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Despite appearing as a promising technology for distributed generation, micro Gas Turbines (mGTs) have not yet managed to penetrate the small-scale Combined Heat and Power (CHP) market. The energy efficiency of mGTs amounts to 80% whenever both heat and electricity are required. However, when the heat demand is low, the hot exhaust gases have to be directly blown off and the electrical efficiency of the unit (∼30%) is not high enough to sustain profitable operation. Water injection, achieved when transforming the mGT into a micro Humid Air Turbine (mHAT), allows making use of the exhaust gas heat in such cases, thus increasing electrical efficiency of the technology and improving its feasibility. Although the enhanced performance of the mHAT cycle has been thoroughly investigated from a numerical point of view, results regarding the experimental behaviour of this technology remain scarce. In this paper, we present the experimental characterisation of the mHAT located at Vrije Universiteit Brussel (VUB) which is based on the T100 mGT equipped with a spray saturation tower. These are the first experimental results of such an engine working at nominal load with water injection. In addition, the control system of the unit has been modified so that it can operate either at constant electrical power output (the default setting) or at constant rotational speed. The latter option allowed better assessing the effect of water injection. Experimental results demonstrate the patent benefits of water injection on mGT performance: at fixed rotational speed, the power output of the mHAT increases by more than 30% while fuel consumption rises only by 11%. Overall, the electrical efficiency in wet operation increases by up to 4.2% absolute points. © 2017 Elsevier Ltd

Introduction of water in a micro Gas Turbine (mGT) has proven to be a very effective method to recover waste heat into the cycle, since it increases the mGT electrical efficiency significantly. Different routes exist for water introduction in the mGT cycle. Classical routes, like injection of steam/preheated water or the micro Humid Air Turbine (mHAT) concept, where water is introduced in the cycle by means of a saturation tower, have shown to have high potential. However none of the previously mentioned cycles exploits the full thermodynamic potential for waste heat recovery through water introduction. More advanced humidified Gas Turbine (GT) cycles have been proposed and studied for large scale GTs. So far, none of these concepts have been applied on mGT scale, despite their high potential. In this paper, we study the impact of these different, more advanced, humidified GT cycle concepts on the mGT performance. The different selected cycles – next to the classical steam injection or injection of (preheated) liquid water in the recuperated cycle and the mHAT – were: micro Humid Air Turbine Plus (mHAT+), Advanced Humid Air Turbine (AHAT) and the REgenerative EVAPoration (REVAP®) cycle concept. The impact of these concepts on the mGT cycle performance has been studied on the Turbec T100 mGT. Simulations indicated that humidifying the air of the mGT has a significant beneficial effect on cycle performance due to the increased waste heat recovery, resulting in a higher electrical power output (at constant rotational speed) or reduced fuel consumption (at constant power output), both leading to an increased electrical efficiency. Depending on the different cycle layout used, more or less waste heat could be recovered from the exhaust gas. The REVAP® concept with feedwater preheat was identified as the optimal cycle layout within the selected options. By applying this concept to the Turbec T100, most waste heat could be recovered, achieving the highest electrical effici