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SJTU team investigating ammonia HCCI combustion in free piston engine

Researchers at Shanghai Jiao Tong University are investigating ammonia-fueled HCCI combustion in a free piston engine. In a paper published in the journal Fuel, they report an optimal compression ratio (CR = 25) for ammonia igniation and an optimal piston trajectory (symmetric trajectory with Ω = 0.5) for ammonia HCCI combustion to enhance thermal efficiency and NOx reduction simultaneously.

Ammonia is a promising carbon–neutral fuel, able to power heavy-duty vehicles, non-road machineries and ocean ships with zero CO2 emission. However, practical challenges still exist when applying ammonia in traditional internal combustion engines (ICEs) due to its high ignition energy, slow flame propagation and significant NOx emissions.

Free piston engine (FPE) is a flexible alternative to ICE whose piston can move freely without the constraints of crankshaft. Therefore, its piston trajectory can be leveraged as a new control means to facilitate ammonia combustion.

—Zhang et al.

To investigate ammonia HCCI combustion in an FPE, the team first developed a model including a unique trajectory synthesizing mechanism and a detailed reaction mechanism of ammonia oxidation. They then applied various asymmetric piston trajectories in the model.

The simulated HCCI combustion was analyzed through six characteristics: indicated thermal efficiency; location of peak pressure; exhaust gas temperature; combustion duration; ignition delay and NOx emissions.


  • Chen Zhang, Biaowu Lu, Jinlong Wang, Lei Zhu, Jin Xiao, Zongxuan Sun, Zhen Huang (2023) “Numerical analysis of ammonia HCCI combustion in a free piston engine through trajectory-based combustion control,” Fuel, Volume 341 doi: 10.1016/j.fuel.2023.127634


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