Jet Engine

― GROUP 3B ―

Jack Connolly

Adam Cook

Jason Bradbrook

Thermodynamics II || Section 10

MECH 2750 || Section 09 Page 1 Group 3B

Abstract

The laboratory experiment pertains to the analysis of a small jet engine. The jet engine is

an application of the Brayton cycle. Using thermocouples and pressure transducers, a display

shows the states of the air within the jet engine. From these values, characteristics of the engine

can be analyzed, such as component efficiencies, propulsion efficiency, and thrust. [1]

Introduction

Jet engines use the Brayton cycle to generate thrust. There are 3 main components of the

Brayton cycle: the compressor, combustion chamber, and the turbine. The cycle intakes fluid and

the compressor compresses the fluid. Then the fluid undergoes a heat addition stage. In the case

of the jet engine, fuel is mixed with the air and combusted to add thermal energy. Finally, the

fluid spins a turbine. The turbine’s shaft drives the compressor. Leftover energy remains in the

fluid. In the case of the jet engine, it is exhausted from the compressor. This extra energy

signifies a change in momentum. The change in momentum across the engine represents the

force of thrust on the engine.

cite

MECH 2750 || Section 09 Page 2 Group 3B

Experimental procedure

1. Ask your TA to load the data acquisition program and run the pre-programmed LabView VI for this lab. The screen should display readings from all sensors. Review the readouts to make sure they are working properly.

2. Make sure the air pressure in the compressed-air-start line is at least 100 psia (not exceeding 120 psia). Ask your lab instructor to check the oil level.

3. MAke the appropriate length measurements and record the required dimensions so you can calculate the inlet area (where the sensors are).

4. Ask for help from your lab instructor to turn on the system and start the engine. After the engine is successfully started, you must first allow the engine to achieve the idle speed before making any measurements. Make sure the throttle is at its lowest point. The idle position is nearly vertical, and is close to the operator (away from the engine).

5. Slowly open the throttle. Start taking data at about 65,000rpm. Make sure that you allow the engine time to reach steady state by monitoring the digital engine rpm indicator on panel. The reading fluctuates somewhat so use your judgement.

6. Take data at three different engine speeds. You will use the data to study how cycle and component efficiencies change with speed.

7. After you are done taking data, turn off the fuel flow switch first. 8. The data will be stored in Excel spreadsheet format.

Diagrams

This diagram shows the internal components of the the SR-30 jet engine, notably including the compressor, combustion chamber, and the turbine. [2]

MECH 2750 || Section 09 Page 3 Group 3B

The main components of the engine are show schematically blow. This is known as the Brayton cycle. [3]

Data

ATMOSPHERIC CONDITIONS

Estimated (10/15)

Atmospheric Pressure (psi) 14.7

Atmospheric Temperature (°F) 68

Measured (10/22)

Atmospheric Pressure (psi) 14.79

Atmospheric Temperature (°F) 50

Compressor Inlet Compressor Exit

Date Recorded

Trial T1 (°F)

P1 (psi)

T2 (°F)

P2 (psi)

10/15/2018

1* 70.9 0.150 219.4 6.47

2* 70.4 0.191 206.2 8.48

3* 70.3 0.255 209.1 10.49

4 70.3 0.321 232.0 12.88

5 70.5 0.376 258.0 15.44

MECH 2750 || Section 09 Page 4 Group 3B

6 72.0 0.603 298.1 23.84

10/22/2018

7 69.0 0.298 220.1 12.15

8 70.0 0.421 271.4 16.67

9 69.8 0.501 294.5 19.17

10 70.0 0.605 323.6 23.48

Turbine Inlet Turbine Exit

Date Recorded

Trial T3 (°F)

P3 (psi)

T4 (°F)

P4 (psi)

10/15/2018

1* 970.3 6.78 1079.6 0.86

2* 987.3 8.82 1084.6 1.13

3* 1031.7 10.83 1081.5 1.39

4 1110.9 13.02 1080.9 1.69

5 1156.3 15.47 1057.2 2.06

6 1169.9 23.99 1114.3 3.42

10/22/2018

7 1124.7 12.39 1080.6 1.66

8 1167.4 16.76 1024.2 2.1

9 1175.5 19.26 1020.9 2.53

10 1206.5 23.67 1116.6 3.26

Exhaust Measured Output

Date Recorded

Trial T5 (°F)

P5 (psi)

Rotation (RPM)

Thrust (lb)

