OCR Text |
Show where: G. is the (mass) stoichiometric ratio of air to fuel; cp is the specific heat of the combustion mixture at exhaust; T g O is the exhaust temperature at Idle; and <t> is the equivalance ratio. We now specify that: the Idle temperatures, TgO, will be the same at different stoichiometries. F or this condition, the temperature terms cancel. For the - : - additional condition that is commonly satisfied, that: Gs » 1, Eq. 14 then reduces as given previously [5] to: where E%/100 is the excess air (percent). In connjunction with Eq. 13, the firing rate values obtained at different stoichiometries can then be recalculated to a common equivalence ratio or excess air value provided, either: that the intrinsic efficiency factor, 0.00, is known; or that the local specific enthalpy values are known (this is the procedure used in this paper). 4. Experimental. The furnace used in these experiments is illustrated in Fig. 1. It consisted essentialy of two small vertical refractory tunnels, side-by-side, connected at the bottom, with a downward-firing gas burner at the top of the left hand tunnel, and a dampered exhaust at the top of the right hand tunnel. The left hand tunnel was the combustion chamber. The burner at its top had a standard industrial FRT burner tip fed from a (pyronics) inspirator flow-mixer. The right hand tunnel contained a stacked water- _ cooled coil that acted as the furnace load; this was designed to be operated either oncethrough, or could be split if the firing rate was so high that the maximum water-flow rate was inadequate to cool the tube in a single-run. The tunnel walls were 2800 series insulating firebrick set on edge to form 4-1/2" walls and otherwise cut to fit. The vertical tunnels created in this way were square section, 6-1/2" on the side and about 15" high. The complete unit was cased in transite to aid control of inleakage. Principal instrunlentation included: separate Schutte-Koertig air and gas flow meters; an S-K flow meter for the water flow rate in the load tubing; mercury-in-glass thermometers ) for the rise in water temperature; and a suction pyrometer to measure the exhaust gas 7 |