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로드 중.... (전체 텍스트 보기)

전체 글

(1)

에너지변환특론

Advanced Energy Conversion

Chapter 3. Otto cycle and Diesel cycle

교수

박 수 한

(2)

참고 .

- http://www.youtube.com/playlist?list=PLX2gX- ftPVXXMDW2aoPCk7nM-58n7nW5M

2

(3)

Operation of IC Engines

How to make the analysis of the engine cycle much more manageable?

- Actual Cycles:

• Mechanical cycle

• Thermodynamics point of view, non-cyclic, open cycle, quasi steady-flow

• Variable composition (combustion) with gas mixtures (Fuel, CO2, H2O, O2, N2)

(4)

4

Simplify to the Air Standard Cycle

Mechanical Cycle  Thermodynamic Cycle

Fuel, Air CO2, N2, H2O

Air

Qin Qout

(5)

Air Standard Cycle

- Air-Standard Cycle:

• Simplified and more manageable

• Determines important design parameters

• Reasonable accuracy, particularly w.r.t. sensitivity to design parameters

• Error involves

(6)

6

Air Standard Assumptions

- Working fluid is Air

- Mass of air (gas phase) is constant (actually variation up to 7%)

- Closed cycle

• Recalculated Air

• Heat Exchangers for heat rejection and addition - No Internal Combustion

(7)

Air Standard Assumptions

- Ideal Processes

• Constant pressure exhaust at 1 atms.

• N/A cycles have constant pressure intake at 1 atms

• Turbo/Supercharged cycles have constant pressure >

1 atms.

- Compression and Expansion are Isentropic with constant specific heats

- Heating is at constant volume (SI), constant pressure (CI), or both (high speed CI)

(8)

8

Thermodynamics - review

- Ideal Gas:

- The First Law of Thermodynamics

- The Second Law of Thermodynamics dT

c du

dT c

dh

RT P

mRT PV

RT Pv

v

p

,

,

, 

w du

q

  

T

ds q

(9)

Thermodynamics – Work and Heat

- For a closed system:

P

w

1

2 T

q

1

2

2

1

Pdv

w q

12

Tds

(10)

10

Thermodynamics - symbols

sound of

speed

work spcific

/

heats speific

,

energy internal

specific

enthapy specific

density

cylinder in

gas of mass

e temperatur

air of constant gas

gas of volume specific

cylinder in

volume

cylinder in

presure gas

c w

c c k c c

u h m T R v V

P

v p v

p

efficiency combustion

power

cycle one

for work

ratio n compressio

fuel of value heating

rate fer heat trans

cycle one

for fer heat trans

mass unit per rate fer heat trans

cycle one

for mass unit per fer heat trans

rate flow mass

ratio fuel air

AF

c c HV

W W r Q

Q Q q q m

exhaust ex

fuel, air,

:

f

a

Subscripts

(11)

Polytropic Process

const

Pv

n

1 1

1 2

2

2 1 1

2

 

 

 

 

 

 

 

 

n n n n

v P

T

v v P

P

RT Pv

from

polytropic 1

const) (

isochoric

const) (

isentropic

const) (T

isothermal

1

const) (

isobaric

0

k n

v n

s k

n n

P n



(12)

12

Polytropic Process

v

P n 0 (isobaric)

l) (isotherma

1 n

) (isochoric



n

c) (isentropi k

n

s T



n

0 n k

n

1 n

(13)

Thermodynamics - review

- Isentropic process:

- Speed of sound

system closed

for )

1 (

) (

) 1

(

) (

constant constant constant

1 2

1 1 2

2 2

1

) 1 (

1

k T T

R k

v P v

w P TP Tv

Pv

k k k

k

 

 

(14)

14

Thermodynamic Properties - Air

- Engine operating conditions:

- Standard conditions:

K - kJ/kg 287

. 0

35 . 1 /

R - BTU/lbm 196

. 0 K - kJ/kg 821

. 0

R - BTU/lbm 265

. 0 K - kJ/kg 108

. 1

v p

v p v

p

c c

R

c c k c c

K - kJ/kg 287

. 0

4 . 1 /

R - BTU/lbm 172

. 0 K

- kJ/kg 718

. 0

R - BTU/lbm 240

. 0 K

- kJ/kg 005

. 1

v p v

p

c c

R

c c

k c c

(15)

Otto Cycle

Real Otto

스파크 점화 기관의 공기표준 사이클

정적 사이클 (constant volume cycle), 일정체적 하에서 연소

1876년 Nikolaus August Otto, 독일

(16)

참고.

