【作者】 黄利亚；

【导师】 夏智勋；

【作者基本信息】 国防科学技术大学 ， 航空宇航科学与技术， 2010， 博士

【摘要】 超高速鱼雷巡航推进系统的应用需求促进了水冲压发动机技术研究的发展。本文以镁基水冲压发动机为研究对象,采用理论分析、试验研究与数值模拟相结合的方法,对水蒸气中镁颗粒着火与燃烧机理、发动机内部燃烧过程以及燃烧组织方法等问题开展了系统深入的研究。采用高速摄影仪、红外测温仪等光学观测手段,研究了水蒸气中镁颗粒的着火与燃烧特性,获得了其着火与燃烧机理。研究发现:镁颗粒在水蒸气中的着火燃烧过程经历了从表面氧化反应到蒸气相燃烧的过渡;颗粒燃烧表现出与其在空气中燃烧不一样的现象,即燃烧过程中火焰上方出现白色絮状物,燃烧后的氧化镁也呈白色絮状结构;镁颗粒着火前反应由化学反应动力学控制,着火后燃烧由扩散过程控制;测量得到的镁颗粒着火温度处于1150~1200K之间。采用高速摄影仪,观测了水蒸气中镁颗粒燃烧寿命随粒径的变化规律。试验发现:镁颗粒燃烧寿命随着粒径的增大而延长,且粒径越小,其燃烧寿命的变化规律越接近D~2定律。根据观测到的现象,在液滴燃烧模型的基础上,考虑镁燃烧过程中表面氧化镁覆盖物对颗粒燃烧速率的影响,获得了修正的D~2定律,通过试验确定了该定律中的覆盖系数。根据获得的水蒸气中镁颗粒着火与燃烧机理,建立了水冲压发动机中的镁滴着火与燃烧模型,以描述发动机中镁颗粒的物理化学变化过程。在镁滴着火与燃烧模型中,根据镁滴着火温度,将水冲压发动机中镁滴的着火与燃烧过程分为着火前的氧化阶段、着火及着火后的燃烧阶段;采用镁在水蒸气中高温氧化动力学方程描述镁滴氧化阶段表面氧化膜厚度变化,采用修正的D~2定律描述镁滴燃烧阶段液滴直径变化。建立了水冲压发动机直连试验方法。对试验系统进水方式进行了改进,试验发现,采用垂直进水的方式能够有效减小进水冲量对发动机轴向测量推力的影响;对不同数据处理方法进行对比分析,确定了采用基于稳定工作段时间的数据处理方法。应用镁滴着火与燃烧模型,建立了水冲压发动机数值模拟方法,并通过发动机直连试验,对该数值模拟方法进行了验证。通过直连试验,研究了点火能量、点火时序、水燃比、进水喷注压降和推进剂金属含量对发动机点火过程的影响规律,确定了高金属含量水冲压发动机点火过程的变化规律及控制机理。试验发现,发动机正常点火时其点火过程分四个阶段:推进剂点燃延迟段、自持燃烧段、一次水反应预燃段和二次水反应预燃段;根据试验结果分析,点火过程的自持燃烧段由固相点火理论控制,而一次水反应预燃段和二次水反应预燃段由气相点火理论控制。综合采用理论分析、直连试验和数值模拟的方法,分析了镁基水冲压发动机内部燃烧过程的特性和规律,建立了发动机分区燃烧模型,以描述发动机内部燃烧过程;系统考察了进水距离、进水角度、水燃比及其分配、以及进水雾化特性对发动机内部燃烧过程的影响规律,提出了燃烧室长度、进水距离和水燃比设计方法,建立了发动机内部燃烧组织方法。在采用73型高金属含量镁基固体推进剂的发动机直连试验中,通过实行有效的燃烧组织,发动机燃烧效率提高到91.02%。更多还原

【Abstract】 Investigations on water ramjets are being extensively conducted for their application inthe cruise propulsion system of high-speed torpedoes currently. Based on amagnesium-based water ramjet engine, this research focuses on combustion mechanismof a magnesium particle in steam, internal combustion processes and combustionoptimizationoftheengine.Approachesoftheoreticalanalysis,numericalsimulationandexperimentalstudywereappliedfortheresearch.A high speed camera and an infrared thermometer were employed to observe thecharacteristics of ignition and combustion of a magnesium particle in steam.Mechanisms of ignition and combustion were determined in the experimental study.The results show that, a transition from surface oxidation to gas-phase combustion tookplace; a different phenomenon from combustion in air occurred, with white flocculesformedabovethe flame, andtheproduct ofmagnesium oxidealso inthe shapeof whitefloccules; the interaction was controlled bychemical kinetics prior to the ignition point,and then by diffusion process afterwards; ignition temperatures were measured withvaluesbetween1150~1200K.A high speed camera was also used to observe the variation of combustion life withdifferent diameters of magnesium particles in steam. Prolonged combustion life wasrecorded with an increasing particle diameter, and the variation rule got closer to theD~2law while the diameter was decreasing. Based on the droplet combustion model, amodified D~2law was established, taking into account the oxide cap covering theparticlesurface.Fromtheexperimentaldata,the coveringcoefficientwas determinedofthemodified D~2law.The magnesium-droplet ignition and combustion model was developed, in order todescribe the transformation of magnesium particles inside water ramjet engines. Inthismodel, the whole procedure is divided into three phases: oxidation phase, ignition andcombustion phase. An oxidation kinetics model is adopted to calculate the thickness ofthe oxide layer in oxidation phase; while in combustion phase, the particle diameter isgovernedbythemodified D~2law.Adirect-connecttestingmethodforwaterramjetengineswasdeveloped.Withwater-jetentering the chamber vertically, the influence of its impulse to axial thrust waseliminated. With a comparison of different data processing ways, a processing methodin terms ofthe stable operation period was confirmed to be more eligible. In addition,the numerical method was improved by employing the magnesium-droplet ignition andcombustionmodel,andthemethodwasverifiedbyasimulationofonetest.Influences of ignition energy, starting sequence, water/fuel ratio, water injection pressure and metal content on the ignition process were studied experimentally, fromwhich the characteristics and mechanism of ignition process were determined. Thewhole ignition process was found to follow four phases: ignition time lag,self-surporting combustion interval, primary precombustion interval and secondaryprecombustion interval. Within the self-surporting combustion interval, the ignition iscontrolled bysolid-phase ignition theory, while forprimaryprecombustion interval andsecondaryprecombustioninterval,thegas-phaseignitiontheorydominatestheignition.Characteristics of combustion processes inside the water ramjet engines were analyzedwith different approaches. A multi-zone combustion model was developed to describethe internal processes.Influences of water injection distance, injection angle, water/fuelration and its partition, and atomization characteristics were estimated on thecombustion processes, from which combustion optimization methods were concluded.A magnesium-based water ramjet engine was designed using the optimization methods,and a testof it was conducted with a Type 73 solid propellant, which has a high metalcontent. The results show that the combustion efficiencyof the engine was enhanced to91.02%aftercombustionoptimization.更多还原