A hydraulic electronic unit injector was proposed for a hydraulic free piston diesel engine. The high pressure pump for the injector was replaced by the high pressure rail used for the engine. With the analysis of hydraulic electronic unit injector principle

the fuel injection characteristics were researched with Inov8 AKRIBIS II. The research focused on the effects of drive pressure and injection frequency on cyclic fuel injection quantity and injection delay. In order to analyze the effect of the rail pressure for the engine valve actuation on fuel injection process

an online test was carried out to measure fuel injection quantity. Results show that the valve actuation enlarges the cyclic fuel injection fluctuation (from -6.9% to +9.5%) because of the connection between the valve actuation and injector through their pressure rail

which affects stable engine operation. After the improvement of the high pressure rail system

a continuous engine test indicates that the fluctuation of cyclic fuel injection quantity and actual injection position affect the stability of engine operation

therefore the fluctuation of cyclic fuel injection quantity and injection delay should be reduced for the purpose of stable continuous engine operation.