INTERNAL COMBUSTION ENGINE • Introduction• Terminology• Otto & Diesel Cycles • Four stroke Vs Two stroke• Efficiency • Fuel and Lubricants• Fuel Estimation • Marine IC Engine

By Sri Ram Kumar K Indian Maritime University - Cochin Campus

Introduction • In 1876 four stroke engine based on Otto cycle was developed by a German engineer Nikolous Otto. Diesel

Engine was developed by another German engineer Rudolf Diesel in the year 1892.

• Engine refers as “Heat engine is a device which converts chemical energy of fuel into Heat energy and this Heat energy further convert into mechanical work”.

• Based on where the combustion of fuel take place. Whether outside the working cylinder or inside the working cylinder

• (a) External combustion engines (E.C.ENGINES), (b) Internal combustion engines (I.C.ENGINES)

Classification of I.C.ENGINES• I.C.ENGINES are may be classified according to

• Type of fuel used as (1)Petrol engine (2)Diesel engine (3)Gas engines (4)Bi-fuel engine (two fuel engine)

• Nature of thermodynamic cycle as: (1)Otto cycle engine (2)Diesel engine cycle (3) Duel or mixed cycle engine

• Number of stroke per cycle as : (1) Four stroke engine (2) Two stroke engine

• Method of ignition as : (1) Spark Ignition engines (Mixture of air and fuel is ignited by electric spark)

(2) Compression Ignition engines (The fuel is ignited as it comes in contact with hot Compressed air)

• Method of Cooling as : (1) Air cooled engines (2) Water cooled engines

• Speed of the engines as : (1) Low speed engines (2) Medium speed engines (3) High speed engines

• Number of cylinder as : (1) Single cylinder engines (2) Multi cylinder engines

• Position of the cylinder as : (1) Inline engines (2) V-engines (3) Radial engines (4) Opposed cylinder engines

(4) Opposed piston engines

Inline Engine V- Engine Opposed Piston Engine

Engine Details

Engine Terminology

• A two-stroke, or two-cycle, engine is a type of internal combustion engine which completes a power cycle with two strokes (up and down movements) of the piston during only one crankshaft revolution.

• This is in contrast to a "four-stroke engine", which requires four strokes of the piston to complete a power cycle

Otto Four stroke cycle• The four stroke petrol engines works on the principle of theoretical Otto cycle. Also known as constant volume

cycle. shown in Fig below

• In four stroke Petrol engine the vale operating for inlet is called inlet valve and the valve operating for exhaust is called Exhaust valve. In Petrol engine SPARK plug fitted at the top of cylinder head initiates the ignition of the air fuel mixture.

• The piston performs four strokes to complete one working cycle. • The four different strokes are ; (1) SUCTION STROKE (2) COMPRESSION STROKE

(3) POWER STROKE (4) EXHAUST STROKE.

Four stroke cycle

DIESEL FOUR STROKE CYCLE• The four stroke Diesel Engine works on the principle of Diesel Cycle , also called CONSTANT

PRESSURE HEAT ADDITION PROCESS shown in Fig.

• The four stroke Diesel engine is also consists of SUCTION, COMPRESSION,POWER and EXHAUST strokes.

• The basic construction of a four stroke diesel engine is same as that of four stroke petrol engine, except instead of spark plug, a fuel injector is mounted in its place .

Working of Four stroke Engine

Difference between Petrol and Diesel Engine

The basic differences between Petrol and Diesel Engine given below PETROL ENGINE DIESEL ENGINE

Works on Otto cycle . Works on Diesel Cycle .Petrol is used as fuel . Diesel is used as fuel .Air and fuel mixture enters in cylinder during suction stroke .

Only Air is drawn during the suction stroke .

Low compression ratio ranging from 6 to 10 . High compression ratio ranging from14 to 20 .The compressed charge is ignited by the spark plug. The fuel injector is used in Diesel engine.

High engine speed of about 3000 RPM . Low to medium engine speed ranging from 500 to 1500 RPM.

The Thermal efficiency is lower due to lower Compression ratio .

The Thermal efficiency is higher due to high Compression ratio .

Lighter in weight because maximum pressure and Temperature is less .

Heavier in Weight because maximum pressure and temperature is high .

Less Costlier . More Costlier .Maintenance cost is Less . Maintenance cost is Slightly higher .Easier starting even in cold weather . Difficult to start in cold weather .Running cost Higher because petrol is Costlier . Running cost is Less because diesel is Cheaper .

Two Stroke Cycle • As the name itself implies, all the processes in two stroke cycle engine are completed

in two strokes. • In four stroke engine cycle Two complete revolutions of crank shaft is required for

completing one cycle .

