More on Origins of Exhaust Hydrocarbons - Effects of Zero Oil Consumption, Deposit Location, and Surface Roughness 720939
Three investigations are reported which clarify the mechanism of exhaust hydrocarbon (HC) emission and suggest new ways to reduce these emissions from reciprocating, 4-stroke, spark-ignition engines. The work was carried out on an engine using the sealed ring-orifice (SR-O) piston, which effectively eliminates exhaust HC emission caused by the piston-bore-ring crevice. This reduces HC emission substantially, making other effects more apparent.
In the first investigation, exhaust HC concentrations were unchanged when the engine was run first with oil and then water in the crankcase. This means that oil did not contribute to exhaust HC emission in the SR-O engine.
In the second investigation, small patches of simulated deposit attached at different locations in the combustion chamber caused exhaust HC concentration increases which varied by a factor of 10, depending on deposit location.
In the last experiment, exhaust HC concentration dropped 17.1 ppm C6 when the rough cast surface of the combustion chamber was smoothed from about 540 μin to about 160 μin, rms.