TEP4 1 1 5 / 4 1 2 0 Term odynam ikk 5 / 0 ody Kap 9: Gas Power - - PDF document

TEP4 1 1 5 / 4 1 2 0 Term odynam ikk 5 /

• dy

Kap 9: Gas Power Systems Kap 9: Gas Power Systems Del 1 Olav Bolland

Begreper: Fig. 9.1/2, side 374

4 Stroke Engine Process

• *Intake Stroke
• Compression Stroke
• Power Stroke (Expansion)
• Exhaust Stroke

* For Spark Ignition engines, intake is of an air/fuel mixture. For Diesel engines, intake is air only

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air only.

Work closed/open systems

First law for a closed system:

First law for an open system (steady-state): dU

2 1

Relating heat to entropy: Q W U U   

1 2 2 2 2

Relating heat to entropy: dU Q W m h m h dt         

2 1

Q T dS T dS dU PdV   



2 2 2 1 1 1

and and Q T dS dU pdV T dS dU PdV T dS dH Vdp       

  

2 2 2 1 1 1

T dS dU PdV Q T dS dU pdV     

  

2 2 1 1

H U pV dU dH pdV Vdp Q dH V dp         

 

2 2 1 2 1 1

U U pdV W U U     



1 1 2 2 1 1

Q m dh V dp   

 

  

2

2 1

W pdV  

2 2 1 1 2 1 2

( ) ( ) m h h V dp W m h h W V dp         

 

     

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W V dp   

Air Standard Analysis Air Standard Analysis

The following assumptions are made: The following assumptions are made:

• Air, an Ideal Gas, is the working fluid
• Combustion is replaced with Heat Addition

(see Chap 13 for details)

• No exhaust and intake strokes – constant

volume heat rejection volume heat rejection

• All processes are internally reversible

For Cold-Air Standard, Specific Heats are also assumed constant

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For Cold Air Standard, Specific Heats are also assumed constant

Otto Cycle Otto Cycle

*Cycle Analysis: Cycle Analysis:

12 1 2

W u u m   m

34 3 4

W u u  

3 4

m

23

Q u u  

4 Internally Reversible Processes:

• Isentropic Compression

3 2

u u m 

41

Q

• Fig. 9.3, page 376
• Isentropic Compression
• Constant Volume Heat Addition
• Isentropic Expansion
• Constant Volume Heat Rejection

41 1 4

Q u u m  

* Sign Conventions (Work in ti t ) ti

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Constant Volume Heat Rejection negative, etc.) are sometimes changed for cycle applications

Diesel Cycles Diesel Cycles

*Cycle Analysis: Cycle Analysis:

12 1 2

W u u m   m

34 3 4

W u u  

3 4

m

 

23 2 3 2

W p v v  

Fig 9 5 page 406 4 Internally Reversible Processes:

• Isentropic Compression

23

Q h h 

 

2 3 2

p v v m

• Fig. 9.5, page 406
• Isentropic Compression
• Constant Pressure Heat Addition
• Isentropic Expansion
• Constant Volume Heat Rejection

3 2

h h m  

41

Q

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Constant Volume Heat Rejection

41 1 4

Q u u m  

Ottomotor - prinsipp

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Otto 4-takts motor

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Totakts-motor

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http://science.howstuffworks.com/two-stroke2.htm

Diesel vs Otto

• Diesel engines, with higher compression ratios (20: 1 for a typical

diesel vs. 8: 1 for a typical gasoline engine), tend to be heavier than an equivalent gasoline engine than an equivalent gasoline engine

• Diesel engines, because of the high compression ratio, tend to

have lower maximum RPM ranges than gasoline engines. This g g g makes diesel engines high torque rather than high horsepower.

• Diesel engines must be fuel injected, and in the past fuel

injection was expensive and less reliable

• Diesel engines tend to produce more smoke and "smell funny"
• Diesel engines are harder to start in cold weather, and if they

contain glow plugs, diesel engines can require you to wait before starting the engine so the glow plugs can heat up

• Diesel engines are much noisier and tend to vibrate

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Hva er bensin/diesel ?

CmHn bensin (C9H20), diesel (C14H30), paraffin (C12) flytende ved omgivelsestilstand flytende ved omgivelsestilstand Greit å huske 1 liter bensin = 9.710 kWh varmeverdi (35 MJ) 1 liter diesel = 11.4 11 kWh varmeverdi (41 MJ) 1 Sm3 naturgass  10 kWh varmeverdi 1 Sm3 naturgass  10 kWh varmeverdi Sm3 er vanlig mengdemål for naturgass (trykk 1.013 bar, 15 °C) S g g g ( y , C) Nm3 er ellers vanlig mengdemål for gasser (trykk 1.013 bar, 0 °C)

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Verdens største dieselmotor

Wärtsila-Sulzer RTA96-C Total engine weight: 2300 tons Height: 13.4m Max power: 108920 hp at 102 rpm Max power: 108920 hp at 102 rpm 81 MW

Emma Maersk 81 MW from RTA96-C

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30 MW from 5*Caterpillar 397m long, >1400 containers 157 tonnes (deadweight)

Stirling motor - prinsipp

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Stirling motor - prinsipp

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