RECIPROCATING ENGINE V GTE OPERATION CYCLES

Question 1

What are the similarities between an ICE and a GTE?

Answer 1

Both heat engines
Use air as working fluid
Employ same 4 basic process - Induction, compression, combustion and exhaust

Question 2

What cycle does an ICE operate on?

Answer 2

Otto Cycle

Question 3

What cycle does a GTE operate on?

Answer 3

Brayton Cycle

Question 4

What is the purpose of an ICE?

Answer 4

To convert thermal energy of burning fuel into mechanical energy

Question 5

Explain the Otto cycle for an ICE

Answer 5

Stage 1 - air-fuel mixture drawn into the cylinder, ready to be compressed

Stage 1- 2 - Air-fuel mixture compressed

Stage 2- 3 - Heat added to air fuel mixture, causing it to combust at a constant volume
and increases air pressure

Stage 3- 4 - Expanding gasses force piston and connecting rod down the cylinder, crankshaft then rotates and produces mechanical power

Stage 4-1 -burnt gasses exhausted into atmosphere

Question 6

What is constant during the combustion phase in an otto cycle?

Answer 6

Volume

Question 7

Why do ICE cylinders need to be heavily constructed?

Answer 7

Because of fluctuating peak pressures that occur during the complete operating cycle
Power production is intermittent

Question 8

What is the purpose of a GTE?

Answer 8

Convert thermal energy from burning fuel into kinetic energy then mechanical energy through the medium of a working fluid to produce thrust or shaft horsepower

Question 9

Explain the gas flow through a basic turbo jet

Answer 9

• Pressure increases during compression
• stays almost constant rate during combustion
• Pressure decreases when combustion gasses are expanded through the turbine due to divergent duct

-Velocity decreases gradually through the compressor due to divergent duct
-continues to decrease through combustion
-begins to increase after combustion due and propelled out via a convergent duct
- Velocity increases due to NGVs acting as a convergent duct, increasing kinetic energy then transferring to mechanical energy when passing through turbine blades
- velocity remains almost constant after turbine until it is propelled through exhaust via a convergent nozzle

Pressure increase in the turbine is 2x as much as the pressure decrease through the turbine

Question 10

Why is a GTE more efficient than an ICE?

Answer 10

• Continuous power by eliminating 3 idle strokes
• More fuel can be burnt in a shorter period, giving greater power output for a smaller engine
• Lightly fabricated combustion chamber due to no fluctuating pressures