internal combustion engine (skmv 3413)zkarnain/userfiles/downloads/skmm 4413... · 2015. 2. 16. ·...
TRANSCRIPT
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INTERNAL COMBUSTION ENGINE
(SKMV 3413)
Dr. Mohd Farid bin Muhamad Said
Room : Block P21, Level 1, Automotive
Development Centre (ADC)
Tel : 07-5535449
Email: [email protected]
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• Actual Cycles:
– Variable Composition (combustion) with
Gas Mixtures (CO2, H2O, N2)
– Open Cycle
• Air-Standard Cycle:
– Simplified and more manageable
– Determines Important Design Parameters
ENGINE CYCLE
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• Working Fluid is air for the entire cycle.
• Most of the gas in cylinder is air. (about 7% fuel vapor).
• Closed Cycle the gases being exhausted are fed back
into the intake system.
• The combustion process is replaced with a heat addition
term Qin of equal energy value. No combustion.
• The open exhaust process is replaced with a closed
system heat rejection process Qout of equal energy value.
AIR STANDARD CYCLE
Assumptions
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• Ideal Processes
– Constant pressure exhaust at 1 atms.
– Normally aspirated cycles have constant pressure intake at 1 atms
– Turbo/Supercharged cycles have constant pressure > 1 atms.
– Compression and Expansion are isentropic processes (reversible and adiabatic)
– With constant specific heats
AIR STANDARD CYCLE
Assumptions
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• Heating is at constant volume (SI) or constant
pressure (CI)
• Cooling Heat Rejection at constant volume
• All processes are reversible
AIR STANDARD CYCLE
Assumptions
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• It is considered as an ideal gas
dTcdh
RTP
mRTPV
RTPv
p
AIR STANDARD CYCLE
Applicable Equations
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where,
AIR STANDARD CYCLE
Applicable Equations
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• Air flow before it enters an
engine is usually closer to
standard temperature.
KkgkJvcpcR
vcpc
k
KkgkJvc
KkgkJpc
./287.0
35.1
./821.0
./108.1
• For analyses within engine
during operating cycle and
exhaust flow.
AIR STANDARD CYCLE
Applicable Equations
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• Otto Cycle
• Diesel Cycle
• Real Air-Fuel Cycle
• Spark Ignition Cycle
• Exhaust Process
• Dual Cycle
• Miller Cycle
AIR STANDARD CYCLE
Types of Cycles
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• 1-2: Isentropic Compression
• 2-3: Constant Volume Heat Addition
• 3-4: Isentropic Expansion
• 4-5: Constant Volume Heat Rejection
• 5-6: Exhaust at Ambient Pressure
• 6-1: Intake at 1 atms
– Higher than 1 atms if super/turbo-charged
OTTO CYCLE
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Real Otto
OTTO CYCLE
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P-v T-s
OTTO CYCLE
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• Applying Applicable Thermodynamic Equations
at WOT
6-1: Intake
1-2: Compression
2-3: Constant Volume Heat Addition
3-4: Power Stroke (Expansion)
4-5: Constant Volume Heat Rejection
5-6: Exhaust
OTTO CYCLE
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OTTO CYCLE
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OTTO CYCLE
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OTTO CYCLE
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OTTO CYCLE
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OTTO CYCLE
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OTTO CYCLE
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• Only cycle temperatures need to be known.
• The equation can be simplified further by applying
ideal gas relationship.
OTTO CYCLE
Thermal Efficiency
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Ideal gas
relationship
OTTO CYCLE
Thermal Efficiency
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• Only compression ratio is
needed to determine the
thermal efficiency of the Otto
Cycle at WOT.
• As the compression ratio
goes up, the thermal
efficiency will increase.
• This is the Indicated Thermal
Efficiency.
OTTO CYCLE
Thermal Efficiency
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Example 1
A 4 cylinders, 2.5 liter, SI engine operates at WOT on a 4-stroke air-
standard Otto cycle at 3000 rpm. The engine has a compression
ratio of 8.6 : 1, a mechanical efficiency of 86%, and a stroke-to-bore
ratio S/B = 1.025. Fuel is isooctane with AF = 15, a heating value of
44,300 kJ/kg, and combustion efficiency = 100%. At the start of the
compression stroke, conditions in the cylinder combustion chamber
are 100 kPa and 600C. It can be assumed that there is a 4% exhaust
residual left over from the previous cycle.
• Do a complete thermodynamic analysis of
this engine.