Dedicated EGR on a Natural Gas Engine, 03-R8457
Inclusive Dates: 04/01/14 – Current
Background — The novel solution of SwRI's HEDGE technology with dedicated exhaust gas recirculation (D-EGR™) has shown the potential for significant improvement in efficiency for gasoline engines. Combining the D-EGR concept with a heavy-duty natural gas engine has the potential of matching or exceeding the efficiency of a diesel engine, which has been a goal for many years. D-EGR was initially conceptualized in 2007 as a solution to the combustion deterioration associated with high levels of EGR dilution and to simplify EGR controls for gasoline engines. The concept is to take the exhaust from one or more cylinders of a multi-cylinder engine and route its exhaust to the intake to create the entirety of the EGR for the engine. A closed EGR system enables using combustion temperature and pressure to reform fuel by running fuel rich, but without the conventional chemical energy loss associated with rich operation. With natural gas, a D-EGR engine can take advantage of the high hydrogen-to-carbon ratio and combustion characteristics of natural gas and the potential for greater hydrogen production over gasoline. This brings up the possibility of a six-cylinder engine with two dedicated cylinders with a nominal EGR rate of 33 percent. This configuration is shown in Figure 1.
Approach — The objective of this project is to investigate the characteristics of a six-cylinder D-EGR engine with natural gas as the fuel. Baseline testing on a Cummins ISX12-G natural gas engine will be conducted at steady-state conditions. The engine will then be converted to a D-EGR configuration with the assistance of a GT-power model and the same steady-state test points will be conducted. Results from the D-EGR configuration will be compared to the baseline of this engine, and change in efficiency will be documented. The goal is to operate at a nominal EGR rate of 33 percent in all cylinders, but other configurations with different EGR rates should be possible with this engine.
Accomplishments — A Cummins ISX12-G was installed in a steady-state test cell, and a baseline test was conducted at steady-state test points. The steady-state test points include the 13 modes used for emission certification along with additional points to obtain a more complete map of the engine. The conversion of the engine to the D-EGR configuration along with a SwRI control system to operate the engine has been completed and testing has started. The GT-power model of the ISX12-G in the D-EGR configuration has been completed and was used to provide guidance for the D-EGR configuration.