Experimental Investigation on Lean Blow Out of a Piloted Aero-Engine Burner

Abstract

One of the preferred ways to reduce NOX formation in an aero-engine is to operate lean throughout the whole operational range; however the lean combustion suffers from poor stability. To avoid the problem associated with stability, often a rich pilot flame is used along with a main flame to act as a source of heat and radicals to the main flame. The focus of the paper is to discuss the influence of the liquid fuel spray characteristics and effect of flow parameters on the lean blow out (LBO) limits of a piloted burner. In order to understand the observed remarkable LBO limits of the pilot flame with Jet A-1 (LBO = 145 kg-air to kg-fuel at 0.1 MPa of combustor pressure), velocity field measurements by laser Doppler Anemometry (LDA) technique have been performed. Furthermore, the flame structure has been analyzed with OH* chemiluminescence imaging. Experimental results show that the LBO limits of the burner running with liquid fuel further improves with an increase in combustor pressure. Such improvement in LBO limits is attributed to the change in the liquid fuel distribution caused by the change in the combustor pressure. For gaseous fuel measurements, results indicate that the equivalence ratio and the momentum ratio of the pilot jet to the co-annular flow are the dominating parameters that control the mixing process in the combustor and the ensuing effect on the flame structure and location of flame stabilization is substantial. The flame stabilizes either along the centreline or along the shear layer between two jets. Such information is useful in designing a lean partially premixed combustion system where a pilot flame is required to stabilize a main lean flame.

Investigation of differences in lean blowout of liquid single-component fuels in a gas turbine model combustor

“…There is general interest in understanding lean blowout as modern combustors are operated under lean conditions to reduce emissions. [23][24][25] In their reviews Cavaliere et al 26 and Marinov et al 24 show that a significant body of work regarding lean blowout of gaseous fueled swirling flames exists. However, lean blowout of spray flames has been studied in much less detail.…”

“…Further studies on lean blowout of swirling spray flames found improved lean limits with increased combustion air preheat temperature 43 and with increased combustor pressure. 25 Colby et al 23 investigated spray characteristics near lean blowout in an airblast atomised spray flame and highlight the importance of the production of small droplets (d < 10 µm) for the stability of lean combustion. Yang et al 44 found atomisation performance of their pilot spray to dominate the lean blowout process.…”

Influence of the Pilot Flame on the Morphology and Exhaust Emissions of NH3-CH4-Air Swirl Flames Using a Reduced-Scale Burner at Atmospheric Pressure

“…Experiments using NH 3 -based fuel blends on micro gas turbines (mGT) have been carried out to understand their performance, combustion efficiency, and exhaust emissions [3][4][5][6]. However, the major barriers to burning NH 3 are the high NO x emission [7][8][9] and its low reactivity, making it challenging to stabilize NH 3 flames in practical applications. Some burners feature a pilot flame to ease flame stabilization by providing continuous heat and radicals as ignition sources and, in turn, preventing the main lean flame from extinguishing [7,8].…”

“…However, the major barriers to burning NH 3 are the high NO x emission [7][8][9] and its low reactivity, making it challenging to stabilize NH 3 flames in practical applications. Some burners feature a pilot flame to ease flame stabilization by providing continuous heat and radicals as ignition sources and, in turn, preventing the main lean flame from extinguishing [7,8].…”