torque , power, volumetric efficiency and their dependence on unit air charge has been discussed

NATIONAL INSTITUTE OF NATIONAL INSTITUTE OF TECHNICAL TEACHERS TECHNICAL TEACHERS

TRAINING AND RESEARCH TRAINING AND RESEARCH CHANDIGARH CHANDIGARH

104/15/23

Vehicle ownership is still growing worldwide

By 2020– 15% vehicle ownership – 1.1 billion vehicles– Circle the earth 125 times

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CONVENTIONAL CONVENTIONAL AUTOMOBILEAUTOMOBILE

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MODERN MODERN AUTOMOBILEAUTOMOBILE

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SIMPLIFIED SIMPLIFIED TEACHINGTEACHINGCONCEPT OF DIESEL AND PETROL ENGINE

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SIMPLIFIED SIMPLIFIED TEACHINGTEACHING

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SIMPLIFIED SIMPLIFIED TEACHINGTEACHING

LOADING ON ENGINE

Purpose of an engine

Converts the heat of burning fuel into useful energy

Internal Combustion Engines

The basic requirements of an engine are to provide:• High power output

• High thermal efficiency and low specific fuel consumption

• Smooth engine operation

• Reduced exhaust pollutants.

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• Volumetric efficiency (v) = (mass of air actually drawn into cylinder) / (mass of air that ideally could be drawn into cylinder)

where air is at ambient = Pambient/RTambient and R - 287 J/kgK for air• Volumetric efficiency indicates how well the engine “breathes” -

what lowers v below 100%?– Pressure drops in intake system (e.g. throttling) & intake

valves– Temperature rise due to heating of air– Volume occupied by fuel– Non-ideal valve timing– “Choking” (air flow reaching speed of sound) in part of intake

system having smallest area

Volumetric Efficiency

nNVdairv /

(measured) mair

• The final parameter to be defined is the volumetric efficiency of the engine; the ratio of actual air flow to that of a perfect engine is

• In general, it is quite easy to provide an engine with extra fuel; therefore, the power output of an engine will be limited by the amount of air that is admitted to an engine.

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Indicated Mean Effective Pressure (Pim):

p-V diagram for an ideal four-stroke cycle engine

Turbochargers & Superchargers

• Superchargers: mechanically driven from engine crankshaft

• Turbochargers: driven by waste exhaust gases increased air mass improves the engine's thermal efficiency (fuel economy) and emissions performance,

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• Engine performance is specified in both in terms of power and engine torque - which is more important?– Wheel torque = engine torque x gear ratio

tells you whether you can climb the hill

Power and Torque

Engine Torque and Power

Torque is measured using a dynamometer.

Load cell

Force FStatorRotor

b

N

The torque exerted by the engine is: T = F b with units: J

The power Wdot delivered by the engine turning at a speed N and absorbed by the dynamometer is:

Wdot = T = (2 N) T w/units: (rad/rev)(rev/s)(J) = Watt

Note: is the shaft angular velocity with units: rad/s

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– Power tells you how fast you can climb the hill– Torque can be increased by transmission (e.g.

2:1 gear ratio ideally multiplies torque by 2) Power can’t be increased by transmission; in fact because of friction and other losses, power will decrease in transmission

– Power tells how fast you can accelerate or how fast you can climb a hill, but power to torque ratio ~ N tells you what gear ratios you’ll need to do the job

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Mathematically different from the British unit1 Power PS = 0.986 BhpPferde Stärke = Horse Strength (German)Power (PS@rpm)

67@5500 65@6200

Torque (Nm@rpm)

99@2800 84@3500

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S No. duo Engine RPM

Number of Cycles /Minute

Unit Air Chargegm/cycle

Total Air Sucked/ Minute in gms

1 500 250 2 5002 1000 500 3 15003 1500 750 4 30004 2000 1000 5 50005 2500 1250 6 75006 3000 1500 5.5 82507 3500 1750 5 87508 4000 2000 4.5 90009 4500 2250 4 900010 5000 2500 3 750011 6000 3000 2 6000

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EngineEngine Type/Model 1.4L SOHC PetrolDisplacement cc 1405Power (PS@rpm) 60PS @4500rpmTorque (Nm@rpm) 105Nm @2500rpmValve Mechanism SOHCBore (mm) 75Stroke (mm) 95Compression Ratio 9:1

No of Cylinders (cylinder) 4

Cylinder Configuration Inline

Valves per Cylinder (valve) 2

Fuel Type PetrolFuel System Carburettor mechanical fuel pump

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• Engine performance is specified in both in terms of power and engine torque - which is

more important?– Wheel torque = engine torque x gear ratio

tells you whether you can climb the hill

Power and Torque

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– Power tells you how fast you can climb the hill– Torque can be increased by transmission (e.g.

2:1 gear ratio ideally multiplies torque by 2) Power can’t be increased by transmission; in

fact because of friction and other losses, power will decrease in transmission

– Power tells how fast you can accelerate or how fast you can climb a hill, but power to torque

ratio ~ N tells you what gear ratios you’ll need to do the job

There is a maximum in the brake power versus engine speed called the rated

brake power.

At higher speeds brake power decreases as friction power becomes significant compared

to the indicated power

There is a maximum in the torque versus speed called maximum brake torque (MBT).

Brake torque drops off: • at lower speeds do to heat losses

• at higher speeds it becomes more difficult to ingest a full charge of air.

Max brake torque

1 kW = 1.341 hp

Rated brake power

Power and Torque versus Engine Speed

2 NITTTR Chandigarh

2 NITTTR Chandigarh

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