상사점 (Top Dead Center, TDC):

피스톤이 크랭크축으로부터 가장 먼 위치 (TDC 이전 –BTDC, TDC 이후-ATDC)

하사점 (Bottom Dead Center, BDC):

피스톤이 크랭크축으로부터 가장 가까운 위치 (BDC 이전 –BTDC, BDC 이후-ATDC)

보어 (Bore): 실린더의 직경 또는 피스톤면의 직경

행정 (Stroke): 피스톤이 상사점에서 하사점 또는 하사점에서 상사점으로 움직인 거리

간극체적 (Clearance Volume):

피스톤이 상사점에 있을 때 연소실의 최소체적

배기량 (Displacement), 행정체적(Displacement Volume)

: 피스톤이 상사점과 하사점을 움직이면서 배제하는 체적

TDC

BDC

l B

L

s

a

Vc

Vd

Vc: clearance volume

Vd: displaced or swept volume B : cylinder bore

L : piston stroke l : connecting rod length

(17)

참고.

압축비 (compression ratio, rc)

C C d

C V

V

r V

volume cylinder

minimum

volume cylinder

Maximum

 SI engine : rc = 8 ~ 12

 CI engine : rc = 12 ~ 24

보어 행정비 (bore to stroke ratio, Rbs)

L Rbs B

 Small & medium size engine = 0.8 ~ 1.2

 Large slow speed CI engine = ~ 0.5

 B  L : under square engine, 저속 대형엔진

TDC

BDC

l B

L

s

a

Vc

Vd

(18)

Otto Cycle

냉각손실 :

압축 후반, 연소 중, 팽창과정에서 연소실 내의

작동유체와 연소실 벽면 등의 온도차로 인해 발생하는 열손실

시간손실 :

이론 사이클에서는 상사점에서 순간적으로 연소가 일어나 지만, 실제로는 그렇지 못하다. 연소에 필요한 시간은 대략 크랭크 각도로 40~60CA가 필요하다. 이처럼 정적연소가 아니라서 생기는 열손실을 말한다.

펌프손실 :

공기가 흡입되는 과정에서 이동통로의 조도, 공기청정기, 인젝터, 스로틀밸브 등을 거치면서 손실되는 양.

스로틀밸브에 의한 손실량이 가장 크다.

배기손실 :

배출가스를 통한 열손실

(19)

Air Standard Otto Cycle

1-2: Isentropic Compression

2-3: Constant Volume Heat Addition 3-4: Isentropic Expansion

4-5: Constant Volume Heat Rejection 5-6: Exhaust at 1 atm

6-1: Intake at 1 atm

(20)

20

Otto Cycle: P-v & T-s Diagrams

(21)

Otto Cycle Thermodynamic Analysis at WOT

(6-1: Constant-pressure intake) 1-2: Isentropic compression

2-3: Constant volume heat addition 3-4: Isentropic expansion

4-5: Constant volume heat rejection

(5-6: Constant-pressure exhaust)

(22)

22

Isentropic Compression (1-2) Process

) (

) (

1 0

) (

) ( const.

2 1

1 1 2

2 2 2 1

1 2 1

1 2

1 1 2

1 1

1

2 1 1 2

T T

c

u u

k v P v

Pdv P w

q

r v P

P v P

r v T

T v T

Pv

k c k

k c k

k

 

 

 

 

 

 

 

(23)

Constant Volume Heat Addition (2-3) Process

) (

) (

0

2 3

3 2

2 3

2 3

3 2

3 2

2 3

T T

c m Q

Q

T T

c u

u q

q w

v v

v m in

v in

(24)

24

Isentropic Expansion (3-4) Process

) (

) (

1 0

1 1 const.

