Dual-Fuel Operation of Biodiesel and Natural Gas in a Model Gas Turbine Combustor

The dual-fuel combustion characteristics of palm biodiesel/methyl esters (PME) and natural gas (NG) in a model gas turbine swirl flame burner are investigated at a thermal power of 9.3 kW. The PME is atomized into a spray, while the gaseous NG is premixed with the main bulk swirling air before entering the combustion chamber. The dual-fuel PME/NG flame structure is similar to the single-fuel PME, where the sooty flame brush is noticeably absent. The PME and PME/NG flames emit higher peak intensity of OH* and CH* radicals as compared to diesel at the same equivalence ratio. Dual-fuel operation results in lower NO but higher CO at phi = 0.9 as compared to pure diesel and PME spray flames. The higher CO emission level for dual-fuel is attributed to poor mixing and incomplete combustion as a result of reduced air flow. At a leaner operation of phi = 0.65, enhanced turbulence due to higher bulk air flow results in improved mixing, lowering the overall CO but increasing the NO emissions because of the more intense flame core. The study shows that optimization of the multiphase dual-fuel injection system is needed to achieve low emissions in a gas turbine combustor.