01 I C Engine Intro
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Transcript of 01 I C Engine Intro
I C ENGINES
B. E. SEMESTER: VIB. E. SEMESTER: VI
HEAT ENGINES
TYPES OF HEAT ENGINESTYPES OF HEAT ENGINES
FUELFUEL CHEMICAL ENERGY
THERMALTHERMALENRGYENRGY
MECHANICAL MECHANICAL WORKWORK
What is an Engine?What is a Heat Engine?
1. External combustion engines
2. Internal combustion engines
1. External combustion engines
2. Internal combustion engines
1. Rotary Engines
2. Reciprocating Engines
1. Rotary Engines
2. Reciprocating Engines
CLASSIFICATION OF HEAT ENGINES
Application
• AutomobileAutomobile
• MarineMarine
• Special vehicles (tanks, Special vehicles (tanks, off road vehicles)off road vehicles)
• Aircraft enginesAircraft engines
• Industrial applicationsIndustrial applications
• FarmingFarming
• Power plantPower plant
• Portable machineryPortable machinery
APPLICATIONS OF IC ENGINES
1.1. Which are the most widely used Heat Which are the most widely used Heat Engines? Why?Engines? Why?
2.2. Advantages of Reciprocating IC Engines Advantages of Reciprocating IC Engines over other engines:over other engines:
• Absence of heat exchangers – Mechanical simplicity.Absence of heat exchangers – Mechanical simplicity.
• Engine components working at lower temp Engine components working at lower temp compared to high working fluid temp -> Higher compared to high working fluid temp -> Higher Thermal Efficiency.Thermal Efficiency.
• Less weight to power ratio.Less weight to power ratio.
• Possible to develop engines of very small power Possible to develop engines of very small power output.output.
• Suitable for mobile applications.Suitable for mobile applications.
DISADVANTAGES OF RECIPROCATING IC ENGINES
1.1. Vibration caused by reciprocating Vibration caused by reciprocating components.components.
2.2. Not possible to use a variety of fuel.Not possible to use a variety of fuel.
3.3. Incomplete combustion -> Pollution.Incomplete combustion -> Pollution.
4.4. Costly fuels are used.Costly fuels are used.
BASIC ENGINE COMPONENTS
IC ENGINE NOMENCLATURE
1.1. CYLINDER BORE (BORE), ‘d’CYLINDER BORE (BORE), ‘d’• Nominal inner diameter of the working Nominal inner diameter of the working
cylinder; ‘mm’cylinder; ‘mm’
2.2. Piston Area (A)Piston Area (A)• Area of a circle of dia equal to Bore.Area of a circle of dia equal to Bore.
3.3. Stroke (L)Stroke (L)• Nominal distance piston travels between two Nominal distance piston travels between two
successive reversals of its motion; mmsuccessive reversals of its motion; mm
NOMENCLATURE
4.4. Stroke to Bore Ratio; L/d RatioStroke to Bore Ratio; L/d Ratio• Important parameter in classifying speed of Important parameter in classifying speed of
engine.engine.
• Under square Engine: d < LUnder square Engine: d < L
• Square Engine: d = L Square Engine: d = L
• Over square Engine: d > LOver square Engine: d > L• Over square engine can operate at higher speed.Over square engine can operate at higher speed.
5.5. Dead CentreDead Centre• Top Dead Centre (TDC)Top Dead Centre (TDC)
• Bottom Dead Centre (BDC)Bottom Dead Centre (BDC)
GEOMETRICAL PROPERTIES
Vc – Clearance volumeVc – Clearance volume
Vd – Displacement or Swept Vd – Displacement or Swept volumevolume
VVL L or Vs – Stroke volumeor Vs – Stroke volume
B – Bore DiaB – Bore Dia
L = 2 . aL = 2 . a
Cyl Vol ‘V’ at any crank position:Cyl Vol ‘V’ at any crank position:
Displacement or Swept Volume (Vs)
1.1. Nominal Volume swept by working Nominal Volume swept by working piston when traveling from one dead piston when traveling from one dead centre to other. centre to other.
