NEHRU INSTITUTE OF TECHNOLOGY,
COIMBATORE.
AE 207 - PROPULSION I
(YEAR
2011 -2012)
FOURTH
SEMESTER
AEROSPACE
ENGINEERING
Submitted by
SAMIYAPPAN RAMASAMY
3RD YEAR
AERONAUTICAL
UNIT I
FUNDAMENTALS OF GAS TURBINE ENGINES
1. Define specific heat.
It is the amount of heat required to
rise the temperature of unit mass of a substance through 1˚C.
2. Define specific heat capacity at
constant volume.
It is the amount of heat required to
raise the temperature unit mass of gas through 1˚c at constant volume.
3. Define specific heat capacity at
constant pressure.
It is the amount of heat required to
raise the temperature of unit mass of gas through 1˚c at constant pressure.
4. Define
energy.
It is defined as a capacity of a
body to do work energy can neither created nor destroyed but it can be
converted from one form to other form.
5. Define thermodynamic cycle.
It is the series of process (or)
operation that take place in a system which may cause the working fluid (air)
to return to its original state.
6. What are
the process involved in Carnot cycle
Carnot cycle contain four process
1. Isothermal expansion
2. Isentropic expansion
3. Isothermal compression
4. Isentropic compression
7. Explain process involved in Otto
cycle?
It is also called as constant volume
cycle. This is the theoretical cycle on which the petrol and gas engine work.
It has 4 processes, namely,
*isentropic compression
*constant volume heat addition
*isentropic expansion
*constant volume heat rejection
8. What are the processes involved
in diesel cycle?
*isentropic compression
*constant pressure heat addition
*isentropic expansion
*constant volume heat rejection
9. What are the processes involved
in bray ton’s cycle
It is also called as joule cycle or
constant pressure cycle
*isentropic compression
*constant
pressure heat addition
*isentropic
expansion
*constant pressure heat rejection
10. What are the component used in
open cycle gas turbine
*compressor
*combustion
chamber
*gas
turbine
11. What are the components used in
closed gas turbine
1.Compressor
2. Air
heater
3. Gas
turbine
4. Air
cooler
12. Define thermal efficiency
It is the ratio between net work
done to the heat supplied.
13. What are the types of propulsive
engines?
1. Air breathing engine-combustion:
Here combustion takes place by using atmospheric air.
2. Rocket engine-combustion: Here
combustion takes place by using its own supply of oxygen.
14. What are the classifications of
air breathing engine?
1. Ram jet engine
2. Turbo jet engine
3. Turbo
fan engine
4. Pulse
jet engine
5. Turbo
prop engine
15. What are the components used in
turbo jet engine?
① Diffuser
② Compressor
③ Combustion chamber
④ Gas turbine
⑤Exhaust
nozzle.
16. What are the components used in
turbo prop engine?
① Propeller
② Reduction gear box
③ Compressor
④ Combustion chamber
⑤ Gas turbine
⑥Exhaust
nozzle
17. What are the component used in
turbo fan engine?
① Fan
② Compressor
③ Combustion chamber
④ Turbine
⑤Nozzle
⑦By
bass passage
18. Define thrust.
Thrust is a force which is used to
move the aircraft in the forward direction.
19. Write thrust equation for jet
engine.
Thrust F=ṁa[(1+f) cj-u]+(pi-pa) Aj –(pi-pa) Ai
20. What are the advantages of
Turbojet engines?
1. The power to weight ratio of a
turbojet is about 4 times that of propeller system having reciprocating engine.
2. Turbojet can attain higher flight
speeds than engine propeller aircrafts.
21. What are the disadvantages of
Turbojet engines?
1. The fuel economy at low
operational speeds is extremely poor.
2. It has low take off – thrust and
hence poor starting characteristics.
22. Define specific thrust.
Specific thrust is the ratio of
thrust to unit mass flow rate of air.
23. Define thermal efficiency of
turbojet engine.
Thermal
efficiency of propulsive device is an indication of the degree of utilization
of energy in fuel in accelerating fluid flow and is defined as the ratio of
propulsive power furnished to exhaust nozzle to the heat supplied.
24.
Define propulsive efficiency.
Propulsive
efficiency is the ratio of thrust power to the propulsive power.
