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. Thus, at high speed, wide open throttle, methane control was <lo%, whereas ethene and ethyne were controlled by 80-87% and 100% respectively; benzene emissions were increased by an average of 11%. The work therefore demonstrates that fuel-chemistry not only influences engine-out hydrocarbon composition, but also catalyst efficiency. Nevertheless, the main effect of a warmed-up catalyst is to cause gross reductions in all emissions irrespective of fuel chemistry.