A Method for Improvement in Data Quality of Heat Release Metrics Utilizing Dynamic Calculation of Cylinder Compression Ratio

One of the key factors for accurate mass fraction burned and energy conversion point calculations is the accuracy of the compression ratio. The method presented in this article suggests a workflow that can be applied to determine or correct the compression ratio estimated geometrically or measured using liquid displacement. It is derived using the observation that, in a motored engine, the heat losses are symmetrical about a certain crank angle, which allows for the derivation of an expression for the clearance volume [1]. In this article, a workflow is implemented in real time, in a current production engine indicating system. The goal is to improve measurement data quality and stability for the energy conversion points calculated during measurement procedures. Experimental and simulation data is presented to highlight the benefits and improvement that can be achieved, especially at the start of combustion. The method calculated a compression ratio correction of 0.3 and 0.25 on two different gasoline engines, respectively. At 2000 rpm a deviation in the 5% and 10% energy conversion angles (CA05 and CA10) of 10.48% and 18.66%, respectively, was observed.