internal combustion (ic) engine basicsteacher.buet.ac.bd/zahurul/me401/me401_engine_basics.pdf ·...
TRANSCRIPT
Internal Combustion (IC) Engine Basics
Dr. Md. Zahurul Haq
ProfessorDepartment of Mechanical Engineering
Bangladesh University of Engineering & Technology (BUET)
Dhaka-1000, Bangladesh
[email protected]://teacher.buet.ac.bd/zahurul/
ME 401: Internal Combustion Engines
c
Dr. Md. Zahurul Haq (BUET) Internal Combustion (IC) Engine Basics ME 401 (2016) 1 / 16
IC Engine Classifications
T533
c
Dr. Md. Zahurul Haq (BUET) Internal Combustion (IC) Engine Basics ME 401 (2016) 2 / 16
T555
c
Dr. Md. Zahurul Haq (BUET) Internal Combustion (IC) Engine Basics ME 401 (2016) 3 / 16
Spark or Compression Ignition Engines (SIE vs CIE)
T503
Spark initiates the flame in SIE; high compression in CIE
generates high temperature for ignition in CIE.
Part-load efficiency of CIE is better as load is regulated by fuel
injection adjustment; in SIE throttling is used to reduce load
which increases pumping work.
SIEs are high speed engines with higher temperature exhaust.
c
Dr. Md. Zahurul Haq (BUET) Internal Combustion (IC) Engine Basics ME 401 (2016) 4 / 16
Four Stroke Reciprocating IC Engine
Four stroke cycle events
c
Dr. Md. Zahurul Haq (BUET) Internal Combustion (IC) Engine Basics ME 401 (2016) 5 / 16
Two Stroke Reciprocating IC Engine
Two stroke cycle events
c
Dr. Md. Zahurul Haq (BUET) Internal Combustion (IC) Engine Basics ME 401 (2016) 6 / 16
4s vs. 2s IC Engines
T515 T516
Basic difference: 2s engine accomplishes the four processes (intake,
compressing, expansion & exhaust) in a single revolution.
Advantages of 4s engines: better fuel economy, better lubrication
and easier control.
Advantages of 2s engines: fewer moving parts, lighter weight and
smoother operation.
c
Dr. Md. Zahurul Haq (BUET) Internal Combustion (IC) Engine Basics ME 401 (2016) 7 / 16
Wankel Four Stroke Rotary SI Engines
◮ smooth rotary motion, ◮ sealing is critical.
c
Dr. Md. Zahurul Haq (BUET) Internal Combustion (IC) Engine Basics ME 401 (2016) 8 / 16
Gas Turbine
T371
A comparison between the working cycle of a turbo-jet engine and a
piston engine.
c
Dr. Md. Zahurul Haq (BUET) Internal Combustion (IC) Engine Basics ME 401 (2016) 9 / 16
Engine Cycles
Four Stroke Reciprocating SI Engine: Otto Cycle
T498
P-v diagram of Otto cycle
T500
Cycle with gas-exchange processes
1-2: Isentropic compression from BDC to TDC
2-3: Constant-volume heat addition at TDC
3-4: Isentropic expansion from TDC to BDC
4-1: Constant-volume heat rejection at BDC
c
Dr. Md. Zahurul Haq (BUET) Internal Combustion (IC) Engine Basics ME 401 (2016) 10 / 16
Engine Cycles
thermal efficiency, ηth,otto = 1− 1rk−1
→ compression ratio, r = VBDC/VTDC
→ ratio of specific heat capacities, k = cp/cv
T501 T502
c
Dr. Md. Zahurul Haq (BUET) Internal Combustion (IC) Engine Basics ME 401 (2016) 11 / 16
Engine Cycles
Actual 4s SI engine cycle vs. Otto cycle
T499
c
Dr. Md. Zahurul Haq (BUET) Internal Combustion (IC) Engine Basics ME 401 (2016) 12 / 16
Engine Cycles
T528
c
Dr. Md. Zahurul Haq (BUET) Internal Combustion (IC) Engine Basics ME 401 (2016) 13 / 16
Engine Cycles
Air Standard Diesel Cycle
T504
1-2: Isentropic compression from BDC to TDC
2-3: Constant-pressure heat addition at TDC
3-4: Isentropic expansion to BDC
4-1: Constant-volume heat rejection at BDC
T505
◮thermal efficiency, ηth,diesel = 1− 1rk−1
[
βk−1k(β−1)
]
; cut-off ratio, β ≡V3
V2
c
Dr. Md. Zahurul Haq (BUET) Internal Combustion (IC) Engine Basics ME 401 (2016) 14 / 16
Engine Cycles
Air Standard Dual Cycle
T506
1-2: Isentropic compression from BDC to TDC
2-3: Constant-volume heat addition at TDC
3-4: Constant-pressure heat addition at TDC
4-5: Isentropic expansion to BDC
5-1: Constant-volume heat rejection at BDCc
Dr. Md. Zahurul Haq (BUET) Internal Combustion (IC) Engine Basics ME 401 (2016) 15 / 16
Engine Cycles
Comparison: Otto, Diesel & Dual Cycle
T603T509
c
Dr. Md. Zahurul Haq (BUET) Internal Combustion (IC) Engine Basics ME 401 (2016) 16 / 16