4 3

4 3

3 3 4

4 4 4 3

3 4 3

3 4

3 3 4

1 3

1

4 3 3

4

T T

c

u u

k v P v

Pdv P w

q

P r v

P v P

T r v

T v T

Pv

v

k

c k

k

c k

k

















(25)

Constant Volume Heat Rejection (4-1) Process

) (

) (

0

4 1

5 4

4 1

4 1

4 5

5 4

1 4 5

4

1 4

5

T T

c m Q

Q

T T

c u

u

u u

q q

w w

v v

v

v m out

v out

(26)

26

Thermodynamic Properties

r

c

v v v

v

v v

v v

3 4 2

1

3 2

1

4

and

2 3 1

4

T T T T

1-2 & 3-4 processes are isentropic

(27)

Indicated Thermal Efficiency of Otto Cycle

 

 

1

2 1 2

3 1 4 2

1

2 3

1 4

2 3

1 4

in out in

net OTTO

/ 1 1

1 1 ) / (

1 ) / 1 (

) (

) 1 (

) (

) 1 (

1













k c v v t

r

T T T

T T T T

T

T T

T T

T T

c

T T

c

q q q

w

• k = 1.3 ~ 1.4 and rc > 1

 Thermal efficiency increases with compression ratio

(28)

28

Example Problem 3-1

- Given

• 4-Cylinder, 2.5L, SI engine, WOT, 4-Stroke

• Air standard Otto cycle, 3000 RPM

• Compression ratio = 8.6:1, mech. eff. = 86 %

• S/B = 1.025, AF = 15

• iso-octane: HV = 44,300 kJ/kg, comb. eff. = 100 %

• Initial conditions: P1 = 100 kPa, T1 = 60°C

• Exhaust residual: 4%

- Calculate parameters for one cylinder

- Do a complete thermodynamic analysis

(29)

Example Problem 3-1

(30)

30

Real Air-Fuel Engine Cycles

1. Real engines operate on an open cycle

• Changing gas composition via combustion

• Changing mass for CI cycle via fuel addition

2. Properties differ from air

• Fuel & combustion products

• Specific heat varies by up to 30 % (300 K to 3000 K)

3. Heat losses during the cycle (up to 12 %)

(31)

Real Air-Fuel Engine Cycles

4. Combustion requires finite time (~ 6 %)

• 30 to 60 degrees of crank rotation

• More compression work, Less expansion work

Finite time combustion losses

(32)

32

Real Air-Fuel Engine Cycles

5. Blowdown process requires a finite time (~2 %)

• Exhaust valve opens bBDC

• Work loss at the end of power stroke

Early Exhaust Valve Opening Loss

(33)

Real Air-Fuel Engine Cycles

6. Intake valve closes aBDC

• Improves volumetric efficiency

• Momentum of entering air continues flow through intake valve after piston starts up

• Reduces effective compression ratio

• Reduces T and P due to compression

7. Finite valve opening and closing times

• To assure the fully opened valves at TDC

• Valve overlap at TDC

(34)

34

Real Air-Fuel Cycle vs. Ideal Cycle

- Errors due to the differences between real air-fuel cycles and ideal air standard cycles

- Some errors tend to cancel, e.g., specific heats

- The efficiency of real cycle efficiency is less than that of air standard cycle

 

t actual

0 . 85  

t OTTO

(35)

SI Engine Cycle at Part Throttle

Negative pump work – P1 is lower than Po

?

(36)

36

SI Engine Cycle with T/C or S/C

Positive pump work – P1 is higher than Po

?

(37)

Part Throttle, T/C or S/C

– Part throttled: Negative – T/C or S/C: Positive

W

pump

net

( P

i

P

ex

) V

d

(38)

38

Exhaust Process

Exhaust stroke

Blowdown

EVO

(39)

Real Exhaust Blowdown P-v

KE h

h

o

s

(40)

40

Real Exhaust Blowdown T-s

KE h

h

o

s

(41)

Real Exhaust Blowdown Equations

o ex

k k k o

k ex

P P

P

P T P

P T P

T

 

 

 

 

 

 

7

) 1 (

4 4

) 1 (

4 4

7

where,

-

Approximated by Isentropic Process

(42)

42

Exhaust Residual

-

Residual exhaust gas in clearance volume, V

c

, at TDC starting intake stroke

m ex

r

m

xm

Mass of exhaust gas carried into the next cycle

Mass of gas mixture within the cylinder for the entire cycle

(43)

