Effect of Alternative Fuels on Emissions and Engine Compatibility

Given the increasing focus on climate change and emissions, alongside the motivation to combat these phenomena, it is prudent to consider alternative fuels for gas turbines, a significant source of emissions. Adopting some form of alternative fuels could reduce the carbon footprint as well as the emissions output from gas turbines to manageable levels, provided alternative fuels are coming from overall low life cycle emissions sources. In this chapter, the effects of alternative fuels on the gas turbines performance and their emissions are discussed. With respect to gaseous emissions, it has been found that alternative fuels provide no clear advantage in terms of emissions reduction compared to standard petroleum derived fuels. However, it has been found that the CO₂ emissions of a given fuel is contributed to by the H/C ratio of the fuel. An increase of the H/C ratio could lead to reduction in CO₂ emissions, though energy per unit mass of fuel goes down. The effect of alternative fuels on PM emissions however are more positive if alternative fuels are used, but PM emissions are dependent upon the aromatic content and its species in the fuel. The availability of alternative fuels from F-T processes, as well as bio-derived fuels with very low or no aromatic content, leads to very low PM emissions from alternative fuels. With respect to seal swell in fuel systems, it has been found that some alternative fuels may struggle to maintain good seal swell performance as seal swell has been historically related to aromatic content of the fuel. Therefore, it has been deemed that further research is required to find an alternative. When considering the noise and vibrations from a turbine, there appears to be insufficient data to draw clear correlations between fuel type and amount of noise and vibrations generated, however it has been noted that noise and vibration emitted is a function of the vapour pressure, surface tension and flame velocities used which in turn to a certain extent depend upon the fuel used. In terms of thermal stability, it has been noted that paraffinic fuels are better at absorbing heat and dissipating it without forming carbon deposits on the fuel system components.