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NASA’s “Environmentally Responsible Aircraft” (ERA) N+2 advanced, low NOx combustor technologies program is looking at combustion technologies suitable for the 2020 time frame. The objective of this program is to develop fuel-air mixing concepts and associated fuel control valves. The low emissions combustor concept must be capable of meeting or exceeding the N+2 LTO NOx goal of 75% reduction from the ICAO standard adopted by CAEP 6 at engine pressure ratios of at least 55. Goodrich Engine Components is working with NASA to demonstrate concepts with these capabilities. In the early 2000’s, Goodrich partnered with NASA in demonstrating the ability of a multipoint lean direct injection (LDI) concept to achieve very low NOx emissions index (EI) levels as tested at NASA test facilities. The program was successful in demonstrating the ability of the multipoint concept to deal with NOx at high power conditions but was not optimized to perform equally as well at low power conditions such as start, ground idle, and flight idle conditions. After review of previous work, Goodrich is investigating a new multipoint combustor design for the N+2 program. The basic multipoint premise of injecting fuel through a large number of injection sites to promote rapid mixing has been retained, but at a much reduced number of nozzles compared to the original work. In the new version, nozzles are arranged in a staggered array pattern and are manifolded in radial stages. The radial stages can be utilized to control radial temperature distribution to the turbine. Radial staging is also being used to maintain sufficient temperature levels around specific nozzles at low power conditions to provide adequate emissions and stability at these conditions. In addition to the modifications of the general arrangement, injector design features are optimized by stage such that much higher air/fuel mixing rates with lower central recirculation zones dominate high power conditions while more conventional swirl stabilization dominates at low power conditions when inlet temperatures are low. The design work is being guided by CFD analysis as well as qualitative and quantitative rig testing before the final configurations are fabricated and tested at the NASA flame tube rigs. This paper will discuss elements of prior designs compared to current designs and discuss the status of Computational Fluid Dynamic (CFD) simulations completed in the first phase of this program.

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

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