Effect of Fuel Dissolved in Crankcase Oil on Engine-Out Hydrocarbon Emissions from a Spark-Ignited Engine

A single-cylinder, spark-ignited engine was run on a certification test gasoline to saturate the oil in the sump with fuel through exposure to blow-by gas. The sump volume was large relative to production engines making its absorption-desorption time constant long relative to the experimental time. The engine was motored at 1500 RPM, 90° C coolant and oil temperature, and 0.43 bar MAP without fuel flow. Exhaust HC concentrations were measured by on-line FID and GC analysis. The total motoring HC emissions were 150 ppmC₁; the HC species distribution was heavily weighted to the low-volatility components in the gasoline. No high volatility components were visible. The engine was then fired on isooctane fuel at the above conditions, producing a total engine-out HC emission of 2300 ppmC₁ for Φ = 1.0 and MBT spark timing. The heavy end components observed during motoring were still present, but their mole fractions decreased by approximately a factor of 5.5±1 relative to the motoring HC emissions. The contribution of crankcase-derived HC emissions is estimated to be approximately 1.5±0.5% of the total HC emissions during steady-state, fully warmed-up operation of this engine on gasoline fuel.