Performance Evaluation of Dedicated EGR on a 12 L Natural Gas Engine

Southwest Research Institute (SwRI) converted a Cummins ISX 12 G in-line six-cylinder engine to a Dedicated EGR^TM (D-EGR^TM) configuration. D-EGR is an efficient way to produce reformate and increase the EGR rate. Two of the six cylinders were utilized as the dedicated cylinders. This supplied a nominal EGR rate of 33% compared to the baseline engine utilizing 15-20% EGR. PFI injectors were added to dedicated cylinders to supply the extra fuel required for reformation. The engine was tested with a high energy dual coil offset (DCO®) ignition system. The stock engine was tested at over 70 points to map the performance, 13 of these points were at RMC SET points.

The D-EGR converted engine was tested at the RMC SET points for comparison to the baseline. The initial results from the D-EGR conversion show a 4% relative BTE improvement compared to the baseline due to the increased EGR rate at 1270 rpm, 16 bar BMEP. At this test point the DCO system was able to operate the dedicated cylinders up to an equivalence ratio of 1.4. The A25 and B25 test points showed the largest relative improvement from a large increased in EGR rate at that load condition. At low loads the main cylinders become more stable as the dedicated cylinder equivalence ratio was increased from improved 0-2% burn duration. The dedicated cylinders were the first to become unstable due to the rich limit.