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This study investigated the effects of piston Crevice geometry on the steady-state engine-out hydrocarbons (HC) from a Saturn DOHC four-cylinder production engine. A 50% reduction in top-land height produced about 20-25% reduction in HC emissions, at part loads. The effect of top-land radial clearance on HC emissions was found to depend on the value of top-land height, which suggests a complex relation between flame propagation in the piston crevice and crevice geometry. For idle, increasing top-land clearance resulted in an increase in HC emissions. This trend is opposite to the trend at part load. A simple model was developed which predicts surprisingly well the contribution of piston crevices to HC emissions. It was estimated that for the test engine, piston crevices contribute about 50% of the engine-out hydrocarbons. Finally exhaust gas recirculation appears to decrease the sensitivity of HC emissions to crevice dimensions.

This study is an experimental and computational investigation of the influence of injection timing, fuel spray orientation, and in-cylinder air motion on the combustion, fuel economy, and engine-out emissions of a single-cylinder, 2-valve, spark-ignition direct-injection (SIDI) engine, operating under stratified-charged conditions. For the best compromise between fuel consumption, combustion stability, engine-out hydrocarbon emissions and smoke, the engine required relatively retarded injection timings (in comparison to other charge- or wall-controlled DI engines), high swirl levels, and a spray orientation that is directed towards the intake-valve side and targets the ridge wall of the piston.

The potential sources of hydrocarbon (HC) emissions from a single-cylinder, divided-chamber diesel engine were investigated in this study. To evaluate the relative importance of these sources, the variations of HC emissions with engine speed, air-fuel ratio, combustion timing, intake-air temperature, coolant temperature and oil temperature were examined. Included in the diagnostics of this investigation were: ignition-delay measurements, combustion-chamber surface temperature measurements and heat-release modeling. Lubricating oil was found to contribute significantly to HC emissions. In addition, the results suggested that bulk quenching of flame and non-flame reactions is a primary source of HC emissions. On the other hand, lean mixing during the ignition delay period and wall interactions appear to be secondary sources.

Comparative experiments were performed on an experimental divided-chamber diesel engine for three coolant conditions: baseline (water at 82°C), high coolant temperature (glycol at 120°C) and a differential cooling condition where the antechamber was kept cold (water at 20°C) and the main chamber was kept hot (glycol at 120°C). High-temperature cooling was found to provide a significant brake-specific-fuel-consumption advantage at low-speed and low-load conditions and at very retarded combustion-timing conditions. In general, high coolant temperature caused an increase in hydrocarbon (HC) emissions. Lowering the antechamber surface temperature at the low-speed conditions was found to cause an increase in gaseous emissions and a reduction in smoke and particulate emissions.

This study investigated the effects of three fuel delivery systems (port fuel injection with production injectors, port fuel injection with air-assisted injectors and a premixed, prevaporized fuel system) on engine-out hydrocarbon (HC) emissions from a four-cylinder spark ignition engine. Comparative tests were run at three part-load conditions and a wide range of EGR. Other engine parameters examined were intake-air and coolant temperatures, and injection timing. The observed effects of injection timing on HC emissions were related to the intake-flow events, which, in turn, affect in-cylinder fuel evaporation and combustion.

This study evaluated multi-layer steel and composite head gaskets of various thicknesses (0.43 to 1.5 mm) and fire-ring diameters to determine the influence of head gasket crevices on engine-out hydrocarbon (HC) emissions. The upper limit in the percent reduction in HC emissions from gasket-design modifications is estimated to be about 15%. At part-load conditions, the lowest HC emissions were measured for head-gasket thickness of about 1 mm. Significantly smaller thicknesses of the order of 0.4 mm result in an increase in HC emissions. Substantial hydrocarbon-emissions advantage may be realized by minimizing the gasket-to-cylinder bore offset.

Exhaust-port hydrocarbon (HC) concentration measurements were made using a Fast Response Flame Ionization Detector (FRFID) in order to investigate the mechanisms by which mixture preparation affects engine-out HC emissions. The mixture preparation was varied by: (a) using fuels of different volatility, (b) varying the injection timing, and (c) decreasing the coolant temperature. The observed increases in HC emissions which resulted from lowering the coolant temperature or employing open valve injection are primarily attributed to the resulting increase in the in-cylinder liquid fuel, which is deposited mainly on the cylinder walls and in the piston crevices. The HC attributed to the liquid fuel deposited on cylinder walls exit the engine cylinder roughly in the middle of the exhaust process. On the other hand, the HC attributed to the liquid fuel stored in the piston crevices, and which represent the largest fraction, exit the cylinder during the end of the exhaust process.

Suppression of the heat rejection to the coolant was achieved by the use of an air-gap-insulated piston, an antechamber that was partially insulated by an air-gap, and high-temperature coolant (ethylene glycol at 120°C). In comparison to the standard configuration (STD) of the engine, the low-heat-rejection configuration (LHR) resulted in a small increase in brake thermal efficiency for light-load conditions, in a reduction in volumetric efficiency, in an increase in the exhaust energy, and in an increase in the heat rejection to the lubricating oil. Heat-release analysis performed on the two engines showed higher overall fuel burning rates, and consequently shorter combustion durations, in the LHR engine than in the STD engine. This is believed to cause the observed higher nitric oxide emissions. Also, the LHR engine was found to have higher hydrocarbon emissions but slightly lower particulate emissions.