Abstract
In-cylinder imaging of unburned hydrocarbon (UHC) distributions was performed via planar laser-induced fluorescence (PLIF) in a light-duty diesel engine employing a partially-premixed compression ignition (PPCI) combustion scheme. Measurements were acquired in the bowl and clearance volume at a light load baseline condition with optimized injection timing. With the fueling rate held constant, the injection timing was both advanced and retarded to help clarify the source of high level UHC emissions. The UHC composition was further investigated by spectral analysis of the fluorescence signal. Three major UHC sources were identified: nozzle dribble from the injector tip, low-temperature mixture of incomplete reactants within the cylinder core surrounding the injector and crevice region fuel accumulation along the cylinder sidewalls. Injection timing was found to influence UHC composition and concentration in each of the identified regions.
