Reduction of Unburnt Hydrocarbon Emissions from Spark Ignition Engines Using In-Cylinder Catalysts

Exhaust unburnt hydrocarbons (HC) in spark ignition engines arise from a number of sources, including flame quenching at the entrance of crevice volumes and at the combustion chamber wall, absorption and desorption of fuel vapour into oil layers on the cylinder wall, partial burning and misfiring. All sources other than partial burning and misfiring are in close proximity to the wall surfaces of the combustion chamber. The significance of this observation is that unburnt HC emissions from spark ignition engines may be reduced at their sources of production using in-cylinder catalysts on the surfaces of the combustion chamber wall. This paper examines in detail a novel approach to reduce exhaust HC emissions using an in-cylinder catalyst on the combustion chamber walls, in particular, the surfaces of the crevice volumes. Platinum-rhodium coating on the piston crown led to a reduction of approximately 20 per cent in engine-out HC emissions over a wide range of engine operating conditions.