25.
Define overall efficiency?
The
overall efficiency of the propulsive system is defined as the ratio of useful
propulsive work to chemical energy supplied.
26.
What are factors affecting performance of thrust?
Turbine
inlet temperature, size of nozzle area, weight of fuel flow, engine rpm, amount
of air bleed from compressor, speed of aircraft, temperature of air, pressure
of air and humidity etc are the factors affecting performance of thrust.
27.
What is thrust augmentation?
The
poor take off characteristics of the turbojet engine can be improved by
augmenting the thrust. The process of augmenting the thrust is called as thrust
augmentation.
28.
What are the methods used for augmenting the thrust?
1.
After burning
2.
Injection of water – alcohol mixture
3.
Bleed burn cycle.
29.
Write short notes on after burning method.
In
this method, additional fuel is burned in the tailpipe between the turbine
exhaust section and entrance section of the exhaust nozzle. This method of
thrust augmentation increases jet velocity.
30.
Describe water – alcohol mixture injection method?
In
this method, injecting the refrigerants, water or water – alcohol mixture at
some points between inlet and exit sections of the air compressor. This method
of thrust augmentation increases mass flow rate.
31.
Define thrust specific fuel consumption.
Thrust
specific fuel consumption is the ratio of fuel consumption rate per unit
thrust. It is represented by SFC or TSFC. Unit: Ns / kg.
32.
Explain bleed burn cycle?
In
this method, a small percentage of high pressure air from the compressor is
bled to an auxiliary combustion chamber by by-passing the turbine. In auxiliary
combustion chamber the bled air is heated by an additional fuel supply to a
higher temperature. Then the hot gasses are then discharged forming an
additional jet.
UNIT II
SUBSONIC AND SUPERSONIC INLETS FOR JET ENGINES
33. Define diffuser?
It is a device which is used to increase the pressure and
decrease the velocity of fluids.
34. What are the types of diffuser?
1. Convergent diffuser
2. Divergent diffuser
3. Convergent-divergent diffuser.
35. How the performance of the inlet can be evaluated?
The performance of the inlet can be evaluated based on total
pressure ratio, uniformity of flow, good starting and stability, minimum weight
and low cost while meeting life and reliability goals.
36. What are the design variables for the subsonic inlets?
1.
Engine location on wing or fuselage
2.
Aircraft attitude envelope
3.
Flow field interaction between nacelle, pylon, and wing
4.
Noise suppression requirements.
37.
List out the characteristics of supersonic inlets?
1.
It must provide adequate subsonic performance
2.
Need good pressure distribution at the compressor inlet
3.
It must provide high pressure recovery ratio
4.
It must operate efficiently at all ambient pressures.
38. What is upstream capture area?
The
imaginary area from which quantity of air sucked into the aircraft inlet is
called as upstream capture area.
39.
What is the purpose of diffuser?
The
purpose of the aircraft gas turbine engine diffuser is to provide a sufficient
air supply to the compressor with a minimum pressure loss as possible.
40.
What is meant by shock swallowing by
area variation?
In
this method, the throat area will be increased from actual throat area. As the
result, in the throat region, the flow of air will be accelerated from sonic
velocity to supersonic velocity. So, the shock from the entrance of inlet is
swallowed to downstream of the throat.
41.
Define boundary layer.
Consider
an air flowing over a surface with a velocity “v”. A very thin layer of air,
which is in the immediate contact of the surface. This layer of air behaves
like a coating to the boundary of the surface. This thin layer is known
boundary layer thickness.
42.
What is boundary layer separation?
When
the flight flying with supersonic speed, shock wave is developed. Due to the
shock wave, the boundary layer fluid is removed from the walls between which
the shock is located. This is called as boundary layer separation. This
separation may have a large effect on the structure of the shock.
43.
Define convergent diffuser.
If
the cross sectional area is gradually decreased from entry section to outlet
section then the diffuser is said to be convergent type of diffuser. Here, M
>1.
44.
Define divergent diffuser.
If
the cross sectional area is gradually increased from entry section to outlet
section then the diffuser is said to be divergent type of diffuser. Here, M
<1.
45.
List out the types inlet modes of operations?
1.
Critical inlet operation
2.
