Estimation of instantaneous exhaust gas flowrate based on the assumption of a polytropic process

Estimation of instantaneous exhaust gas flowrate is very useful in engine-related studies such as calculation of crank angle resolved mass flowrates of hydrocarbons, boundary conditions for exhaust gas flow study and so on. The study provides a simple but reasonably accurate tool to calculate the flowrates based on the assumption of a polytropic gas expansion process. The only information needed to calculate the flowrates is cylinder pressure. The polytropic exponent n is obtained from the logarithmic-scale plot of measured cylinder pressure. The calculated instantaneous mass flowrates of the exhaust gas confirm accuracy of within ±5 per cent except for low engine speed, compared with measured intake flowrates. The characteristics of the flowrates also show blowdown and displacement flow regimes typically observed in internal combustion engines.