A team at Beijing University of Technology has evaluated four load control strategies—throttle, ammonia-hydrogen ratio, air–fuel ratio, and variable valve timing—for an ammonia-hydrogen dual fuel Miller cycle spark ignition engine in a hybrid system. A paper on their work appears in the journal Fuel.
The engine—a Miller cycle engine with a compression ratio of 10.7—was modified with a set of hydrogen common rail and ammonia common rail installed on the intake manifold to realize the controllable supply of ammonia and hydrogen.
In the 1960s, the researchers noted, GM studied the performance of ammonia combustion engines and found them to be significantly less thermally efficient than gasoline-fueled engines. However, hydrogen burns fast, has a wide flammable limit, and has low ignition energy, making it very suited as an additive to ammonia.
The team found that the throttle strategy provides the widest output range, and the BMEP is raised from a minimum of 1 bar to 7.4 bar. The ammonia-hydrogen mixing ratio strategy is suitable for cold start conditions, fully utilizing the good combustion characteristics of hydrogen, and at the same time reducing the amount of hydrogen used in the heat engine process as much as possible. T
The air–fuel ratio strategy provides the highest thermal efficiency with a maximum BTE approaching 40%. It satisfies the energy-saving demand under the single-point working condition of the engine in the series hybrid mode.
The variable valve timing strategy can realize switching between BMEP between 3.5 bar and 6.5 bar, and keep BTE above 33%. The valve timing strategy can not only provide a wider load adjustment range but also maintain high thermal efficiency, they found.
… combining the effects of the four control strategies and the typical operating modes of the hybrid system, this study suggests that the throttle strategy is suitable for the feed mode, the VVT strategy is suitable for the parallel mode, the ammonia-hydrogen mixture ratio strategy is suitable for the cold start condition, and the air–fuel ratio control is suitable for the series mode.
—Xin et al.