Subcritical inlet operation
3.
Supercritical inlet operation
46.
Write short notes on critical inlet
operation.
When
the inlet can accept mass flow rate of air required to position the terminal
shock just inside the cowl lip. This is called as critical operation. In the
critical operation, the fraction of air spilled around the inlet is a minimum
and the inlet is said to to be matched to the engine.
47.
Describe subcritical inlet
operation.
When
the inlet is not matched to the engine, the normal shock moves upstream. This
is called as subcritical operation. In this case, the fraction of air is
spilled is increased.
48.
Explain supercritical inlet
operation?
When
the inlet can not capture the mass flow required by the engine, the terminal
shock is sucked down into the diffuser. This is called as supercritical
operation. This operation increases the corrected mass flow rate to the engine.
UNIT III
COMBUSTION CHAMBER
49. What is the function of combustion chamber:
In the combustion chamber the chemical energy of the fuel is
converted into heat energy which is later converted into work by the turbine.
The main function of the gas turbine combustion chamber is to provide for the
complete combustion of fuel and air, the air being supplied by the compressor
and the products of combustion being delivered to the turbine.
50. Define combustion process?
1.
The mixture of a fine spray of fuel
droplets with air.
2.
Vaporization of the fuel droplets.
3.
The breakdown of heavy hydro carbons
into lighter fraction.
4.
The intimate mixing of molecules of
these hydrocarbons with oxygen molecules.
5.
Finally the chemical reaction
themselves.
51. What are the factors affecting
combustion chamber design?
1.
Exit temperature of the gases at the exit of the combustion chamber.
2.
Velocity of the air in the combustion chamber.
3.
Air and fuel ratio.
4.
Formation of carbon deposits.
5.
Pressure loss.
6.
Stable combustion.
52.
What are the methods of flame
stabilization?
1.Use of swirl vanes.
2. Upstream injection method.
53. What are the methods of flame tube cooling?
1. Passing by pass air between casing and flame tube.
2. Welding fins between casing and flame tube.
3. Providing ring of small holes in flame tube.
54. What are the factors affecting performance of combustion
chamber?
1. Pressure loss.
2. Combustion intensity.
3. Combustion efficiency.
55. Define combustion intensity.
The combustion intensity is the ratio of energy release
raste to the product of combustion volume and pressure.
Combustion intensity = energy release rate / (volume X
pressure)
56. Define combustion efficiency?
It is the ratio between the actual temperature rise to the
theoretical temperature rise.
57. What is the function of flame holder.
Flame holder is a component of jet engine designed
to help maintain a continuous combustion in the combustion chamber. All
continuous combustion jet engines require a flame holder. A flame holder
creates a low speed eddy in the engine to prevent the flame from being blown
out. The design of the flame holder is an issue of balance between a stable
eddy and drag
58. Explain the basic elements of combustion chamber?
1.
Casing.
2.
Perforated inner liner.
3.
Fuel injecting system.
4.
Some means for initial ignition
5.
A fuel drainage system to drain off
unburned fuel, after the engine shutdown.
59.
What are the types of zones in combustion chamber?
1.
Primary zone.
2.
Secondary zone.
3.
Tertiary zone.
60.
What are the types of combustion chamber?
1.
Can type.
2.
Annular type.
3.
Can-annular type.
61.
Explain can type combustion chamber?
Multiple
numbers of chambers are placed around the shaft connecting compressor and
turbine. Each chamber is supplied with separate system of air and it is having
one fuel jet from common supply line. This type of layout suitable for aircraft
engine with centrifugal compressor. Because the air stream is already divided
by diffuser canes. For maintenance individual chamber can be removed and
replaced without disturbing the operation. This type is used in aircraft and
marine engines.
62.
Explain annular type combustion chamber?
This
type is suitable for aircraft engine with axial flow compressor. The annular
combustion chamber consists of single chamber with multiple fuel inlet located
bête=ween compressor and turbine.
63.
Describe can-annular combustion chamber?
It
consists of both annular and can type. This chamber gets air through common
pipe line and with separate fuel inlet.
64.
Define flame tube cooling?
The
flame tube cooling receives heat from convection from the hot gases and
radiation from the flame.
65.
Define flame stabilization?
