N+3 and N+4 Generation Aeropropulsion Engine Combustors Part 5: NOx, CO, HC and Smoke Emissions

Previous studies showed that the rich-dome takeoff NOxEI technology status of small, medium and large engines is presented well by the following expression: NNNNN = 0.04 × NOO1.8957 However, the same set of engines when plotted in terms of LTO NOx versus rated takeoff thrust give a large scatter band leading one to propose several different correlations. For example, the following expression for the Trent1000 LTO NOx passes well through the CF6-80C2LEC data indicating that perhaps several rich-dome combustors have very similar LTO NOx technology capability. LLN NNNTTTTT1000 = 12.753e0.0048×F LTO NOx of the nine large and very large modern richdome engines (viz. #10 through #17) were correlated well by the following generalized expression leading to their classification into four groups defined as α1 = 15,α2 = 0,α3 = −10 and α4 = −25, namely the 1, 2, 3 and 4 groups; the latter being the lowest LTO NOx RQL engine. LLN NNNRRR = 0.175 × F + αi The corresponding expression for the 2 generation lean dome (viz. #17) is represented well by LLN NNNRTLT = 0.226 × F − 40 which is not much different from the lowest NOx RQL engine specified as LLN NNNRRR = 0.175 × F − 25 if one knew how to scale down from nominal 500kN engine to 300kN engine size, viz. #12. Therefore, the next generation 500kN size engine needs to target for LLN NNNRTLT = 0.226 × F − 80. Therefore, the N+3 and N+4 combustion system goal is to further reduce LTO NOx from the 2 generation lean dome (viz. #18 which emits ~30 g of NO2/kN at 300kN) by 2/3 to 10 g of NO2/kN. Simultaneously, it should have LTO HC and LTO CO competitive with the N+1 generation RQL engines, namely: LLN HHN+3 ≤ 37.62e−0.0115×F LLN HNN+3 ≤ 170.7e−0.006×F NIIe HHNNN+3 ≤ 24.89e0.011×F NOMENCLATURE ACT-E: Advanced combustion technology for reducing emissions ASK: Available seat km BPR: Fan bypass ratio CAA: Clean Air Act Amendments 1970 edb-12: the ICAO aircraft engine emissions databank updated January 2012 EI: Emission index, g of pollutant/kg fuel EPA: Environmental Protection Agency F: Sea-level rated takeoff thrust, KN FB: LTO specific fuel burn, kg/kN GEA: General Electric Aviation ICAO: International Civil Aviation Organization LEC: Low Emissions Combustor belonging to the richdome vintage LD: Lean dome combustors LTO: Landing takeoff M: Mach number MPG: Miles per gallon OPR: SLSS takeoff pressure ratio (overall pressure ratio) P&W: Pratt and Whitney RF: Radiative forcing RPK: Revenue passenger km RQL: Rich-Quench-Lean approach used for lowering NOx from rich-dome combustors RR: Rolls Royce SLSS: Sea level standard day static (M=0) VOC: Volatile Organic Compounds INTRODUCTION Continuing emphasis on efficiency, and concerns on global warming, local air quality and human health have brought in many changes in the gas turbines and resulting advances in combustion technolgy during the last forty years. Several innovative approaches are currently underway to further improve propulsion system efficiency which motivated the team for an academic study and initiation for the N+3 and N+4 combustion technology and attendant research activities as briefly described in the following paragraphs. Extension and calibration of ACT-E process to propulsion engines combustion products ranging in the rated takeoff thrust from 30kN to more than 500kN has been summarized in regard to the best classes of combustors for NOx, CO and HC emissions. The mission fuel burn is covered in Mongia’s Part 4 paper followed by this paper to summarize NOx, CO, HC and smoke tradeoffs. CO2, CH4, N2O, and several other fluorinecontaining halogenated substances are the most important constituents of the greenhouse gases (GHG) directly emitted by humans. It should be mentioned that the Global Warming Potentials (100-Year Time Horizon), GWP of CH4 and N2O are 21 and 310, respectively compared to CO2. As shown in Figure 1, the U.S. GHG emissions have increased by 8.7 percent from 1990 to 2011 with an average annual increase of 0.4%