The purpose of this paper is to introduce and investigate a new application of hydrogen to a special internal combustion engine (free-piston engine generator). The development of a full-cycle zero-dimensional dynamic simulation model is described, and an extensive coupled research method is presented by the iteration simulation between the zero dimensional dynamic model and a multi-dimensional computational fluid dynamics engine model of combustion process, giving insight into the operating characteristics and performances of the new hydrogen fueled engine. The influences of the piston motion on combustion process are analyzed. The performance characteristics of the new hydrogen engine are found to differ significantly from those of a corresponding traditional hydrogen engine and a free-piston gasoline engine. The results indicate that compared with the above-mentioned traditional hydrogen engine, the free-piston hydrogen engine has a higher piston acceleration around top dead center (TDC) and a advantage in terms of emissions formation due to faster power stroke expansion, but the indicated efficiency is slightly lower due to the longer late combustion process. Moreover, the indicated efficiency, combustion velocity and peak pressure are both larger, compared with the free piston engine combusting gasoline, and the concentration of NO emission also has an advantage. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.