Because the experiment only studied the 4-stroke secondary expansion mode, a 1D simulation model was established by GT-Power for evaluating the 4-stroke secondary expansion mode to complete the study. GT-Power is a widely used engine simulation tool based on one-dimensional gas dynamics, representing the flow and heat transfer in piping and in the other components of an engine system. In addition to the fluid flow and heat transfer capecialized models required for engine system analysis, such as combustion, emission, friction and so on.