Condensation of Fuel on Combustion Chamber Surfaces as a Mechanism for Increased HC Emissions from SI Engines During Cold Start 972884
Condensation of fuel vapor on the cold surfaces within the combustion chamber is investigated as a possible mechanism for increased HC emissions from SI engines during cold start. A one-dimensional, transient, mass diffusion analysis is used to examine the condensation of single-species fuels on the surfaces of the combustion chamber as the pressure within the cylinder rises during compression and combustion, and re-vaporization during expansion, blowdown, and exhaust. The effects of wall temperature, fuel volatility, and engine load and speed on this mechanism are also discussed. This analysis shows that low-volatility fuel components can condense on the surfaces of the combustion chamber when the surface temperatures are sufficiently low. This condensed fuel may re-vaporize during the power and exhaust strokes, or it may remain in the combustion chamber until surface temperatures rise, perhaps tens of seconds later. It is also shown that a significant portion of the condensed fuel does not re-vaporize until blowdown, at which time bulk gas temperatures are too low for complete in-cylinder oxidation. It is also shown that flame passage may not significantly affect the re-vaporization rate under some circumstances. Although it is difficult to quantify the contribution of this mechanism to the total cold-start HC emissions from a port-fuel injected engine, this analysis may provide a better understanding of the cold-start HC emissions behavior from gasoline-fueled engines. It also appears that the proposed mechanism may be most important for experiments involving pure (single species) fuels, for prevaporized gasoline studies, and for direct injection gasoline engines.
Citation: Stanglmaier, R., Roberts, C., Ezekoye, O., and Matthews, R., "Condensation of Fuel on Combustion Chamber Surfaces as a Mechanism for Increased HC Emissions from SI Engines During Cold Start," SAE Technical Paper 972884, 1997, https://doi.org/10.4271/972884. Download Citation
Rudolf H. Stanglmaier, Charles E. Roberts, Ofodike A. Ezekoye, Ronald D. Matthews
The University of Texas
International Fuels & Lubricants Meeting & Exposition
Combustion and Emission Formation in SI Engines-SP-1300