| Peak cylinder pressure and power per litre of diesel engines gradually go up with the use of high-pressure fuel injection and turbocharging,thus higher thermal and mechanical load need extra durability and reliability of components of the engine.In order to prevent the failure of pistons and guarantee durability and reliability of components,most of the diesel pistons in heavy duty engines are oil cooled with cooling galleries.Study on oil flow and heat transfer in galleries could not only provide reference for optimum design of galleries,but lead to concise boundary conditions and analytical foundation for FEA analysis of pistons as well Hence CFD simulation and experiments on flow patterns and heat transfer in piston cooling galleries are of great practical significance.Since there is no specific CFD simulation method of flow patterns and heat transfer in piston cooling galleries,not to mention relevant gallery-oscillation test-bed,in this paper,cooling gallery of a piston in an high pressure common rail diesel engine was set as research subject CFD simulation model of which was then established to investigate simulation analysis methods of galleries.Based on studies of cooling gallery test-beds at home and broad,a gallery-oscillation test-bed for observation of oil motion was independently developed using CAD/CAE technology,theory of similarity,vibration controlling technology and PLC.Main oscillating system,oil supply system,power system as well as measurement and control system were designed and developed in detailFirst,numerical simulation methods of piston galleries was systematically investigated.To be specific,mathematical models,geometric model,turbulence model,etc.were studied and CFD simulation method of galleries was proposed through comparisons between different simulation results.Then since we need to conduct piston-gallery oscillation experiments,plus there is no commercial test-bed of this type available,a gallery-oscillation test-bed was designed and developed.The test-bed developed in this paper include:main oscillating system,oil supply system,power system as well as measurement and control system,which are introduced as follows:Main oscillating system includes a regulate device of the length of the crank,a slider-crank mechanism Function of main oscillating system is to convert rotary motion of the motor into reciprocating motion,making galleries oscillating in a regular periodic fashion.Power system includes a servo motor and its accessory equipment:power output of the motor is connected to crankshaft.Function of this system is to drive the crankshaft and to stabilize the rotating speed of the crankshaft.In the oil supply system,oil is injected from nozzle to the inlet of the gallery at a certain pressure and position.Also,oil failing to get into gallery and coming out of the outlet is collected.The nozzle is aimed at inlet of the gallery using position adjustment device.Accumulator stabilizes pressure fluctuation of oil in the system In the measurement and control system,rotating speed,injection pressure,oil flow along with temperature are measured and controlled using PLC and PC.Also,the reciprocating motion of the oil inside the gallery and other data are collected by high speed camera.Through investigation of simulation methods and the design and development of the gallery-oscillation test-bed,simulation method of flows and heat transfer in piston cooling galleries was specified and proposed:geometric model is simplified to a whole model containing entire fluid domain with viscous and multiphase flow model as k-s and CLSVOF.In addition,second-order accuracy PISO should be set as pressure velocity coupling algorithm.Results show that this method could improve simulation accuracy with a relatively low calculation cost.Above all,a test-bed that could accurately measure efficiency of the nozzle and observe the reciprocating motion of oil inside the gallery,providing experimental basis for investigation of heat transfer of the galleries in reciprocating motion. |
PDF Full Text Request