Calculating Exhaust Residual

o ex

k

o ex

k

P P P

P v

v P

P

P P P

P v

v P

P

3 3

3 7 7

3

4 4

4 7 7

4

 

 

 

 

 

 

7 1 7

5 5

7

v

V v

V v

m V

ex

(44)

44

Calculating Exhaust Residual

 

 

 

 

 

 

 

 

 

 

 

 

4

7 2 7

7 7

2

1

/

P P T

T x r

V V v

V v

V m

x m

ex r

m ex r

7 2 7

6

7 7 2

2 1

1

and v

V v

m V

v V v

V v

m V

ex m

 

(45)

Calculating Exhaust Residual

a r

ex r

m

x T x T

T ) ( 1 )

(

1

  

m m

a a ex

ex

h m h m h

m  

a

ex

T T

T

7

where,

(46)

46

Exhaust Residuals in Real Engines

- Exhaust residual amount

• SI engine at WOT: 3~7 %

• SI engine at part throttle: up to 20 %

• CI engine: Generally less than for SI engine

- The effect of exhaust residual

• Less heat addition

• Dilution  Max. temperature decreases

• Volumetric efficiency decreases

(47)

Diesel Cycle

Real Diesel

(48)

48

Air Standard Diesel Cycle

1-2: Isentropic Compression 2-3: Constant Pressure Heat Addition

3-4: Isentropic Expansion 4-5: Constant Volume Heat Rejection

5-6: Exhaust at 1 atm 6-1: Intake at 1 atm

(49)

Diesel Cycle: P-v & T-s Diagrams

(50)

50

Diesel Cycle Thermodynamic Analysis

(6-1: Constant-pressure intake) 1-2: Isentropic compression

2-3: Constant pressure heat addition 3-4: Isentropic expansion

4-5: Constant volume heat rejection

(5-6: Constant-pressure exhaust)

(51)

Isentropic Compression (1-2) Process

1 0

) (

) ( const.

1 1 2

2 2 2 1

1 2 1

1 2

1 1 2

1 1

1

2 1 1 2

k v P v

Pdv P w

q

r v P

P v P

r v T

T v T

Pv

k c k

k c k

k

 

 

 

 

 

 

 

(52)

52

Constant Pressure Heat Addition (2-3) Process

) (

) (

) (

) (

1) AF

(

) (

2 3

2 2

3 3

2 3

2

2 3

2 3

3 2

2 3

2 3

3 2

v v

P u

u q

w

h h

T T

c q

q

T T

c Q

T T

c m Q

m Q

Q

p in

p c

HV

p m c

HV f

in

– Cutoff ratio (Load ratio)

2 3 2

3 2

3

T T v

v V

V

• Heat addition period

r

1

(53)

Cut-off Ratio for Indicated Thermal Efficiency

(54)

54

Isentropic Expansion (3-4) Process

) (

) (

1 0

1 1 const.

4 3

4 3

3 3 4

4 4 4 3

3 4 3

3 4

3 3 4

1

3 1

4 3 3 4

T T

c

u u

k v P v

Pdv P w

q

P r v

P v P

T r v

T v T

Pv

v

k

c k

k

c k

k

















2 1 3

: 4

Note v

v vv 

(55)

Constant Volume Heat Rejection (4-1) Process

) (

) (

0

4 1

5 4

4 1

4 1

4 5

5 4

1 4 5

4

1 4

5

T T

c m Q

Q

T T

c u

u

u u

q q

w w

v v

v

v m out

v out

(56)

56

 

 





) 1 (

) 1 (

1 1

) (

) 1 (

1

1 DIESEL

2 3

1 4

in out in

net DIESEL

 

k r

T T

c

T T

c q

q q

w

k k c t

p t v

Indicated Thermal Efficiency of Diesel Cycle

• β  1, then (βk -1)  0

• β  rc, then state 3  state 4

 

t DIESEL

 

t OTTO

 

decreases to the lowest value

(57)

Cut-off Ratios and Thermal Efficiencies

(58)

58

Dual Cycle

Real

Dual

Pre-mixed Combustion

Non-premixed Combustion

(59)

