The control of hydrocarbon emissions from spark ignition engines is
important and there is a need for a better understanding of the
mechanisms contributing to this source of emissions.
The absorption/desorption mechanism is believed to be a significant
contributor to hydrocarbon emissions. The aim of the project has been
to validate the absorption/desorption model experimentally.
Modelling studies predict that sufficient fuel vapour is absorbed
into the cylinder wall oil film on the compression and early firing
strokes with subsequent desorption late in the expansion stroke to
seriously affect hydrocarbon emissions in the exhaust, as
temperatures are too low for adequate oxidation.
The experimental investigation which follows develops a method to
allow accurate measurement of hydrocarbon specie levels in the
exhaust of a spark ignition engine. The object of the experiment was
to detect and measure differences in hydrocarbon levels for two
fuels, Iso-octane and Iso-pentane, at identical engine conditions and
therefore establish whether the absorption/desorption effect is
significant to hydrocarbon emissions. The theory behind this relies
upon the varying solubilities of both fuels in a given oil with
temperature wh ich shoul d refl ect a varyi ng base fuel hydrocarbon
emissions level for each fuel if absorption/desorption is in fact
Samples of exhaust were taken from a Ricardo-hydra test engine and
analysed chromatographically. Experimental results (which compare
favourably with prediction from modell ing studies) indicate about 30
percent of total hydrocarbons are due to the absorption/desorption
In conclusion, the results suggest that the solubility of the fuel in
the engine oil has a significant effect on hydrocarbon levels in the
A Master's Thesis submitted in partial fulfilment of the requirements for the award of M.Phil of Loughborough University.