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Combustor for Jet Engines

Combustor for Jet Engines. P M V Subbarao Professor Mechanical Engineering Department. Creation of Geometry to Hold A Reliable Flame…. Basics Thermodynamic Process in Combustor.

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Combustor for Jet Engines

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  1. Combustor for Jet Engines P M V Subbarao Professor Mechanical Engineering Department Creation of Geometry to Hold A Reliable Flame….

  2. Basics Thermodynamic Process in Combustor Combustor is a control Volume to facilitate flow or air and fuel to undergo through a complete Exothermic chemical reactions. Air

  3. Reciprocating Engine Vs Jet Engine

  4. Thermodynamics of Actual Combustion

  5. Specific Heat of gases

  6. Jet Fuels • Jet fuel is a specific blend of fuels used in aviation to run turbine powered engines for both military and civilian use. • Military fuels differ from commercial use in a few different ways. • The most common commercial Jet fuel is Jet A, Jet A-1 and Jet B. • These are cheaper and less refined versions of the Jet fuel blend and does not contain all the chemicals used in military blends. • The most common military blend of Jet fuel is JP-8, JP-5 and JP-4 which are engineered for military use. • The biggest difference in the two blends is there freezing points and ability to handle high heat.

  7. Organic Chemistry of Jet Fuels • Jet fuels are basically mixtures of kerosene and gasoline. • Half-&-half for JP-4, 99.5% kerosene for JP-5 JP-8 • 100% kerosene for Jet A-1. • Kerosene consisting of C9-C16 paraffins (53%), cycloparaffins (31%), aromatics (16%), and olefins (0.5%) • Special additives (1..2%) : corrosion inhibitor, anti-icing, anti-fouling, and anti-static compounds. • Jet A-1 comprises hydrocarbon chains with 9 to 15 carbon atoms. • Average molecular composition of Jet A-1 is C11.6H22.3 . • Jet A-1’s surrogate is 1-dodecene C12H24, M = 0.1683 kg/mol. • Jet 4 4 comprises hydrocarbon chains with distribution from 5 to 15 carbon chains. • JP-4’s surrogate is n-decane C10H22

  8. Sulfur Content in Jet Fuels • Commercial aviation fuel (Jet A/A-1) contains sulfur at concentrations of 400-800 ppm. • Road transportation fuel is subject to an ultra-low sulfur fuel standard of 15 ppm, which is about 97% less than jet fuel.

  9. Chemistry of Combustion • CXHYSZ +e 4.76 (X+Y/4+Z) AIR + Moisture in Air + Moisture in fuel → P CO2 +Q H2O +R SO2 + T N2 + U O2 + V CO • Exhaust gases: P CO2 +QH2O+R SO2 + T N2 + U O2 + V CO kmols. • Excess air coefficient : e. • Volume fraction = mole fraction. • Volume fraction of CO2 : x1 = P * 100 /(P+R+ T + U + V) • Volume fraction of CO : x2= VCO * 100 /(P +R+ T + U + V) • Volume fraction of SO2 : x3= R * 100 /(P +R+ T + U + V) • Volume fraction of O2 : x4= U * 100 /(P +R+ T + U + V) • Volume fraction of N2 : x5= T * 100 /(P +R+ T + U + V) • These are dry gas volume fractions. • Emission measurement devices indicate only Dry gas volume fractions.

  10. Emission Standards • 15% oxygen is recommended in exhaust. • NOx upto 150 ppm. • SO2 upto 150 ppm. • CO upto 500 ppm. • HC upto 75 ppm. • Volume fractions of above are neglected for the calculation of specific heat flue gas.

  11. Control and Computation of Turbine Inlet Temperature For a given mass flow rate of fuel and air, the temperature of the exhaust can be calculated using above formula. Select a suitable value for excess air ratio,  Guess approximate value of specific heat of flue gas. Calculate approximate value of TIT. Calculate cp,fluegase. Re calculateTIT Repeat till the value of TIT is converged.

  12. Simple Burner Burning Velocity Air Flow velocity Fuel • Burning Velocity > Flow Velocity : Flash Back Limit • Burning Velocity < flow Velocity : Blow Off Limit • Burning Velocity = Flow Velocity : Stable Flame.

  13. Stability & Flammability Limits • Burning Velocity > Flow Velocity : Flash Back Limit • Burning Velocity < flow Velocity : Blow Off Limit • Burning Velocity = Flow Velocity : Stable Flame. Rich Mixture Fuel Flow rate Flash Back Stable Flame Blow off Lean Mixture Air Flow rate

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