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Investigation of Fuel Composition Contribution to Hydrocarbon Emission of SI Engines
Technical Paper
92A225
Sector:
Language:
English
Abstract
The current requirement for a decrease of hydrocarbon emissions
of spark-ignition engines needs a better understanding of the
chemical mechanisms leading to the production on unburnt
hydrocarbons. Therefore, it is necessary to analyse in details the
composition of exhaust gases.
C1-C8 hydrocarbons are measured on an engine test bench using an
on-line gas chromatography technique. First, the formation of light
hydrocarbons (methane, ethane, ethylene, porplyene and acetylene)
is studied and the repeatability of this analysis is assessed on a
single-cylinder engine fuelled with iso-octane or propane.
Then, on a multi-cylinder engine, the influence of two operating
variables (spark-timing and equivalence ratio) on the exhaust
hydrocarbon distribution are studied in steady-state conditions
with unleaded-gasoline. Changes in the concentrations of individual
species occur as spark-timing or equivalence ratio is modified.
Methane increases by more than 400% and unburned iso-octane only by
100% when equivalence ratio risen from 0.95 to 1.05. The
benzene/toluene ratio is modified when the two operating parameters
above are changed.
On the same multi-cylinder engine, a study of the distribution
of engine-out hydrocarbon emissions is also realized with two
unleaded fuels, whose different octane numbers are different, in
various engine speed conditions, namely 1500 rpm/1 bar, 2000 rpm/2
bar and 3500 rpm/5 bar. The results show that the differences in
emissions between these two fuels are the concentrations in
ethylene and acetylene. The difference in ethylene contents can be
explained by the different paraffin levels of the fuels.