In common rail diesel fuel injector system, currently there are two kinds of servo-hydraulic type piezo-driven injector; 3-way and bypass-circuit type, in order to amplify the extension of the piezo stack. The pilot valve driven by piezo stack can control the flow of fuel at a pressure chamber, which is accurately regulated by 3-way or bypass-circuit mechanism. Even though fuel injection events are triggered electrically, the main actuation forces to move injector needle inside nozzle are hydraulic force which is the key object aimed to eliminate in this study. In this study, two experiments were carried out using a constant volume chamber and a single cylinder CR direct-injection diesel engine. The driving force for air-fuel mixing process in diesel diffusion combustion is the energy contained within the spray. So, LED back illumination in constant volume chamber experiment for Mie scattering applied on the initial liquid spray visible of a direct needle-driven piezo injector and compared with conventional solenoid-driven injection cases as well. Also, the effects of direct needle-driven single injection was investigated on combustion performance through experiment approach of a single cylinder diesel CR direct-injection engine. As some results, a direct needle-driven diesel injector with no-hydraulic circuit has better control capability, good potential for higher injection rate, and desired accuracy of injected fuel quantity thanks to high performance of the piezo stack.