The Effect of Gasoline Composition on Stoichiometry and Exhaust Emissions

Six full range gasolines were tested in two engines (one with a catalyst) operated at 4 steady states. Engine-out regulated emissions responded to equivalence ratio, {Phi}, in the accepted manner. For both CO and NO{sub x}, there was a characteristic, single emissions response to changes in {Phi}. Changing fuel composition will primarily alter the production of these emissions by modifying the stoichiometric air/fuel ratio, projecting engine operation onto another part of the {Phi} response curve. These {Phi} effects, which are independent of engine design, also determine how operating conditions affect engine-out CO and NO{sub x}. Speciated hydrocarbon measurements at engine-out and tail-pipe confirm results seen in previous test-cycle based programmes. 24 refs., 11 figs., 3 tabs.

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