Analysis of Turbojet Engine Akhil Jaiswa Jaiswal, l, Akhil Praveen, Pr aveen, ASP Gautam, Amal Amal Jyothis V, V , Amit Amit Kamboj, K amboj, Anand Kumar, Anurag Singh B. Tech. Aerospace Ae rospace Engi Engineering, Indian I ndian Institute of Spac Spacee Science and Technology Technology Abstract — An An experiment was conducted in the Propulsion lab in
IIST on the Turbojet Engine to study the Brayton cycle efficiency at different rpm and to find net thrust developed by the SR30 jet engine. The efficiency of the Brayton cycle is found to increase with the rpm of the engine. Also the net thrust developed by the jet engine is observ observed ed to increase with the rpm. rpm.
Both the jet engines and gas turbines use Brayton Cycle for power gen eration.
Keywords Keywords-- Tu rbojet Engi ne, Gas Turbi ne, Effi ciency, ciency, Brayton Cylce, Th ru st.
I.
I NT NT RODUCTION RODUCTION
A gas turbine, also called a combustion turbine, is a type of internal combustion engine. It has an upstream rotating compress compress or coupled to a downstream turbine, and a co mbus tion [1] chamber in-between . The basic operation of the gas turbine is similar similar to t hat of the s team power plant plant e xcept that air is used instead of water. They use rotating compressors to compress air, and then mix it with fuel and burn the mixture to produce hot exhaust gases that drive turbines. The turbines drive the compressors and also provide power for other things, such as wheels or a propeller or generators or whatever. Gas turbine engines can be used in many different ways e.g. driving a propeller prop eller o r a fan th at is us ed for thrust production prod uction etc. As the name suggests, this type of engine is operated by gas rather than one operated, for instance, by steam or water. The gas which operates the turbine is the product of the combustion that takes place when a suitable fuel is mixed and burned with the air passing th rough the engine. engine.
[2]
Figure 2. Br ayton Cycle
[3]
Figure 3(a). T-S Diagr Diagr am for for Ideal Ideal Brayton Cycle
Figure 1. Sche matic matic of Turbojet Engine
A turbojet engine or jet engine uses only jet exhaust as its means of propulsion. The turbine blades spin to compress air, the fuel is added and after combustion the force of the exhaust leaving the engine provides the thrust to move the aircraft i.e. i.e. they produce propulsion propulsion at least in part b y sho oting oting hot e xhaus t gases at high speed out of the back of the engine. That’s why it is said that all jet engines are gas turbine engines, but bu t not all gas turbine en gines are jet engines .
[3]
Figure 3(b). P-V Diagram for Ide Ide al Brayton Cycle Cycle
II.
EXPERIMENT
The experiment was performed on a turbojet engine .The setup has a turbojet fitted with a hush unit for the reduction in the noise .The turbojet consists of five parts .1st part is the compress or inlet, 2nd part is co mpress or exit, 3rd is the turbine inlet, 4th the turbine exit and 5th part is the nozzle exit. In between the 2nd and 3rd part combus tor is placed . The turbine and compressor are connected. The work output from the turbine is used to run the compressor. The turbojet is assumed to undergo a Brayton cycle. Fuel used is kerosene (White petrol). The initiat ion of turbo jet is don e with help of the compress ed air fro m the tank.
III.
PROCEDURE
The pressure tank is connected to the turbojet. The turbojet is started and the throttle is adjusted so that the ignition is started. Once the ignition is started the turbojet is self- sustained and the compressed air is cut off. The values of pressure and temperatures at various points are noted with the help of a digital interface connec ted to co mputer. The value thrust is also noted. The same experiment is repeated for various throttles. The experi mental thrus t is compared w ith the theoretical thrust and effic iency of the cycle is calculated.
IV.
OBSERVATIONS
Table 1 Pressure Readings
Figure 4(a) S etup showi ng Readouts and throttle control
Compressor inlet Pressure PSIG
Compressor exit Pressure PSIG
Turbine Inlet Pressure PSIG
Turbine Exit Pressure PSIG
Nozzle Exit Pressure PSIG
Thrust
0.072
4.995
5.015
0.56
0.21
8
0.105
7.396
7.422
0.772
0.35
9
0.141
9.677
9.747
0.936
0.49
10
0.18
12.622
12.611
1.151
0.68
11
0.239
16.191
16.203
1.359
0.94
13
0.302
20.518
20.512
1.58
1.33
16
0.406
26.814
26.802
2.498
2.01
20
Lbs
Table 2 Temperature Readings
Compressor inlet Temp
Compressor Exit Temp
deg C
deg C
Turbine inlet Temp deg C
Turbine Exit Temp deg C
Exhaust Gas Temp deg C
31
112
585
578
504
30
127
611
586
509
30
144
610
599
519
30
162
611
598
533
30
184
636
595
549
30
206
654
594
562
29
241
725
610
589
Figure 4(b) Digi tal re ad-out displ aying Values
V.
