Costanzo, V. and Heywood, J., "Effect of In-Cylinder Liquid Fuel Films on Engine-Out Unburned Hydrocarbon Emissions for an SI Engine," SAE Technical Paper 2012-01-1712, 2012, doi:10.4271/2012-01-1712.
An experimental study was performed in a firing SI engine at conditions representative of the warmup phase of operation in which liquid gasoline films were established at various locations in the combustion chamber and the resulting impact on hydrocarbon emissions was assessed. Unique about this study was that it combined, in a firing engine environment, direct visual observation of the liquid fuel films, measurements of the temperatures these films were subjected to, and the determination from gas analyzers of burned and unburned fuel quantities exiting the combustion chamber - all with cycle-level resolution or better.A means of deducing the exhaust hydrocarbon emissions that were due to the liquid fuel films in the combustion chamber was developed. An increase in exhaust hydrocarbon emissions was always observed with liquid fuel films present in the combustion chamber. This increase depended upon both the location of the film and the temperature of that location, and correlated directly with estimates of the mass of fuel in the film.Also identified was when, during the exhaust event, fuel from the liquid fuel films was actually exhausted. Moreover, natural luminosity images of radiating soot particles formed near the liquid fuel films were obtained that aid and support the interpretation of these results.