Download - THERMODYNAMICS:Otto vs Diesel cycle
![Page 1: THERMODYNAMICS:Otto vs Diesel cycle](https://reader034.vdocuments.site/reader034/viewer/2022042706/577cc1a01a28aba71193818a/html5/thumbnails/1.jpg)
Gas Power Cycle Advanced Thermo-fluidsGas Power Cycles1
Carnot Cycle Otto Cycle Diesela CycleStirling & Ericsson Cycle Brayton Cycle
Contents:
Carnot cycleOtto cycleDiesel cycleStirling cycleEricsson cycle Brayton cycle
Jet Gas Turbine
![Page 2: THERMODYNAMICS:Otto vs Diesel cycle](https://reader034.vdocuments.site/reader034/viewer/2022042706/577cc1a01a28aba71193818a/html5/thumbnails/2.jpg)
Gas Power Cycle Advanced Thermo-fluidsGas Power Cycles2
Carnot Cycle Otto Cycle Diesel Cycle Stirling & Ericsson Cycle Brayton Cycle
Gas power cycles Heat engines in which working fluid is gas
Heat sink
Heat source
QH
QL
WnetHeat engineSample
applications
Internal Combustion Engines
Gas Turbines
Introduction
![Page 3: THERMODYNAMICS:Otto vs Diesel cycle](https://reader034.vdocuments.site/reader034/viewer/2022042706/577cc1a01a28aba71193818a/html5/thumbnails/3.jpg)
Gas Power Cycle Advanced Thermo-fluidsGas Power Cycles3
Otto Cycle Diesel Cycle Stirling & Ericsson Cycle Brayton CycleCarnot Cycle
Represents most efficient cycle that operates
between two fixed temperatures TH and TL
Efficiency of Carnot heat engine:
Not practical for real-life applications
H
LCarnotth T
T−=1,η
Acts as reference against which actual cycles can be compared.
Carnot Cyle
Carnot
![Page 4: THERMODYNAMICS:Otto vs Diesel cycle](https://reader034.vdocuments.site/reader034/viewer/2022042706/577cc1a01a28aba71193818a/html5/thumbnails/4.jpg)
Gas Power Cycle Advanced Thermo-fluidsGas Power Cycles4
Otto Cycle Diesel Cycle Stirling & Ericsson Cycle Brayton Cycle
Carnot Cyle
Carnot Cycle
Processes in a Carnot cycle:
1 - 2 Isothermal heat addition
2 - 3 Isentropic expansion
3 - 4 Isothermal heat rejection
4 - 1 Isentropic compression
Enclosed area in T-s & P-v diagrams
=> net work done by the cycle
![Page 5: THERMODYNAMICS:Otto vs Diesel cycle](https://reader034.vdocuments.site/reader034/viewer/2022042706/577cc1a01a28aba71193818a/html5/thumbnails/5.jpg)
Gas Power Cycle Advanced Thermo-fluidsGas Power Cycles
5Diesel Cycle Stirling & Ericsson Cycle Brayton Cycle
Reciprocating engines
Carnot Cycle Otto Cycle
Examples of gas power cycle applications that involve piston-cylinder units
Types of reciprocating engine
Combustion initiated by a spark
Ideal process described by Otto cycle
Spark-ignition engine
Compression-ignition engine
Combustion initiated by compression
Ideal process described by Diesel cycle
![Page 6: THERMODYNAMICS:Otto vs Diesel cycle](https://reader034.vdocuments.site/reader034/viewer/2022042706/577cc1a01a28aba71193818a/html5/thumbnails/6.jpg)
Gas Power Cycle Advanced Thermo-fluidsGas Power Cycles6
Diesel Cycle Stirling & Ericsson Cycle Brayton Cycle
Reciprocating engines
Carnot Cycle Otto Cycle
TDC : Top dead centre
BDC : Bottom dead centre
Stroke : Distance between TDC and BDC
Bore : Diameter of the piston
Clearance volume : Minimumvolume when piston at TDC
TDC
BDC
VV
VV
r ==min
max
r : Compression ratio
![Page 7: THERMODYNAMICS:Otto vs Diesel cycle](https://reader034.vdocuments.site/reader034/viewer/2022042706/577cc1a01a28aba71193818a/html5/thumbnails/7.jpg)