EQUATIONS AND SAMPLE CALCULATION
Part I: To find the n et thrust To find out the thrust due to intake air at co mpressor inlet, Diameter of the engine intake bell section at Pitot static tube location, Dc = 0.06604 (m) Figure 5 Experi ment Setup
Diameter of d = 0.01905 (m)
the
taco
generator
housing,
2
Cros s sect ional area at Pitot s tatic tube location, (m ) A=
Part II: To find th e thermodynamic efficienc y of Brayton cycle
Pitot st atic pressure at compressor inlet s ide, (Pa)
Let h1, h2, h3 and h4 are the specific enthalpy values of the corresponding state points,
Temperature at compressor inlet, (K) T1
Specific (kJ/kgK)
3
Density of air corresp onding to p1 and T1 (kg/m )
Velocity o f air at co mpressor inlet, (m/s)
Vo lume flow rate of air into the compressor ,
Thrust du e to intake air,
Mach number of the air flow at th is s ection,
work
done
by
the
Heat added due to the co mbustion p rocess, (kJ/kgK) Specific work for the Turbine, (kJ/kgK)
Net sp ecific work don e by the cycle, (kJ/kg K)
Thermodyn amic efficiency of th e cy cle,
VI.
GRAPHS
To find out the thrust due to e xit gas at no zzle exit, Diameter at nozzle exit, De = 0.056 m 2 Cros s sect ional area at nozzle exit (m ),
Pitot static pressure at Nozzle exit (Pe ),
Temperature at Nozzle exit (K), Te
3
Density of exit gas co rresponding to pe and Te, (kg/m )
Graph 1 Speed vs. Efficiency
Velocity of ai r at co mpressor inlet, (m/s)
3
Vo lume flow rate of air into the compressor, (kg/ m )
Thrust due to intake air, (N)
Net Thrus t of engine, (N)
Thrust Specific Fuel Consumption,
compressor,
Graph 2 TSFC vs. Mach Inlet
Design Thrust Mass flow rate Compression
: 178 N : 0.5 kg/s : 2.5:1
A PPENDIX II Sample Calculation: # For reading 1 Compressor Inlet pressu re, p1 = 0.072 PSIG = 496.422 Pa Compressor exit pressure, p1 ’ = 4.995 PSIG = 34439.31 Pa Turbine inlet pressure, p2 = 5.015 PSIG = 34577.21 Pa Graph 3 Speed vs. Net Thrust Turbine exit pressure, VII. R ESULT p2 ’= 0.560 PSIG = 3861.06 Pa In the experiment on turbojet engine, the calculated thrust force Nozzle exit pres sure, increases with the rpm from 4.0125N at 40537 rpm to pe = 0.21 PSIG = 1447.899 Pa 50.6601N at 78711 rpm. The observed thrust force reading is Fuel consu mption 35.585N at 40537 rpm and 88.964N at 78711 rpm. The corresponding calculated inlet Mach number increased from = 3.12 *3.78541 litre/hr *density 0.0835 to 0.1960. In the second set of calculations the = 3.12*3.78541 *0.81 kg/hr efficiency of the Brayton cycle was calculated. The efficiency =9.566 kg/hr was found to increase from 17.86% to 65.39% at the above Density of fuel is 0.81 kg/litre mentioned rpm. Speed = 40357 RPM Compressor inlet te mperature, VIII. CONCLUSION T1 = 31 = 304K On increasing the speed of the engine, the efficiency of the Compressor exit temperature, Brayton cycle increases. This is also evident from the enthalpy T1 ’ = 112 = 385 K differences obtained from the readings at high rpm. The work Turbine inlet temperature, done by the turbine and the work done on the compressor, T2 = 585 = 858 K increase rapidly with increase in rpm. The amount of heat Turbine inlet temperature, added does not vary much with rpm. This can be explained as T2 ’ = 578 =851 K heat input d epends on fuel flow rate and it’s calorific