Models, methods and performance when estimating the compression ratio based on the cylinder pressure

Four methods for compression ratio estimation of an engine from cylinder pressure traces are described and evaluated for both motored and fired cycles. The first three methods rely upon a model of polytropic compression for the cylinder pressure, and it is shown that they give a good estimate of the compression ratio for simulated cycles at low compression ratios. For high compression ratios, this simple model lack the information about heat transfer and the model error causes the estimates to become biased. Therefore a fourth method is introduced where heat transfer and crevice effects are modeled, together with a commonly used heat release model for firing cycles. This method is able to estimate the compression ratio more accurately at low as well as high compression ratios.