Air Standard Dual Cycle

1-2: Isentropic Compression 2-x: Constant Volume Heat Addition

x-3: Constant Pressure Heat Addition

3-4: Isentropic Expansion 4-5: Constant Volume Heat Rejection

5-6: Exhaust at 1 atm

(60)

60

Dual Cycle: P-v & T-s Diagrams

(61)

Dual Cycle Thermodynamic Analysis

(6-1: Constant-pressure intake) 1-2: Isentropic compression

2-x: Constant volume heat addition x-3: Constant pressure heat addition 3-4: Isentropic expansion

4-5: Constant volume heat rejection

(62)

62

Constant Volume Heat Addition (2-x) Process

2 2

2

2 3

2 3

2 2

2

) (

) (

) (

) (

0

u u

T T

c q

T T

c m m

T T

c m Q

w

v v

v

x x

v x

v f a

v m x

x

TDC x

– Pressure ratio









1 3 2

2 3 2

1

P P r

T T P

P P

P k

c x

x

(63)

Constant Pressure Heat Addition (x-3) Process

) (

) (

) (

) (

1) AF

(

) (

2 3

2 2

3 3

2 3

2

2 3

2 3

3 2

2 3

2 3

3 2

v v

P u

u q

w

h h

T T

c q

q

T T

c Q

T T

c m Q

m Q

Q

p in

p c

HV

p m c

HV f

in

– Cutoff ratio (Load ratio)

x

x T

T V

V v

v v

v 3

2 3 2

3

3

(64)

64

Indicated Thermal Efficiency of Dual Cycle

   

 

 

1 )

1 (

) 1 (

1 1

) (

) (

) 1 (

1

1 DUAL

3 2

1 4

in out in

net DUAL

 

k r

T T

c T

T c

T T

c q

q q

w

k k c t

x p

x v

v t

− Heat in

) (

)

( 2 3

3

2 x x x x

in q q u u h h

q

− Thermal efficiency

(65)

Comparison of Otto, Diesel, and Dual Cycles

α  1: dual cycle  Diesel cycle β  1: dual cycle  Otto cycle

 

 

1 )

1 (

) 1 (

1 1

1

DUAL   

 

k r

k k c t

(66)

66

Comparison of Cycles – Fixed r

c

 

t OTTO

 

t DUAL

 

t DIESEL

(67)

Comparison of Cycles – Fixed P

max

 

t DIESEL

 

t DUAL

 

t OTTO

(68)

68

Atkinson Cycle

(69)

Miller Cycle

N/A T/C

(70)

70

Comparison of Miller Cycle and Otto Cycle

(71)

New Design and New Product

- What is all about the design in mechanical engineering?

• Optimization with constraints including

performance, cost, endurance, operation etc.

- How can the new technology/product be accepted by customers?

• No sacrifice on old functions

• Additional functions, convenience, price

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72

New Design and New Product

- How can it be achieved?

• Advances in many fields such as

manufacturing, new technology, electronics, control, materials etc.

- New constraints

• Environmental

• Economy

• Life style . . .

참조

관련 문서

*단어 사이의 공통성과

This command checks power supply current CV(Constant Voltage) CC(Constant Current) This command checks power supply current CV(Constant Voltage), CC(Constant Current)

그 외 사회 전반에 적용되는 광의의 플랫폼 - 공용플랫폼/ 디자인 플랫폼/ 브랜드 플랫폼 등. 플랫폼은 공용하고 차량의 스타일 등을 결정하는

■ 인접 플랫폼이나 신규 플랫폼을 상시 모니터링 하여 자사의 플랫폼 전략에 반영할 필요 있음. 외부 환경과 기업 상황에 맞는

http://blog.naver.com/op2330

If the volume of the system is increased at constant temperature, there should be no change in internal energy: since temperature remains constant, the kinetic

the material balance for a reaction component must be made for a differential element of volume dV.. For constant-volume reaction.. The integral can be evaluated in any

그러므로 ㉥ ‘김 선생님’은 현재의 담화 상황에 참여하지 않는 인물을 지칭하는 표현이라는 설명은 적절하다.. 그러므로 ㉤이 아버지가 지금까지 은주와 나눈 대화의 화제