Characterization of a Novel Porous Injector for Multi-Lean Direct Injection (M-LDI) Combustor

Jianing Li, Umesh Bhayaraju, San-Mou Jeng
2017 Volume 4A: Combustion, Fuels and Emissions   unpublished
A generic novel injector was designed for multi-Lean Direct Injection (M-LDI) combustors. One of the drawbacks of the conventional pressure swirl and prefilming type airblast atomizers is the difficulty of obtaining a uniform liquid sheet under all operating conditions. Micro-channels are needed inside the injector for uniformly distributing the fuel. The problem of non-uniformity is magnified in smaller sized injectors. The non-uniform liquid sheet causes local fuel rich/lean zones leading to
more » ... igher NOx emissions. To overcome these problems, a novel fuel injector was designed to improve the fuel delivery by using a porous stainless-steel material with 30 μm porosity. The porous tube also acted as a prefilming surface. Liquid and gaseous fuels can be injected through the injector. The current study investigates the aerodynamics, spray quality, fuel-air mixing and emission characteristics of the novel injectors at 4% pressure drop and atmospheric conditions. The injectors have two configurations with different counter-rotating radial-radial swirlers. And the injector 1 has a SN of 0.75 and SN of injector 2 is 0.6. The characteristics of the novel injectors are also compared with a typical airblast injector having a peanut nozzle with flow number of 1. A Central Toroidal Recirculation Zone (CTRZ) and Corner Recirculation Zone (CRZ) are observed from the aerodynamics study. Spray measurements are carried out at various equivalence ratio conditions without a confinement. D10, D32 and D0.5 are investigated on Jet-A, GTL and blended fuels. There is no significant influence of fuel types on the spray behavior due to their similar physics properties. The porous injectors generate a fine spray with weighted SMD ~45 µm at equivalence ratio of 0.6. Gaseous Fuel-air mixing studies are carried out at different equivalence ratios with and without a ii confinement. A fully premixed mixing profile was obtained at 0.43" downstream of the injector exit. Flame characterization and emission measurements are carried out at elevated inlet air temperature and various equivalence ratio conditions. Natural gas is used as the gaseous fuel, Jet-A, GTL and blended fuels are used as liquid fuels during combustion studies. Symmetric blue flames are observed at fuel lean conditions. Injector 1 has a shorter flame than injector 2 at same condition due to the smaller axial velocity. The effects of inlet air temperature and combustion flame temperature on the NOx emissions are studied. NOx emissions increase with inlet air temperature and flame temperature for injector 1. For injector 2, NOx emissions decrease as inlet air temperature is increased from 400℉ to 500℉. NOx emissions increase as the inlet air temperature rises over 500℉. Chemkin simulations are carried out to investigate the NOx emissions with various chemical reaction mechanisms. GRI Mech 3.0 is used to simulate natural gas, two reaction mechanisms from NASA and CNRS are used to simulate Jet-A and GTL fuels. A model with a PSR and a PFR is utilized. The comparison between the simulation and experiments is investigated. The simulation results closely match the experimental data under 1900 K flame temperature, and overpredict at higher flame temperature conditions. iii iv
doi:10.1115/gt2017-63981 fatcat:c5ihgxzltzd23ouiym5osdmhxm