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Technical Paper

The Influence of Mixture Preparation on the HC Concentration Histories from a S.I. Engine Running Under Steady-State Conditions

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.
Technical Paper

Thermal Loading of the Cylinder Head of a Divided - Chamber Diesel Engine

Time-averaged combustion chamber surface temperatures and surface heat fluxes were measured at three locations (one in the antechamber and two in the main chamber) on the head of a single-cylinder, divided-chamber diesel engine. In general the surface temperature and heat flux were found to increase with increasing engine speed, fuel-air ratio and intake-air temperature, decreasing coolant temperature and advancing combustion timing. At motored conditions the highest heat flux was at the antechamber location. This was caused by the high swirl flows present in the antechamber. In contrast, at all other conditions the highest heat flux was measured at the location in the main chamber near the valves. This was attributed to the convective action of the high-temperature stream of combustion gases exiting the antechamber during the expansion stroke. Lastly, the local surface heat flux measurements were correlated in terms of the air and fuel consumption rates of the engine.
Technical Paper

Gaseous and Particulate Emissions from a Single - Cylinder Divided-Chamber Diesel Engine

In this study, the effects of engine speed, air-fuel ratio, combustion timing, intake-air temperature, and coolant and oil temperature on exhaust gaseous emissions (nitric oxide, carbon monoxide and hydrocarbons) and particulate emissions (particulates, volatiles and smoke) were investigated in a single-cylinder, divided-chamber diesel engine. In addition, the trade-off behavior of the pollutants was investigated. To aid in the interpretation of the experimental findings, a single-chamber, single-zone heat release model utilizing experimental main-chamber pressure-time data was employed. The large increase in nitric oxide emission index caused either by increasing the air-fuel ratio or by advancing the combustion timing is attributed to the proportionally larger amounts of fuel that burn at near TDC conditions.
Technical Paper

Inventory of Heat Losses for a Divided–Chamber Diesel Engine

A series of experiments was performed to characterize the various components of heat losses from a single-cylinder divided-chamber diesel engine. This investigation included studies (a) to determine the contribution of piston friction to the heat rejection to the coolant, (b) to measure the amount of heat rejected through the exhaust port to the coolant and (c) to evaluate the heat losses to the surroundings. The above measurements were used to evaluate the total heat losses to the combustion chamber by the working fluid during the engine cycle. These losses were then compared to the heat losses during the closed portion of the cycle (intake valve closing to exhaust valve opening) that were computed with the aid of pressure-time data.
Technical Paper

Hydrocarbon Emissions from a Single-Cylinder, Divided-Chamber Diesel Engine

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.
Technical Paper

The Effects of Coolant Temperature on the Performance and Emissions of a Single-Cylinder Divided-Chamber Diesel Engine

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.
Technical Paper

The Influence of Partial Suppression of Heat Rejection on the Performance and Emissions of a Divided-Chamber Diesel Engine

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.
Technical Paper

The Distribution of Heat Rejection from a Single-Cylinder Divided-Chamber Diesel Engine

The effects of engine speed, load, and injection timing on the distribution of heat rejection to the coolant were examined in a single-cylinder divided-chamber diesel engine. The cooling system was separated into four zones: cylinder liner, intake port, exhaust port, and ante-chamber. The fractions of the total amount of heat rejected to the coolant from the four cooling zones were moderately affected by load and injection timing, but were not affected by engine speed. Typical values of these fractions are: cylinder liner - 53%, exhaust port - 22%, antechamber -18%, and intake port - 7%. The total amount of heat rejected to the coolant increased with engine speed and load; injection timing had a smaller but significant effect. Finally, the heat rejected to each cooling zone was correlated with the rate of fuel consumption.
Technical Paper

Effects of Mixture Preparation on HC Emissions of a S.I. Engine Operating Under Steady-State Cold Conditions

The effects on engine-out HC emissions of a premixed propane system, and three PFI systems employing different types of injectors and using Phase II gasoline were investigated on a four-cylinder DOHC spark-ignition engine. Cold conditions resulted in significant increases in engine-out HC emissions. Phase II gasoline caused much higher emissions of HC than propane fuel. The difference in the HC emissions from the two fuels increased dramatically with lowering the coolant temperature of the engine. At cold conditions, liquid fuel entering the combustion chamber appears to be the primary source of engine out HC emissions. At the coldest temperature tested the estimated percent contribution of in-cylinder liquid fuel to the observed increase of HC emissions was as much as 96%.