Air-Breathing Engine Performance Parameters MAE 5350: Gas Turbines Air-Breathing Engine Performance Parameters and Future Trends Mechanical and Aerospace Engineering Department Florida Institute of Technology D. R. Kirk

LECTURE OUTLINE Review General expression that relates the thrust of a propulsion system to the net changes in momentum, pressure forces, etc. Efficiencies Goal: Look at how efficiently the propulsion system converts one form of energy to another on its way to producing thrust Overall Efficiency, hoverall Thermal (Cycle) Efficiency, hthermal Propulsive Efficiency, hpropulsive Specific Impulse, Isp [s] (Thrust) Specific Fuel Consumption, (T)SFC [lbm/hr lbf] or [kg/s N] Implications of Propulsive Efficiency for Engine Design Trends in Thermal and Propulsive Efficiency

FLUID MECHANICS: DERIVATION OF THRUST EQUATION Chemical Energy Thermal Energy Kinetic Energy Flow through engine is conventionally called THRUST Composed of net change in momentum of inlet and exit air Fluid that passes around engine is conventionally called DRAG

THERMODYANMICS: BRAYTON CYCLE MODEL 1-2: Inlet, Compressor and/or Fan: Adiabatic compression with spinning blade rows 2-3: Combustor: Constant pressure heat addition 3-4: Turbine and Nozzle: Adiabatic expansion Take work out of flow to drive compressor Remaining work to accelerate fluid for jet propulsion Thermal efficiency of Brayton Cycle, hth=1-T1/T2 Function of temperature or pressure ratio across inlet and compressor

P-V DIAGRAM REPRESENTATION Thermal efficiency of Brayton Cycle, hth=1-T1/T3 Function of temperature or pressure ratio across inlet and compressor

EXAMPLE OF LAND-BASED POWER TURBINE: GENERAL ELECTRIC LM5000 Modern land-based gas turbine used for electrical power production and mechanical drives Length of 246 inches (6.2 m) and a weight of about 27,700 pounds (12,500 kg) Maximum shaft power of 55.2 MW (74,000 hp) at 3,600 rpm with steam injection This model shows a direct drive configuration where the LP turbine drives both the LP compressor and the output shaft. Other models can be made with a power turbine.

CROSS-SECTIONAL EXAMPLE: GE 90-115B Compressor Nozzle Fan Turbine Inlet Combustor Why does this engine look the way that it does? How does this engine push an airplane forward, i.e. how does it generate thrust? What are major components and design parameters? How can we characterize performance and compare with other engines?

EXAMPLE OF MILITARY ENGINE: TURBOJET OR LOW-BYPASS RATIO TURBOFAN Extreme Temperature Environment Compressor Combustor Turbine Afterburner

MAJOR GAS TURBINE ENGINE COMPONENTS Inlet: Continuously draw air into engine through inlet Slows, or diffuses, to compressor Compressor / Fan: Compresses air Generally two, or three, compressors in series Raises stagnation temperature and pressure (enthalpy) of flow Work is done on the air Combustor: Combustion or burning processes Adds fuel to compressed air and burns it Converts chemical to thermal energy Process takes place at relatively constant pressure

MAJOR GAS TURBINE ENGINE COMPONENTS Generally two or three turbines in series Turbine powers, or drives, the compressor Air is expanded through turbine (P & T ↓) Work is done by the air on the blades Use some of that work to drive compressor Next: Expand in a nozzle Convert thermal to kinetic energy (turbojet) Burning may occur in duct downstream of turbine (afterburner) Expand through another turbine Use this extracted work to drive a fan (turbofan) Nozzle: Flow is ejected back into the atmosphere, but with increased momentum Raises velocity of exiting mass flow

BYPASS RATIO: TURBOFAN ENGINES Bypass Air Core Air Bypass Ratio, B, a: Ratio of bypass air flow rate to core flow rate Example: Bypass ratio of 6:1 means that air volume flowing through fan and bypassing core engine is six times air volume flowing through core

TRENDS TO HIGHER BYPASS RATIO 1958: Boeing 707, United States' first commercial jet airliner 1995: Boeing 777, FAA Certified Similar to PWJT4A: T=17,000 lbf, a ~ 1 PW4000-112: T=100,000 lbf , a ~ 6

ENGINE STATION NUMBERING CONVENTION 2.0-2.5: Fan 3: Combustor 0: Far Upstream 1: Inlet 4: Turbine 2.5+: Compressor 5: Nozzle One of most important parameters is TT4: Turbine Inlet Temperature Performance of gas turbine engine ↑ with increasing TT4 ↑

MAE 4261 REPRESENTATION OF AN ENGINE Compressor Combustor Turbine Inlet Nozzle Freestream 1 2 3 5 4

