Abstract

Crank-angle resolved cylinder pressure data is valuable for characterizing engine performance and various techniques have been developed for post-processing the pressure traces to understand the rate of heat release and its overall impact on engine performance. However, many of these techniques rely on accurate knowledge of the compression ratio, which may not be well-known because of uncertainties in component dimensions for new and rebuilt engines. Additionally, uncertainties in cylinder pressure referencing and top dead center (TDC) offset can lead to variation in the calculation of these parameters.

A method was developed to estimate the compression ratio and heat transfer sensitivity for large bore diesel engines using GT-Power and experimental cylinder pressure traces. An injector cutout method was used on a 228.6mm bore 16-cylinder engine to record motoring cylinder pressure traces for an individual cylinder. The cylinder pressure traces were pegged thermodynamically by matching the slope of a 40-deg window of the compression trace with that of a GT-power simulation of a similar condition. Once the cylinder pressure was properly referenced, it was found that the compression ratio of the cylinder could be estimated by matching the slope of the compression trace over a larger crank angle window. Additionally, it is shown that the location of peak cylinder pressure is dependent on heat transfer and if the location of peak cylinder pressure relative to top dead center is accurately known, then the heat transfer coefficients in GT-Power can be estimated.

For an engine where the exact compression ratio may not be known due to variations in hardware dimensions (for both new and rebuilt engines), this method provides a simple path to estimating compression ratio. Furthermore, by measuring the exact location of TDC and comparing that to the location of peak cylinder pressure, heat transfer can be estimated.

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