科创中国

Most researches on transient fuel control of port fuel injection S.I. engine are carried out from the perspective of advanced mathematical theories. When it comes to practical control, there exist many limitations although they are more intelligent. In order to overcome the fuel wetting effect of PFI engine, the application-oriented transient fuel control is studied by analyzing the key parameters which are closely related with the engine transient characteristics. Both validity and simplicity are taken into consideration. Based on the fuel wall-wetting theory and popular fuel compensation strategy, short-term transient fuel(STF) and long-term transient fuel(LTF), as well as their individual decay approaches, are introduced. STF is to compensate the drastic fuel film loss caused by sudden throttle change, while the function of LTF is to compensate the fuel film loss by manifold air pressure(p) fluctuation. Each of them has their respective pros and cons. The engine fuel mass and air mass are also calculated for air-fuel ratio(AFR) according to ideal gas state equation and empirical equations. The vehicle acceleration test is designed for model validation. The engine experiences several mild and heavy accelerations corresponding to the gear change during vehicle acceleration. STF and LTF control are triggered reliably. The engine transient fuel control simulation adopts the same inputs as the test to ensure consistency. The logged test data are used to check the model output. The results show that the maximum fuel pulse width(FPW) error reaches 2 ms, and it only occurs under engine heavy acceleration condition. The average FPW error is 0.57 ms. The results of simulation and test are close overall, which indicates the accuracy of steady and transient fuel. The proposed research provides an efficient approach not only suitable for practical engineering application, but also for AFR prediction, fuel consumption calculation, and further studies on emission control.

The transient behavior of centrifugal pumps during transient operating periods,such as startup and stopping,has drawn more and more attention recently because of urgent needs in engineering.Up to now,almost all the existing studies on this behavior are limited to using water as working fluid.The study on the transient behavior related to solid-liquid two-phase flow has not been seen yet.In order to explore the transient characteristics of a high specific-speed centrifugal pump during startup period delivering the pure water and solid-liquid two-phase flow,the transient flows inside the pump are numerically simulated using the dynamic mesh method.The variable rotational speed and flow rate with time obtained from experiment are best fitted as the function of time,and are written into computational fluid dynamics(CFD)code-FLUENT by using a user defined function.The predicted heads are compared with experimental results when pumping pure water.The results show that the difference in the transient performance during startup period is very obvious between water and solid-liquid two-phase flow during the later stage of startup process.Moreover,the time for the solid-liquid two-phase flow to achieve a stable condition is longer than that for water.The solid-liquid two-phase flow results in a higher impeller shaft power,a larger dynamic reaction force,a more violent fluctuation in pressure and a reduced stable pressure rise comparing with water.The research may be useful to understanding on the transient behavior of a centrifugal pump under a solid-liquid two-phase flow during startup period.

Eddy current pulsed thermography(ECPT) is an emerging Non-destructive testing and evaluation(NDT & E) technique, which uses hybrid eddy current and thermography NDT & E techniques that enhances the detectability from their compensation. Currently, this technique is limited by the manual selection of proper contrast frames and the issue of improving the efficiency of defect detection of complex structure samples remains a challenge. In order to select a specific frame from transient thermal image sequences to maximize the contrast of thermal variation and defect pattern from complex structure samples, an energy driven approach to compute the coefficient energy of wavelet transform is proposed which has the potential of automatically selecting both optimal transient frame and spatial scale for defect detection using ECPT. According to analysis of the variation of different frequency component and the comparison study of the detection performance of different scale and wavelets, the frame at the end of heating phase is automatically selected as an optimal transient frame for defect detection. In addition, the detection capabilities of the complex structure samples can be enhanced through proper spatial scale and wavelet selection. The proposed method has successfully been applied to low speed impact damage detection of carbon fibre reinforced polymer(CFRP) composite as well as providing the guidance to improve the detectability of ECPT technique.