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Technical Paper

A Rapid Compression Machine Study of the Influence of Charge Temperature on Diesel Combustion

Difficulties in the starting and operation of diesel engines at low temperatures are an important consideration in their design and operation, and in selection of the fuels for their use. Improvements in operation have been achieved primarily through external components of the engine and associated subsystems. A Rapid Compression Machine (RCM) has been modified to operate over a wide range of temperatures (−20°C to 100°C). It is used to isolate the combustion chamber in an environment in which all significant parameters are carefully defined and monitored. The influence of temperature and cetane number on the ignition and combustion processes are analyzed. Examination of the combustion characteristics show that temperature is by far the most influential factor affecting both ignition delay and heat release profiles. Cetane number (ASTM D-613) is not found to be a strong indicator of ignition delay for the conditions investigated.
Technical Paper

Effects of Oxygenated Fuels on DI Diesel Combustion and Emissions

Experiments to study the effects of oxygenated fuels on emissions and combustion were performed in a single-cylinder direct-injection (DI) diesel engine. A matrix of oxygen containing fuels assessed the impact of weight percent oxygen content, oxygenate chemical structure, and oxygenate volatility on emissions. Several oxygenated chemicals were blended with an ultra-low sulfur diesel fuel and evaluated at an equivalent energy release and combustion phasing. Additional experiments investigated the effectiveness of oxygenated fuels at a different engine load, a matched fuel/air equivalence ratio, and blended with a diesel fuel from the Fischer-Tropsch process. Interactions between emissions and critical engine operating parameters were also quantified. A scanning mobility particle sizer (SMPS) was used to evaluate particle size distributions, in addition to particulate matter (PM) filter and oxides of nitrogen (NOx) measurements.
Technical Paper

The Effect of Fuel Characteristics on Combustion in a Spark-Ignited Direct-Injection Engine

An experimental study was conducted on a spark-ignited direct-injection engine burning fuels with different evaporation and autoignition characteristics. The test engine was a single-cylinder Direct-Injection Stratified-Charge (DISC) engine incorporating a combustion process similar to the Texaco Controlled Combustion System. Two fuels were tested and compared with a baseline gasoline fuel: diesel fuel, and gasoline mixed with an ignition improver. The tests were done at low to medium engine loads. Diesel fuel was found to have similar levels of hydrocarbon (HC) emissions as gasoline but had different characteristics. The optimum timing for diesel fuel was retarded from that for gasoline and combustion variability was much less with diesel than with gasoline. Gasoline with a commercial ignition improver normally used to increase the cetane number of diesel fuel was also tested. The effect of changing the autoignition quality of the fuel depended on the injector used.