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Show Engine: Application of the analy is to engine data follows the same procedure. In this case, we have used data from engine dynamometer tests supplied by General Motors' Powertrain Division for a GM 3.4 L V6 engine [11]. The engine performance data are presented in Fig. 5 and Table 2. The engine data also are converted to the same units basis as the previous boiler data for ease of comparison. Again, as an initial approximation, the wall loss is assumed to be constant with output. Also, since an internal combustion engine recycles some of the energy it produces to do compression work on the incoming gas mixture, the energy balance must be modified to consider energy recovery. This yields the following equation: (8) where H, is the amount of energy recovered to do compression work, and the net useful output is given by W defined by: = H , + W (9) The Firing Equation then takes on the same form as in Eq. (5), with changes only in nomenclature, such as the introduction of a,o the modified intrinsic efficiency to denote a device that recovers energy from the output. w (10) Figs. 6 and 7 show the results of fitting the operational parameters to these data, in which there are two features of note. First, in Fig. 6 two data points lie off the Firing Curve corresponding to the typical peak in horsepower observed for spark ignition engines. The peak in engine power arises from a combination of effects such as decreasing volumetric efficiency and rising frictional losses as engine speed increases beyond a certain point [12]. This analysis can account for the variation of frictional losses and combustion inefficiencies with output or firing rate, but it does not account for the internal heat release and fluid mechanical effects that give rise to a peak in engine output. Second, in Fig. 7 the results for the Heat Utilization Factor, a, show that at lower output (i.e., engine speed) the variation of losses is not linear with output since a is diverging upward from the expected trend. 10 |