柴油机纯氧燃烧过程及缸内喷水影响的模拟研究

Simulation Study of Oxy-Fuel Combustion Process and Effect of Direct Water Injection in a Diesel Engine

摘要:

针对高压共轨柴油机搭建流体动力学仿真模型，研究不同进气氧体积分数对柴油机纯氧燃烧过程的影响，并验证缸内喷水对热效率的优化能力。结果表明，氧含量的提高增加了缸内比热比，使压缩行程缸内压力及温度提高，并促进缸内燃烧反应，进一步提升缸内湍流强度，燃烧相位提前；在5 °CA ATDC(上止点后)向缸内喷入160 °C的高温高压水，可实现对缸内燃烧过程的控制，并通过吸收燃烧放热、汽化膨胀，推动活塞做功，可提高热效率约3.75%。

Abstract:

In this paper, a CFD model coupled with detailed chemical mechanism is established based on a common rail diesel engine test platform, the effect of oxygen concentration on diesel engine combustion process is investigated, and the enhancement in thermal efficiency with direct water injection is verified. The calculation results indicate that the in-cylinder specific heat ratio can be improved by increasing oxygen concentration, which results in an elevated in-cylinder pressure and temperature during compression stroke, promotes in-cylinder combustion reactions, enhances in-cylinder turbulence kinetics, and results in an advanced combustion phase. By injecting 160°C high temperature and high pressure water at 5°CA ATDC, the in-cylinder combustion process can be optimized. The injected water absorbs combustion heat and evaporates into steam which further propels the piston during expansion stroke, thus increasing the overall thermal efficiency of the diesel engine by about 3.75%.