It
is the process of stabilize the height of the flame on the combustion is
underway.
66.
Describe swirl vanes method in flame stabilization?
The
basic combustor consists of small swirl vanes around the fuel injectors with
large number of small holes. It mix the air and fuel over the cross section and
gives a recirculation pattern.
67.
Write short notes on upstream injection method of flame stabilization?
In
this method the air will be injected directly into the center of the fuel
injection zone.
68.
What are the types of flame holders?
1. Can type flame holder
2. H – gutter flame holder
3. V – gutter flame holder
69.
What are the advantage and disadvantage of upstream method?
Advantage:
In
this possibility of to improved mixing.
Disadvantage:
In this possibility of over heating the fuel pipes and
injectors. So proper cooling is required in this method.
UNIT IV
NOZZLES
70. Define nozzle?
The main purpose of nozzle is to collect the hot gasses from
the turbine and to increase the velocity of the exhaust gases before discharge
from the nozzle.
71. What is the function of nozzle?
1.
To increase the velocity of the gas
flow with minimum total pressure loss
2.
It allow for thrust reversing.
3.
Suppress the jet noise.
4.
It should allow for cooling of
walls.
72. Define Mach number?
The ratio of velocity of the fluid to the velocity of the
sound is called as mach number
.
73. What is shock wave?
The
fluid flow is in supersonic speed one layer is formed. It is called shock wave.
74. Define
normal shock wave?
Shock wave may be situated at right angles to the flow. They
are called as normal shockwaves.
75. What
is stagnation state?
It
is obtained by decelerating a gas isentropically to zero velocity at zero
elevation. The stagnation state of gas often used as a reference state.
76. What
is stagnation temperature?
It is defined as it is the temperature of gas when it is
isentropic ally decelerated to zero velocity at zero elevation.
77. Define
stagnation pressure.
It is defined as it is the pressure of gas when it is
isentropic ally decelerated to zero velocity at zero elevation.
78. Define
stagnation density.
It is defined as it is the density of gas when it is
isentropic ally decelerated to zero velocity at zero elevation.
79. Define
stagnation velocity of sound.
It is defined as it is the velocity of sound when the gas is
isentropic ally decelerated to zero velocity at zero elevation.
80. What
are the types of nozzle?
1.
Convergent nozzle
2.
Divergent nozzle
3.
Convergent-divergent nozzle
81. What
is meant by over expanded nozzle?
If the exit pressure is below the back pressure, then the
nozzle is said to be over expanded nozzle.
82. What
is meant by under expanded nozzle?
If the exit pressure is above the back pressure, then the
nozzle is said to be under expanded nozzle.
83. What
is impulse function?
The
sum of pressure force and impulse force gives the function
84. Differentiate
between adiabatic flow and diabatic flow?
Diabatic flow:
It is the flow in a constant area duct with heat transfer
and without friction is known as diabatic flow (Rayleigh flow)
adiabatic flow:
It is the flow in a constant area duct with friction and
without heat transfer is known as adiabatic flow(fanno flow)
85. What
is chocked flow through a nozzle?
The mass flow rate of nozzle is increased by decreasing the
back pressure the maximum mass flow conditions are reached when the throat
pressure ratio achieves critical value. After that there is no further increase
in mass flow with decrease in back pressure. This condition is called chocking.
At chocking condition M=1.
86. What
type of nozzle used for sonic flow and supersonic flow?
Constant area duct nozzle is used for sonic flow and
divergent nozzle is used for supersonic flow.
87. When
does the maximum mass flow occur for an isentropic flow with variable area?
Mass flow rate will be maximum at throat section where the
mach number is one.
88. What
is convergent-divergent nozzle?
Convergent-divergent
nozzle is duct which cross sectional area first decreases from the inlet to
throat and then increases from its throat to exit.
89. Define
stagnation enthalpy.
It is defined as it is the pressure of gas when it is
isentropic ally decelerated to zero velocity at zero elevation.
90. Define
Reynold’s number.
Reynold’s number is the ratio of ratio of inertia force to
viscous force.
91. Define
bulk modulus.
Bulk
modulus is defined as the ratio of change in pressure to change in volume.
92. What
are the losses in nozzles?
1.
