Study on combustion characteristics of lean coalbed methane engines based on hydrogen jet ignition
Hydrogen is a highly reactive gas,and using hydrogen jet flames as seed flames has become one of the hot research directions for the combustion application of low-grade gases,such as low concentration coalbed methane.Hydrogen jet ignition for engine applica-tions induces different ignition modes due to the phase difference between direct injection and ignition,thereby influencing engine per-formance.This study employed numerical simulation methods to establish a three-dimensional model of a large-bore engine with direct injection ignition of premixed lean coalbed methane+hydrogen.By comparing the effects of hydrogen injection ignition phase difference(φ)on engine cylinder flame propagation,flame structure,and engine indicated thermal efficiency,the impact of hydrogen jet ignition mode on engine combustion characteristics was investigated.Results reveal that when φ＞70 ℃ A,post-ignition in-cylinder conditions are characterized by homogeneous combustion;when 20° CA≤φ≤ 70° CA,post-ignition conditions exhibit inverse concentration stratification combustion;while when φ＜20℃A,flame feathering ignition combustion occurs.At a hydrogen injection timing of 30℃A BTDC and ig-nition angel of 25℃A BTDC,flame feathering ignition combustion achieves the highest indicated thermal efficiency of 39.3％.Compar-atively,in contrast to homogeneous combustion and inverse concentration stratification,flame feathering ignition reduces flame develop-ment period by 11.9％and 22.1％,and combustion duration by 1.1％and 1.6％,respectively.
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