Visualisation and performance evaluation of biodiesel/methane co-combustion in a swirl-stabilised gas turbine combustor

Abstract

While dual fuel firing of power generation combustion systems can improve 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 combustion turbines 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. Methane was increasingly injected into swirling combustion air flow while simultaneously reducing the biodiesel spray flowrate across a pressure atomiser, thus maintaining an overall equivalence ratio of 0.7 while delivering a thermal power output of 15 kW in all cases, except for flame stability range trials. Direct flame imaging, CH* and C2* chemiluminescence imaging, post combustion emissions as well as stability performance of the flames were evaluated. NOX emissions were found to decrease by 29% and unburnt hydrocarbons increased by 10% as the fraction of methane in fuel mix increased to 30%. 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 CH* and C2* species chemiluminescence point to at least an 8% improvement in flame stability when 30% of flame heat output is supplied by methane compared to neat biodiesel burn. Also, it was found that flame stability limits reduce as methane partly replaces biodiesel in the flame.