Rigorous emission levels are huge challenge for automotive industries to come up with unprecedented ideas of improving existing technologies. In advancing diesel engine technology, the crucial thing is to invest in further development of a piezoelectric fuel injector in the common-rail system for heavy duty diesel engine. The design and conception of a new mechanical component usually requires extensive testing and man-hours for achieving the desired results. Hence, the utilisation of a numerical simulation to predict the design configuration trends, can help to reduce cost in an engineering project. A Solenoid injector model was studied and modified in order to introduce the piezo actuation with the purpose to have more efficient fuel injection, achieve an adequate needle lift, and response quickly.