Two Stroke Cycle Engines

• In two stroke Engine cycle Operations Suction , Compression , Expansion and Exhaust are completed in One Complete revolution of the crank shaft in two stroke Engines.

• These engines have one Power stroke per revolution of the crank shaft.

• In two stroke engines there is two openings called PORTS are provided in place of valves of four stroke engines.

• These Ports are opened and closed by Reciprocating Motion of the Piston in the Cylinder. One port is known as INLET PORT and another port is known as EXHAUST PORT .

Two Stroke Diesel Engine

FOUR STROKE ENGINE TWO STROKE ENGINEFour piston strokes require to complete one cycle . Only two piston strokes required to complete one cycle .

Two complete revolutions of crank shaft is required to complete one cycle. Only one complete revolution of crank shaft is required to complete one cycle .

Equal to half of the speed of engine crank shaft . Number of power stroke/min. n=N/2

Equal to the speed of engine crank shaft . Number of power stroke/min. n=N

Power is developed in every alternate revolution of crank shaft . Power is also developed in every revolution of crank shaft hence for same cylinder.

The power is developed in every alternate revolution, hence heavy fly wheel is required .

The power is developed in every revolution , hence lighter flywheel is required .

These engines are Heavier, larger and required more space. These engine are lighter more compact and require less space.

The inlet and exhaust valve are require and they are operated by valve operated by valve operating mechanism.

In place of valve, ports are used which opens and close by motion of piston itself.

Lubricating oil consumption is less . Lubricating oil consumption is more because lubricating oil is mixed with fuel

Thermal efficiency is higher . Less Thermal efficiency.

Mechanical efficiency is Low because of more number of moving parts . Mechanical efficiency is High because of less number of moving parts .

These Engines are used basically in High Power Application Where more space is available like Cars , Truck, Tractors , Buses etc .

These Engines are used basically in Low Power Application Where less space is available like Mopeds ,Scooters ,Motor cycle etc .

Difference Between Two Stroke and Four Stroke Engines

ENGINE PARAMETERS

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Combustion Chamber

Crank Shaft

Piston

Connecting Rod

TDC

BDC

Gasket

VC

VS Stroke

Stroke

Bore

Crank Radius (crank throw)

Crank Radius

Cylinder

Compression ratio (r)

• VC = Clearance volume• VS = Swept volume = /4 D2 L

where: L (stroke) = 2 ρ, ρ is the crankshaft radius- Increasing the compression ration increases the thermal

efficiency, compression is limited by the knock limit.

C

SC

VVV

r

C

S

VV

1r

TDCatpistonaboveVolumeBDCatpistonaboveVolumer

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Engine Displacement, Swept Volume or Engine Capacity (Ve):

• Ve = VS n • Ve = (/4) D2 L nWhere:

Ve = engine capacity, Vs = cylinder swept volumen = number of cylinders, L = stroke, D = bore diameter

Stroke VS

Bore

VS VS VS

TDC

BDC

22

Volumetric Efficiency V

ntDisplacemeEngineEnginetheEnteringAirηV

23

Volumetric Efficiency V (cont.)•Engines are only capable of 80% to 90% volumetric efficiency.

• Volumetric efficiency depends upon throttle opening and engine speed as well as induction and exhaust system layout, port size and valve timing and opening duration.

•High volumetric efficiency increases engine power.

•Turbo charging is capable of increasing volumetric efficiency up to 50%.

24

Indicated mean effective pressure (imep)

Compression ratio

Air/fuel ratio

Volumetric efficiency

Ignition timing

Valve timing and lift

Air pressure and temperature

FACTORS AFFECTING

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Pressure, Force, Work & Powerp = imep (N/m2)

A (m2)

F= P.A (N)

L (m)

F (N)

Work (W) = F.L (N m)

Time (t) = 60 / (Ne /k) (s)

Indicated power (Pi) cylinder = W/t = F.L .Ne/(k*60) (W)

(Pi) cylinder = (imep.A.L.Ne) / (k . 60)

(Pi) engine = imep. (A.L.n) Ne / (k . 60)

(Pi) engine = [imep. Ve . Ne/ (k . 60)] (W)

a

b

c

k = 2 (four stroke)k = 1 (two stoke)

26

Engine Indicated Power (Pi)Engine power factors:•Engine capacity (Ve)•Engine Speed (rpm) (Ne)•Number of strokes “k” k=2, four stroke engine k=1, two stoke engine• (imep):volumetric efficiency, compression ratio, ignition quality, mixture strength, temperature …

Pi = imep.Ve.Ne / (60. k)

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Engine frictionThree types of friction-bearing surfaces in automobile engines:

•Journal•Guide•Thrust

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Engine Brake Power (Pb)-This is the power developed at the crankshaft or flywheel. -The term brake originated from the method used to determine an

engine’s power output by measuring the torque using some form of friction dynamometer.

