In-cylinder CO and UHC Imaging in a Light-Duty Diesel Engine during PPCI Low-Temperature Combustion 2008-01-1602
Two-dimensional planar imaging and one-dimensional, spectrally-resolved line-imaging of laser-induced fluorescence from CO and UHC are performed to help identify the sources of these emissions in a light-duty diesel engine operating in a partially-premixed compression ignition combustion regime. Cycle-averaged measurements are made in the clearance volume above the piston crown at a 3 bar IMEP, 1500 rpm baseline operating condition. Sweeps of injection timing, load, and O2 concentration are performed to examine the impact of these parameters on the in-cylinder spatial distributions of CO and UHC.
At the baseline operating condition, the main contributions to UHC from the clearance volume stem from regions near the cylinder centerline and near the cylinder wall, where UHC likely emanates from the top ring-land crevice. Broadly distributed CO within the squish volume dominates over CO observed near the cylinder centerline. Advanced or retarded injection forms rich or over-lean mixtures, respectively, in the squish volume-resulting in increased UHC from this region. Advanced injection produces more CO in the squish volume; retarded injection initially produces less. Later in the cycle, higher CO levels are observed with retarded injection than in the baseline case. Increased load richens the mixture in the squish volume region, with little impact on UHC but a reduction in CO. Decreased load results in increased UHC and CO in the squish volume and, eventually, at all radial locations. With decreased O2 concentration, UHC and CO are generally increased throughout the cylinder; combustion within the squish volume is particularly impacted by dilution.
Engine-out emission levels deduced from fluorescence measurements made during the exhaust process are also shown to correlate well with conventional exhaust gas emissions measurements.