【作者】 张鹏；

【导师】 高世伦；

【作者基本信息】 华中科技大学 ， 动力机械及工程， 2011， 博士

【摘要】 以二甲醚(DME)为燃料基于柴油机实现均质充量压缩燃烧(HCCI)可以有效降低NOx和碳烟的排放,解决柴油供应日益紧张的局面,但存在燃烧不易控制,负荷范围窄的问题。使用缸内直喷柴油与进气道喷射DME两套喷射系统,在不同的工况下分别实现CIDI与HCCI两种燃烧方式,各取所长,是现阶段将HCCI实用化可行的技术方向。本文围绕双模式发动机的燃烧特点和模式切换过程的控制策略进行了模拟和实验研究。本研究以气相计算软件包CHEMKIN为平台,采用敏感性分析法简化了DME和正庚烷的详细化学反应动力学机理,建立了用于分析HCCI和CIDI两种燃烧方式的三维模型,该模型以Fluent为计算平台,采用六面体网格,处理了活塞和气门运动的动网格,以离散相模型计算柴油喷雾过程,并将简化化学反应动力学机理耦合到三维模型中实现燃烧过程的模拟。模拟计算对比了两种燃烧方式各自的特点,预测了两种燃烧方式下的缸内温度分布,混合气浓度分布,HC以及NOx排放物分布,模拟结果与实验数据吻合。以三维模拟为基础,预测了适合HCCI燃烧的工况范围,为实验提供参考。同时,基于Matlab-Simlink平台建立了用于控制策略仿真的发动机平均值模型。加入了用于预测HCCI燃烧过程燃烧始点和燃烧温度及燃烧放热率的模型,对柴油燃烧的求解则采用stick公式计算滞燃期长短,以双Vibe曲线模拟放热过程。基于该模型设计了模式切换过程的模糊控制策略,并同传统PID控制进行了比较。结果表明:模糊控制在动态特性上相比PID控制有优势,在切换工况点改变时,模糊控制的适应性较好,稳定性较强,鲁棒性好。本研究构建了进气道电喷装置与电机油门驱动机构,设计了ECU控制单元与数据采集系统,实现了在进气道喷射二甲醚进行均质压燃(HCCI)和缸内直喷柴油(CIDI)两种燃烧模式。通过ECU控制进气道和缸内直喷两套喷油系统的喷油量,在临界工况点实现了CIDI-HCCI和HCCI-CIDI燃烧方式的切换。实验结果表明,在柴油机上实现模式切换时,前后循环间的依赖度较小,切换过渡时间较汽油机上实现SI-HCCI和HCCI-SI短,闭环控制在切换过程中有较好的适应性,能够满足转速在一定范围内波动的要求;而开环控制则更容易实现,应用于HCCI-CIDI模式切换时也能达到较理想的效果。更多还原

【Abstract】 The HCCI (homogenous Charge Compression Ignition) combustion can reduce NOx and soot either by using the fuel dimethyl ether (DME). It can also resolve the increasingly tense situation in the supply of diesel oil. Meanwhile HCCI has the drawback of uncontrollable combustion phase and narrow work range. By the way of using both intake pipe injection and in-cylinder injection, HCCI and CIDI combustion can be implemented in different work point. This paper present the simulation and experiment research for dual-mode engine.The numerical simulations based on the gas phase computation software CHEMKIN. Sensitivity analysis theory was used to get the reduced mechanism for both DME and n-heptane. A three-dimensional model was developed based on the diesel engine. The model use the hexahedral mesh to get the best quality, the movement of piston and valves were implemented. The discrete phase model was used for diesel oil injection, and the reduced mechanisms were coupled to compute the combustion process. The numerical simulation compared two combustion modes in temperature distribution, NOx distribution, the start of combustion and so on.A mean value model was setup for simulation the mode transition strategy. The engine model contains the combustion start time and heat release rate model for HCCI and CIDI. The model uses the dual Vibe curve to compute the diesel oil combustion process, and uses stick formula to compute the ignition delay. A Fuzzy logic control strategy was designed. A PID control strategy was setup to compare Fuzzy Logic control. The results show that Fuzzy logic control strategy gets the better dynamic performance.This research developed intake pipe injection system and motor-accelerator driven system. The ECU was designed for control the mode transition process. The experiment results show that cycle to cycle dependence is smaller than mode transition in gasoline engine, and close-loop control is more adaptive than open-loop control. But the open-loop control is easier to implement, it can also obtain the good transition process in the HCCI-CIDI mode transition.更多还原