| Hot film air flow meter is an important tool to measure air flow, which is a keypart in automotive fuel injection system. It is installed between air filter and throttle,directly reflecting the volume of air flow in direct detection of engine, and providesECU to determine the amount of fuel injection. So hot film air flow meter makessignificant sense in ensuring normal operation of engine, improving fuel economy,energy conservation and emission reduction.However, in current study few thorough researches on installation location areunder discussion. Therefore, It’s crucial to determine the best installation positionwhere minimal effect is brought to the meter; in this way, the measurement would bemore accurate.This thesis introduces the structure and detection principle of thermal film typeair flow meter. Firstly we use AJR engine training device of Santana2000as the testobject, and measure the volume of air under specific engine speed (800r/min,2000r/min,3000r/min); as rotational speed increases, the volume of air raisescorrespondingly. Then we change the installation location of hot film air flow meter,placing it at the position0.5d,1d,2d,2.4d within front-straight pipe and0.5d,1d,3.5d,12d,30d within rear-straight pipe, and proceed with several groups ofexperiments. The result demonstrates that due to fully transition, errors becomerelatively large near the entrance. As the bend extends, value of errors change fromnegative to positive; and errors, which have a good consistency with theoretical valuein front-straight pipe, are smaller than those of rear-straight pipe.It’s known that the more stable where the speed is, the less influence onflow-meter, and such place is appropriate for measurement. The thesis simulates thevelocity field where hot film air flow meter is placed with Fluent. The simulation datais almost consistent with experimental data; and exactly verify the validity of thesimulation. Besides, it’s showed that errors of rear-straight pipe are larger than thoseof front-straight pipe. Due to the diversity of installation environment, the thesisexamines three types of double-bend pipes: Z type, inverted-U type, rear-L, anddiscusses the best installation location, guaranteeing at least3.5d long for double-bend pipes.In order to fully consider the limitation of inner space of car, not only shouldinstallation be short, but precision should be improved with smaller errors. Therefore,we propose a kind of sealing design for rectifier of hot film air flow meter, discuss thesituation where the meter is at the position of1d in pipe, and compare the results. Byshortening installation, the initial assumption can be verified. The thesis provides agood starting point for further study of this field. |
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