Abstract
In the polytropic model of compression process, exponent of polytropic compression curve was replaced with a power polynomial in which the piston travel was used as its argument. It was shown that 3rd order polynomial is optimum one. In the model were taken into account the following: design parameters of cylinder, influence of cylinder wear and gas blow-by on compression process, error in determining the piston's Top Dead Centre (TDC) location, measurement error due to indicator diagram's truncation. The presented solution of the non-linear model is based on its partial linearization, use of the least squares method as well as on application of the optimum determination methods known in the theory of experiment. The model makes it possible to determine TDC location on indicator diagram dealing with combustion, determination of total compresion ratio, pressure value of indicator diagram truncation, as well as determination of maximum values of compression pressure on the diagrams in which self-ignition occurs before reaching the TDC.