Simulation and Measurement of Transient Fluid Phenomena within Diesel Injection
Simulation and Measurement of Transient Fluid Phenomena within Diesel Injection
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DOI：
10.4271/2019-01-0066
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发表时间：
2019-01
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影响因子：
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通讯作者：
M. Gold;R. Pearson;J. Turner;Daniel Sykes;V. Stetsyuk;G. de Sercey;C. Crua;Mithun Murali-Girija-Mithun-Murali-Giri
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文献类型：
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作者：
M. Gold;R. Pearson;J. Turner;Daniel Sykes;V. Stetsyuk;G. de Sercey;C. Crua;Mithun Murali-Girija-Mithun-Murali-Giri
近年来，现代柴油喷射系统的轨压显着增加，大大改善了主燃油喷射事件的雾化和燃烧过程的空气利用率。对将燃料引入气缸的过程的控制的不断改进导致人们对与瞬态响应相关的流体现象的关注。高速显微镜已用于可视化汽车柴油喷油器在打开、关闭和后喷射过程中近喷嘴区域周围的详细流体动力学。已经进行了补充计算流体动力学 (CFD) 模拟，以阐明这些高度瞬态事件期间液相和气相的相互作用，包括对紧密耦合注入的评估。显微成像显示在喷射的初始阶段形成活塞流，并快速过渡到初级分解状态，过渡到精细雾化喷雾以及随后的燃料汽化。在喷射器关闭期间，喷雾崩溃，有证据表明旋转破碎结构以及不稳定的燃料韧带破碎成大的缓慢移动的液滴。这导致由较早、更充分发展的喷雾形成的发展火焰锋中的燃烧不理想。模拟结果预测了这些观察到的现象，包括由于大的缓慢移动的液滴和液体燃料的喷射后排放而导致的喷射器表面润湿。这项工作表明，燃料的喷射后排放在喷射器外表面上沉积物的初始形成和随后的积累的机制中发挥着一定作用。对于多次注射，打开事件受到前一次注射关闭动态的影响；这些现象已在模拟中进行了研究。
Rail pressures of modern diesel fuel injection systems have increased significantly over recent years, greatly improving atomisation of the main fuel injection event and air utilisation of the combustion process. Continued improvement in controlling the process of introducing fuel into the cylinder has led to focussing on fluid phenomena related to transient response. High-speed microscopy has been employed to visualise the detailed fluid dynamics around the near nozzle region of an automotive diesel fuel injector, during the opening, closing and post injection events. Complementary computational fluid dynamic (CFD) simulations have been undertaken to elucidate the interaction of the liquid and gas phases during these highly transient events, including an assessment of close-coupled injections. Microscopic imaging shows the development of a plug flow in the initial stages of injection, with rapid transition into a primary breakup regime, transitioning to a finely atomised spray and subsequent vaporisation of the fuel. During closuring of the injector the spray collapses, with evidence of swirling breakup structures together with unstable ligaments of fuel breaking into large slow-moving droplets. This leads to sub-optimal combustion in the developing flame fronts established by the earlier, more fully-developed spray. The simulation results predict these observed phenomena, including injector surface wetting as a result of large slow-moving droplets and post-injection discharge of liquid fuel. This work suggests that post-injection discharges of fuel play a part in the mechanism of the initial formation, and subsequent accumulation of deposits on the exterior surface of the injector. For multiple injections, opening events are influenced by the dynamics of the previous injection closure; these phenomena have been investigated within the simulations.