There are heat losses during the cycle of a real engine that are neglected in ideal air standard analysis. In
this paper, the effects of heat transfer on the net work output and the indicated thermal efficiency of an air
standard Dual cycle are analyzed. Heat transfer from the unburned mixture to the cylinder walls has a
negligible effect on the performance for the compression process. Additionally, the heat transfer rates to the
cylinder walls during combustion are the highest and extremely important. Therefore, we assume that the
compression and power processes proceed instantaneously so that they are reversible adiabatics, and
the heat losses during the heat rejection process can be neglected. The heat loss through the cylinder wall is
assumed to occur only during combustion and is further assumed to be proportional to the average temperature
of both the working fluid and the cylinder wall. The results show that the net work output versus
efficiency characteristics and the maximum net work output and the corresponding efficiency bounds are
strongly influenced by the magnitude of the heat transfer. Higher heat transfer to the combustion chamber
walls lowers the peak temperature and pressure and reduces the work per cycle and the efficiency. The
effects of other parameters, in conjunction with the heat transfer, including combustion constants, cut-off
ratio and intake air temperature, are also reported. The results are of importance to provide good guidance
for the performance evaluation and improvement of practical Diesel engines.
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