A team from Beijing University of Technology and Beijing Automobile Research Institute Company has used ammonia as a combustion inhibitor to mitigate or eliminate knock and to expand power in a direct-injection hydrogen engine.

A paper on their work is published in the journal Fuel.

Hong et al.

Knock-free operation of direct-injection (DI) hydrogen engines at stoichiometric and wide-opening throttle (WOT) conditions is attractive, but combustion knock hinders the implementation of this idea, which inspires the present study. In this work, ammonia, as a combustion inhibitor, is added to the DI hydrogen engine, which is expected to utilize the low reactivity of ammonia and the crowding out of the intake charge to suppress knock and extend speed and λ corresponding to knock limits.

All tests are conducted at WOT conditions. In Part 1, λ is 1.6, and the speed corresponding to the knock limit is elevated from below 1600 rpm to 2000 rpm by injecting ammonia. In Part 2, the speed is kept at 1600 rpm, and the realization process of the engine shifting from lean operation to stoichiometric operation reflects the effectiveness of ammonia addition in suppressing knock.

Then, using the critical knocking state as a boundary, dynamically adjusted ammonia injection enables the engine to achieve stoichiometric operation and prominent power expansion at various speeds. Especially at 3000 rpm, the brake power varies from below 21.0 kW to about 44.2 kW. Furthermore, the suppression mechanism of knock by ammonia addition is revealed by analyzing the mapping relationship between combustion characteristic parameters and knock.

—Hong et al.

Resources

• Chen Hong, Song Xu, Shihao Zhao, Huachuan Zhang, Fangxu Su, Shuofeng Wang, Changwei Ji, “Analysis of ammonia as a combustion inhibitor for combustion knock and power expansion in a DI hydrogen engine,” Fuel, Volume 375, 2024, doi: 10.1016/j.fuel.2024.132481