No abstract

While dual fuel firing of power generation combustion systems can provide energy security by improving the fuel flexibility of such systems, several studies on compression ignition engines have also shown a positive impact on NOX and PM emissions. Previous multiphase fuel combustion studies for gas turbine engines are limited, thus the present study addresses that gap by fuelling a model swirl stabilised gas turbine combustor with a blend of waste cooking oil-derived biodiesel and methane. Increasing amounts of methane were injected into the swirling combustion air flow while simultaneously reducing the biodiesel spray flowrate across a pressure atomiser, thus maintaining an overall thermal power output of 15 kW and a global equivalence ratio of 0.7 in all cases, except for flame stability range trials. Direct flame imaging, C2* and CH* chemiluminescence imaging, post combustion emissions as well as stability performance of the flames were evaluated. Emissions results indicate a reduction in NOx emissions whereas unburned hydrocarbons emissions increased when the dual fuel tests were compared with neat biodiesel combustion with further reduction of these emissions as gas fraction in the fuel mix increases. Further, flame images suggest increased wrinkling and perturbing of the flame front as gas fraction of the biodiesel/methane flame increases. However, the temporal variation of integral intensity of C2* and CH* species chemiluminescence point to lesser fluctuation in the rate of heat release hence improved flame stability and reduced combustion noise as methane partially replaces biodiesel in the combustion process. Also, it was found that flame stability limits reduce as methane partly replaces biodiesel in the flame; an average of 17% decrement in lean extinction limit is observed as methane content of combusted fuel increases from 0 to 20%.

No abstract

Exhaust gas recirculation (EGR) is one of the main techniques studied over the years to enable the use of oxyfuel combustion for carbon capture and storage (CCS). However, the use of recirculated streams with elevated carbon dioxide poses different challenges from the control of the flow rates and flue stream characteristics to the suppression of unwanted instabilities during the combustion process. Therefore, this study evaluates the use of various CO2 enriched methane blends and their response towards the formation of a great variety of structures that appear in swirling flows, which are the main mechanism for combustion control in current gas turbines systems. The study uses a 100kW acoustically excited swirlstabilised burner to investigate the flow field response. The results showed improved thermal efficiency of the system with high swirl and forcing while the blend of CO2 with methane balanced the heat release fluctuation with a corresponding reduction in the acoustic amplitudes of the system for a smooth running, suggesting that certain CO2 concentrations in the fuel can provide more stable flames at a certain carbon dioxide concentration.

Exhaust gas recirculation (EGR) is one of the main techniques to enable the use of oxyfuel combustion for carbon capture and storage (CCS). However, the use of recirculated streams with elevated carbon dioxide poses different challenges. Thus, more research is required about the cumulative effects on the desirable outcomes of the combustion processes such as thermal efficiency, reduced emissions and system operability, when fuels with high CO2 concentration for CCS exhaust gas recirculation or biogas are used. Therefore, this study evaluates the use of various CO2 enriched methane blends and their response towards the formation of a great variety of structures that appear in swirling flows, which are the main mechanism for combustion control in current gas turbines systems. The study uses 100 kW acoustically excited swirl-stabilised burner to investigate the flow field response to the resultant effects of the variation in the swirl strength, excitation under isothermal condition and the corresponding effects during combustion with different fuels at various CO2 concentrations. Results show changes in size and location of flow structures as a result of the changes in the mean and turbulent velocities of the flow field, consequence of the imposition of different swirl and forcing conditions. Improved thermal efficiency is also observed in the system when using high swirl and forcing while the blend of CO2 with methane balanced the heat release fluctuation with a corresponding reduction in the acoustic amplitudes of the combustion response, suggesting that certain CO2 concentrations in the fuel can provide more stable flames. Concentrations between 10 to 15% CO2 volume show great promise for stability improvement, with the potential of using these findings in larger units that employ CCS technologies.