and the combustion pressure data were performed. The fuel was injected both at closed intake valve (CV) and open intake valve (OV). The spark timing was changed to identify the maximum brake torque and the knocking limit. Butanol blend allowed working in more advanced spark timing without occurrence of abnormal combustion. For the blend BU20, the duration of injection (DOI) was increased to obtain a stoichiometric mixture. For both fuels, at stoichiometric conditions, DOI in OV was maintained shorter than that in CV, due to the lower amount of fuel deposited on intake port and on piston surface.

The combustion images showed a different combustion behavior injecting the fuel in CV and in OV conditions. In OV condition, several light spots were observed in the flame front region due to the condensed fuel attached on the optical piston wall. In CV condition, the light spots are bigger but less in number than in OV condition. For BU20 the previous phenomena were less evident due to the chemical composition of the blend that reduces the amount of fuel attached to the piston wall. For both fuels and at all engine conditions, a low variation of IMEP was observed (≺5%). For BU20 injected at CV condition, the lowest IMEP value was measured for all spark timings.