Estimation of Hydrocarbon Oxidation by Measuring HC Concentrations in an SI Engine Exhaust Port

Using a solenoid-driven fast sampling system and gas chromatography (GC), the profiles of unburned hydrocarbons (HCs) and non-fuel HCs in a propane-fueled-engine were obtained at several positions in the exhaust port during the exhaust process. Changes in the total HC concentration and HC fractions of major components along the exhaust port are discussed and compared with other research results. The results show that the stratification of HC concentration exists around the exhaust valve. The increase of 10% in the fraction of non-fuel components along the exhaust port reflects significant HC oxidation. The results also show that a bulk gas with relatively high HC concentration comes out through the bottom of the exhaust valve. A cycle simulation and plug flow modeling were used to estimate the mass-averaged percentage of the HC oxidation in the exhaust port. Model predictions of HC oxidation are consistent with current and previous experimental results. The percentage of the HC oxidation in the exhaust port ranges between 26% and 36%, depending on the engine operation conditions. Retarded spark timing and lean operating conditions increases HC oxidation at the exhaust port.