| The problems of energy crisis and environmental pollution become more and more serious, renovations in the traditional energy technology are being focused. As a main energy consumer and the main emission source of pollution, the automotive engine faces double stresses as energy saving and environmental protection. Porous medium(PM) engine, as a newborn thing, is characterized with the advantages, such as flammability, low-pollution, high-efficiency and extended ignition limits, which will be received more attentions in future. With the background of PM engine, this dissertation is concerned the numerical study of the interactions between fuel spray and hot PM for understanding the mechanism of mixture formation in the PM. Numerical simulation about the properties of compression ignition, combustion and emission of two types of PM engine is another subject in the dissertation. The principle ai,m of this work underling the thesis has been to have a primary recognition about the working characteristics of PM engine, with the purpose of providing some theoretical foundations for its application.Firstly, in order to study the formation of homogenous mixture in PM, numerical simulations about the interaction between fuel spray and hot PM were performed.(1) An impingement model was improved for simulating the process of fuel droplets collision with hot wall, where Leidenfrost phenomena occurred. The velocity of splashed droplets was calculated by the method of probability density function, and the number of the splashed droplets was derived based on the mass conservation. In the model, four parcels are used to represent all of the splashed droplet and heat transfer between droplets and hot wall was described with the formula proposed by Senda.. Under the experimental conditions of Senda, the process that fuel spray vertically impinges on a high temperature wall was simulated by using the modified KIVA-3V. Compared with the results by original KIVA-3V, the results by the modified KIVA-3V made more well agreement with experimental results.(2) Numerical simulations were conducted for investigating the interactions between fuel spray and three simplified models of PM with the modified KIVA-3V, which was implemented with the new impingement model. In all of computational results, the single fuel spray was separated into several small fuel streams in the PM after colliding with the PM, which provided the conditions for the fast evaporation of droplets and the formation of homogenous mixture. There were four characteristic phases of fuel spray interaction with the PM, the first represented Outlet from the nozzle and free jet formation, the second represented jet interaction with PM-interface, and the third represented liquid distribution throughout the PM-volume and the fourth represented liquid leaving the PM-volume.Each of the three simplified models of the PM deserved advantages and defects. The influences of ambient pressure and spray parameters on the interactions between fuel spray and PM were studied computationally. The variation in ambient pressure can modify the resistant force to fuel droplets. Spray cone angel and droplet diameter are the most influential factors in affecting the interactions. The interaction between pressure swirl spray and the first simplified model of PM was simulated. The effects of porosity on the interactions were also evaluated in the second and third simplified model of PM.KIVA-3V was improved by incorporating with the chemical kinetics software Chemkin-3.0. An additional energy conservation equation for describing the temperature of the solid phase in the PM was included in KIVA-3V. The dispersion effects of the PM on energy and species diffusion were also considered. The working processes of two types of PM engine, fueled with gas fuel and liquid fuel, were simulated respectively, and the effects of some important factors on the working of PM engine were also analyzed.(3) The characteristics of combustion and emission of PM engine fueled with gas fuel and liquid fuel, with permanent contact between PM and working gas in engine cylinder, were investigated numerically. The GRI 1.2 chemical kinetic mechanism was used for modeling the oxidation of CH4 in the PM engine. We investigated the effects of various parameters that were expected to control the onset of the compression ignition of the PM engine, such as the initial PM temperature, the PM structure and fuel injection timing. The emission properties of the PM engine were investigated by using the GRI 3.0 chemical kinetic mechanism.In the simulation cases about the working processes of the PM engine fueled with liquid fuel, a skeleton mechanism for iso-octane oxidation was used and the interactions between fuel spray and the PM were considered by applying the second simplified model of PM and the impingement model developed in chapter two. The effects of different operating conditions on the characteristics of ignition and emission of the PM engine fueled with iso-octane were evaluated.The evaporation rate of iso-octane is the most important factor in controlling the combustion velocity of the PM engine fueled with iso-octane. The dispersion effects of the PM can accelerate the mixing process between the fuel vapor and air, and decrease the time needed to achieve the ignition conditions. The fuel injection timing has outstanding influences on the working of the-PM engine fueled with iso-octane. Over-early or over-late fuel injection timing induce the reduction of the maximum value of average pressure, and over-late fuel injection timing also make the increase of the NO amount. (4) The characteristics of combustion and emission of PM engine fueled with gas fuel and liquid fuel(iso-octane), with periodic contact between PM and working gas in engine cylinder, were investigated numerically. The close and open processes of the valve between the PM and engine cylinder were simulated by changing the properties of the computation cells at the interface. The GRI 3.0 chemical kinetic mechanism and the skeleton mechanism were used for simulating the oxidation of CH4 and iso-octane, respectively. The interactions between fuel spray and the PM were considered by applying the second simplified model of PM and the impingement model developed in chapter two. The effects of the initial PM temperature, the PM structure and valve opening timing on the characteristics of ignition and emission of the PM were discussed.The characteristics of the PM engine, with periodic contact between the PM and working gas in engine cylinder, are completely different from those of PM engine with permanent contact between the PM and working gas. The mixture formation is not important factor in determining the onset of ignition and controlling combustion velocity. Regardless of the type of fuel, the combustion period is very short and the heat release rate is also very high in the PM engine. From the point of view of the emission, the PM with enhanced intensity of heat exchange between the solid and gas phase should be adopted. The timing of valve opening has influences on the temperature in the PM and the NO amount. For obtaining power and low emission, the timing of valve opening should be an optimal value.
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