Studies On High-Pressure Combustion With Combustion Gases Recirculation

The technology of Combustion Gases Recirculation (CGR) has successfully solved the problem of high-pressure combustion of Stirling engine. The technology of CGR combustion declines the temperature of flame, depresses the emission of NOX, and enhances thermal efficiency of engine. Compared with other similar technologies, CGR combustion has advantages of simplicity, effectiveness, easy-to-use, and so on. But the researches on this technology are still insufficiency.Now, most of applied CGR combustors use gases ejector as driving component. Chemical stoichiometric analysis and one-dimension thermodynamic analysis are carried out in this thesis, and two kinds of descriptive equations are established. A simple model on CGR combustion is set up, which forecasts the manner of CGR combustion parameters. A numerical simulation on a simple CGR gas combustor is done, and the results show that the flame temperature is depressed obviously with CGR. The calculation results also validate the consistency of the two descriptive equations from two foundations.Experimental studies on external-combustion system of Stirling engine are introduced in this thesis, witch including: experiment of single ejector with high backpressure, experiment of fuel oil spray in combustor and experiment of high-pressure combustion on Stirling engine. Test results show that ejection efficiency of ejector with high pressure is in proportion to mass flow rate of injection flow, but litter influencing by pressure of injection flow; cyclone in combustor is in favor of fuel oil spray, enhancing cyclone results in decline of Sauter Meaning Diameter (SMD) of oil droplets; the cooperation of nozzle and cyclone in combustor do influences the SMD of oil droplets; mildly elevating thenozzle induces inclining of temperature of thermocouple of heat exchange tubes, declining of temperature of flame thermocouple, elongating of flame and minishing of diameter of fireball.Measuration in high-pressure combustor is always difficult and costly. With the development of computer technology and modern Computational Fluid Dynamic (CFD), numerical simulation of combustor is taking more and more important role on combustor design and research. In this thesis, studies on methodology of combustion simulation are done. And a series of numerical simulations are implemented on combustor and key components of external combustion system of Stirling engine. A cone rolling flame is got with an annular high temperature cohering obstruct cover in the combustor simulation. The traces of oil droplets are influenced by cyclone in combustor, and the droplets distributed asymmetric on circumferential direction. Other simulation results on flow, heat transfer and two-phase flow of gas ejector, fuel oil nozzle and cyclone generating baffles show that the pressure near gas nozzle do influences the ejection efficiency of ejector; the operation parameters of ejector affect the ejection efficiency greatly, and the optimal geometrical parameters of ejector changes with them; the static pressure on throat tube of ejector achieves minimum indicates the optimal operation condition of ejector; the diameter of gas nozzle impacts ejection efficiency, in some cases, minishing nozzle diameter makes for efficiency inclining; triangle oil slot mixes and warn-up oil effectively, which declines pressure loss and simplifies machining technics; cyclone generating baffles affect combustor internal flow greatly, and the flow changes the shape of droplet cluster, increases relative velocity of droplets, which is in favor of breakup of droplets.It is the first case to set up a simple model on CGR combustion driving by gas ejector. These works will be a very important reference to farther research on CGR combustion.