Tractor Test & Performance _1

5/27/2018 Tractor Test & Performance _1

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Department of Agric Engineering, Faculty of Agriculture, University of Ruhuna, Sri Lanka

Prepared by

KT Ariyawansha

B.Sc (Ruhuna), M.Sc (Peradeniya)


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Students should gain knowledge about

Indicated power

Break power

Drawbar powerEngine performance curves

Testing and evaluation methods


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Test

An examination, experiment, or trial, as to prove the

value or ascertain the nature of something

EvaluationEvaluation is systematic determination of merit, worth,

and significance of something or someone using

criteria against a set of standards

PerformanceThe way in which someone or something functions


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Checking of specificationPower testing

The fuel consumption

Power lift & hydraulic performance test

Brake test

Noise measurement

Air cleaner oil pull over test

Mechanical vibration measurementLocation of centre of gravity


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Turning ability

VisibilityField tests

Mould board/Disc ploughing

Disc harrowing

Cultivation/dry rotavationPuddling under actual field condition and followed by WaterProof Test.

Haulage test with 2/4 wheel trailers and therecommended

Evaluation of adjustments, breakdown & repairs duringTest

Components & assembly inspection


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1. Overall dimensions

2. Type of engine

3. Control systems

4. Type of PTO

1. Ground PTO

2. Independent PTO

1. 540rpm

2. 1000rpm5. Linkage mechanism

1. 3point linkage(Category I,II,III)

2. Draw bar

6. Steering system

7. Wheel

8. Seating arrangement

9. Lighting

10.Vision

11.Others


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Indicated power

Brake Power

Drawbar pull and power

P.T.O. power

Specific fuel consumption

Thermal efficiency

Engine performance curve


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Fuel energy Useful mechanical power

EkJ 0.5EkJ


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The fuel is the source of the engine power.

The power embodied in the fuel is called fuel equivalent power , Pfe,

Pfe

Pb

Pf

Pi

Rejected heat


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Pfe= fuel equivalent power,( kW )

mf= fuel consumption rate, (kg/h )

H g = gross (higher) heating value of the fuel,(kJ/kg )

3600

gf

fe

HmP


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1. A two wheel tractor engine(435cc, 4 stork, one cylinder) operate at

2000 rpm and Your Index number , the fuel consumption and torque at

the flywheel of the engine was reported as 798ml/hr and 16.5Nm,

the gross heating value of diesel was 43MJ/Kg, the specific gravity of

diesel is 0.85, indicated mean effective pressure was 700kPa,

1. Find the fuel equivalent power

2. Fined the indicated power

3. Find the break horsepower

4. Calculate the friction power

Answer send to - [email protected] before 30thSept 2011 at 11.59 pm


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where

qf= fuel consumption rate, L/h

f= fuel density, kg/L

3600

gff

fe

HqP

If the fuel consumption is measured volumetrically, thefollowing equation is used to calculate fuel equivalent

power:


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Burning of the fuel produces high pressure on each piston

Variation of this pressure with cyliner volume called P-V diagram

To day several equipments


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The imep is the averageheight of the p-v

diagram.

That is the area within

the p-v diagram dividedby the displacementvolume of one cylinder.

Use of a pressure/volume diagram

to determine indicated meaneffective pressure.


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where

Pi= indicated power in W

P = indicated mean effectivepressure in Pa (Nm-2)

A = area of the top of each pistonin m2

L = stroke length in m

n = Number of cylindersN = engine speed in r/min (rpm)

If engine 2 Stork N = rpm

If engine 4 Stork N = rpm/2

60

PLANnP

i


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The power at the head of the pistons.

These are:

Increase the engine size

Increase the engine speedIncrease the internal pressure and consequentlythe stress on the engine

increasing the compression ratio

increasing the fuel delivery rateor by other techniques


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The indicated power is not immediately available for

useful work

Must first be transmitted to the flywheel of the engine.

Some of the indicated power is absorbed within the

engine to overcome friction and to run such accessories

as the oil pump, fan, alternator, and so on.