Gas Power Cycle Advanced Thermo-fluidsGas Power Cycles7
Diesel Cycle Stirling & Ericsson Cycle Brayton Cycle
Reciprocating engines
Carnot Cycle Otto Cycle
MEP : Mean Effective Pressure : Fictitious pressure that if it
acted on piston during entirepower stroke would producesame amount of net workproduced during actual cycle
minmax VVw
MEP net
−=
![Page 8: THERMODYNAMICS:Otto vs Diesel cycle](https://reader034.vdocuments.site/reader034/viewer/2022042706/577cc1a01a28aba71193818a/html5/thumbnails/8.jpg)
Gas Power Cycle Advanced Thermo-fluidsGas Power Cycles8
Diesel Cycle Stirling & Ericsson Cycle Brayton Cycle
Otto cycle
Carnot Cycle Otto Cycle
Represents ideal cycle for spark-ignition (SI) engines
Processes in 4-stroke engine cycle:
Air-fuel mixture is
compressed
Spark plug ignite and
combustion starts
High pressure gas
drives piston down
Exhaust gas driven out by piston
Fresh air-fuel mixture
drawn in
Otto: stroke by stroke
![Page 9: THERMODYNAMICS:Otto vs Diesel cycle](https://reader034.vdocuments.site/reader034/viewer/2022042706/577cc1a01a28aba71193818a/html5/thumbnails/9.jpg)
Gas Power Cycle Advanced Thermo-fluidsGas Power Cycles9
Diesel Cycle Stirling & Ericsson Cycle Brayton Cycle
Otto cycle
Carnot Cycle Otto Cycle
Differences between Otto and actual 4-stroke engines
![Page 10: THERMODYNAMICS:Otto vs Diesel cycle](https://reader034.vdocuments.site/reader034/viewer/2022042706/577cc1a01a28aba71193818a/html5/thumbnails/10.jpg)
Gas Power Cycle Advanced Thermo-fluidsGas Power Cycles10
Diesel Cycle Stirling & Ericsson Cycle Brayton Cycle
4-stroke engine
Carnot CycleOtto Cycle
1 - 2 1. Piston moves upward from BDC to TDC 2. Air-fuel mixture is compressed isentropically.
Isentropic compression (Compression stroke)
2 - 3 1. Spark plug fires and combustion takes place 2. Piston moves downward from TDC to BDC,
converting heat energy to work
Constant-volume heat addition (Power or expansion stroke)
3 - 4 1. Piston moves upward from BDC to TDC 2. Exhaust valve open and exhaust gas is removed
Isentropic expansion (Exhaust stroke)
4 - 1 1. Piston moves downward from TDC to BDC 2. Intake valve open and air-fuel mixture drawn in
Constant-volume heat rejection (Intake stroke)
Actual Cycle
Otto Cycle
![Page 11: THERMODYNAMICS:Otto vs Diesel cycle](https://reader034.vdocuments.site/reader034/viewer/2022042706/577cc1a01a28aba71193818a/html5/thumbnails/11.jpg)
Gas Power Cycle Advanced Thermo-fluidsGas Power Cycles11
Diesel Cycle Stirling & Ericsson Cycle Brayton Cycle
2-stroke cycle
Carnot Cycle Otto Cycle
All four processes in take place in 2 strokes
![Page 12: THERMODYNAMICS:Otto vs Diesel cycle](https://reader034.vdocuments.site/reader034/viewer/2022042706/577cc1a01a28aba71193818a/html5/thumbnails/12.jpg)
Gas Power Cycle Advanced Thermo-fluidsGas Power Cycles12
Diesel Cycle Stirling & Ericsson Cycle Brayton Cycle
2-stroke cycle
Carnot Cycle Otto Cycle
Compression stroke: Air-fuel mixture drawn in,squeezed in combustion chamber
Power stroke: Combustion takes place, burned gas removed
![Page 13: THERMODYNAMICS:Otto vs Diesel cycle](https://reader034.vdocuments.site/reader034/viewer/2022042706/577cc1a01a28aba71193818a/html5/thumbnails/13.jpg)
Gas Power Cycle Advanced Thermo-fluidsGas Power Cycles13
Diesel Cycle Stirling & Ericsson Cycle Brayton Cycle
