Component Performance - Inlet, Burner and Nozzle

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Austin Horatio Phillips
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1 Component Performance - Inlet, Burner and Nozzle Introduction Changes in gas properties as it flows through the engine Sources of losses and figures of merit Efficiencies of the inlet, burner and exhaust nozzle

Enthalpy h, specific heat c p and ratio of specific heats γ for fuel and air combustion product are dependent on

Inhibitor (FSII) Corrosion Inhibitor and Lubricity Improver (CILI) Figure 5-1 Enthalpy vs Temp.

Mattingly Variation in Gas Properties h and c p increase with temperature and the fuel/air ratio γ decreases with

2 Enthalpy h, specific heat c p and ratio of specific heats γ for fuel and air combustion product are dependent on temperature T fuel/air ratio f Variation in Gas Properties JP8 is Jet A-1 fuel with additives: Fuel System Icing Inhibitor (FSII) Corrosion Inhibitor and Lubricity Improver (CILI) Figure 5-1 Enthalpy vs Temp. for JP-8 and Air Combustion Product Adapted: Elements of Propulsion: Gas Turbines and Rockets by Jack D. Mattingly Variation in Gas Properties h and c p increase with temperature and the fuel/air ratio γ decreases with temperature and the fuel/air ratio Figure 5-2 Specific Heat vs Temp. Figure 5-3 Ratio of Specific Heats vs Temp. Adapted: Elements of Propulsion: Gas Turbines and Rockets by Jack D. Mattingly

Constant c p and γ Representative Values Use constant c pc and γ c. f= 0 (typical values: c pc = 1.005 kj/(kg K); γ c = 1.4) Use constant c pt and γ t (typical values: c pt = 1.148 kj/(kg K); γ t = 1.

3 Constant c p and γ Representative Values Use constant c pc and γ c. f= 0 (typical values: c pc = kj/(kg K); γ c = 1.4) Use constant c pt and γ t (typical values: c pt = kj/(kg K); γ t = 1.333) Adapted: Elements of Propulsion: Gas Turbines and Rockets by Jack D. Mattingly Figure of Merit Each engine component will be characterised by its figure(s) of merit - Model the component performance - Facilitate cycle analysis of real engines - Examples: Pressure ratio, total temperature ratio, efficiency of the component

$Isentropic Efficiency Actual performance / Idealized performance (isentropic) Degree of degradation of energy in steady-flow devices Most processes are considered adiabatic (loss) η d = A/B (fraction$

4 Isentropic Efficiency Actual performance / Idealized performance (isentropic) Degree of degradation of energy in steady-flow devices Most processes are considered adiabatic (loss) η d = A/B (fraction of inlet dynamic temperature (B) made available for isentropic compression) (A) (B) T-s Diagram of Inlet States Adapted: Elements of Propulsion: Gas Turbines and Rockets by Jack D. Mattingly Inlet & Diffuser Pressure Recovery Inlet losses Intake can be considered adiabatic duct τ d = 1 Losses mainly due to wall friction and shock waves (in supersonic inlet) Wall friction and shock wave result in drop in total pressure π d < 1 Adapted: Elements of Propulsion: Gas Turbines and Rockets by Jack D. Mattingly

5 Inlet & Diffuser Pressure Recovery The isentropic efficiency of the inlet is defined as (loss) Figure of Merit for inlet π d (A) (B) Adapted: Elements of Propulsion: Gas Turbines and Rockets by Jack D. Mattingly Subsonic Inlet Efficiency For subsonic inlets, Adapted: Elements of Propulsion: Gas Turbines and Rockets by Jack D. Mattingly

Supersonic Inlet Pressure Recovery In inlets at supersonic speeds, losses arise due to Wall friction and Shock waves Causes loss in total pressure and affects ram recovery Defineη r = portion of π d

6 Supersonic Inlet Pressure Recovery In inlets at supersonic speeds, losses arise due to Wall friction and Shock waves Causes loss in total pressure and affects ram recovery Defineη r = portion of π d that is recovered from ram in the presence of shock waves Define π d max = portion of π d that is due to wall friction only In the absence of shock waves, π d = π d max (max ram recovery possible) Thus, π d = π d max η r Supersonic Inlet Pressure Recovery Reference to American Department of Defense (MIL-STD 5008B) for Ram Pressure Recovery Factor, η r Adapted: Elements of Propulsion: Gas Turbines and Rockets by Jack D. Mattingly

7 Burner Efficiency & Pressure Loss Key losses in the burner (combustor) : Incomplete combustion of fuel Total pressure loss. The combustion efficiency η b is defined as The total pressure loss can be obtained from The figures of merit for the burner are η b and π b Exhaust Nozzle Loss Loss due to: Over or under-expansion at exit Duct total pressure loss from turbine to exit π n can be found by π n is used as figure of merit for the nozzle Nozzle is considered adiabatic, thus

8 Summary Gas properties change as it flows through the engine Use of representative values Define figures of merit due to component inefficiencies for: Inlet Burner Exhaust nozzle Reflection Question Consider the similarities between the inlet and the exhaust nozzle and discuss the choice of the figures of merit for these components.

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