All such power is lumped together into a category called

friction power (Pf)

By definition

bif PPP Pb-

Brake Power


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Torquecan be described as a turning effort

F1 F2

L1

L2

T = F.L


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Engines must produce torquein order to rotate the drivewheels when a tractor is

pulling a load

Work Vs Torque

Work was defined as a forceacting through a distance

In contrast, torque is a forceacting perpendicular to adistance, the distance beingmeasured from a center ofturning to the point of

application of the force


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FL

Work(W) = Force x Distance

Distance = 2r

W = F x 2r

W= Fx 2 L

T= FL


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where

Pb= brake power in kW

T = engine torque in N.m

N = engine rotational speed in rpm

60000

2 NTPb


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bmep is the average pressure on the pistonduring the power stroke, derived from themeasurement of brake power output

No direct method to measure

can be calculated from the Equation

ALN

60Pbbmep

Wher,

Pb berak power(W)

A cross sectional area of piston(m2)

L stork length (m)

N

rpm of engine


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Engine torque variesdirectly with bmep.

For a given size of engine, torque can beincreased only by increasing the bmep.

The bmep can be increased by increasingthe imepand/or by reducing the fmep.

2

1000bmepALT


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The fmepis a losscaused by the

oil pump,

fan,

alternator and

so on,

and increases withengine speed, as shownin Figure.

Thus, both fmepandfriction power can bereduced by reducingengine speed.

Friction mean effective pressure

in a typical diesel engine


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Several efficiency terms have been used for describing howwell engines convert fuel energy into useful power.

Indicated thermal efficiency (eit)

Mechanical efficiency (em )

Brake thermal efficiency (ebt)


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The fraction of fuel equivalent power that is converted to

indicated power

Indicated thermal efficiency (eit)


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The fraction of the newly created indicated power that is

delivered as useful power from the engine:

Mechanical efficiency (em )


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The overall efficiency of the engine inconverting fuel power into useful power

An indication of the fraction of the energy in thefuel that is converted to power at the flywheel

Brake thermal efficiency (ebt)


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The brake thermal efficiency can also be calculated using

the following equation:

Forgood overall efficiency, an engine must bemechanicallyefficientand have anefficient combustion process


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The mechanical and overall efficiencies of an engine vary

with load

The reason becomes clear when we get the following

equation for mechanical efficiency


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Tractor Power

1. Indicate power -2. Friction power -

3. Brake power4. Power Take Off power

1. The power delivered by a tractorthrough its PTOshaft.

5. Drawbar power1. The power of a tractor measured at the

end of the drawbar.


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Dynamometer

A dynamometer is an instrument for measuring enginepower usually by the independent measure of forcetime and distance through which the force is moved.


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Classification of dynamometer

According to theworking procedure

According to the dispositionof the energy

Brake AbsorptionTorsionDrawbar Transmission


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A prony brake is the simplest type of dynamometer.

Measures the power applied and at the same time

converts it to some other forms of energy, usually heat.

Prony Brake

Absorption Dynamometer


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L

DrumBrake shoes

Hand knob

Scale

Lever arm


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The drum (a) is connected to the crankshaft of the engine and rotates at engine speed.

Surrounding the drum are brake shoes (b) that create a torque drag on the drum.

The torque is controlled by tightening or loosening hand knob (c).

The torque is measured by a scale (d) located at the end of a lever arm (e).

A tachometer also must be provided for measuring the engine speed.

After the torque and speed are measured, the power can be calculated using following equation

=

L

ab

c

d

e

=


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Prony brakes have been replacedby more modern dynamometers.

Electric generator being used as a

dynamometer.When an electrical load is appliedto the generator the housingattempts to rotate, but it isrestrained by a load arm.

A scale on the end of the loadarm measures the torque.


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Use same dynamometer used in brake power test,


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Drawbar dynamometers are commonly employed to

determine the drawbar pull of power units or toascertain the draft of field implements.

Drawbar pull = Directs reading from dynamometerDraft= Pull x cos

is the angle between ground and pullDrawbar power = Draft x Speed

Types;Spring DynamometerHydraulic Drawbar DynamometerStrain gage Dynamometer


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The simplest and most obvious type of drawbar unitconsists of a spring that elongates under tension orshortens under compression.

Such a dynamometer is suitable for

rough measurements of forces - because of rapid

variations in load such as are commonly found inconnection with agricultural implements,


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It uses a hydraulic cylinder to transmit the drawbar farceto the dynamometer car.

The pressure is measured by a pressure transducer,

A hydraulic cylinder for measuring drawbar pull has an

advantage over a spring dynamometer in that thefluctuations can be reduced by a throttling valve.


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One method of measuring the drawbar pull is by meansof a dynamometer that uses electrical resistance strain

gages to sense the strain.

Strain gage force transducer

Digital recorder


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With the advent of machinery operated by tractor

power-take-off shafts a great deal of interest has been

displayed in devices for the measurement of power as

transmitted by rotating shafts.


