A new internal combustion engine is proposed. This engine is one example of gas generator engines, configured according to a newly proposed cycle principle. Turbocharging with intercooling is employed to reduce the energy loss of engine exhaust. A reciprocating piston-gasifier is used to further boost the pressure and to raise the turbine inlet temperature near its material limit.To study the feasibility of the proposed engine, a piston-gasifier is designed to consist of manifolds and pairs of cylinders with different bores. To simulate the operations of the piston-gasifier, a numerical model is developed. The manifolds and cylinders are treated as open systems and combustion is described as a one-zone heat release process. Subprocesses are described in sufficient detail. The operating characteristics of the piston-gasifier are predicted and analyzes over a broad range of operating parameters. In the second part of this article these results are used to predict the operating performance of the whole engine system.