Study On Numerical Simulation Of The Variable Intake Manifolds On Intake Flow Characteristics And Performance For Gasoline Engine

As one of the key technologies of electronic ejection engine, variable intake manifolds enable the engine have the better performance at a wider speed range, enhance the flow coefficient under the different speed. And it also ensure that the engine has more fresh charge under the high-speed and the cylinder gas has a stronger swirl and tumble flow motion under the low-speed, so that to improve the engine power and efficiency, and reduce the exhaust emission. By using numerical simulation method, this paper mainly researches the influence of variable intake manifolds on intake flow characteristics and performance for gasoline engine.Firstly, the wave resonance and the energy loss of intake manifold were researched in detail. Then the principle of length-variable intake manifolds in increasing the fresh charge in cylinder by resonant intake charging, and the function of section-variable intake manifolds in enhancing the swirl and tumble motion, speeding up the combustion rate and improving the engine performance were analyzed. On the base ,this paper pointed out that the variation control strategy of intake manifolds should be rationally optimized, and both the requirements of engine for airflow motion under low-speed and flow coefficient under high-speed should be taken into account.After studying the numerical simulation of unsteady flow in intake manifolds, a certain gasoline engine model was set up by using simulation software AVL-BOOST. Through one-dimensional engine cycle and gas exchange simulation, the influence of the manifold length on engine performance was found out. Then a set of scheme for length determination of variable intake manifolds was summarized.The theory of CFD assisted in engine analysis was studied. Moreover, the mesh structure was researched which was the key point to compute precision. The three-dimensional numerical simulation of airflows in the plenum-variable intake manifolds-intake ports -cylinder system of gasoline engine was performed using CFD software FIRE. The simulated flow field provided a detailed insight into the influence of rotary-blade style section-variable intake manifolds on flow characteristics, swirl and tumble motion. The result of simulation indicated that this device could change the swirl or tumble ratio in some degree and give some adjustment to the motion and flow...