2-stroke cycle
Carnot Cycle Otto Cycle
2-stroke engines generally less efficient than 4-stroke due to:
incomplete expulsion of exhaust gases
partial expulsion of fresh air-fuel mixture
Advantages of 2-stroke engines:
simple and inexpensive
high power-to-weight and power-to-volume ratios
=> suitable for small size and light applications
![Page 14: THERMODYNAMICS:Otto vs Diesel cycle](https://reader034.vdocuments.site/reader034/viewer/2022042706/577cc1a01a28aba71193818a/html5/thumbnails/14.jpg)
Gas Power Cycle Advanced Thermo-fluidsGas Power Cycles14
Diesel Cycle Stirling & Ericsson Cycle Brayton Cycle
1st. Law Analysis:
Carnot Cycle Otto Cycle
v
P
1
2
3
4
Qin
Qout
s
T
1
2
3
4
Qin
Qout
uwq ∆=−For closed system:
outinnet
out
in
qqwuuquuq
−=−=−=
14
23
in
netOttoth q
w=,η
![Page 15: THERMODYNAMICS:Otto vs Diesel cycle](https://reader034.vdocuments.site/reader034/viewer/2022042706/577cc1a01a28aba71193818a/html5/thumbnails/15.jpg)
Gas Power Cycle Advanced Thermo-fluidsGas Power Cycles15
Diesel Cycle Stirling & Ericsson Cycle Brayton Cycle
1st. Law Analysis:
Carnot Cycle Otto Cycle
If specific heat is considered constant (i.e. approximate method):
)()(
14,14
23,23TTcuuqTTcuuq
avvout
avvin−=−=−=−=
1,11−
−= kOttoth rη Attention:
*Use suitable method(exact or approximate)
consistently*
v
p
CC
k
r
=
= ration compressio
![Page 16: THERMODYNAMICS:Otto vs Diesel cycle](https://reader034.vdocuments.site/reader034/viewer/2022042706/577cc1a01a28aba71193818a/html5/thumbnails/16.jpg)
Gas Power Cycle Advanced Thermo-fluidsGas Power Cycles16
Diesel Cycle Stirling & Ericsson Cycle Brayton Cycle
Some notes:
Carnot Cycle Otto Cycle
Efficiency of Otto cycle increases with compression ratio and specific heat ratio 1,
11−
−= kOttoth rη
At high compression ratio (above 8):
further increase in efficiency is
insignificant
premature ignition occurs =>
engine knock. Reduced by anti-
knock agent, e.g. tetraethyl lead
Typical efficiency of SI engines: 25 - 30%
![Page 17: THERMODYNAMICS:Otto vs Diesel cycle](https://reader034.vdocuments.site/reader034/viewer/2022042706/577cc1a01a28aba71193818a/html5/thumbnails/17.jpg)
Gas Power Cycle Advanced Thermo-fluidsGas Power Cycles17
Stirling & Ericsson Cycle Brayton CycleCarnot Cycle Otto Cycle Diesel Cycle
Represents ideal compression-ignition (CI) engine
Diesel Cycle:
Consists of 4 processes
=> Almost similar to Otto cycle
Air compressed to pressure & temperature above self-ignition temperature of fuel
Combustion starts on contact as fuel is injected to hot air
![Page 18: THERMODYNAMICS:Otto vs Diesel cycle](https://reader034.vdocuments.site/reader034/viewer/2022042706/577cc1a01a28aba71193818a/html5/thumbnails/18.jpg)
Gas Power Cycle Advanced Thermo-fluidsGas Power Cycles18
Stirling & Ericsson Cycle Brayton CycleCarnot Cycle Otto Cycle Diesel Cycle
1st. Law analysis:
Exact method: variable specific heat
Approximate method: constant specific heat
)(,)( 1423 TTCqTTCq voutpin −=−=
ratio cutoff2
3
2
31, ,
)1(111 ===
−−
−= − vv
VVr
rkr
r cc
kc
kDieselthη
), 1423 UUqhhq outin −=−=
in
netDieselth q
w=,η
![Page 19: THERMODYNAMICS:Otto vs Diesel cycle](https://reader034.vdocuments.site/reader034/viewer/2022042706/577cc1a01a28aba71193818a/html5/thumbnails/19.jpg)
Gas Power Cycle Advanced Thermo-fluidsGas Power Cycles19