Thrust loss due to the loss of mass
flow rate.
2.
Thrust loss due to leakage through
nozzle walls.
3.
Thrust loss due to blockage of
nozzle.
4.
Thrust loss due to non uniform flow.
5.
Thrust loss due to boundary layer
friction.
93. Define oblique shock wave?
The
shock waves are located at an angle to the upstream flow. They are called
oblique shock.
UNIT V
COMPRESSORS
94. What
is the purpose of compressor?
The purpose of compressor is to increase the pressure of
air. The compressor used in a turbojet can be either centrifugal type or axial
flow compressor.
95. What are the basic requirements of compressors?
1. High
air flow capacity per unit frontal area
2. High
pressure ratio per stage
3. High
efficiency
4. Discharge
direction suitable for multistaging.
96. What
is the application of axial flow compressor?
The axial flow compressors are most suitable for large size
gas turbine plants and aircraft engines.
97. What
are the main components in axial flow compressor?
1.
Outer casing
2.
Sets of fixed blades
3.
Sets of moving blades
4. Rotor
and drive shaft.
98. Define
degree of reaction for axial flow compressor.
The degree of reaction for axial flow compressor is defined
as the ratio of actual change in enthalpy in the rotor to actual change in
enthalpy in the stage.
99. Define
flow coefficient.
Flow coefficient is defined as the ratio of axial velocity
to peripheral speed of the blades.
100. Define
loading coefficient.
The loading coefficient is defined as the ratio of the
actual stagnation enthalpy rise in the stage to enthalpy equivalent to
peripheral speed of the rotor.
Flow coefficient = Actual work / u2
101. What
are the advantages of centrifugal compressors?
1. It
occupies a small length than the equivalent axial flow compressor.
2. It
is able to operate effectively over a wide range of mass flow rate at any
particular rotational speed.
102. List
out essential parts of a centrifugal compressor.
1. The
inlet casing with converging nozzle
2. The
impeller
3. The
diffuser
4. The
outlet casing.
103. What
are the types impeller blades used in centrifugal compressor?
1. Forward
cured vanes
2. Backward
curved vanes
3. Radial
blades
104. What
are the assumptions made on radial vane type of impeller?
1. Loss due to friction is
negligible.
2. Energy loss or gain due to heat transfer is very small.
3. The gas leaves tangential velocity is equal to impeller
velocity.
105.
What is the purpose of inlet casing
with converging nozzle?
The purpose of inlet casing with converging nozzle is to
accelerate the fluid to the impeller inlet.
106.
What is the function of impeller?
The function of the impeller is to increase the kinetic
energy of the air and the static pressure.
107.
Define rotor pressure loss
coefficient.
It is defined as the ratio of pressure loss in the rotor due
to relative motion of air to the pressure equivalent of relative inlet
velocity.
108.
Define rotor enthalpy loss
coefficient.
It is defined as the ratio of difference between the actual
and isentropic enthalpy to the enthalpy equivalent of relative inlet velocity.
109.
Define stator pressure loss
coefficient.
It is defined as the ratio of pressure loss in the stator or
diffuser due to flow velocity to the pressure equivalent of actual inlet
velocity of the diffuser.
110.
Define stator enthalpy loss coefficient.
It is defined as the ratio of difference between the actual
and isentropic enthalpy to the enthalpy equivalent of absolute velocity of flow
at diffuser inlet.
111.
What are the applications for
centrifugal compressor?
1.
It is suitable for supercharging
I.C. engines.
2.
It is suitable for refrigeration
units
3.
It is suitable for aircraft jet
engine where low pressure ratio is required.
112.
What is the exit blade angle for
different types of impeller vanes?
(i)
For forward curved vanes, the exit
blade angle is more than 90o
(ii)
For backward curved vanes, the exit
blade angle is less than 90o
(iii)
For radial vanes, the exit blade
angle is equal to 90o
113.
Define efficiency of the compressor.
The efficiency of the compressor is defined as the ratio of
ideal enthalpy difference to the actual enthalpy difference.
114. Define
degree of reaction for centrifugal compressor.
The degree of reaction for centrifugal compressor is defined
as the ratio of actual change in static enthalpy in the impeller to actual
change in stagnation enthalpy in the stage.
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