Improving Heavy Duty Natural Gas Engine Efficiency: A Systematic Approach to Application of Dedicated EGR

The worldwide trend of tightening CO₂ emissions standards and desire for near zero emissions is driving development of high efficiency natural gas engines for a low CO₂ replacement of traditional diesel engines. A Cummins Westport ISX12 G was previously converted to a Dedicated EGR® (D-EGR®) configuration with two out of the six cylinders acting as the EGR producing cylinders. Using a systems approach, the combustion and turbocharging systems were optimized for improved efficiency while maintaining the potential for achieving 0.02 g/bhp-hr NO_X standards. A prototype variable nozzle turbocharger was selected to maintain the stock torque curve. The EGR delivery method enabled a reduction in pre-turbine pressure as the turbine was not required to be undersized to drive EGR. A high energy Dual Coil Offset (DCO®) ignition system was utilized to maintain stable combustion with increased EGR rates. High compression ratio, reduced squish pistons were designed to maintain MBT combustion phasing and fast burn rates along the torque curve. The final engine configuration was tested on the Heavy-Duty Supplemental Emissions Test (SET), a 13-mode steady-state engine dynamometer test. The engine was able to achieve a weighted average efficiency improvement of 12% over the baseline configuration with a peak BTE of 41.7%.