Characterisation of Lean Burn Module Air Blast Pilot Injector With Laser Techniques

Abstract

For lean burn combustor development in low emission aero-engines, the pilot stage of the fuel injector plays a key role with respect to stability, operability, NOx emissions, and smoke production. Therefore it is of considerable interest to characterize the pilot module in terms of pilot zone mixing, fuel placement, flow field and interaction with the main stage. This contribution focusses on the investigation of soot formation during pilot-only operation. Optical test methods were applied in an optically accessible single sector rig at engine idle conditions. Using planar laser-induced incandescence (LII), the distribution of soot and its dependence on air/fuel ratio, as well as geometric injector parameters, was studied. The data shows that below a certain air/fuel ratio, an increase of soot production occurs. This is in agreement with smoke number measurements in a standard single sector flame tube rig without optical access. Reaction zones were identified using chemiluminescence of OH radicals. In addition, the injector flow field was investigated with PIV. A hypothesis regarding the mechanism of pilot smoke formation was made based on these findings. This along with further investigations will form the basis for developing strategies for smoke improvement at elevated pilot only conditions.

Improvement on ignition and lean blowout performances of a piloted lean-burn combustor

“…Only pilot burner is fueled at the low power settings, such as idle and approach conditions, and the pilot and main burner are both fueled at high power settings, such as climb and take-off conditions. Compared with fuel injection devices in previous work, [6][7][8][9] the pilot swirl cup injector optimizes both the pressure swirl atomizer and swirler to improve the spray quality in terms of fuel/air mixing and spatial distribution by adjusting characteristics of primary spray, structure of venturi prefilmer, and air mass flow ratio of two swirlers, etc. such as, enlargement of spray cone for enhancing interactions between primary spray and swirling air, and augment of the operating range of pressure swirl atomizer in pilot stage for ensuring spray quality both at the low and high power settings.…”

“…Such pilot flames produce high smoke, CO, and UHC emissions and have poor stability. Recently, Meier et al 8 studied the effect of air/fuel ratio on soot formation during pilot-only operation by planar laser-induced incandescence (LII), it was found that soot is formed predominantly in the upstream directed part of the shaped pilot flow near the interface to the outer main flow. Kobayashi et al 9 investigated effects of swirler angle and swirler lip configurations on ignition performance, ignition performance was improved by extending heat shield to suppress the interaction of pilot flame and the main air stream, but other important performances of combustion were ignored.…”