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Combustion images are not simple to be obtained in conventional engines. Therefore, some experimental apparatus, such as a rapid compression machine (RCM), are useful to conduct this kind of study. Imaging techniques allow flame front propagation analysis, which is a very important parameter to understand engine performance, using different fuels and also to generate data to improve fuel modeling in engine simulation softwares. A RCM was adapted to operate in a spark ignition engine mode. It was used to obtain cylinder pressure measurements of gasoline-ethanol combustion synchronized with high-speed photos of flame propagation. Contour plots of the flame front profiles, assumed to be spherical, were used in successive frames to calculate the propagation speeds toward the cylinder walls. So, it was possible to correlate images, pressure curves and flame speeds of gasoline-ethanol blends.

Rapid Compression Machine (RCM) is an experimental tool developed to study engine combustion parameters. The RCM used is a pneumatically and hydraulically driven device which reproduces a single combustion shot, considering a compression and a partial expansion stroke. This paper describes RCM adaptations made in order to run Otto cycle tests using Brazilian regular gasoline (E25) [1]. These adaptations enable pre-vaporized air-fuel mixture combustion tests, representative of port fuel injection engines, by using a gasoline direct injection (GDI) injector. It is also presented RCM piston displacement and cylinder pressure comparisons to a real engine and RCM comparative results for different spark timings and compression ratios. These results show that RCM reproduced satisfactorily piston displacement and pressure curves during the combustion shots, when compared to real engine curves.