缸内高温喷水量对压燃式内燃兰金循环发动机燃烧及性能影响的试验研究

Experimental Study on the Effect of Direct Water Injection Mass on the Efficiency and Performance of CI-ICRC Engine

内燃兰金循环采用氧气代替空气作为助燃剂,规避了氮氧化物排放物,采用冷凝方式对废气中二氧化碳和水蒸气进行分离回收再利用,实现了高效率与超低排放的内燃动力循环。本文采用自主开发的压燃式内燃兰金循环发动机试验台架进行了缸内高温喷水量对其燃烧及性能影响的试验研究。试验研究发现:在燃烧过程中喷入吸收了排气废热的循环水可以调控燃烧速度,使缸内最大爆发压力相位推迟,上止点附近缸内比热容的增大和水的相变潜热降低缸内温度进而减少压缩负功,闪急沸腾产生的高温高压水蒸气补充了做功工质以增加膨胀正功。随着喷水量的增加,发动机的指示热效率先上升后下降,在97 mg喷水量的试验工况下,实现了46.6%的最佳有效热效率,并且IMEP和燃烧循环稳定性也有明显改善。

Internal combustion Rankine cycle(ICRC) utilize oxygen instead of air as oxidant,therefore avoiding NO;generation. The carbon dioxide and water vapor in the exhaust gas can be separated and recycled through condensation. By doing so, a high-efficiency and ultra-low-emission internal combustion thermodynamic cycle is achieved. In this paper, the effect of high temperature direct water injection mass on cycle efficiency and performance is studied based on a self-developed compression ignition internal combustion Rankine cycle engine(CI-ICRC) test bench. The experimental results show that injecting high temperature and high pressure recycled water during combustion process can optimize combustion rate and postpone the maximum in-cylinder pressure timing. Increment of in-cylinder specific heat capacity and heat absorption through in-cylinder water latent heat reduce in-cylinder temperature which decrease negative compression work and the high temperature and high pressure steam generated through flash boiling of in-cylinder water jet supplements the work fluid quality, therefore enhance cyclic output work. As direct water injection mass increasing, the brake thermal efficiency rises firstly and then falls, under test condition of 97 mg direct water injection mass, an optimum brake thermal efficiency of 46.6% was achieved. Meanwhile,its IMEP and combustion stability have also been significantly improved.