value. Exhaus t as temperature, Te = 504 = 777 K Further there can be sources of error due to which we obtained Density at inlet, using eq (2) & ( 3) discrepancy in results. There could be several reasons for this ρ = 1.167 kg/m3 such as transient variations and fluctuations in load cell Velocity at inlet, Using (4) readings etc. Vi = 29.17 m/s Mach n o at inlet us ing (7) A CKNOWLEDGMENT M = 0.0834 We would like to acknowledge with appreciation the numerous Mass flow rate, Using ( 5) and valuable persons whose contribution has been important in = 0.1068 kg/s this report. We would like to thank our instructor Dr. Deepu M. Thrust at inlet, Using (6) for their valuable help. We also thank our lab assistants for F1 = 3.116 N clearing our do ubts. Density at exit, Using (10) 3 ρe = 0.4607 kg/m R EFERENCES Velocity at e xit, Using (11) Vi = 79.27 m/s [1] en.wikipedia.org/wiki/Gas_turbine Mass flow rate, Using ( 12) [2] www.couleurs-cabanes.fr = 0.0899 kg/s [3] dc443.4shared.com Thrust by nozzle, Using (13) [4] Dr. Rajesh S, Dr. Deepu M, IIST Lab Hand Out F2 = 7.128 N Net Thrus t = F1 -F2 A PPENDIX I = 4.012 N TSFC = 2.38 kg hr -1 N-1 Specifications
Turbojet engine
: SR30, 17cm diameter X 27cm long
For therma l efficiency
Since we know the pressure and temperature values at respective locations therefore we can use gas tables to find corresponding enthalpies h 1 = -166.703 kJ/kg h 2 = -84.297 kJ/kg h 3 = -416.603 kJ/kg h 4 = 408.801 kJ/kg Work done by compressor, Using (16) W c = 81.776 kJ/kg Heat added due to the combust ion process , Using (17) Q = 501.53 kJ/kg Specific work for the Turbine, Using (18) W T = -7.802 kJ/kg Net sp ecific work don e by the cycle,Using (19) W = 89.578 kJ/kg Using (20) Efficiency = 17.86% A PPENDIX III Tables for Part-I Table 1 Observed Pressure readings in SI units Serial No.:
Compressor inlet Pressure
Compressor exit Pressure
Turbine Inlet Pressure
Turbine Exit Pressure
Nozzle Exit Pressure
Pa
Pa
Pa
Pa
Pa
1
496.42
34439.31
34577.21
3861.06
1447.90
2
723.95
50993.62
51172.89
5322.75
2413.17
3
972.16
66720.57
67203.20
6453.49
3378.43
4
1241.06
87025.63
86949.78
7935.87
4688.43
5
1647.85
111633.02
111715.7
9369.98
6481.07
6
2082.22
141466.63
141425.2
10893.7
9170.03
7
2799.27
184876.02
184793.2
17223.1
13858.46
Table 5 Calculation Table
Tables for Part-II
Table 6 Enthalpy Values at different locations Serial No.:
Enthalpy at point 1
Enthalpy at point 2
Enthalpy at point 3
Enthalpy at point 4
kJ/kg
kJ/kg
kJ/kg
kJ/kg
1
-166.70
-84.93
416.60
408.80
2
-167.71
-69.71
445.68
417.72
3
-167.71
-52.43
444.56
432.24
4
-167.71
-34.08
445.68
431.12
5
-167.71
-11.59
473.78
427.77
6
-167.71
10 .99
494.10
426.65
7
-167.71
47 .08
574.89
444.56
Table 7 Work i nteraction of the cycle Work done by compressor
Heat added during combustion
Specific work for the turbine
Net specific work done by the cycle
kJ/kg
kJ/kg
kJ/kg
kJ/kg
Thermodynami c e fficiency of the cycle
81 .78
501.53
-7.80
89 .58
17 .86
98 .00
515.39
-27.96
125.96
24 .44
115.29
496.98
-12.32
127.60
25 .68
133.63
479.76
-14.56
148.19
30 .89
156.12
485.37
-46.01
202.14
41 .65
178.70
483.11
-67.45
246.14
50 .95
214.79
527.80
-130.33
345.12
65 .39
Where, Point 1 : Compressor inlet Point 2 : Compressor outlet Point 3 : Turbine inlet Point 4 : Turbine outlet