TYPICAL PRESSURE DISTRIBUTION THROUGH ENGINE

GE J85 J85-GE-1 - 2,600 lbf (11.6 kN) thrust J85-GE-5 - 2,400 lbf (10.7 kN) thrust, 3,600 lbf (16 kN) afterburning thrust J85-GE-5A - 3,850 lbf (17.1 kN) afterburning thrust J85-GE-13 - 4,080 lbf (18.1 kN), 4,850 lbf (21.6 kN) thrust J85-GE-15 - 4,300 lbf (19 kN) thrust J85-GE-17A - 2,850 lbf (12.7 kN) thrust J85-GE-21 - 5,000 lbf (22 kN) thrust

TURBOJET / MODERATE BYPASS TURBOFAN

P&W F100 and 229 P&W 229 Overview Type: Afterburning turbofan Length: 191 in (4,851 mm) Diameter: 46.5 in (1,181 mm) Dry weight: 3,740 lb (1,696 kg) Components Compressor: Axial compressor with 3 fan and 10 compressor stages Bypass ratio: 0.36:1 Turbine: 2 low-pressure and 2 high-pressure stages Maximum Thrust: 17,800 lbf (79.1 kN) military thrust 29,160 lbf (129.6 kN) with afterburner Overall pressure ratio: 32:1 Specific fuel consumption: Military thrust: 0.76 lb/(lbf·h) (77.5 kg/(kN·h)) Full afterburner: 1.94 lb/(lbf·h) (197.8 kg/(kN·h)) Thrust-to-weight ratio: 7.8:1 (76.0 N/kg)

ANTONOW AN 70 PROPELLER DETAIL UNDUCTED FAN, a ~ 30

“HYBRID” DUCTED FAN + TURBOJET

EFFICIENCY SUMMARY Overall Efficiency What you get / What you pay for Propulsive Power / Fuel Power Propulsive Power = TUo Fuel Power = (fuel mass flow rate) x (fuel energy per unit mass) Thermal Efficiency Rate of production of propulsive kinetic energy / fuel power This is cycle efficiency Propulsive Efficiency Propulsive Power / Rate of production of propulsive kinetic energy, or Power to airplane / Power in Jet

PROPULSIVE EFFICIENCY AND SPECIFIC THRUST AS A FUNCTION OF EXHAUST VELOCITY Conflict

COMMERCIAL AND MILITARY ENGINES (APPROX. SAME THRUST, APPROX COMMERCIAL AND MILITARY ENGINES (APPROX. SAME THRUST, APPROX. CORRECT RELATIVE SIZES) GE CFM56 for Boeing 737 T~30,000 lbf, a ~ 5 Demand higher efficiency Fly at lower speed (subsonic, M∞ ~ 0.85) Engine has large inlet area Engine has lower specific thrust Ue/Uo → 1 and hprop ↑ Demand high T/W Fly at high speed Engine has small inlet area (low drag, low radar cross-section) Engine has high specific thrust Ue/Uo ↑ and hprop ↓ P&W 119 for F- 22, T~35,000 lbf, a ~ 0.3

EXAMPLE: SPECIFIC IMPULSE PW4000 Turbofan SSME Space Shuttle Main Engine T ~ 2,100,000 N (vacuum) LH2 flow rate ~ 70 kg/s LOX flow rate ~ 425 kg/s Isp ~ 430 seconds Airbus A310-300, A300-600, Boeing 747-400, 767-200/300, MD-11 T ~ 250,000 N TSFC ~ 17 g/kN s ~ 1.7x10-5 kg/Ns Fuel mass flow ~ 4.25 kg/s Isp ~ 6,000 seconds

PROPULSIVE EFFICIENCY FOR DIFFERENT ENGINE TYPES [Rolls Royce]

OVERALL PROPULSION SYSTEM EFFICIENCY Trends in thermal efficiency are driven by increasing compression ratios and corresponding increases in turbine inlet temperature Trends in propulsive efficiency are due to generally higher bypass ratio

FUEL CONSUMPTION TREND U.S. airlines, hammered by soaring oil prices, will spend a staggering $5 billion more on fuel in 2007 or even a greater sum, draining already thin cash reserves Airlines are among the industries hardest hit by high oil prices “Airline stocks fell at the open of trading Tuesday as a spike in crude-oil futures weighed on the sector” JT8D Fuel Burn JT9D PW4084 Future Turbofan PW4052 NOTE: No Numbers 1950 1960 1970 1980 1990 2000 2010 2020 Year

CRUISE FUEL CONSUMPTION vs. BYPASS RATIO

SUBSONIC ENGINE SFC TRENDS (35,000 ft SUBSONIC ENGINE SFC TRENDS (35,000 ft. 0.8 Mach Number, Standard Day [Wisler])

AEROENGINE CORE POWER EVOLUTION: DEPENDENCE ON TURBINE ENTRY TEMPERATURE [Meece/Koff]

PRESSURE RATIO TRENDS (Jane’s 1999)