【作者】 段俊法；

【导师】 刘福水；

【作者基本信息】 北京理工大学 ， 动力机械及工程， 2015， 博士

【摘要】 氢气来源广泛、燃烧清洁且可再生,是较为理想的内燃机代用燃料,被认为是解决能源危机和环境污染问题的有效办法。氢燃料内燃机因成本低和可靠性高更加具有应用于车辆的优势。先前的研究者对氢内燃机作了较为系统的研究,但在氢空气稀释燃烧特性、氢空气化学反应机理、氢内燃机的NO控制策略等方面的研究还不够深入和系统,制约了氢内燃机的实际应用。传统内燃机EGR中的主要热惯性成分为CO2,而氢内燃机燃烧产物中几乎没有CO2,因而氢内燃机的EGR作用机理与传统内燃机存在本质的差别。氢内燃机中热EGR气体的主要成分是H2O+N2,冷EGR气体的主要成分是N2,因此本文主要围绕这两种EGR方式的作用机理、燃烧和排放特性展开研究。本文首先构建了定容燃烧测试系统,研究了H2O+N2和N2两种稀释方式下的氢空气燃烧特性。试验结果表明,在两种稀释方式下,氢空气层流燃烧速度和已燃区温度都随着稀释率的增大而显著降低,马克斯坦长度随稀释率的增大而略微降低。表明两种稀释对于抑制NO的生成均有显著的作用。在此基础上,基于化学动力学分析软件CHEMKIN研究了氢空气燃烧化学反应过程,分析了燃烧进程中各基元反应对氢空气反应速度和生成物的影响规律,得到了16基元24步反应的简化反应机理,能够在保证仿真可信度的前提下大幅度地降低仿真计算量。为了深入分析氢内燃机的燃烧过程,基于CONVERGE软件建立了包含喷射模型、湍流模型、点火模型和化学反应动力学简化机理氢内燃机三维仿真模型,并据此分析了不同工况下氢内燃机的工作过程。发现燃烧过程中,火焰前锋面内存在高浓度的OH,已燃区的温度略高于火焰前锋面的温度,因而在已燃区产生了很高浓度的NO区域,随着火焰的传播,NO的总质量不断增大。燃烧结束后,缸内温度迅速降低,NO的质量因部分分解而有所降低。在缸内局部最高温度降低至1800K时,NO的分解速率很慢,NO的质量基本保持不变。仿真结果表明,随着EGR率的增大,缸内最高爆发压力迅速下降,同时燃烧持续期增大;缸内温度随着稀释率的增加而迅速减小,进而导致NO浓度迅速降低。进而提出了一种“四级渐进式控制策略”,其控制难度较先前的“三级跨越式控制策略”显著降低,控制过程中最大EGR率也有显著的下降,有益于提高氢内燃机的效率。更多还原

【Abstract】 Hydrogen energy, which is clean, renewable and has multi sources, is regarded as the final energy in the future to deal with energy shortage and the environment pollution problem. Hydrogen fueled internal combustion engine(HICE) is cheap and reliable, so it is the most probably applied method for hydrogen energy used in vehicles. The previous researchers have investigated combustion characteristics of HICEs for a long time. But there are still some questions such as hydrogen-air laminar combustion characteristics under diluted conditions, hydrogen-air chemical reaction mechanism and NOx formation laws have not been explained clearly and reasonable.CO2, which has the large Cp and thermal inertia, is an important component of Exhaust gas of traditional engine. So the EGR gas of traditional engine can dilute fuel-air mixture and decrease the temperature of burned zone in cylinder. But the Exhaust gas of HICE is composed of H2 O and N2. H2 O or N2 has small Cp compared with CO2,. So the EGR of HICE has entirely different mechanisms. This paper investigates the combustion and emission formation mechanisms of HICE under H2 O and N2 diluted conditionsFirstly, laminar combustion characteristics of diluted Hydrogen-Air mixtures are investigated using global shape combustion bomb. The test results show that H2O+N2 and N2 diluted mixture also have much lower laminar combustion speed and temperature in burned zone. Laminar combustion speed and temperature in burned zone are decreased substantially with the diluted rate. Markstein Length is decreased slightly with the diluted rate. It indicates that exhaust gas recycle is a useful method to control NO concentration.Secondly, Hydrogen-air combustion process is investigate using hydrogen-air detailed chemical reaction mechanisms with CHEMKIN software. Then a reduced reaction mechanism with 16 elements and 24 step reactions is got. It is verified that the reduced reaction mechanism can calculate hydrogen-air combustion process accurately with high calculating speed.Then, a three dimension CFD model which involves spray sub model, turbulence sub model, ignition sub model and reduced chemical reaction mechanism combustion sub model is established for simulating of HICE. It is founded that there has a high concentration OH zone in flame. In the first stage of combustion process, high concentration OH zone is spread like a thin wall ellipsoid. Temperature in the flame is always slightly lower than that in burned zone. NO formation is always related closely to temperature of burned zone. Total NO mass in cylinder increasing quickly with flame transmission process. When the combustion is finished, temperature in cylinder decreases slowly, then NO mass in cylinder will decrease with temperature. NO mass will keep steady with temperature when the maximum temperatures lower than 1800 K.It can be found that the maximum average pressure and temperature in cylinder will decrease quickly with the incensement of EGR ratio, and the combustion duration will increase with the incensement of EGR ratio based on three dimension CFD simulations. It in turn reduces NO formation. A four stage continues control strategy with not-high EGR ratio is development for NO concentration control. This control strategy is easy to achieve than the former strategy named“three stage stride across control strategy”更多还原