Intermediate Pressure Combustion Research of a Multipoint Low NOx Combustion System

Abstract

In response to the NASA Environmentally Responsible Aviation program, United Technologies Aerospace Systems has designed, fabricated and tested a new Multipoint Lean Direct Injection system. This design consists of an array of pressure atomizing pilot injectors and novel high-shear airblast main injectors. Staging of the fuel injector manifolds allows the array to achieve low NO x at high power, in line with the program's goals of reducing landing and takeoff cycle NO x by 75%. Additionally, optimizing fuel splits between banks yields low power emissions in line with current state-of-the-art combustors. Emissions predictions of the design were computed utilizing computational fluid dynamics, and validated with a scaled power sector test on the NASA CE-5B-1 combustion rig. Rig testing indicated air leakage around the interface between the dome plate and the rig, which drove up emissions levels versus the design intent of the injector array. Even so, compared to a previously published multipoint array, the recorded emissions data showed lower levels of NO x at low power condition, but slightly higher levels at high power. There was also a good match to CFD predictions, although the discrepancy was larger at lower fuel-to-air ratios. This validates the CFD NO x predictions and shows that the array will be near the 75% reduction desired during actual takeoff conditions. NomenclatureCAEP = Committee on Aviation Environmental Protection CO = Carbon monoxide ΔP = Pressure drop across injectors as fraction of inlet pressure EI = Emissions Index (grams of constituent/kilogram of fuel) ERA = Environmentally Responsible Aviation program FAR = Fuel-to-air ratio by mass ICAO = International Civil Aviation Organization LTO = Landing and takeoff cycle MLDI = Multipoint lean direct injection NO x = Oxides of nitrogen P 3 = Combustor inlet pressure P4 = Absolute combustor pressure T3 = Combustor inlet temperature UHC = Unburnt hydrocarbons W 3 = Combustion air mass flow W f = Fuel mass flow

A Third-Generation Swirl-Venturi Lean Direct Injection Combustor With a Prefilming Pilot Injector

“…9 parts c and d, showing V4 and V3 have similar high power NO x emissions. The high power combustion efficiency of V3 is also similar to that of V4, with both greater 11 It is well known that this type of extrapolation is not highly accurate. The way the NO x reduction is stated "85-90% reduction" reflects this uncertainty.…”

“…The value a=0.7 was used because it was the typical value found when the adiabatic flame temperature was above 1700 K. The value a=1 was used because it was slightly higher than the highest a value found by examining the data; thus, it should serve as an upper bound for NO x emissions. LTO NO x emissions are estimated to be 85-90% below the CAEP/6 standard, exceeding the 80% NO x reduction goals set by AATT 11 .…”

“…Since it does not have a separate premixing zone, LDI promotes this rapid fuel-air mixing by replacing one traditionally-sized fuel-air mixer with several smaller fuel-air mixers. This is called multipoint LDI [6][7][8][9][10][11][12][13][14][15].…”

Parametric Design of Injectors for LDI-3 Combustors

“…The emissions and performance characteristics for NASA Glenn led LDI efforts for the 1 st generation (LDI-1) are summarized by [Tacina 2005] followed by the 2 nd generation LDI-2 by [Tacina 2014] and [Zink 2014]. …”