• Vs = A x LVs = A x L
• Vs = (Vs = (ΠΠ/4).d/4).d2 2 LL
CUBIC CAPACITY OR ENGINE CAPACITY
Displacement volume of a cylinder Displacement volume of a cylinder multiplied by number of cylinders (K).multiplied by number of cylinders (K).
Cubic Capacity = VCubic Capacity = Vss x K x K
CLEARANCE VOLUME, VCCLEARANCE VOLUME, VC
Nominal volume of the combustion Nominal volume of the combustion chamber above the piston when it is at chamber above the piston when it is at the top dead center (cc)the top dead center (cc)
COMPRESSION RATIO , r
1.1. Ratio of the total cylinder volume when Ratio of the total cylinder volume when the piston is at the BDC, Vthe piston is at the BDC, VTT, to the , to the
clearance volume, Vclearance volume, Vc.c.
r = Vr = VT T ÷÷ VVc c = (V= (Vc + c + VVss) ) ÷÷ VVcc
Example 1
1.1. The engine capacity of a four The engine capacity of a four stroke four cylinder engine of L/D stroke four cylinder engine of L/D ratio of 1.1 is 980 cc. If the ratio of 1.1 is 980 cc. If the clearance volume of one cylinder clearance volume of one cylinder is 27.2 cc; calculate the bore, is 27.2 cc; calculate the bore, stroke and CR of this engine. stroke and CR of this engine.
Working of IC engines
4 Stroke S I Engine4 Stroke S I Engine
4 Stroke CI Engine4 Stroke CI Engine
2 Stroke S I Engine2 Stroke S I Engine
2Stroke C I Engine2Stroke C I Engine
ANIMATED SLIDESHOW
FOUR STROKE SPARK IGNITION ENGINE
FOUR STROKE SPARK IGNITION ENGINE
1.1. Four strokesFour strokes
2.2. Stroke and valve positionsStroke and valve positions
3.3. Indicator diagramsIndicator diagrams• IdealIdeal
• ActualActual
4.4. Valve timing Valve timing
PETROL ENGINE
1.1. OTTO CYCLEOTTO CYCLE
2.2. FOUR STROKE FOUR STROKE CYCLECYCLE
3.3. TWO STROKE TWO STROKE CYCLECYCLE
Process 1-2: Reversible adiabatic compression of air.Process 2-3: Heat addition at constant volume.Process 3-4: Reversible adiabatic expansion of air.Process 4-1: Heat rejection at constant volume.
FOUR STROKE SI ENGINE – OTTO CYCLEFOUR STROKE SI ENGINE – OTTO CYCLE
1. Suction Stroke (0 1)2. Compression Stroke (1 2)3. Power Stroke (3 4)4. Exhaust Stroke (1 0)
0
4
3
2
1
4 Cycle Process
Intake StrokeIntake valve opens,
admitting fuel and air.Exhaust valve closed
for most of stroke
Compression StrokeBoth valves closed,Fuel/air mixture is
compressed by rising piston. Spark ignitesmixture near end of
stroke.
IntakeManifold
Spark PlugCylinder
Piston
Connecting Rod Crank
Power StrokeFuel-air mixture burns,increasing temperature
and pressure, expansionof combustion gases
drives piston down. Bothvalves closed - exhaust valve opens near end
of stroke
1 2 3 4
Exhaust StrokeExhaust valve open,exhaust products are
displaced from cylinder.Intake valve opens near end of stroke.
Crankcase
ExhaustManifold
Exhaust ValveIntake Valve
Briggs Engine - Intake
Compression
Power Stroke
Exhaust Stroke
2 Stroke Process
Compression(ports closed)Air Taken Into
Crankcase
Combustion(ports closed)
Exhaust(intake port closed)
Air compressed in crankcase
Scavengingand Intake
(ports open)
2 STROKE ANIMATION
FOUR STROKE CI ENGINE
• Stroke 1 (intake) – only air enters cylinder.