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The development of theelectrical resistance straingage has made practical

the measurement of torque

and force on farm tractorsand machines. Manytorque meters employing

strain gages have beendeveloped.

Torque meter usingelectrical resistance strain

gages and slip rings tomeasure pto torque


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Fuel consumptionThe rate at which an engine consumes fuel (in kg/h or lb/h)

It varies with; its efficiency

its size and load, - a large, heavily loaded engine will alwaysconsume more fuel than a small, lightly-loaded one.

Although engine efficiency affects fuel

consumption, fuel consumption alone is not agood indicator of engine efficiency

Specific Fuel Consumption


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The termSpecificFuelConsumption(SFC), has beendeveloped to indicate fuel consumption in relation to the

amount of workthat is being done by the engine

SFC is defined as;

SFC = mfP

Where;

SFC = specific fuel consumption in kg/kW.h

Mf= fuel consumption rate in kg/h

P = power in kW


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Brake Specific Fuel Consumption (BSFC).

Brake power is measured in engine tests,

Indicated Specific Fuel Consumption (ISFC)

The indicated power was measured.

There are not widely accepted terms for SFC to be

reported relative to PTO power or drawbar power.


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Volumetric efficiencyis a measure of the air-pumpingefficiency of an engine.

The theoretical air-pumping capacity of an engine is

expressed as follows:

Mt -theoretical air consumption of engine in kg/hrD - engine displacement in m3N = engine speed in r/min (rpm)a= air density in kg/m3

Mt= 60NALa


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Where;

M- Mass of dry air /second, kg

A- Area of orifice, m2

C- Orifice coefficient

w-density of water kg/m3

a-Density of air kg/m3

h- Pressure drop across orifice mm H2O


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The theoretical air consumption rate is the amount ofair the engine would consume if each combustionchamber were completely filled with atmospheric airduring each intake stroke.

In a naturally aspirated engine (an engine without aturbocharger or supercharger), the pistons create apartial vacuumduring each intake stroke, and thecombustion chambers do not completely fill with

atmospheric air.


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Therefore, the volumetric efficiency is defined as follows:

=Ma

Mt

ev = volumetric efficiency (a decimal)

Ma = actual air consumption rate in kg/hMat= theoretical air consumption rate in kg/h


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The volume of air entering to cylinder depends on,

The pressure, temperature and proportionalvolume of the residual gases left in the cylinderwhen the inlet valve opens.

Efficiency of the induction and exhaust system.

Engine speed Valve timing and No. of cylinder


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Torque Curve:Breke power curve

Specific Fuel Consumptioncurve

In desirable torque curve; Torque

increased significantly asspeed decrease & after that itstable

Low speed are better for gettingmore torque from engine

A diesel tractor engine normallyhave less speed variation for agiven change in torque than acomparable gasoline engine


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Lugging ability is used for torque curve as it

combines the performance of the transmission

and engine and to the users of tractors it is more

easily understood than a torque curve


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Tractors and their power unitsFourth edition

John B. Liljedahl, Paul K. Turnquist, David W. Smith,

Makoto Hoki (629.255)

Engineering Principles of Agricultural Machinery

Ajit K. Srivastava, Carroll E. Georing, Roger P. Rohrbach

Some publication from the technical library of American Societyof Agricultural and Biological Engineering (ASABE)


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1. A single-cylinder four-stroke motorcycle enginewith bore and stroke of 88.9 mm is coupled to aprony brake dynamometer when running at4800 rpm. The mechanical efficiency is 91%. The

break load is 160 N. Find(i) Break Power

(ii) Indicated Power

(iii)Break Mean Effective Power


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2) Following result are give from tractor brake power

testing,

1. Draw the engine performance curves

I. Torque curve

II. Brake power curve

III. Specific fuel consumption curve

2. Find the optimum engine speed range

rpm 1000.001500.002000.002500.00

Balance reading(kg) 1.26 1.84 1.96 1.64

SFC(kg/kW/hr) 680.76 396.07 331.62 338.41


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3. A six cylinder petrol engine of 60 mm bore 100

mm stroke, consumes 1.4 m3 of air/min when

running at 2000 rpm and developing 17.15 kW.Fuel is consumed at the rate of 0.146 l/min.

(Relative density of petrol 0.731 and dry air has

a density of 1.2754 kg/m3)

(i) Volumetric Efficiency

(ii) Specific Fuel consumption kg/kWh

Documents

Tractor Test & Performance _1