Stirling & Ericsson Cycle Brayton CycleCarnot Cycle Otto Cycle Diesel Cycle
Some notes:
At same compression ratio, Otto has greater efficiency than Diesel engines
Advantages of Diesel engines:☺ able to operate at much higher
compression ratio (12 to 24)i.e higher efficiency (35 - 40%)
☺ able to use cheaper fuel, becauseless constraint on premature ignition problem
![Page 20: THERMODYNAMICS:Otto vs Diesel cycle](https://reader034.vdocuments.site/reader034/viewer/2022042706/577cc1a01a28aba71193818a/html5/thumbnails/20.jpg)
Gas Power Cycle Advanced Thermo-fluidsGas Power Cycles
20Brayton CycleCarnot Cycle Otto Cycle Diesel Cycle
Stirling & Ericsson cycle:
Stirling & Ericsson Cycle
Stirling: Two constant-volume regeneration
Ericsson: Two constant-pressure regeneration
Robert Stirling
![Page 21: THERMODYNAMICS:Otto vs Diesel cycle](https://reader034.vdocuments.site/reader034/viewer/2022042706/577cc1a01a28aba71193818a/html5/thumbnails/21.jpg)
Gas Power Cycle Advanced Thermo-fluidsGas Power Cycles21
Brayton CycleCarnot Cycle Otto Cycle Diesel Cycle Stirling & Ericsson Cycle
Stirling Engine
![Page 22: THERMODYNAMICS:Otto vs Diesel cycle](https://reader034.vdocuments.site/reader034/viewer/2022042706/577cc1a01a28aba71193818a/html5/thumbnails/22.jpg)
Gas Power Cycle Advanced Thermo-fluidsGas Power Cycles22
Brayton CycleCarnot Cycle Otto Cycle Diesel Cycle Stirling & Ericsson Cycle
Advantages:
☺ Ideal Stirling and Ericsson cycles
have Carnot cycle efficiency
☺ Combustion can be done externally
=> more choices of fuel types
Disadvantages:
Difficult to achieve in practice:
- involve heat transfer through
small temperature difference.
- require very large heat transfer
area and very long time.
![Page 23: THERMODYNAMICS:Otto vs Diesel cycle](https://reader034.vdocuments.site/reader034/viewer/2022042706/577cc1a01a28aba71193818a/html5/thumbnails/23.jpg)
Gas Power Cycle Advanced Thermo-fluidsGas Power Cycles23
Carnot Cycle Otto Cycle Diesel Cycle Stirling & Ericsson Cycle Brayton Cycle
Brayton cycle:
Actual gas turbine operate on open cycle
Assumptions:Combustion process => const-pressure heat additionExhaust process => const-pressure heat rejection
Represents ideal gas-turbine engine cycle
![Page 24: THERMODYNAMICS:Otto vs Diesel cycle](https://reader034.vdocuments.site/reader034/viewer/2022042706/577cc1a01a28aba71193818a/html5/thumbnails/24.jpg)
Gas Power Cycle Advanced Thermo-fluidsGas Power Cycles24
Carnot Cycle Otto Cycle Diesel Cycle Stirling & Ericsson Cycle Brayton Cycle
Made up of 4 processes:
1 - 2 Isentropic compression (compressor)
2 - 3 Const Pressure heat addition (heat exchanger)
3 - 4 Isentropic expansion (turbine)
4 - 1 Const Pressure heat removal (heat exchanger)
![Page 25: THERMODYNAMICS:Otto vs Diesel cycle](https://reader034.vdocuments.site/reader034/viewer/2022042706/577cc1a01a28aba71193818a/html5/thumbnails/25.jpg)
Gas Power Cycle Advanced Thermo-fluidsGas Power Cycles25
Carnot Cycle Otto Cycle Diesel Cycle Stirling & Ericsson Cycle Brayton Cycle
1st law analysis:
1423 , hhqhhq outin −=−=
1
2/)1(, ,11
PPr
r pkkp
Braytonth =−=−
η
in
netoutBraytonth q
w ,, =η
If specific heats are assumed constant (approximate method)
4312 , hhwhhw outin −=−=
inoutnetout www −=,
outinnetout qqw −=,
