OCR Text |
Show (4) After substitution and manipulation of terms, we obtain the Firing Equation, which relates the variation of the thermal input, H f' with the useful output, Hs' combined with definitions for the operational and intrinsic device efficiencies. These three equations include three empirical Firing Constants, H/, a", and Hsm, the Idle heat, the Intrinsic Efficiency, and the Maximum Output, respectively. The qualitative performance of a general combustion device can be described by these three equations and their graphical representations. Firing Equation (5) Operational Thermal Efficiency (6) Heat Utilization Factor (HUF) and Intrinsic Thermal Efficiency (cf): (7) The curves representing these equations are illustrated in qualitative form in Figs. 2 and 3, along with data that will be discussed later. Fig. 2 illustrates the fIring curve, and its chief characteristics are: (1), that it is concave upwards, showing that the fuel demand increases non-linearly with increasing output; (2), that there is a finite energy supply rate at zero output -- the "Idle Heat" -- that is determined by the "wall losses" and related factors; (3), that the firing rate, theoretically, goes to infinity at a finite maximum output, thus carrying the inference that the maximum can not be achieved in practice. Fig. 3 illustrates both the Heat Utilization Factor (HUF) a and the operational efficiency, 17, showing: (1) that the HUF is a linearly declining line with the two major characteristics that: it goes to zero at the (theoretical) maximum output; and goes to a maximum value -- the "Intrinsic 5 |