DRY ULTRALOW NOX GREEN THUMB COMBUSTOR FOR ALLISONS 501-K SERIES INDUSTRIAL ENGINES

This paper describes the progress made in developing an external ultra low oxides of nitrogen (NOx) ''Green Thumb'' combustor for the Allison Engine Company's 501-K series engines. A lean premixed approach is be ing pursued to meet the emissions goals of 9 ppm NOx, 50 ppm carbon mo noxide (CO), and 10 ppm unburned hydrocarbon (UHC). Several lean premi xed (LPM) module configurations were identified computationally for th e best NOx-CO trade-off by varying the location of fuel injection and the swirl angle of the module. These configurations were fabricated an d screened under atmospheric conditions by direct visualization throug h a quartz liner; measurement of the stoichiometry at lean blow out (L BO); measurement of the fuel-air mixing efficiency at the module exit; and emissions measurements at the combustor exit, as well as velocity measurements. The influence of linear residence time on emissions was also examined. An LPM module featuring a radial inflow swirler demons trated efficient fuel-air mixing and subsequent low NOx and CO product ion in extensive atmospheric bench and simulated engine testing. Measu rements show the fuel concentration distribution at the module exit im pacts the tradeoff between NOx and CO emissions. The effect of varying the swirl angle of the module also has a similar effect with the gain s in NOx emissions reduction being traded for increased CO emissions. A uniform fuel-air mixture (+/-2.5 percent azimuthal variation) at the exit of the module yields low NOx (5-10 ppm) at inlet conditions of 1 MPa (similar to 10 atm) and temperatures as high as 616 K (650 degree s F). The combustion efficiency at these conditions was also good (>99 .9 percent) with CO and UHC emissions below 76 ppm and 39 ppm, respect ively. This LPM module was resistant to flashback, and stability was g ood as LBO was observed below phi = 0.50. Tests with multiple modules in a single liner indicate a strong intermodule interaction and show l ower NOx and CO emissions. The close proximity of adjacent modules and lower confinement in the liner most likely reduces the size of the re circulation zone associated with each module, thereby reducing the NOx formed therein. The CO emissions are probably lowered due to the redu ced cool liner surface area per module resulting when several modules feed into the same liner.