袁成威，刘博，江枭枭，周磊，陈锐，卫海桥.缸内直喷天然气低速船机压力振荡抑制方法数值研究[J].内燃机工程,2019,40(6):56-63.
缸内直喷天然气低速船机压力振荡抑制方法数值研究
Numerical Study on Pressure Oscillation Suppression of Low-Speed Marine Engine with In-Cyinder Direct Injection of Natural Gas
DOI：10.13949/j.cnki.nrjgc.2019.06.009
关键词:低速船用发动机；双燃料；压力振荡；米勒循环；喷射策略  计算流体力学
Key Words:low-speed marine engine  dual fuel  pressure oscillation  Miller cycle  injection strategy  CFD
基金项目:船用低速机工程（一期）研制项目（CDGC01-KT0308）
作者单位
袁成威，刘博，江枭枭，周磊，陈锐，卫海桥 1.天津大学 内燃机燃烧学国家重点实验室，天津 300072； 2.中船动力研究院有限公司，上海 201206； 3.拉夫堡大学 航空与汽车工程系，拉夫堡 LE11 3TU， 英国 
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摘要:基于计算流体力学（CFD）软件CONVERGE建立了大型低速2冲程柴油引燃缸内直喷天然气船用发动机燃烧仿真模型。首先通过试验结果对模型进行了验证，进而开展了天然气高压喷射模式（high pressure direct injection，HPDI）下米勒循环和天然气两次喷射策略对发动机压力振荡的抑制效果研究。结果表明，推迟排气门关闭时刻，整体燃烧压力降低，燃烧相位推迟，发生剧烈压力振荡的时刻也推迟。排气门关闭时刻推迟较小时压力振荡强度降低，但过度推迟反而提高缸内压力振荡的强度，这主要是缸内热力学状态变化和燃料自燃特性相互作用的结果。通过调整预喷射量，可以降低燃烧前形成的可燃混合气量，从而影响燃烧过程中预混合燃烧比例，可以有效抑制压力振荡.但会导致输出功率降低及能耗增大。相比预喷射量，喷射间隔对缸内压力振荡的影响较小，但过大喷射间隔会影响燃烧相位，导致功率损失严重。合理的喷射策略可以在抑制压力振荡的同时保证功率输出。
Abstract:Based on the computational fluid dynamics(CFD) software(CONVERGE), the simulation model of a large low-speed two-stroke marine engine in which pilot diesel and natural gas are injected directly in cylinder was established. Validated by the experimental data from the literature, the model was then applied to studying the suppression effect of the Miller cycle and natural gas two-stage injection strategy on the pressure oscillation in high pressure direct injection mode. The calculation results indicated that when the exhaust valve was closed later, the overall combustion pressure was lower, both the combustion phase and the moment of severe pressure oscillation were delayed. The intensity of pressure oscillation was reduced with smaller delay of exhaust valve closing, while it was increased instead with an excessive delay. This was primarily attributed to the competitive relation between in-cylinder thermodynamic state and auto-ignition characteristics of fuel. Adjusting the pre-injection quantity of natural gas would reduce the formation of premixed combustible mixture before combustion, thus reducing the proportion of premixed combustion in the combustion phase, which could effectively suppress pressure oscillation, but could also reduce the output power and increase the fuel consumption. Compared with the pre-injection quantity, varying injection interval has less effect on the pressure oscillation, but the excessive injection interval would affect the combustion phase, resulting in considerable power loss. A reasonable injection strategy can ensure the power output while suppressing intense pressure oscillation.
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