# Fuel-Water Emulsions as an Alternative Fuel for Gas Turbines: A Project Summary
## 1 Introduction
Moreover, studies conducted on test stands of gas turbine combustion chambers have also led to the conclusion that the addition of water to fuel reduces NOx emissions. In cases where the opposite effect was noted, the determining parameter was the type of fuel or its additive [4], as in [24], where the continuous phase of the emulsion was Redwood 650, which contains more than 10 times more nitrogen than is found in Oil No. 2. Changes in CO emissions resulting from the use of fuel-water emulsions are less predictable than in the case of NOx emissions. In the case of the V94.V3 GT, V84.V3 GT and 9000B turbines, no significant changes in CO emissions were recorded after replacing the classic fuel with emulsion fuel [19; 20; 21; 22]. However, in the J79-GE-10 and C60 turbines, this addition resulted in an increase in emissions [18; 23]. Research carried out at gas turbine combustion chambers also does not provide a clear answer as to the impact of emulsion fuel on CO emissions. Most often, an increase in CO emissions was recorded as a result of adding water to the fuel [4], although there were also cases in which a reduction in emissions was recorded; for example, in [25]. In the process of producing fuel-water emulsions, the addition of a surfactant is often used [2; 4; 26]. The amount of emulsifier in the mixture influences, among other things, the droplet size of the discrete phase of the emulsion [27], which may be a variable affecting the combustion process on a macroscopic scale [28]. The literature emphasizes the paucity of research on the influence of the emulsifier on operating parameters and emissions from the engines [2; 26] and notes that discrepancies in the tested CO and HC emissions may result from the quality of emulsions or be caused by additives [29; 30]. Therefore, understanding the impact of the addition of an emulsifier on the combustion process is particularly important, especially in the context of the previously mentioned research results conducted on single fuel drops. In publications on the combustion of fuel-water emulsions, there is only limited information on the impact of emulsion fuel combustion on the hot section of engines. Intests in which the emulsifier constituted up to 20% of the volume of the fuel mixture, the presence of a \"varnish-type\" coating on the walls of the combustion chamber was found after the tests. In this case, the authors attributed the cause of the precipitate to the emulsifier [31]. In another study, upon completion of testing on a piston engine, a deposit resembling white dust was found in the area of the intake valve after inspection. The tests lasted 500 h, during which the unit was powered by an emulsion fuel with a water content of 13% to 17%, and no engine damage or operational problems were found. In this case, it was also concluded that the cause of the deposit was the presence of an emulsifier in the fuel mixture [32]. Based on the authors' own research conducted on the GTM120 miniature gas turbine engine and literature studies, a lot of effort was made to explain the discrepancies in the literature regarding the results of tests on the combustion of fuel-water emulsions in gas turbines. Although, in general, the change in NOx emissions resulting from the addition of water to the fuel is characterized by a high degree of convergence of the observed change trends, in the case of the tests conducted on the C60 turbine, which is the only small turbine (60 kW) on which this type of research was carried out, a different tendency was shown. Therefore, NOx emission studies conducted on a miniature gas turbine can make a decisive contribution to our understanding of the impact of emulsion fuels on NOx emissions from small units. Moreover, based on experimental research and numerical calculations, an analysis of the impact of the presence of water in the fuel on CO emissions was carried out, which may also contribute to explaining the reasons for the divergent emission results found in the literature.