Improvement in spark ignition gas engine performance by changing inintake valve closure

Recently, according to the environmental crisis and the negative influence of gasoline and Diesel fuels on it,together with these fuels high cost persuaded the manufacturing companies to use natural gas as fuel. Naturalgas will occupy more space because of its much lower density in comparison with liquid fuels and as a result, thevolumetric efficiency will be reduced. In this regard, the Miller cycle as the fifth thermodynamic cycle in internalcombustion engines is discussed. Increasing the expansion ratio along with the compression by changing in theintake valve closure is the main characteristic of this cycle. In this study, AVL FIRE software is used to simulateD87 gas engine. Since the close cycle cannot examine the valve lifting effectively as well as the turbo charging,then one dimensional simulation by GT Power software is used. After their parallelism with each other, 4camshaft timing has been used as well as Otto cycle. Results show that there is a reduction in the maximumpressure and temperature with slight increment in power. Also due to decrease in peak temperature, NOxdiminishes obviously.

Keywords:

Gas engine , CFD , Miller cycle , Valve timing , Engine performance