29

Engine Mechanical Efficiency m

•Pb = Pi - Pf

Where:Pi = indicated

powerPb= brake powerPf = friction power

•m = Pb / Pi

30

Engine Brake Power (Pb) •Pb = Pi m•Pb = (imep Ve Ne / 60 k) m•Pb = (imep m)Ve Ne / 60 k•Pb = bemp Ve Ne / 60 kWhere:bmep = brake mean effective pressurebmep = imep m

* bmep is indication of engine efficiency regardless of capacity or engine speed, 1000 kPa represent high efficiency.

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Gross & Net Brake Power•Gross brake power is measured without the following items:

Cooling fan, coolant pump, radiator, alternator, exhaust system. (SAE)

•Net brake power is measured with all the above items. (DIN)

•Gross power is 10-15% more than net power.

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Engine Torque TeTorque and crankshaft angle: Work is also accomplished when the torque is applied through an angle.

•Distance xy = rθ •W = F . xy = F r θ = T θ •W per one revolution = T (2)•P = W/t = T (2)/t = Tω/1000 Where: ω = 2 Ne/60

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Engine Torque Te (Cont.)•Pb = T ω = Te (2 Ne/60) = Te Ne / 9550 (kW)•bmep . Ve . Ne / k 60 = Te (2 Ne/60)•Te = bmep . Ve / 2 . K Where:Pe = Engine power (kW)Ne = Engine speed (rpm)Te = Engine torque (N m)bemp = brake mean effective pressure (Pa)Ve = engine capacity (m3)k = 2, for 4-stroke engines

1, for 2-stroke engines

34

Engine Torque Te (Cont.) - There is a direct relationship between BMEP and torque output.

- The torque curve with engine rpm is identical to the bmep curve, with different values.

35

Engine Fuel consumption (FC)The amount of fuel an engine consumes can be measured by:

• volume (cm3 or liter) per (sec. or mint, or hr)or

• mass (kg) per (sec, or mint, or hr).

36

Engine Specific Fuel Consumption (SFC)• Specific fuel consumption represents the mass or volume of

fuel an engine consumes per hour while it produces 1 kW of power.

• Typical gasoline engines will have an SFC of about 0.3 kg/(kW.h).

• SFC is an indication of the engine’s thermal or heat efficiency.• (kg/h)/kW or kg/(kW h)

b

.

PSFC m

37

Engine Thermal Efficiency (th)• The efficiency of an engine in converting the heat energy

contained in the liquid fuel into mechanical energy is termed its thermal efficiency.

• The petrol engine is particularly inefficient and at its best may reach 25% efficiency.

• The thermal efficiency of a diesel engine can reach 35% due to its higher compression ratio.

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Thermal Efficiency (th) (Cont.)

where: is the fuel consumption (kg/h)

is the fuel consumption (L/h) CV is the calorific or heat value of 1 kg of the fuel

(kJ/kg or MJ/kg). (CV for gasoline is 40000 kJ/kg) ρ is the relative density (kg/L) of the fuel.

CV.ρ.

P3600)(ηefficiencythermalBrake

CV.

.6060.P)(ηefficiencythermalBrake

V

m.

bth

.b

th

m.

V.

39

Specific Fuel Consumption (SFC) & Thermal efficiency (th)

Where:th = thermal efficiency = fuel consumption (kg/h)Pb = brake power (kW)CV = calorific value (kJ)SFC = specific fuel consumption (kg/(kW.h))

CVSFC.3600

CV.)/P(

3600

CV.

P3600ηb

..b

th

mm

m.

40

Specific Fuel Consumption (SFC) & Thermal efficiency (th)•A mirror reflection of the SFC curve shows the shape of the engine’s thermal efficiency curve.

•The lowest point on the SFC curve becomes the highest point on the thermal efficiency curve.

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Power Units•BHP (bhp) = 550 ft lb/s •PS = 75 kg m/s•kW = 1000 (N m/s)

BHP = British and American “horse power”PS ="PferdeStärke“ is "horse power“ in German•PS = 0.986 bhp, BHP = 1.0142 PS •kW = 1.36 PS, PS = 0.73529 kW•kW = 1.341 bhp, BHP = 0.7457 kW

42

Engine Performance CurvesImep

Bemp and torque

Indicated power

Brake power

Indicated thermal efficiency

Brake thermal efficiency

Specific fuel consumption