Effects of exhaust gas recycle loop layout and retarded intake valve closing on variations in combustion in a heavy-duty diesel engine

Abstract

To improve engine response and decrease exhaust smoke and NOx emission during transient operations, variations in cycle-to-cycle and cylinder-to-cylinder combustion were investigated in a two-stage turbocharged, exhaust gas recirculation heavy-duty diesel truck engine. Variations in combustion were confirmed to be caused by insufficient mixing of the exhaust gas recirculation with intake air. And steady operation, by increasing the length of the mixing path, coefficient of variation of the exhaust gas recirculation rate in cylinder 1 declined from 8.12% to 3.68%, while that for the other cylinders decreased from approximately 4.0% to 2.98%. These improvements also caused reductions in coefficient of variations for indicated mean effective pressure and crank angle of 50% fuel burned (CA50). By using an intake valve closing timing retarding actuator system, coefficient of variation of the exhaust gas recirculation rate for cylinder 1 was further decreased from 3.68% to 2.82%. It was interesting to find that EGR/air mixing length revealed a great effect on soot and NOx emissions during transient operations, especially those involving sudden increases in load. By using long mixing path instead of short mixing path combined with suitable fuel injection strategy and exhaust gas recirculation rate, transient response of load was reduced by 10% and transient smoke spike decreased from 0.8m-1 to 0.5m-1.

Study on the Effects of Exhaust Gas Recirculation and Fuel Injection Strategy on Transient Process Performance of Diesel Engines

“…In previous research from Wu et al [50], they mainly analyzed the impact of the EGR mixing time on diesel engine cyclic variation and experimentally compared the impacts of EGR systems with different mixing times on emissions during 1-3 s transient processes. However, since they did not optimize the EGR valve control, the maximum soot emission reduction was only 37.5%.…”

A Review of Energy Loss Reduction Technologies for Internal Combustion Engines to Improve Brake Thermal Efficiency

“…It was concluded that in comparison to VVT engines, CVVL engines have greater potential for minimizing pumping loss at low-to-medium loads, and as the valve lift increases to a certain value, the downtrend of pumping loss becomes slower, approaching the theoretical lower limit. There are many ongoing studies exploring the positive outcomes of VVT and LIVC technologies in diesel engines [64][65][66]. Daimler proposed and patented an asymmetric turbocharger without mobile vane actuation, with more compact parts than the conventional variable-geometry turbocharger (VGT); it provides more effective turbocharging performance, with reduced pumping loss, and is able to drive the EGR rate up to 35% at full load on Detroit Diesel's HD platform [67].…”

Experimental Analysis of Cyclical Dispersion in Compression-Ignited Versus Spark-Ignited Engines and Its Significance for Combustion Noise Numerical Modeling

“…However, recent studies made by Finney et al [6] demonstrated that cyclic variability are not only originated by stochastic fluctuations in the flow field, they postulate that the CCV exhibit a real deterministic behaviour result of the particular conditions reached during the previous cycles. An example of this behaviour is the rebound effect that a partial burning cycle can be succeed by a cycle with a higher expected output due to the unburned fuel present in the residual gases [24].…”