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13 April 2023
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.
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