A combined measurement method was proposed and applied to the study of transient dual fuel injection rate of a high-pressure nature gas and diesel co-direct injection engine.Firstly,since the traditional"momentum method"could only obtain the injection pattern but not the accurate injection rate,a parallel test method was pro-posed to obtain the circular injection quantity by collecting and testing the pressure change in the cavity,and the accurate gas injection pattern curve by combining the transient momentum signal.Then,the measurement and time characteristics of the injector were verified.Finally,the common working conditions of the diesel-natural gas dual fuel injector were tested.The results show that the method solves the problem that two-phase fuel injection rates are difficult to measure in the same field,and achieves the accurate measurement of the instantaneous injection rate of diesel and natural gas in the dual fuel injector.The test error of injection mass is not more than 5％,and the test er-ror at the start moment and end moment of injection is not more than 0.113 ms.Besides,the fluctuation rate of die-sel injection mass and natural gas injection mass is not more than 1.4％and 2.9％,respectively.With the increase of injection pressure,the opening period of the injector decreases and the closing period increases,and the opening and the closing speeds of the internal diesel needle are greater than those of the external gas needle.The injection of diesel injection affects the gas injection mass by affecting the duration of the gas injection,and the gas injection mass fluctuates up and down with the gas-only injection.
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