This article presents the results of an initial design study for a lean fully premixed (LFP) injector for commercial jet engine. The operating point considered is that of an high overall pressure ratio, small core engine at take-off condition. To perform this feasibility study, multiple relevant constraints are taken into account. The three-unit fully premixed injector has been designed by utilizing numerical simulations. The first unit of the injector is intended to perform complete fuel vaporization through heat transfer from the compressed air to the liquid fuel via a compact onboard heat exchanger. The second unit is designed to ensure premixing of the fully evaporated fuel and the air. Finally, the third unit ensures additional premixing and stability of the premixed swirling flame. The autoignition challenge associated with the design of the LFP injector is discussed in this article. The computational modeling approach that was used to design the units of the LFP injector is presented.