Study on Effect of Negative Valve Overlap on Combustion Characteristics of Hydrogen-doped Natural Gas HCCI Engine
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摘要: 为提高掺氢天然气均质压燃(HCCI)发动机性能, 降低NOx排放, 运用GT-power和Chemkin软件搭建发动机仿真模型, 在不同负气门重叠(NVO)方案下, 对发动机缸内燃烧以及NOx的排放进行了仿真分析。结果表明: NVO策略可以降低掺氢天然气HCCI发动机缸内温度和压力峰值, 改善自燃着火特性, 缓解噪声和爆震。3种方案中, 单独改变进气门开启(IVO)时刻的NVO策略对发动机动力损失影响最小, 同时改变IVO和EVC时刻的对称NVO策略, 能最大程度的实现废气缸内稀释作用与加热效果, 使缸内燃烧放热速率的缓和作用以及压力升高率的降低效果最优化, 最大限度的降低NOx排放。Abstract: To improve the performance of hydrogen-doped natural gas homogeneous compression-ignition (HCCI) engine and reduce NOx emissions, a coupled simulation model of HCCI engine was built based on GT-power and Chemkin software and using negative valve overlap (NVO) strategy. The in-cylinder combustion and NOx emission were simulated for different scenarios of NVO. The results show that the NVO strategy can reduce the peak in-cylinder temperature and pressure, improve the auto-ignition ignition characteristics, and mitigate noise and detonation in hydrogen-doped natural gas HCCI engines. Among the three schemes, the NVO strategy that changes the intake valve opening (IVO) moment alone has the least effect on engine power loss, and the symmetric NVO strategy that changes the IVO and EVC moments simultaneously can maximize the in-cylinder dilution effect and heating effect of exhaust gas, optimize the moderating effect of in-cylinder combustion exothermic rate and the reduction effect of pressure rise rate, and minimize NOx emission.
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图 4 排气门早关对缸内EGR率的影响
Figure 4. Effect of early exhaust valve closure on in-cylinder EGR rate
图 5 排气门早关对缸内充气效率的影响
Figure 5. Effect of early exhaust valve closure on cylinder filling efficiency
图 6 排气门早关时刻对缸内压力的影响
Figure 6. Effect of exhaust valve early closing moment on in-cylinder pressure
图 7 排气门早关时刻对缸内温度的影响
Figure 7. Effect of exhaust valve early closing moment on cylinder temperature
图 8 排气门早关时刻对缸内压力升高率的影响
Figure 8. Effect of exhaust valve early closing moment on the rate of pressure rise in the cylinder
图 9 排气门早关时刻对缸内放热率的影响
Figure 9. Effect of exhaust valve early closing moment on cylinder heat release rate
图 10 排气门关闭时刻对NOx排放的影响
Figure 10. Effect of exhaust valve closing moment on NOx emission
图 11 进气门晚开对缸内EGR率的影响
Figure 11. Effect of late opening of intake valve on in-cylinder EGR rate
图 12 进气门晚开对缸内充气效率的影响
Figure 12. Effect of late opening of intake valve on cylinder filling efficiency
图 13 进气门开启时刻对缸内压力的影响
Figure 13. Effect of intake valve opening moment on in-cylinder pressure
图 14 进气门开启时刻对缸内温度的影响
Figure 14. Effect of intake valve opening moment on in-cylinder temperature
图 15 进气门开启时刻对缸内压力升高率的影响
Figure 15. Effect of intake valve opening moment on in-cylinder pressure rise rate
图 16 进气门开启时刻对缸内放热率的影响
Figure 16. Effect of intake valve opening moment on in-cylinder heat release rate
图 17 进气门开启时刻对NOx排放的影响
Figure 17. Effect of intake valve opening moment on NOx emission
图 22 对称NVO对缸内压力升高率的影响
Figure 22. Effect of symmetric NVO on pressure rise rate in the cylinder
图 23 对称NVO对缸内放热率的影响
Figure 23. Effect of symmetric NVO on the exothermic rate in the cylinder
表 1 试验发动机主要参数
Table 1. Main parameters of a test engine
项目 数值 排量 0.815 L 缸径×行程 95 mm×115 mm 压缩比 17∶1 连杆长度×曲柄半径 210 mm×57.5 mm 标定功率/转速 10.6 kW/2 200 r/min 标定燃油消耗率 ≤244.8g/kW·h 最大扭矩/转矩 50.2 Nm/1 760 r/min 排气门开启正时 43 ℃A BBDC 进气门开启正时 15 ℃A BTDC 排气门关闭正时 15 ℃A ATDC 进气门关闭正时 33 ℃A ABDC 
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