| OCR Text |
Show on the assumption of chemical equilibrium). Both data sets are shown because of the difficulty encountered in obtaining reliable temperature measurements at the more fuel-rich equivalence ratios. Fig. 2 shows unburned hydrocarbon and oxygen concentrations in the exit stream for the same conditions as the temperature comparisons shown in Fig. 1. Both the unburned hydrocarbon and oxygen concentration rise as the equivalence ratio increases, indicating a substantial chemical kinetics effect at high equivalence ratio. The predicted CO and C0? distribution also agrees well with the experimental data, as shown in Fig. 3, indicating that the model correctly accounts for combustion inefficiency under fuel-rich conditions. Water and hydrogen were not measured in these experiments. The data comparisons shown in Figures 1-3 represent steady-state operation of a jet-stirred reactor. It is also possible to investigate flame stability using the jet-stirred reactor (and an analogous well-stirred reactor combustor model) by determining the conditions at blowout as a function of equivalence ratio. These conditions can be expressed in terms of a Longwell loading parameter. Fig. 4 shows predicted stability behavior for toluene compared to Longwell's data for benzene, isooctane and toluene (Ref. 11), as well as the data band established by several investigators for propane. Even though experimental data for fuel-rich toluene combustion are not available, the trends indicated by the model predictions appear to be correct. Clearly, the agreement with the data under fuel-lean conditions is very good. Similar comparisons with data have been made for the aliphatic component of the quasiglobal kinetics model, and agreement with the experimental data is as good as or better than that already shown for the toluene component. These comparisons are outlined in detail in Refs. 2 and 10; an example is provided by the exit temperature versus equivalence ratio comparison shown in Fig. 5. The additivity of the aromatic and aliphatic components of the quasiglobal model has been justified by comparison of model predictions with experimental results obtained for these fuel blends. Experimental data is reported in Ref. 6 for jet-stirred combustion experiments carried out for blends of 87.5% and 62.5% by volume of liquid toluene mixed with liquid isooctane. As was the case in the comparisons already considered, these experiments were carried out under near-adiabatic conditions and measured heat losses were used in carrying out the computations. Figures 6 and 7 provide a comparison between experimental results and predicted values of the steady-state temperature for the two blends considered. It is evident from these figures that the agreement between the predictions and the thermocouple-measured 1.2.16 |
