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Researchers find turbulent jet ignition improves combustion of NH3/H2 mixtures

Researchers from the Beijing University of Technology have found that the combustion of NH3/H2 can be effectively improved by using turbulent jet ignition (TJI), especially under high NH3 fraction conditions. A paper on their work appears in the journal Fuel.

Although NH3 is a potential carbon-free fuel with good storage and transportation performance, NH3 is also a low-reactivity fuel, mainly manifested in high ignition energy, narrow flammability limits and low laminar burning velocity. When pure NH3 is applied to ICEs, problems such as difficult ignition and combustion instability caused by low reactivity may occur. Therefore, the blending of highly active fuels is considered necessary for NH3.

H2 is also a carbon-free fuel and has strong reactivity. The physical and chemical properties of H2 lead to its flammable and explosive properties. Although H2 ICEs show high efficiency, they also face the problem of abnormal combustion, such as backfire, knock and pre-ignition. Considering the significant difference in physicochemical properties between H2 and NH3, it is reasonable to use the NH3/H2 mixture as the fuel supply for ICEs.

Compared with traditional spark ignition, better ignition and combustion performance can be obtained by adopting advanced ignition methods. Turbulent jet ignition (TJI) is a potential advanced ignition method that can enhance the ignition and combustion of unburned mixtures. And TJI is already considered one of the reliable ignition methods for ICEs, including passive TJI mode and active TJI mode.

In the TJI system, a small amount of the mixture is ignited in the pre-chamber, then the hot jet enters the main chamber through the connected orifice and ignites the unburned mixture. The distributed ignition source and strong turbulence can be provided by using the TJI system to enhance the combustion of the unburned mixture. And the greater initial flame area can be promoted by the reacting jet, thus it is beneficial for the rapid combustion in the main chamber.

… The main purpose of the present work is to provide insights into the application of NH3/H2 in passive TJI internal combustion engines.

—Wang et al.

The experiment to investigate the effect of fuel composition and equivalence ratio was conducted in a constant volume combustion bomb. The experimental results show that the addition of H2 has a significant positive effect on the ignition and combustion performance.

With the addition of H2, the ignition delay and combustion duration decrease evidently. Hydrogen addition is also beneficial for improving the ignition mechanism and achieving flame ignition. In addition, poor ignition performance may occur under rich conditions due to the fluid-dynamic quenching of the jet.

However, the high flame propagation rate on the rich side leads to lower combustion duration. Increasing the orifices number appropriately can enhance the ignition and combustion performance. The jet strength is weakened by the increased total orifice area and the ignition of NH3/H2 can be improved.


  • Zhe Wang, Changwei Ji, Tianyue Zhang, Shuofeng Wang, Haowen Yang, Yifan Zhai, Jinxin Yang (2024) “Experimental study on the combustion of NH3/H2/air based on the passive turbulent jet ignition,” Fuel, Volume 365, doi: 10.1016/j.fuel.2024.131268.


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