• Stroke 2 (compression) – air is compressed to high extent, raising its temperature.
• Stroke 3 (power) – diesel is injected, high air temperature ignites diesel.
• Stroke 4 (exhaust) – burnt gases are expelled from the engine.
Diesel Engine Operation
Working principle: Diesel engine
1. 1. Induction StrokeInduction Stroke
Starting from TDC, the piston moves Starting from TDC, the piston moves
downwards.downwards.
The inlet valve also opens at the same The inlet valve also opens at the same
time and air is drawn into cylinder with time and air is drawn into cylinder with
out restriction by a throttle valve.out restriction by a throttle valve.
When the piston reaches the BDC, the When the piston reaches the BDC, the
cylinder capacity is the largest.cylinder capacity is the largest.
The four strokes requires 2 The four strokes requires 2 rotations rotations of the crankshaftof the crankshaft..
The four strokes requires 2 The four strokes requires 2 rotations rotations of the crankshaftof the crankshaft..
2. 2. Compression strokeCompression stroke
The inlet and exhaust valves are closed.The inlet and exhaust valves are closed. The piston's upward movement The piston's upward movement
compresses the air to the degree compresses the air to the degree determined by the compression ratio determined by the compression ratio (16:1 to 24:1). (16:1 to 24:1).
The air, in this process, heats up to The air, in this process, heats up to 900°C.900°C.
Near the completion of the Near the completion of the compression stroke, the fuel-injection compression stroke, the fuel-injection system injects the fuel at high system injects the fuel at high pressure (as much as 2000 bar in pressure (as much as 2000 bar in modem engines) in to hot modem engines) in to hot compressed air in the CC. compressed air in the CC.
When the cylinder reaches the TDC, When the cylinder reaches the TDC, the cylinder capacity is at its the cylinder capacity is at its minimum.minimum.
3. Ignition stroke3. Ignition stroke
After the ignition lag (a few degrees After the ignition lag (a few degrees of C/s rotation) the ignition stroke of C/s rotation) the ignition stroke begins.begins.
The finely atomized and easily The finely atomized and easily combustible diesel fuel spontaneously combustible diesel fuel spontaneously ignites and burns.ignites and burns.
As a result, the cylinder charge heats As a result, the cylinder charge heats up even more and pressure in the up even more and pressure in the cylinder rises.cylinder rises.
The mass of the fuel injected (quality The mass of the fuel injected (quality based control) determines the based control) determines the amount of energy released.amount of energy released.
The pressure forces the piston The pressure forces the piston downwards. The C/s drive translates downwards. The C/s drive translates the KE of the piston into torque.the KE of the piston into torque.
44. Exhaust stroke. Exhaust stroke
Just before the piston reaches Just before the piston reaches
the BDC, the exhaust valvethe BDC, the exhaust valve
opensopens..
TheThe hot pressurized gases hot pressurized gases
flow out of the cylinder.flow out of the cylinder.
The upwards movement of the The upwards movement of the
piston forces the remaining piston forces the remaining
exhaust gas out of the exhaust gas out of the
cylinder.cylinder.
1.1. The air inside the diesel The air inside the diesel
engine is engine is compressedcompressed to to
––
• 30...50 bar ( naturally 30...50 bar ( naturally
aspirated engines)aspirated engines)
• 70...150 bar (turbocharged 70...150 bar (turbocharged
supercharged engines)supercharged engines)
2.2. This raises the This raises the
temperature ranging temperature ranging
from 700°C to 900°C.from 700°C to 900°C.
3.3. TheThe ignition ignition
temperaturetemperature of the most of the most
easily combustible easily combustible
components of the components of the
diesel fuel is around diesel fuel is around
250°C.250°C.