![Page 26: THERMODYNAMICS:Otto vs Diesel cycle](https://reader034.vdocuments.site/reader034/viewer/2022042706/577cc1a01a28aba71193818a/html5/thumbnails/26.jpg)
Gas Power Cycle Advanced Thermo-fluidsGas Power Cycles26
Carnot Cycle Otto Cycle Diesel Cycle Stirling & Ericsson Cycle Brayton Cycle
Deviation from ideal Brayton cycle, due to:
pressure drops during heat addition and rejection
irreversibilities in compressor and turbine
a
s
a
scompressor hh
hhww
21
21
−−
≅=η
s
a
s
aturbine hh
hhww
43
43
−−
≅=η
![Page 27: THERMODYNAMICS:Otto vs Diesel cycle](https://reader034.vdocuments.site/reader034/viewer/2022042706/577cc1a01a28aba71193818a/html5/thumbnails/27.jpg)
Gas Power Cycle Advanced Thermo-fluidsGas Power Cycles27
Carnot Cycle Otto Cycle Diesel Cycle Stirling & Ericsson Cycle Brayton Cycle
Efficiency of gas-turbine power plant can be increased significantly by combining with steam power cycle=> combined cycle gas turbine (CCGT)
Main applications of Brayton cycle:electricity generation => gas-turbine power plantsaircrafts => jet propulsion enginesmarine => propeller prime mover
![Page 28: THERMODYNAMICS:Otto vs Diesel cycle](https://reader034.vdocuments.site/reader034/viewer/2022042706/577cc1a01a28aba71193818a/html5/thumbnails/28.jpg)
Gas Power Cycle Advanced Thermo-fluidsGas Power Cycles28
Carnot Cycle Otto Cycle Diesel Cycle Stirling & Ericsson Cycle Brayton Cycle
Jet propulsion cycle:1 - 2 Air pressure increased slightly in diffuser2 - 3 Air is compressed in compressor3 - 4 Heat addition (combustion) process in burner at constant pressure4 - 5 Partial expansion of exhaust gas in turbine, producing just
enough power to drive compressor and other auxiliaries5 - 6 Gas expansion in the nozzle to ambient pressure at high velocity6 - 1 Heat rejection to surrounding at constant pressure
![Page 29: THERMODYNAMICS:Otto vs Diesel cycle](https://reader034.vdocuments.site/reader034/viewer/2022042706/577cc1a01a28aba71193818a/html5/thumbnails/29.jpg)
Gas Power Cycle Advanced Thermo-fluidsGas Power Cycles29
Carnot Cycle Otto Cycle Diesel Cycle Stirling & Ericsson Cycle Brayton Cycle
![Page 30: THERMODYNAMICS:Otto vs Diesel cycle](https://reader034.vdocuments.site/reader034/viewer/2022042706/577cc1a01a28aba71193818a/html5/thumbnails/30.jpg)
Gas Power Cycle Advanced Thermo-fluidsGas Power Cycles30
Carnot Cycle Otto Cycle Diesel Cycle Stirling & Ericsson Cycle Brayton Cycle
![Page 31: THERMODYNAMICS:Otto vs Diesel cycle](https://reader034.vdocuments.site/reader034/viewer/2022042706/577cc1a01a28aba71193818a/html5/thumbnails/31.jpg)
Gas Power Cycle Advanced Thermo-fluidsGas Power Cycles31
Carnot Cycle Otto Cycle Diesel Cycle Stirling & Ericsson Cycle Brayton Cycle
Turbofan engine
Turboprop engine
![Page 32: THERMODYNAMICS:Otto vs Diesel cycle](https://reader034.vdocuments.site/reader034/viewer/2022042706/577cc1a01a28aba71193818a/html5/thumbnails/32.jpg)
Gas Power Cycle Advanced Thermo-fluidsGas Power Cycles32
Carnot Cycle Otto Cycle Diesel Cycle Stirling & Ericsson Cycle Brayton Cycle
SummaryGas power cycles => Heat engineswith gas as working fluidOtto cycle => spark ignitioninternal combustion engine
v
P
1
2
3
4
Qin
Qout
s
T
12
3
4
Qin
QoutDiesel cycle => compression ignition internal combustion engine
Brayton cycle => open cycle gas turbine