The objective of this research was to improve the scavenging process on a heavy-duty, two-cycle, medium speed, diesel engine (710 cubic inches of displacement per cylinder) under high load. It was desired to expel as much of the residual gases in the combustion chamber during the scavenging process, without having the fresh intake air escaping through the exhaust valves. This allowed a cooler intake charge with a higher oxygen concentration to be used. Having a cooler air intake charge was beneficial for emissions and performance. The power assembly configuration for the investigation was a two-cycle engine with intake ports around the bottom portion of the cylinder liner and four exhaust valves in the cylinder head. The main variable in this study was the axial location of every other intake port on the cylinder liner. When the axial location increased, this created pseudo longer intake timing. To keep the amount of trapped mass constant, the exhaust valves remained opened longer. The effectiveness of the scavenging process was estimated by the concentration of trapped oxygen (O2), carbon dioxide (CO2), and water vapor (H2O) along with the average temperature of the intake charge at the end of scavenging. The final part of the research explored each modified cylinder liner under full load, combustion operating conditions, while varying the injection timings. Soot, nitrogen oxides (NOx) and fuel consumption were also examined. A proprietary, multi-dimensional, computational fluid dynamic (CFD) code was used for the modeling work. Sculptor™, a commercial software package, was used to morph the cylinder liner.
The results showed that by increasing the axial location of the intake ports, a cooler intake charge with higher oxygen and lower carbon dioxide and water vapor concentrations resulted. This suggested more exhaust gases were expelled from the combustion chamber and replaced with fresh air. The rate of improvement slowed down after increasing the intake port axial location by 15.0 mm. In the next step, the compression and combustion process of the different port locations was studied. The cases with higher intake port axial locations were found to have lower pressure throughout the compression and power cycles. The temperature was lower for cases with elevated intake ports, until combustion started. The final part of the research studied the modified intake port cases under combustion simulation, while varying the injection timing. Next, the results showed an improvement in soot and fuel consumption with an increase in NOx for a given injection timing. However, while injection timing was varied, it was possible to improve NOx, soot, and fuel consumption simultaneously when compared to the baseline.