DIESEL CYCLEHeat addition takes place at Heat addition takes place at
constant Pressureconstant PressureHeat addition takes place at Heat addition takes place at
constant Pressureconstant Pressure
A
B D
C
T
S
ISENTROPIC
CONSTANT VOLUME
CONSTANT PRESSURE
Pressure-Volume Diagram
1.1. EO- Exhaust opens, EC- Exhaust EO- Exhaust opens, EC- Exhaust closes, SOC-Start of combustion, closes, SOC-Start of combustion, 10-Inlet opens, IC-Inlet closes, 10-Inlet opens, IC-Inlet closes, TDC-Top dead centre, BDC-TDC-Top dead centre, BDC-Bottom dead centerBottom dead center
2.2. PU- Ambient pressure, PL- Charge PU- Ambient pressure, PL- Charge air pressure, Pz-Maximum air pressure, Pz-Maximum cylinder pressure, Vc -cylinder pressure, Vc -Compression volume, Vh - Swept Compression volume, Vh - Swept volume, Wvolume, WMM Useful work, WG- Useful work, WG-Work during gas exchange Work during gas exchange (turbocharger)(turbocharger)
Petrol• Stroke 1 (intake) – air &
fuel mixture enters cylinder
• Stroke 2 (compression) – air & fuel mixture is compressed
• Stroke 3 (power) – spark plug fires, ignites fuel.
• Stroke 4 (exhaust) – burnt gases are expelled from the engine
Petrol• Stroke 1 (intake) – air &
fuel mixture enters cylinder
• Stroke 2 (compression) – air & fuel mixture is compressed
• Stroke 3 (power) – spark plug fires, ignites fuel.
• Stroke 4 (exhaust) – burnt gases are expelled from the engine
Diesel• Stroke 1 (intake) – only air
enters cylinder.• Stroke 2 (compression) –
air is compressed to high extent, raising temperature.
• Stroke 3 (power) – diesel is injected, high air temperature ignites diesel.
• Stroke 4 (exhaust) – burnt gases are expelled from the engine.
Diesel• Stroke 1 (intake) – only air
enters cylinder.• Stroke 2 (compression) –
air is compressed to high extent, raising temperature.
• Stroke 3 (power) – diesel is injected, high air temperature ignites diesel.
• Stroke 4 (exhaust) – burnt gases are expelled from the engine.
Differences in Operations
7 April 2023 I C ENGINES 52
ENGINE PERFORMANCE PARAMETERS
1.1. Indicated Thermal EfficiencyIndicated Thermal Efficiency2.2. Brake Thermal EfficiencyBrake Thermal Efficiency3.3. Mechanical EfficiencyMechanical Efficiency4.4. Volumetric EfficiencyVolumetric Efficiency5.5. Relative Efficiency or Efficiency Ratio Relative Efficiency or Efficiency Ratio 6.6. Mean Effective PressureMean Effective Pressure7.7. Mean Piston SpeedMean Piston Speed8.8. Specific Power OutputSpecific Power Output9.9. Specific Fuel ConsumptionSpecific Fuel Consumption10.10. Air - Fuel RatioAir - Fuel Ratio
7 April 2023 I C ENGINES 53
ENERGY DISTRIBUTION
1.1. Indicated Thermal Indicated Thermal
Efficiency;Efficiency;
ηηithith = IP / E = IP / E
1.1. Brake Thermal Efficiency;Brake Thermal Efficiency;
ηηbthbth = BP / E = BP / E
1.1. Mechanical Efficiency;Mechanical Efficiency;
ηηmm = BP / IP = BP / IP
FP = BP – IPFP = BP – IP
Energy(E)
In Fuel(kW) I P
(kW)B P(kW)
Energy losses in Exhaust, Coolant,
Radiation
Energy losses in Friction, Pumping
etc
7 April 2023 I C ENGINES 54
Volumetric Efficiency, ηv
1.1. Indicates breathing ability of engine.Indicates breathing ability of engine.
2.2. Power output depends on utilization of airPower output depends on utilization of air
3.3. ηηv v is the volume flow rate of air into the intake is the volume flow rate of air into the intake
system divided by the rate at which volume is system divided by the rate at which volume is displaced by the system.displaced by the system.
ηv = da
a
dispa
a
V
m
NV
m
2/
VALVE TIMING DIAGRAM :