In Situ Measurement of Fuel Absorption into the Cylinder Wall Oil Film During Engine Cold Start

The absorption of unburned fuel into the engine cylinder wall oil film has been identified as a source of hydrocarbon (HC) emissions from spark-ignited (SI)engines. While significant work has been done under steady-state operating conditions to quantify the contribution of this mechanism to overall unburned hydrocarbon emissions, little work has focused on cold starting conditions and in situ measurement of the fuel / oil film interaction. The work reported here shows how laser-induced fluorescence (LIF) spectroscopy can be used to make in situ measurements of the absorption of fuel into the cylinder wall oil film of a single cylinder engine. Measurements were made at two points in the engine cycle under cold start conditions. Results indicate that fuel concentration in the oil film reached a maximum of fifty percent (50%) during cold start operation, though fuel was present in the oil film throughout the engine cycle. Thinning of the oil film occurred during higher temperature portions of the cycle and during overall engine warmup so total mass of absorbed fuel was less than during cold start enrichment. These experiments represent a first step in understanding fuel/oil film interaction under transient cold start conditions.