# Fuel-Water Emulsions as an Alternative Fuel for Gas Turbines: A Project Summary
## 3 Research Results and Discussion
### CO Emissions  
Tests of the GTM120 gas turbine showed a decrease in CO emissions due to the addition of water to the fuel (Figure 11). This effect was more intense the more the miniature gas turbine operated at a higher rotational speed. For a revolution of 100 krpm and 12% water addition, a 10% emission reduction was achieved compared with the case in which the turbine was powered by the reference fuel, while at a revolution of 120 krpm and the same water addition, emissions were reduced by over 15%. Considering that the use of fuel-water emulsion reduces the temperature at the outlet of the combustion chamber and reduces NOx emissions (Figure 9), reducing CO emissions is unintuitive. Figure 10: Comparison of temperature distribution and NOx emissions at a turbine rotational speed of 80 krpm powered by standard fuel and an emulsion containing 3% water in its composition. The possibility of oxidizing CO to CO\({}_{2}\) strongly depends on the temperature and the residence time of the molecule in the high-temperature region. High temperature and the longest possible stay of the particle in its area favor this process. In areas where the temperature exceeds 1270 K, CO oxidation dominates according to reaction (1), and at lower temperatures, reaction (2) plays the main role [56; 57]:  
\[\mathrm{CO}+\mathrm{OH}\leftrightarrow\mathrm{CO}_{2}+\mathrm{H}, \tag{1}\]  
\[\mathrm{CO}+\mathrm{H}_{2}\mathrm{O}\leftrightarrow\mathrm{CO}_{2}+\mathrm{H}_ {2} \tag{2}\]  
Therefore, increasing the area in the high-temperature combustion chamber at the expense of reducing the areas with maximum temperatures does not necessarily result in a deterioration of the oxidation process of CO to CO\({}_{2}\). Numerical calculations of the flow with emulsion combustion through the GTM120 gas turbine showed just such an effect (Figure 12). A reduction in the areas of maximum temperature is observed, combined with an expansion and uniformity of the area of relatively high temperatures. In Figure 12, the arrow indicates the direction of the most intense expansion of the reaction area resulting from the addition of 12% water to the fuel mixture. Moreover, two vertical lines mark the area in the central zone of the combustion chamber, where, when comparing two cases, it is easy to see the extension of the high-temperature area of the primary combustion zone and the reduction in the lower-temperature areas. Figure 11: The influence of water content in the emulsion on the change in CO emissions. Figure 12: Temperature distribution for the GTM120 turbine operating at a rotational speed of 100 kppm in the case of the combustion of a base fuel and an emulsion containing 12% water. (The arrow indicates the direction of the most intense expansion of the reaction area resulting from the addition of 12% water to the fuel mixture.) The factor that hinders the oxidation of CO is the contact of CO molecules with the cooled engine walls. If a CO particle is placed in the area affected by the cold wall, further oxidation processes will be frozen due to the reduced enthalpy of the medium [61]. In the case where the GTM120 turbine is fed with a fuel-water emulsion, there is a tendency to increase the average temperature of the combustion chamber walls with an increase in the share of water in the fuel. However, it was increased by a maximum of 11K, which means that this factor was not likely to be decisive in the recorded CO emissions. The numerical calculations leading to this conclusion are described in [41]. Based on the research results presented so far in the literature, it is difficult to formulate a clear hypothesis regarding the reasons for the discrepancies occurring in research on the impact of fueling a gas turbine with a fuel-water emulsion. In six of the fourteen groups of studies described in the literature so far, an increase in CO emissions was noted after adding water to the fuel, in five, there were no significant changes, and in three, changing the fuel mixture resulted in a decrease in emissions (Figure 13).