Analysis of Jet & Rocket Propulsion Systems P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Controllable and Economic Propulsion Systems

Propulsion Systems

Jet Engine Vs Ramjet Vac 6 3 4 5 2 1 Vjet

Measure of Extra Life Generation by Compressor 2 3 Isentropic active compression

Combustion Chamber : Enhancement of Energy of would be Jet Vac 4 3 Vjet Define total temperature ratio across combustion chamber as 3 -- 4 s : increasing T: increasing p : constant???

Energy Balance in Combustor : 3-- 4 For unit flow rate of air thru the Jet engine: How much fuel should be added to get a compact jet engine ? How to achieve better fuel economy?

Turbine : Look for a Slave to Drive Compressor Vac 4 5 Vjet 4 -- 5 s = constant T : decreasing p : decreasing

Sizing of Turbine : Just Enough Power 4 5 T C 2 3 Duty of the Turbine is to drive the compressor : just enough power. Enhanced vigor of Jet:

The Thrust Generator with better Inlet Conditions Isentropic Expansion in a Passive Device (Nozzle)

Nozzle : Steady State Stead Flow 5 6 First Law for unit mass flow rate of gas: No heat transfer and no work transfer & No Change in potential energy.

Performance of Turbojet Engine Specific Thrust S   Thrust Specific Fuel Consumption TSFC

Performance of a Ideal Turbojet Engine : effect of Mach Number r0p,comp = 10 0,cc=4.5 S TSFC kg/ kN.hr Specific Thrust kN.s/kg TSFC Mac

Parametric Cycle Analysis of Ideal Turbo Jet Engine Selection of Safe Cruising Conditions….

Effect of Flight Mach Number on Fuel Economy 0,cc=4.5 r0p=1 r0p=2 r0p=3 TSFC kg/ kN.hr r0p=5 r0p=10 r0p=20 r0p=30 Mac

Effect of Flight Mach Number on Compactness 0,cc=4.5 r0p=20 r0p=30 r0p=10 r0p=5 r0p=3 r0p=2 r0p=1 Specific Thrust kN.s/kg Mac

Summary of Turbojet Performance A high compressor pressure ratio is desirable for subsonic flight for good specific thrust and low fuel consumption. A special care must be used in selecting the compressor pressure ratio for a supersonic flight. Rapid drop in specific thrust with pressure ratio at supersonic conditions. Rapid fall in specific thrust under supersonic conditions is still a serious concern for emergency/war use.

Turbo Jet with Afterburner inlet 1 2 7 5 3 6 4

Comparative Study of Jet Performance with AB & w/o AB rp = 10 & 0,cAB= 0,cc W AB W AB W/O AB TSFC Specific Thrust W/O AB

Energy Flow in Jet Engine Energy input Long distance travel demands high flight velocity. A Single hot Jet was creating huge noise. High flight velocity leads to drop in compactness and fuel economy. A Single hot jet is blackmailing the jet engine !!!

An Evolved design of Turbojet Inlet 2 3 cj 7 or hj 4 1 5 6 Total thrust may be Shared by both cold and hot jets.. In 1939-1941 Soviet designer Arkhip Lyulka elaborated the design of turbojet and created an evolved turbojet. Created the world's first turbofan engine, and acquired a patent for this new invention on April 22, 1941.

Special Design Variable for an Ideal Turbofan Engine Inlet 2 1

Sizing of Fan Inlet 2 3 1 Design Parameter : Fan Total Pressure ratio

Design Parameter : Compressor total pressure ratio Sizing of Compressor Inlet 4 2 3 1 Design Parameter : Compressor total pressure ratio

Sizing of Combustor 5 Inlet 4 2 3 1

Combined Gas Dynamic & Thermodynamic SSSF model for Turbine 5 Inlet 4 2 3 6 1

Generation of Thrust : The Capacity Specific Thrust based on total flow

Thrust Specific Fuel Consumption TSFC

Influence of Fan: Pressure Ratio: Mac = 0.75 r0,p,comp=15.0 a=4.0 T0max=1200K

Best Selling Turbofans in World CFM series

Current Turbofan Engines Model Thrust Bypass ratio Pressure ratio Applications CFM56-7B18 (86.7 kN) 5.5 32.7 Boeing 737-600 CFM56-7B20 (91.6 kN) 5.4 Boeing 737-600, Boeing 737-700 CFM56-7B22 (101 kN) 5.3 CFM56-7B24 (108 kN) Boeing 737-700, Boeing 737-800, Boeing 737-900

Optimum Fan Pressure Ratio for Fuel Economy =3 a =4 =6 =5 r0,p,comp=24 T0max=1800K Mac =0.9 7 12 8 10 TSFC Fan Pressure Ratio

Turboprop Engine V

Power Generated by A Turboprop The total propulsive power generated by an ideal turboprop is given by:

Pratt & Whitney PW127G Turboprop The result is class-leading fuel consumption and low green house emissions.

Propulsion in Space Sky is the Limit

Travel Cycle of Modern Spacecrafts

Basics of Rocket : generation of Thrust Rocket takes mass stored inside combustion chamber and throws it backwards, to use the reaction force to propel the vehicle. This is known as Rocket Propulsion Rocket ejects mass at a given momentum rate from the nozzle and receives a thrust in the opposite direction. Momentum rate of ejects:

Basic Forces Acting on A Rocket T = Rocket thrust D = Rocket Dynamic Drag Vr = Velocity of rocket mejects = Mass flow rate of ejects mr= Mass of the rocket

Rocket Velocity Equation Rocket mass X Acceleration = Thrust – Drag -gravity effect

Series Stage Rocket 3rd Stage Thrusting

Gas Turbine Technology : Flying Machine to Ground Utilities Self Study

Brayton Cycle 1-2 Isentropic compression (in a compressor) 2-3 Constant pressure heat addition 3-4 Isentropic expansion (in a turbine) 4-1 Constant pressure heat rejection

Analysis of Components 1 –2 : Specific work input :     2 – 3 : Specific heat input :     3 – 4 : Specific work output :     4 – 1 : Specific heat rejection :     Two Isentropic Processes sandwiched between two isobaric pressures:

Pressure Ratio Vs Efficiency  

Pressure Ratio Vs Specific Work Output  

1872, Dr Franz Stikze’s Paradox

Condition for Compact Gas Turbine Power Plant

At maximum power: Two Important Comments: What if I am not interested in Compactness. Should I prefer high Pressure Ratio for Efficient Plant? Why the plant is compact at this condition? What else can be inferred form this condition?

Condition for Economic Gas Turbine Power Plant

T0

T01 /T03 T01 /T03 T01 /T03

T0 s

GT24 (ISO 2314 : 1989) Fuel Natural gas Frequency 60 Hz  Gross Electrical output  187.7 MW*  Gross Electrical efficiency  36.9 %  Gross Heat rate  9251 Btu/kWh   Turbine speed  3600 rpm  Compressor pressure ratio  32:1  Exhaust gas flow  445 kg/s  Exhaust gas temperature  612 °C  NOx emissions (corr. to 15% O2,dry)  < 25 vppm

Fuel  Natural gas  Frequency  60 Hz  Gross Electrical output  187.7 MW*  Gross Electrical efficiency  36.9 %  Gross Heat rate  9251 Btu/kWh   Turbine speed  3600 rpm  Compressor pressure ratio  32:1  Exhaust gas flow  445 kg/s  Exhaust gas temperature  612 °C  NOx emissions (corr. to 15% O2,dry)  < 25 vppm