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An experimental study was conducted using the dumping technique (total cylinder sampling) to produce cylinder mass-averaged nitric oxide histories. Data were taken using a four stroke diesel research engine employing a quiescent chamber, high pressure direct injection fuel system, and simulated turbocharging. Two fuels were used to determine fuel cetane number effects. Two loads were run, one at an equivalence ratio of 0.5 and the other at a ratio of 0.3. The engine speed was held constant at 1500 rpm. Under the turbocharged and retarded timing conditions of this study, nitric oxide was produced up to the point of about 85% mass burned. Two different models were used to simulate the engine run conditions: the phenomenological Hiroyasu spray-combustion model, and the three dimensional, U.W.-ERC modified KIVA-II computational fluid dynamic code. Both of the models predicted the correct nitric oxide trend.

Oxygen enhancement in a direct injection (DI) diesel engine was studied to investigate the potential for particulate matter and NOx emissions control. The local oxygen concentration within the fuel plume was modified by oxygen enrichment of the intake air and by oxygenating the base fuel with 20% methyl t-butyl ether (MTBE). The study collected overall engine performance and engine-out emissions data as well as in-cylinder two-color measurements at 25% and 75% loads over a range of injection timings. The study found oxygen enhancement, whether it be from intake air enrichment or via oxygenated fuels, reduces particulate matter, the effectiveness depending on the local concentration of oxygen in the fuel plume. Since NOx emissions depend strongly on the temperature and oxygen concentration throughout the bulk cylinder gas, the global thermal and dilution effects from oxygen enrichment were greater than that from operation on oxygenated fuel.