TERMODINAMIKA

dan PEMBAKARAN

Satworo Adiwidodo, S.T., M.T

SIKLUS OTTO

SI Engine Cycle vs Thermodynamic Otto Cycle

A

I

R

Combustion

Products

Ignition

Intake

Stroke

FUEL

Fuel/Air

Mixture

Air TC

BC

Compression

Stroke

Power

Stroke

Exhaust

Stroke

Qin Qout

Compression

Process

Const volume

heat addition

Process

Expansion

Process

Const volume

heat rejection

Process

Actual

Cycle

Otto

Cycle

Actual SI Engine cycle

TC

BC

Ignition

SIKLUS OTTO

Process 0 1 intake

Process 1 2 Isentropic compression

Process 2 3 Constant volume heat addition (isovolumetric)

Process 3 4 Isentropic expansion

Process 4 1 Constant volume heat rejection (isovolumetric)

Process 1 0 Exhaust

Qout

Qin

3

4

2

1

v

v

v

vrv

Analysis of Otto Cycle

12 Isentropic Compression, entropy (s) constant

m

W

m

Quu in )( 12

k

vrv

v

T

T

P

P

2

1

1

2

1

2

AIR

)( 12 uum

Win

1

1

2

1

1

2

k

v

k

rv

v

T

T)()( 1212 TTcuu

m

Wv

in

1

2

1

2

r

r

v

v

v

v Jika s1= s2

cold air standar analysis constant k

air standar analysis from tabel

23 Constant Volume Heat Addition

m

W

m

Quu in )()( 23

)( 23 uum

Qin

2

3

2

3

T

T

P

P

AIR Qin

TC

Analysis of Otto Cycle

air standar analysis from tabel

)( 23 TTcm

Qv

in

cold air standar analysis constant k

3 4 Isentropic Expansion

AIR m

W

m

Quu out )( 34

)( 43 uum

Wout

krv

v

T

T

P

P 1

4

3

3

4

3

4

1

1

4

3

3

4 1

k

k

rv

v

T

T

Analysis of Otto Cycle

air standar analysis from tabel

cold air standar analysis constant k

)( 43 TTcm

Wv

out

3

4

3

4

r

r

v

v

v

v Jika s3= s4

4 1 Constant Volume Heat Removal

AIR Qout m

W

m

Quu out )( 41

)( 41 uum

Qout 1

1

4

4

T

P

T

P

BC

Analysis of Otto Cycle

air standar analysis from tabel

cold air standar analysis constant k

)( 41 TTcm

Qv

out

23

1243

uu

uuuu

Q

W

in

cycle

th

23

14

23

1423 1uu

uu

uu

uuuu

Cycle indicated thermal efficiency:

Net cycle work:

1243)( uumuumWWW inoutcycle

1

2

1

23

14 111

)(

)(1

k

v

vth

rT

T

TTc

TTc

Analysis of Otto Cycle

Air standar analysis:

Cold Air standar analysis:

Work per cycle is represented in terms of a mean effective

pressure and the displacement.

p

V

MEP = Mean effective pressure

X = Displacement

thin

thincycle

r

r

u

mQ

kr

r

VP

Q

P

imep

VV

Wimep

1

/

1

1

1 111121

Indicated mean effective pressure is:

Indicated mean effective pressure

Efek Kompresi rasio terhadap effisiensi thermal

1

11

kconst cth

rV

Traditional

SI engines

9 < r < 11

k = 1.4

• Spark ignition engine compression ratio limited by T3 (autoignition)

and P3 (material strength), both ~rk

• For r = 8 the efficiency is 56%

Efek Specific Heat Ratio terhadap Efisiensi Thermal

1

11

kconst cth

rV

Specific heat

ratio (k)

Cylinder temperatures vary between 300K and 2000K so 1.2 < k < 1.4

k = 1.3 most representative

The net cycle work of an engine can be increased by either:

i) Increasing the r (1’2)

ii) Increase Qin (23”)

P

V2 V1

Qin Wcycle

1

2

3

(i)

4

(ii)

Faktor yang berpengaruh terhadap kerja per siklus

1’

4’

4’’

3’’

thincycle

r

r

V

Q

VV

Wimep

1121

Sambungan …

Tabel T-9E=A-22E (Book)

Sambungan …

Sambungan …

Otto Cycle

9.1 An air-standard Otto cycle has a compression ratio of 8.5. At

the beginning of compression, p1= 100 kPa and T1 = 300 K.

The heat addition per unit mass of air is 1400 kJ/kg. Determine

(a) the net work, in kJ per kg of air.

(b) the thermal efficiency of the cycle.

(c) the mean effective pressure, in kPa.

(d) the maximum temperature in the cycle, in K.

9.2 Solve Problem 9.1 on a cold air-standard basis with specific

heats evaluated at 300 K.

Latihan

9.3 At the beginning of the compression process of an air standard Otto

cycle, p1 1 bar, T1 290 OK, V1 400 cm3. The maximum temperature in the

cycle is 2200 OK and the compression ratio is 8. Determine

(a) the heat addition, in kJ.

(b) the net work, in kJ.

(c) the thermal efficiency.

(d) the mean effective pressure, in bar.

9.4 Solve Problem 9.3 on a cold air-standard basis with specific heats

evaluated at 300 OK.

Latihan