Injection Rate Shaping Investigations on a Small – Bore DI Diesel Engine 2009-01-0850
So far, the effect of injection rate shaping on the diesel combustion in small-bore DI diesel engines has not been extensively investigated, especially at high part load conditions with high EGR rates. The benefit of injection rate shaping is already verified for heavy duty engines at high load conditions with and without EGR. For this investigation, single cylinder engine investigations were conducted at the VKA / RWTH Aachen University.
In order to meet the future NOx legislation limits like US-Tier2Bin5 it is crucial to reduce NOx especially at the high load points of the certification cycles, as FTP75 or US06. For the single cylinder investigations two part load points were chosen, which have relevance for the mentioned certification cycles. The experimental work focuses on different rate shapes as rectangular (Common-Rail type), ramp and boot shape at high EGR rates.
Ramp and boot shapes were optimized in terms of angle (ramp shape) and length and height (boot shape) in order to find the best emission, efficiency and combustion noise result.
The resulting rate shapes were compared in variations of injection timing for constant EGR rates.
The measurement data was analyzed in order to find explanations for the observed engine behavior. This was done by means of zero-dimensional heat release calculations and three-dimensional CFD calculations with the open-source program KIVA 3V.
Additionally, CFD calculations were conducted by the Institute of Technical Combustion, using a Representative Interactive Flamelet (RIF) model. This paper contains the model calibration to the experimental results and first emission calculations.
The comparison of rectangular, ramp and boot injection shows, as expected, a retardation of the combustion for the ramp shape and especially the boot shape in comparison to the rectangular shape. For constant start of injection and constant EGR rate, this leads to reduced NOx emission and improved combustion noise especially for the boot injection shape, without drawbacks in the other emissions or engine efficiency.