1* 890.5 0.67 45172 0.2

2* 909.1 0.85 50769 0.7

3* 900.2 1.06 55524 2.6

MECH 2750 || Section 09 Page 5 Group 3B

10/15/2018 4 910.7 1.33 60147 5.7

5 931.7 1.63 64461 9.6

6 1063.5 2.95 76727 25.6

10/22/2018

7 895.2 1.24 58698 N/A

8 945.3 1.62 66683 N/A

9 979.8 2.24 70211 N/A

10 1206.5 23.67 1116.6 3.26

*The cycle was not operating properly for trials 1-3. It can be observed that the temperature does not decrease across the turbine, meaning the start up compressed air was still running the jet, not the engine itself. Additionally, the strain gage was not installed correctly, so the measured thrust of the system is not recorded properly, and must be calculated manually.

Results

Compressor Inlet Compressor Exit

Date Recorded

Trial T1 (°F)

P1 (psi)

h1 (BTU/lb)

T2 (°F)

P2 (psi)

h2 (BTU/lb)

10/15

4 70.3 14.850 126.7 232.0 27.58 165.6

5 70.5 14.891 126.7 258.0 30.14 171.9

6 72.0 14.955 127.1 298.1 38.54 181.6

10/22

7 69.0 15.088 126.4 220.1 26.94 162.7

8 70.0 15.211 126.6 271.4 31.46 175.2.

9 69.8 15.291 126.6 294.5 33.96 180.8

10 70.0 15.395 126.6 323.6 38.27 187.8

MECH 2750 || Section 09 Page 6 Group 3B

Turbine Inlet Turbine Exit

Date Recorded

Trial T3 (°F)

P3 (psi)

h3 (BTU/lb)

T4 (°F)

P4 (psi)

h4 (BTU/lb)

10/15

4 1110.9 21.48 388.2 1080.9 16.39 380.2

5 1156.3 23.52 400.2 1057.2 16.76 373.9

6 1169.9 25.53 404.0 1114.3 18.12 389.0

10/22

7 1124.7 27.81 391.9 1080.6 16.45 380.2

8 1167.4 30.26 403.2 1024.2 16.89 365.1

9 1175.5 38.78 405.6 1020.9 17.32 364.3

10 1206.5 27.18 413.9 1116.6 18.05 389.8

Exhaust Measured Output

Date Recorded

Trial T5 (°F)

P5 (psi)

h5 (BTU/lb)

Rotation (RPM)

Thrust (lb)

10/15

4 910.7 16.03 335.4 60147 5.7

5 931.7 16.33 341.0 64461 9.6

6 1063.5 17.65 375.7 76727 25.6

10/22

7 895.2 16.03 331.4 58698 N/A

8 945.3 16.41 344.5 66683 N/A

9 979.8 17.03 353.5 70211 N/A

10 1206.5 17.75 413.9 1116.6 3.26

Date Recorded

Trial Air Flow Rate (slugs/s)

Fuel Flow Rate (gal/h)

10/15

4 0.016 2.53

5 0.017 2.93

MECH 2750 || Section 09 Page 7 Group 3B

6 0.022 3.98

10/22

7 0.015 2.44

8 0.018 3.14

9 0.02 3.47

10 0.022 3.95

Trial

Turbine Efficiency

(ɳɳT)

Compressor Efficiency

(ɳɳC)

Propulsion Efficiency

(ɳɳP)

