Research On Performance Of Pressure-wave Supercharger For Automotive Engine

Pressure-wave supercharger (PWS) is a kind of technology to boost the engine intake air pressure by utilizing the energy of the exhaust gas. PWS has several wonderful advantages such as higher torque even at low engine speed, rapid response to varied load, less emission (especially NOx emission), and without"turbo lag"problem. All these advantages permit the PWS to be suitable for the automotive engines even with frequently changed load. In this thesis, the research object is a pressure-wave supercharger for automotive engine, whose performance is analyzed and investigated by using the method of experiment together with modeling simulation basing on the method of Computational Fluid Dynamics (CFD).First, key influence factors were identified by analyzing the experimental data of a PWS diesel engine. On the basis of the experimental results of a diesel engine supercharged by PWS, a new system theory, grey system theory, was adopted to calculate and analyze the test data. Grey relational analysis was used to calculate the degrees of grey incidence of some parameters to PWS diesel engine performance. The grey relational analysis results show that there are two key factors—air mass flow and exhaust gas temperature, which have the most importance influence on PWS diesel engine performance. Thus, it is more efficient to improve the performance by controlling the two factors on purpose. At the suggestion of the grey relational analysis the volume of the intake manifold was increased to introduce more intake air flow while the exhaust manifold was wrapped by asbestos with an iron cover to preserve the high exhaust temperature. The experimental results after those changes indicate that the PWS diesel engine performance has been improved. A flexible PWS test system has been constructed which is available to test the PWS performance without being matched with engine. The experiments of testing PWS performance were completed on the PWS test system. Basing on the grey relational analysis, the two key factors are both parameters in high energy part of the PWS. As a result, the parameters in high energy part were the primary test objects during constructing the separate PWS test system. More attentions were given to how to test the parameters of ports in high-energy part than those in low-energy part. All the parameters were tested by sensors. In the PWS test system, the PWS was driven by a motor to easily control the PWS rotational speed. The mechanical accessories to support and fix PWS and sensors were carefully designed and machined. The high-temperature and high-pressure air was supplied by an electric heater, giving heat to the air until to high temperature, as well as an air compressor to press air to high pressure. All the data were acquired by an acquisition card managed by a developed VB program during experiment and then inputted into the computer for analysis. The PWS performance tests were done after all parts were mounted and the system was adjusted well. All the parameters were used as boundary data for modeling simulation and compared with the modeling simulation results. Two kinds of test methods were applied. One was done on the dependent PWS test system; another way was to test PWS performance by using a vehicle gasoline engine as the heat source providing the test system with high energy gas. Both test methods show that the pressure, temperature and PWS rotational speed in the energy-in port have influence on the parameters in energy-out part inside the PWS. The temperature and PWS rotational speed have more effects than pressure does. Reasonable controlling of the parameters at the energy-in port is effective to improve PWS performance.The 3D unsteady flow model of the PWS was built and the flowing situation was simulated by using Computational Fluid Dynamics (CFD) methods. Two different 3D unsteady flow models of PWS were worked out. One was for the integrated PWS including the rotor and casings, the other model based on only two symmetry rotor channels. Both 3D unsteady flow models of PWS simulated the flowing at different PWS rotational speeds. The CFD simulation results were also compared with the test data. The simulations argue that the integrated PWS 3D unsteady flow model is available to describe the flow in the PWS. The model simulation results also demonstrate that the calculated air mass flow has good agreement with the experimental data, especially at the middle and high rotational speeds. At the same time, the solution of the integrated PWS model illustrates that the high flow velocity at the fresh air inlet is useful to improve the flow inside the rotor and lead to a satisfied efficiency. Relatively, the rotor channel model has much larger calculation errors at high PWS rotational speed. However, the rotor channel model shows much better accuracy at the lower PWS rotational speed that it is more suitable for lower PWS rotational speed situation. Meanwhile, differing from the integrated PWS model, the channel model simulates the different periods in a working cycle of rotor. It can be used to analyze the flowing in every period of a working cycle in detail. In addition, the boundary between air and high-energy gas is able to be worked out by the rotor channel model, which is helpful to investigate the mixing of two gases. For this reason, the channel model is a supplementary method for the integrated PWS 3D unsteady flow model. Both 3D models of PWS are available to describe and illustrate the flowing inside the PWS.Basing the PWS 3D unsteady flow model, a further new simulation was worked out aiming to study the structure's effect on flow in PWS. In the simulation some structure parameters of PWS model were modified. These changes were to vary the position angels between rotor and casings, as well as the distance between two rotor channels. The model simulation of changed position angelθ1 shows that less perfect performance of PWS is to achieve due to varied angleθ1. When the angle is slightly decreased, PWS performance at low speed is a little better while tending to deteriorate at other working rotational speeds. It is necessary to decide appropriateθ1 together with the consideration of PWS rotational speed. Simultaneously, as far as the rotor channel concerned, the altered structure of channel is to cause much larger influence on PWS. The calculation results of varying distance between two channels demonstrate that the PWS behaves badly since the changed value deviates from the designed ideal value. Therefore, it is wise to decide the reasonable structure parametes of channel and casings together with the consideration of PWS flow, speed and the boosting requirements when designing the PWS structure.