双燃料发动机LNG供给系统参数优化及其工作特性的仿真分析

发布时间：2019-03-09 16:32

【摘要】：天然气以其巨大的储备量,成为我国在未来21世纪重要的发动机可替代燃料。目前在发动机领域对天然气的运用多处于气态形式,存在充气效率低下,结构布置复杂,爆震可能性高等问题。LNG缸内液态直喷不仅能够可以很好的解决这一类问题,还能有利于稀薄燃烧,在燃烧过程中释放大量冷能,显著改善发动机的排放性能,目前还处于理论研究阶段。其所对应的LNG燃料供给系统的开发是该理论实现的难点。在现有的缸内液态直喷燃料供给方式中,高压共轨系统以其无法比拟的优势——极高的喷射压力和柔性的控制策略,为发动机性能的提升留下了巨大空间。高压共轨系统在多缸发动机的应用方面存在轨压波动性大的问题,降低轨压波动性也是目前高压共轨系统的重要发展方向之一。本文主要目的是优化某中速柴油/LNG双燃料发动机LNG电控共轨式燃料供给系统,解决其目前存在的轨压波动量范围较大和建立目标轨压时间较长的问题,提高整个系统的控制精度。本文是以控制轨压波动为目标,对某中速柴油/LNG双燃料发动机LNG电控共轨式燃料供给系统进行参数优化。利用AMESim软件,根据燃料供给系统内高压泵、共轨管、喷射器的原理结构对LNG电控共轨式燃料供给系统进行建模,并修改原来系统的模型。计算并分析高压泵各个关键影响参数对供油特性的影响和对共轨管内压力变化规律的影响。同时为该柴油/LNG双燃料发动机设计与之匹配的电子控制单元(ECU)。确定LNG-柴油双燃料发动机燃料喷射系统ECU的控制策略和算法,并在仿真软件中对控制策略进行模拟,分析不同控制参数对轨压的影响,提高整个高压共轨系统的控制精度。本文经过对比分析,得出以下几点结论:第一,供油相位改变对轨压的波动相位影响更加明显,其中供油起始位置为5度,65度时,轨压波动幅度较小,但是供油相位对于供油特性的影响较小;第二,柱塞升程和柱塞直径对于轨压波动幅度和供油特性的影响都较大;第三,出油阀阀体质量应当选取合适的大小,过大过小都会造成轨压波动量较大,出油阀孔径的过大会造成轨压建立时间较长,出油阀阀体结构参数的对于供油特性影响也较为明显,大于供油相位,小于柱塞升程和柱塞直径;第四,占空比越大,轨压建成时间越短,且轨压波动幅度会明显变大;第五,控制脉冲频率过低会造成轨压波动量过大,但是对轨压建立时间影响不大。
[Abstract]:Natural gas, with its huge reserves, will become an important alternative fuel for engines in the 21st century. At present, the application of natural gas in the field of engine is mostly in the form of gas, the gas filling efficiency is low, the structure arrangement is complex, and the possibility of detonation is high. Liquid direct injection in LNG cylinder can not only solve this kind of problem very well. It is also beneficial to lean combustion, releasing a large amount of cold energy during combustion and improving the emission performance of the engine significantly. At present, it is still in the stage of theoretical research. The development of the corresponding LNG fuel supply system is the difficult point to realize the theory. Among the existing in-cylinder direct injection fuel supply, the high-pressure common rail system, with its incomparable advantages, such as extremely high injection pressure and flexible control strategy, has left a huge space for the improvement of engine performance. The high pressure common rail system has the problem of high pressure fluctuation in the application of multi-cylinder engine. Reducing the rail pressure fluctuation is one of the important development directions of the high-pressure common rail system at present. The main purpose of this paper is to optimize the LNG electronically controlled common rail fuel supply system for a medium-speed diesel / LNG dual-fuel engine, and to solve the problems of the wide range of orbital pressure wave momentum and the long time to establish the target rail pressure. Improve the control accuracy of the whole system. In order to control the rail pressure fluctuation, the parameter optimization of a medium-speed diesel / LNG dual-fuel engine LNG electronically controlled common-rail fuel supply system is presented in this paper. According to the principle structure of high pressure pump, common rail tube and injector in the fuel supply system, the AMESim software is used to model the LNG electronically controlled common rail fuel supply system and modify the model of the original system. The influence of the key parameters of the high-pressure pump on the fuel supply characteristics and the pressure variation in the common rail tube are calculated and analyzed. At the same time, a matching electronic control unit (ECU).) is designed for the diesel / LNG dual fuel engine. The control strategy and algorithm of LNG- diesel dual fuel engine fuel injection system ECU are determined, and the control strategy is simulated in the simulation software. The influence of different control parameters on rail pressure is analyzed, and the control precision of the whole high pressure common rail system is improved. Through comparison and analysis, this paper draws the following conclusions: first, the change of fuel supply phase has more obvious influence on the fluctuating phase of rail pressure, in which the initial position of oil supply is 5 degrees, and the fluctuation range of rail pressure is small at 65 degrees. However, the phase of oil supply has little effect on the fuel supply characteristics. Secondly, plunger lift and plunger diameter have great influence on rail pressure fluctuation and oil supply characteristics. Thirdly, the mass of the outlet valve should choose the appropriate size, too large and too small will cause the rail pressure wave momentum to be larger, and the overpass of the oil outlet valve aperture will cause the rail pressure to be established for a long time. The structure parameters of the valve body also have obvious influence on the oil supply characteristics, which is larger than the oil supply phase and smaller than the plunger lift and plunger diameter. Fourth, the higher the duty cycle, the shorter the rail pressure build-up time, and the rail pressure fluctuation amplitude will obviously increase; fifthly, the low control pulse frequency will cause the rail pressure fluctuation to be too large, but has little effect on the rail pressure establishment time.
【学位授予单位】：江苏科技大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TK403

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