The aim of this work is the chemical composition emulation of solid oxide fuel cell (SOFC) outlet flow, with the hybrid system emulator rig developed by TPG at the University of Genoa. To emulate this chemical composition studying its effects on a commercial machine, the layout of the test rig facility (T100 machine coupled with a modular vessel) was re-designed and expanded. This plant was equipped with a steam generator system to inject super-heated steam immediately upstream of the machine combustor. Since it is not possible to re-generate the actual SOFC outlet composition with just steam injection (fuel cell outlet flow has higher percentage value of steam and CO2 than an expander inlet of a standard machine), this new system is essential to operate the test rig at specific chemical composition similitude condition. The objective of this new component is the developing of experimental data related to a commercial machine coupled with a fuel cell. In details, this paper deals with fuel cell outlet composition effects on main gas turbine properties because it is essential to know machine behaviour when it operates inside a hybrid system (important aspect to prevent risks such as surge). This new layout of the facility is essential to study the effect of steam rich mass flow rate on machine behaviour. For this reason, several tests at different operative conditions were carried out with the T100 machine operating in both electrical grid-connected and stand-alone modes. (C) 2011 Elsevier Ltd. All rights reserved.