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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, Φ, in the accepted manner. For both CO and NOx, there was a characteristic, single emissions response to changes in Φ. 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 Φ response curve. These Φ effects, which are independent of engine design, also determine how operating conditions affect engine-out CO and NOx. Speciated hydrocarbon measurements at engine-out and tail-pipe confirm results seen in previous test-cycle based programmes.

Speciated hydrocarbon emissions were measured at steady-state conditions in pre- and post-catalyst exhaust from a modern multi-valve fuel-injected and closed-loop controlled European gasoline engine tested on toluene, isooctane and diisobutylene. Unburned fuel contributed 70-80% of the total engine-out hydrocarbon emissions on toluene, but only 24% and <10% on isooctane and diisobutylene respectively except at idle where values were 71% and 47% respectively. Emissions from both of the aliphatic fuels were dominated by photochemically-reactive olefins such as isobutene and propene, plus ethyne, methane and formaldehyde. With the exception of ethyne, emissions of these compounds were much less from toluene. Even at rich conditions, most hydrocarbons were catalytically controlled to some extent, but the catalyst efficiency was dependant upon hydrocarbon composition.