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

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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

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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

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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 :