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高效清洁燃烧

摘要

Knocking combustion remains the main obstacle in improving engine thermal efficiency of spark-ignited engines for decades. Meanwhile, jet ignition is increasingly deemed as a promising way to increase engine thermal efficiency for it helps to promote burning velocity when compared to conventional spark ignition. Insights into knocking combustion under jet ignition under jet ignition is therefore of great importance, which has still not been fully understood yet. This work provides insights into the knocking characteristics and end-gas auto-ignition behaviors under jet ignition system by applying high-speed photography and high-frequency pressure acquisition. Experiments with spark ignition were also conducted for comparison. Different knocking characteristic and auto-ignition modes were observed under jet ignition astride wide initial thermodynamic conditions. Results shows that the jet ignition holds the capability in reducing both combustion duration and knocking intensity when compared with single spark plug condition. The end-gas auto-ignition mode undergoes non-auto-ignition, auto-ignition and detonation successively with the increase in initial pressure, similar to that of SI modes except the position of end-gas region. Thermodynamic analysis indicates that the auto-ignition under jet ignition tends to occur at higher thermodynamic condition due to less heat loss compared with SI mode, which in turn leads to a smaller Livengood-Wu integration at auto-ignition timing. Finally, the experimental results also show good agreement with the Dat-Ret diagram. Cases with auto-ignition and detonation onset are all located in Mixed/DDT region and strong ignition region, exhibiting good fidelity.

关键词

jet ignition;auto-ignition;detonation;ignition regime

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