Investigation of a Novel Fuel Injector for Dry Low NOx Combustor

Abstract

In the present investigation, a novel fuel injection concept is developed for Dry Low NOx combustors. A multi-injector block is used for fuel-air mixing and flame stabilization. The injectors in the multi-injector block are equally spaced in a rectangular grid of 3×3. Each injector of the multi-injector block has a porous concentric tube through which fuel is injected into the annular space around the porous tube. The porous tube is made up of stainless steel with 30 μm porosity. Air enters the annular space around the porous tube through eight tubes that surround the porous tube. The fuel and air mix in the annular space between the injector wall and the porous tube. A CO2 mixing technique is adopted to investigate the fuel-air mixing quality under non-reacting atmospheric conditions. CO2 is used to simulate the fuel. The CO2 concentrations are converted to fuel mass fractions for comparison. The experiments are carried out at pressure drop of 4% across the injector. The fuel mass fraction contours show an annular ring of low fuel concentration downstream of the individual injectors with a high concentration in the Central Toroidal Recirculation zone (CTRZ). Furthermore, PIV measurements are conducted to study the injector aerodynamics under the same operating conditions. The PIV measurements also show CTRZ downstream of the individual injector. The jet emanating from the injectors expands gradually downstream. An outer weak recirculation zone (ORZ) is also observed between the jets. Preliminary combustion experiments are carried out to observe the flame shape and heat release distribution. The flame shape follows the velocity contours. The combustion studies show that the flame length is longer. The long flame length is due to the high velocities at the exit of the injector. A probability density function (pdf) is generated for the fuel mixture fraction. The pdf is based on the mixture fraction and velocity data obtained at the exit of the injector block. Chemkin analysis is carried out to estimate the emissions based on the experimentally obtained pdfs.