| Precise measurement and calibration of fuel injection rate is very essential to analysis the formation of mixed gas and processes of combustion in diesel engine cylinder. By examining the methods for fuel injection rate at home and abroad, most of them apply to an injector can not measure the fuel injection rate of a nozzle directly and accurately. In view of this, according to the principle of momentum conservation, a new test rig for fuel injection rate based on momentum method was designed in this paper, and it can be used for measuring the fuel injection rate of single nozzle accurately.The test rig for fuel injection rate based on momentum method was built on a fuel injection pump test-stand (since using flat plate-type force sensor for measuring element, hereafter referred to as flat plate method). According to the specific test requirements, a piezoelectric quartz force sensor was selected with perfect measurement accuracy and frequency response; A injection flat plate with good sealing and negligible deformation was designed, which was made by45steel after quenching and tempering; A rotated bracket was built to adjust injection distance and injection angle between nozzle and injection flat plate easily.A modified measuring installation for fuel injection law based on Bosch tube method or called Bosch tube method for short was set up on the same pump test-stand. Through the consistency analysis of the two test results, optimal injection distance and injection angle were calibrated completely in the process of measuring the injection rate of nozzle with flat plate method. So, the optimal injection distance value is5mm and the optimal injection angle value is90°, and at the time of obtaining the optimal injection distance, the correction coefficient K was calculated:K≈0.5. Comparative analysis of the impact of the variable injection starting pressure and the variable fuel injection quantity on fuel injection rate measurement was made. Through the comparative analysis in a single fuel injection quantity of the injector under the two methods of measurement, relative error of a single fuel injection quantity and the actual measured values were calculated respectively, and the relative measurement error of the flat plate method:μ≤4.5%, and the relative measurement error of Bosch tube method:μ≤3.6%. Therefore, we can see that the results of flat plate method were certified completely with the better accuracy and reliability and which were close to the Bosch tube method.With numerical simulation method, injection flow fields in the test were computed by fluid analysis software FLUENT under different injection distance to verify the reliability of flat plate method, and transient pressure curve of injection flat plate and the experimental values were made an investigation and comparison. The results show that the transient pressure curve of injection flat plate by numerical simulation are consistent with the experimental values, and especially, when the distance of the injector nozzle and injection flat plate is5mm, simulation and experimental curves coincide best, which also are consistent with Bosch tube method test calibration, and on the other hand, the good accuracy and reliability of the fuel injection rate of nozzle based on momentum method is proven once again. |
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