Effects of hydrogen addition on combustion characteristics of a free-piston linear engine with glow-assisted ignition

In this paper, the combustion characteristics of a methane-fueled free-piston linear engine (FPLE) with glow-assisted ignition (GAI) under different hydrogen fractions were studied by numerical simulations. The results showed that the chain-branching reactions start to process after the ignition source appears. The fuel-air mixture can be successfully ignited under the compression of the piston. Hydrogen addition to the fuel accelerates the elementary reaction and helps enhance the ignition and combustion processes. Compared with that of pure methane, the maximum HRR increases by 9.4%, 49.4%, 75.6%, 124.7%, and 241.4% with hydrogen fractions of 1.0%, 3.0%, 5.0%, 7.0%, and 9.0%, respectively. High hydrogen concentration (greater than 7.0%) can bring the occurring of over-advanced combustion, resulting in higher compression negative work. With the hydrogen fractions changing from 0% to 9.0%, the CA0e10 first decreases and then increases, with its minimum value at alpha(H2) = 7:0%, and the CA10-90 is gradually decreased. The hydrogen addition raises the combustion temperature, which in turn, results in higher NOx emission. High combustion temperature helps convert carbon monoxide into carbon dioxide, decreasing the emission amount of CO. Hydrogen addition to methane has competition effect on soot emission. On one hand, it reduces the soot emission by soot oxidation. Another hand it causes chemical effect leading to higher soot nucleation and surface growth rates. In this paper, the result of competition suppresses soot formation. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Automated summary

In this study, numerical simulations were used to investigate the combustion characteristics of a methane-fueled free-piston linear engine with glow-assisted ignition under different hydrogen fractions. The results showed that hydrogen addition accelerates elementary reactions and enhances ignition and combustion processes. Furthermore, hydrogen addition increases combustion temperature, leading to higher NOx emissions.