Cylinder Pressure Based Engine Calibration of a Formula SAE Racing Engine

Formula SAE racing engines must provide high output with maximum fuel efficiency despite the air restriction imposed by the rules. Throttle response and engine load control are very important due to the track characteristics with a few straights zones and many curves. In-cylinder pressure cyclic variations harm vehicle control and increase fuel consumption, due to the torque fluctuations. In order to reduce fuel consumption and improve vehicle drivability, engine calibration having the in-cylinder as a feedback parameter is an essential procedure and will be the focus of this paper. Test bench data with combustion analysis will be performed, using the COV_IMEP as a combustion stability index. Tests were carried out on a motorcycle engine modified to run under the Formula SAE competition rules. A piezoelectric sensor was installed inside the combustion chamber to provide instantaneous pressure readings, which were used to on-line calculate the IMEP and perform a 200 cycle COV_IMEP evaluation. The objective was to reduce the combustion variability at speeds and loads conditions which were defined as critical when analyzing track logged data from previous competitions. Air-fuel ratio and spark timing were varied and combined to reach a good compromise among COV_IMEP, torque and fuel consumption. Values in the range of 2-5% on COV_IMEP were achieved at part load operation conditions with an increase on torque and an expressive reduction on fuel consumption.