4 63.5% 28.7% 7.0%

5 63.3% 72.7% 8.5%

6 72.7% 41.1% 8.8%

7 62.8% 21.7% 9.6%

8 60.5% 63.5% 11.6%

9 60.5% 50.4% 13.9%

10 61.6% 55.0% 14.2%

Average 63.6% 47.6% 10.5%

MECH 2750 || Section 09 Page 8 Group 3B

Sample Calculations

Calculating Isentropic Efficiency of the Compressor

ηCompressor = h −h2 1

h −h2s 1

where is the enthalpy at and p2h2s s1

At state 1, trial 4, p = 18.850 psi and T = 70.3°F

So h and s can be fixed from the tables: BTU/lb, BTU/lb°R26.7h1 = 1 .618s1 = 1

At state 2, trial 4, p = 27.58 psi, T = 232°F

So h can be fixed from the tables: BTU/lb65.6 h2 = 1

For isentropic efficiency, s = c, So for and p = 27.58 psi,s2 = s1

BTU/lb51.4 h2s = 1

63.5%ηCompressor = 165.6−151.4151.4−126.7 =

MECH 2750 || Section 09 Page 9 Group 3B

Calculating Isentropic Efficiency of the Turbine

ηT urbine = h −h3 4h −h3 4s

where is the enthalpy at and p4h4s s3

At state 3, trial 4, p = 21.48 psi and T = 1110.9°F

So h and s can be fixed from the tables: 388.2 BTU/lb, BTU/lb°Rh3 = .880 s3 = 1

At state 4, trial 4, p = 16.39 psi, T = 1080.9°F

So h can be fixed from the tables [3]: BTU/lb80.2 h4 = 3

For isentropic efficiency, s = c, So for and p = 16.39 psi,s3 = s4

BTU/lb60.3 h4s = 3

8.7%ηT urbine = 388.2−360.2388.2−380.2 = 2

Calculating Propulsion Efficiency

ηprop = T hrust v* 1ṁ HHVfuel * kerosne

Thrust is typically measured by the experiment set-up with the strain gage. However, in this

example it must be calculated because the thrust measurements are incorrect/unavailable.

hrust momentum momentumT = Σ in − Σ out

hrust T = mrate exhaust * vexh − mrate air * vin

mrate exhaust = mrate fuel + mrate air

mrate fuel = ρfuel * V rate fuel

vexh = p 144 Area5* * nozzle

m 53.3 Trate exhaust* * 5

vin = m 53.3 Trate air* * 1p 144 Area1* * compressor

MECH 2750 || Section 09 Page 10 Group 3B

For trial 4,

= 0.016 slugs/s, = 2.53 gal/h, HHVkerosene = 18487 BTU/lb,mrate air V rate fuel

= 70.3°F, = 910.7°F, 14.850 psi, and 16.03 psiT 1 T 5 p1 = p5 =

ηprop = ρ [4] V HHVfuel * rate fuel* kerosne

(ρ V +m ) −m ( )fuel* rate fuel rate air * p 144 Area5* * nozzle

(m +m ) 53.3 Trate fuel rate air * * 5rate air*

m 53.3 Trate air* * 1p 144 Area1* * compressor

2

ηprop = 6.673/3600 2.53 18487* *(6.673/3600 2.53 gal/hr+0.016 32.3) −0.016 32.3 ( )* * * 16.03 144 1.23/144* *

(6.673/3600 2.53+0.016 32.3) 53.3 (910.7+460)* * * * * * 14.85 144 4.75/144* *(0.016 32.3) 53.3 (70.3+460)* * * 2

8.488%ηprop =

Discussion/Analysis

The data shows some interesting characteristics of the jet engine. Perhaps the largest

observation is the increased efficiency at increased engine performance. In other words, as the

shaft of the jet increases its revolutions per minute, the engine increases its efficiency. This

behaves the same as a car might, with higher fuel economy on the highway than during a city

drive. The propulsion efficiency shows how much of the chemical energy of the fuel is actually

converted to thrust. It shows how little of the fuel actually propels the jet.

MECH 2750 || Section 09 Page 11 Group 3B

Conclusions

This experiment showed the basic components and inefficiencies within a jet engine.

Generally the compressor was more efficient than the turbine, and was also more consistent (less

variation in the efficiency). The turbine was generally less efficient but was more sporadic. This

could have been due to fuel injection. Depending on the fuel injection and combustion rate, the

performance of the turbine would change dramatically. A possible next step would be to test

each component individually to determine how to improves its efficiency.

References

[1] Department of Mechanical Engineering and Technology, “Thermodynamic II Laboratory Manual: Brayton Cycle Experiment - Jet Engine”, Wentworth Institute of Technology, Boston MA.

[2] Ibrahem, Ibrahem M.A. “Neural Modeling and Predictive Control of a Small Turbojet Engine (SR-30)”. 10th International Energy Conversion Engineering Conference, At Atlanta, Georgia. Accessed from https://www.researchgate.net/publication/324756715_Neural_Modeling_and_Predictive_Control_of_a_Small_Turbojet_Engine_SR-30

[3] Moran, Sharipo, et al. “Property Tables”. Fundamentals of Engineering Thermodynamics, 8th edition. Pg 970. Print.

[4] “Fuels - Higher and Lower Calorific Values”. The Engineering ToolBox. Accessed from https://www.engineeringtoolbox.com/fuels-higher-calorific-values-d_169.html