Investigation On The Variable Intake Manifold System Of Gasoline Engine

With the fast development of national economy,the demands of automobile rise with a high speed. In 2007 our country car production & sales both break 8,800,000. Passenger is still the main drive of the growth, the car market is extremely active.The popular car market will inevitably bring about the development of car engines. Because of the protection of the environment and sustainable human development requirements, low fuel consumption and low emission automotive engine becomes the main development goals. People continually tap the potential of their engines, engine design trend in electronic and variable parameters control. As one of the key technologies of electronic ejection engine, the variable intake manifold system technology can not only have a tremendous impact on engine torque characteristics, and to a certain extent, but also improve fuel economy, reduce engine emissions, so it is valued for a long time.By resonant intake charging, the length-invariable intake manifold technology enable the engine enhance the fresh charge under the different speed, improve the engine power performance, reduce the exhaust emission. The length-invariable intake manifold system most greatly may cause the engine effective average torque to increase 8.5%, under the situation the speed is lowered, the maximum torque may increase 12% to 14%. Using the section-invariable intake manifold technology, 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 speed up the combustion rate and improve the engine power and efficiency.As an important design topic in the engine profession, the engine intake system numerical simulation method not only can provide the powerful analysis tool and the method for the intake system design question, the performance prediction question, but also can provide many performance parameters which are very difficult or at present unable to survey, thus it greatly reduces the experimental quantity, reduces the research cycle, reduces the research cost. Because the engine work process circulation simulation and the air intake system CFD hydrodynamics numerical simulation have important instruction function to design and research work, it has been widely applied to the engine design, the development, and production process.This article has mainly studied the influence of length-invariable intake manifold technology on engine performance and flow characteristic through the numerical simulation method. And based on four cylinders four strokes air intake electronic ejection gasoline engine G4BA, a set of electric controlled length-variable intake manifold system was designed and developed.Firstly, this article synthesized the domestic and foreign each kind of invariable intake manifold system, considered engine's usable space and the control mechanism and so on limit, according to the existing technical level chose the appropriate graduation length-variable intake manifold design proposal for the engine.The wave resonance was researched in detail. Then the principle of length-variable intake manifolds in increasing the fresh charge in cylinder by resonant intake charging was 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 air flow motion under low-speed and flow coefficient under high-speed should be taken into account.By using AVL-BOOST software, a numerical model for a four-cylinder four-stroke EFI (PFI) G4BA Gasoline engine was set up basing on the theory of CFD one-dimensional engine cycle and gas exchange simulation, and the model was compared with experimental results to verify the validity. The theory of CFD assisted in engine analysis was studied. Through one-dimensional simulation the impact of different diameters of the engine intake manifold on the engine performance was presented, and the diameter was determined. Through adding and shorten the length of the intake manifold, the effect of different length intake manifolds on the engine performance was analyzed, and the length of the variable intake manifold was determined.Using the determined length of variable intake manifold, the engine performance under the two different manifold length was simulated, from the torque performance, a set of scheme for length determination of variable intake manifolds was summarized---the speed of the switch point.According to the results of simulations, some structural parameters are recommended to improve the performance of this Intake Manifold and the engine performance was simulated. In accordance with the torque characteristics the switching point (conversion rate) of the variable intake manifold was determined.Through simulation, we got the basic parameters of the variable intake manifold. Using UG (3D design software) we design the three-dimensional model, and then change the three-dimensional model into STL data format, spread it to rapid prototyping and manufacturing center, produce the rapid prototypes.We developed and tested a set of electric-controlled length-variable intake manifold system.We conclude from test that: As one of the key technologies of electronic ejection engine,length-variable intake manifolds enable the engine have the better performance at a wider speed range,enhance the flow coefficient under the different speed. It enabled G4BA gasoline engine torque curve tend to smooth, slow-twisting, increased torque at low speed areas, improved acceleration. Electronic variable intake manifold system mechanism was simple and feasibility. The product cost was low, There was relatively small changes on the engine but with high usability.The study on one-dimensional numerical simulation of the variable intake manifolds on intake flow characteristics and performance for gasoline engine was using computer assistance analysis method and carried on a quite comprehensive analysis to the influence of length-variation technology for intake manifolds. This paper has some reference value in engine simulation ,design and analysis on variable intake manifolds.