Petersen, B., Ekoto, I., and Miles, P., "An Investigation into the Effects of Fuel Properties and Engine Load on UHC and CO Emissions from a Light-Duty Optical Diesel Engine Operating in a Partially Premixed Combustion Regime," SAE Int. J. Engines 3(2):38-55, 2010, https://doi.org/10.4271/2010-01-1470.
The behavior of the engine-out UHC and CO emissions from a light-duty diesel optical engine operating at two PPCI conditions was investigated for fifteen different fuels, including diesel fuels, biofuel blends, n-heptane-iso-octane mixtures, and n-cetane-HMN mixtures. The two highly dilute (9-10% O₂) early direct injection PPCI conditions included a low speed (1500 RPM) and load (3.0 bar IMEP) case~where the UHC and CO have been found to stem from overly-lean fuel-air mixtures~and a condition with a relatively higher speed (2000 RPM) and load (6.0 bar IMEP)~where globally richer mixtures may lead to different sources of UHC and CO. The main objectives of this work were to explore the general behavior of the UHC and CO emissions from early-injection PPCI combustion and to gain an understanding of how fuel properties and engine load affect the engine-out emissions.The UHC and CO emissions from an emissions certification diesel fuel and several soy- and palm-based biofuel blends were found to partially collapse when plotted as a function of the premixed burn duration for the low speed and load condition. Significant reductions in both UHC and CO were observed with the biofuel blends. The engine-out UHC and CO emissions and premixed burn duration, which directly correlates with the magnitude of the peak heat-release, were shown to depend on three general parameters: (1) the injection timing, which controls the targeting and the initial thermodynamic state of the ambient gases; (2) the mixing time between the fuel and ambient gases during the ignition delay period; and (3) the premixed combustion phasing, which controls the temperature, pressure, and mixture state during premixed combustion. In order to investigate the effects of ignition quality and volatility in greater detail, a controlled parametric study involving nine different fuels was conducted. The fuels were selected to provide an orthogonal fuel matrix in which ignition quality and volatility were varied independently. The advancement of the combustion phasing for fuels with higher ignition quality was found to significantly decrease the UHC and CO emissions, while fuel volatility was determined to have a much smaller effect on the engine-out emissions. The emissions from the higher speed and load condition were found to be mainly dependent on the injection timing and were less sensitive to fuel type. This is consistent with previous studies that have attributed the behavior of the UHC and CO emissions at higher loads to bulk mixing processes controlled by the targeting of the injected fuel spray.