The Diesel engine is a commercially attractive powerplant, however it is noted to have significant specific output of harmful emissions under some operating conditions. One possible solution for reduction of the harmful emissions from the Diesel engine is greater control over the fuel injection event.
To gain further understanding of liquid phase Diesel fuel injection spray characteristics, a 2.44 liter displacement, 4 stroke engine was modified for optical access and fitted with a Caterpillar Hydraulic Electronic Unit Injection (HEUI) system. The data collection system consisted of a high repetition rate diode pumped Nd:YAG laser frequency doubled to 532 nm for visible illumination and a Kodak High Speed Motion Analyzer for recording fuel spray images.
The engine was motored under various inlet conditions to create an engine combustion chamber environment typical of those found in commercial engines of similar per cylinder displacement class. Parameters studied as independent variables that could affect fuel injection characteristics were; combustion chamber density and combustion chamber temperature at top dead center, engine speed measured in revolutions per minute, fuel injection pressure and fuel injection duration. Liquid fuel spray characteristics measured were; maximum linear penetration distance, maximum spray spreading angle and average penetration velocity. Coupled with penetration distance is also the occurrence of spray to wall impingement.
Spray penetration distance, spreading angle and velocity are important in the effort to gain greater understanding of spray behavior in the engine combustion chamber environment. Spray to wall impingement is of interest due to its perceived role in increased emission of soot and unburned hydrocarbons.
Results showed that similar to fixed volume chamber studies, increase in combustion chamber density or temperature at top dead center and specific to engines, an increase in engine RPM, would cause a decrease in spray penetration distance, spreading angle and velocity. An increase in fuel injection pressure was noted to cause a decrease in spray penetration while increasing spreading angle and penetration velocity. Changes in fuel injection event duration did not show a clearly discernable trend. Spray to wall impingement was noted to occur at lower combustion chamber densities and engine speeds.