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Low-temperature combustion of diesel fuel was studied in a heavy-duty, single-cylinder, optical engine employing a 15-hole, dual-row, narrow-included-angle nozzle (10 holes × 70° and 5 holes × 35°) with 103-μm-diameter orifices. This nozzle configuration provided the spray targeting necessary to contain the direct-injected diesel fuel within the piston bowl for injection timings as early as 70° before top dead center. Spray-visualization movies, acquired using a high-speed camera, show that impingement of liquid fuel on the piston surface can result when the in-cylinder temperature and density at the time of injection are sufficiently low. Seven single- and two-parameter sweeps around a 4.82-bar gross indicated mean effective pressure load point were performed to map the sensitivity of the combustion and emissions to variations in injection timing, injection pressure, equivalence ratio, simulated exhaust-gas recirculation, intake temperature, intake boost pressure, and load.

The influence of nitrogen dilution and charge-gas temperature on in-cylinder combustion processes and engine-out NOx and smoke emissions was investigated in an optically accessible heavy-duty DI diesel engine using a high-cetane-number, oxygenated fuel. Engine-out measurements of NOx and smoke emissions and in-cylinder images of natural luminosity were obtained for charge-gas oxygen concentrations from 9% to 21% and TDC charge-gas temperatures of 680 and 880 K. Charge-gas temperature was found to have a significant influence on engine-out NOx emissions, but NOx emissions levels less than 0.2 g/ihp-hr were achieved at both the 680 and 880 K charge-gas temperatures within the investigated range of oxygen concentrations. An indicated engine-out NOx emissions level of 0.09 g/ihp-hr at 18 bar IMEP was achieved using charge-gas dilution and 3.0 bar intake boost pressure.