Internal Combustion Engines Engine Testing - ULisboa · PDF file1 - Internal Combustion...

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- Internal Combustion Engines -

Internal Combustion Engines

Engine Testing

Guide to the laboratory work

1 - Objectives

Laboratory work on engine testing is intended to bring students into contact with running engines,

allowing the student

a) to learn the basic procedures of engine testing ;

b) to verify, measure, and interpret engine performance and how this performance changes when

the test conditions change ; and

c) to “feel” the engine, i.e., to develop sensorial awareness to how a running engine sounds,

smells, vibrates, realises heat, etc.

In particular it is intended that each student is directly involved in (and responsible for) one of the

following engine tests (and writes the corresponding report), and participates in at least one of the

other tests:

(2) influence of load at constant speed in a Diesel engine;

(3) influence of load at constant speed in a Diesel engine with retarded injection;

(4) influence of load at constant speed in a spark ignition (SI) engine;

(5) influence of engine speed in a SI engine for constant throttle position;

(7) influence of ignition timing at constant speed and constant throttle position in a SI engine;

(8) influence of air/fuel ratio at constant speed and constant throttle position in a SI engine;

(9) influence of compression ratio at constant speed and constant throttle position in a SI engine.

(Note: tests (1) and (6) will not be performed)

2 - Rigs

The tests will be carried out in two test benches with two particular engines: tests (2) and (3) with a de

Prony Brake and a Deutz Diesel engine, and tests (4), (5), (7), (8), and (9) with a Plint TE15 electric

brake bench and a Petter-Plint W 1 spark ignition engine.

2.1 - Diesel engine and test bench

The Diesel engine is an old Deutz single-cylinder from

the 30’s of the XX century (fig. 1). It is a naturally

aspirated, 4-stroke, indirect injection, water- cooled

engine. There is very little data available on the engine.

Bore and stroke are, respectively, 190 mm and 320 mm,

and the compression ratio is unknown. Maximum engine

speed used to be 500 rpm, but presently it is restricted to

450 rpm.

The engine has one intake and one exhaust valve, and

those are located in the pre-chamber (fig. 2). This was a

common geometry in the 30’s but it has been abandoned

long time ago. The pre-chamber is aligned with the

cylinder, and the injector is at the top of the pre-chamber.

The engine is equipped with a centrifugal engine speed

regulator that regulates the injected fuel amount so that

Fig. 1 - Diesel engine

Fig. 2 - Pre-chamber, valves, and injector

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- Engine testing -

engine speed is kept constant.

Hourly fuel consumption hC is measured by measuring

the time needed to consume a given volume of fuel and

knowing the fuel’s density fρ . The density is measured

with a densimeter (fig. 3), and time with a chronometer.

The volume of fuel is measured using a graduated pipette

(fig. 4). There are two pipettes, with the volumes of

100.0 cm3 and 250.0 cm

3.

There is no equipment available to measure gas flow

rates (air or exhaust). Nevertheless, the air flow rate am&

can be easily estimated by assuming a value for the

volumetric efficiency vη .

Exhaust temperature is measured by a thermocouple

located at near downstream of the exhaust valve, and the

temperature is directly read in an analogue gauge (fig. 5).

Although there is equipment to measure engine

emissions, those will not be measured in the present

academic year.

Figs. 3 & 4 – Densimeter and fuel

measuring system

Figs. 5 – Analogue gauge of the

thermocouple

The de Prony Brake is a brake, as show in

figure 6. A drum of radius r is attached to the

driveshaft. The drum is embraced by a metal

stripe with a series of wooden brake blocks.

The metal stripe can be tightened by means of

a wheel around the drum, and is attached to a

lever of length b, and it has a variable weight F

at its extremity. The lever can oscillate within

certain limits, but when it is steady, the torque

of the friction force between the wooden brake

blocks and the drum is balanced by the

moment of the lever. The determination of this

stripe

wooden

brakeblocks

wheel

b

drum

F

lever

Fig. 6 – De Prony Brake

moment allows the torque at the drum to be known, and that torque is the engine brake torque eB .

The entire de Prony Brake has a certain weight, which, together with the distance of its application

point to the axis of the drum, represents a certain torque. If that weight is reported to the application

point of the variable weight F, then that virtual weight W should be added to F, and the moment is then

given by b (F + W). Therefore

( )WFbBe += (1)

The values of b and W in IST’s ICE Laboratory are,

respectively, 1.200 m and 73.5 N.

Brake power is obtained multiplying the torque eB by the

driveshaft angular speed ω. This speed can be converted to

rotations per unit of time. In the laboratory this is measured by

a mechanical tachometer (fig. 7). The appropriate scale of the

tachometer should be chosen, and the rubber end mounted on

its axis should be pressed (strongly) against the engine

driveshaft.

Fig. 7 - Tachometer

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2.2 - Spark ignition engine and test bench

The spark ignition engine is a demonstration

and instructional Peter-Plint engine. It is a

naturally aspirated, 4-stroke, side valve,

water-cooled, variable compression ratio,

single cylinder engine (fig. 8 & 9).

“Basically, it is a conventional design engine,

but the cylinder head has the special feature

that the volume of the combustion chamber

may be varied by means of a counter-piston.

The compression ratio is changed by

adjusting the position of the water-cooled

cylinder head cast iron counter-piston fitted

to a bore in the water-cooled cylinder head.

The counter-piston, which carries the

sparking plug, is sealed by means of cast

iron compression rings and silicone rubber O

rings. Its end forms the top surface of the

combustion chamber. The counter-piston is

moved by rotating a gear at the top of the

cylinder head.

Fig. 8 – SI engine and test bench

Fig. 9 – Transverse cross section of the engine

The engine is exceptionally robust and the

bearings and running gear are adequate to

withstand severe knock.

An externally mounted gear pump delivers oil to

a splash lubrication system for the large end

bearing, cylinder and cam shaft. The crank shaft

main bearings are pressure fed.

It is equipped with an up-draught carburettor

fitted with an adjustable main jet to permit

variation of mixture strength (fig. 10).

Ignition is by magneto and the spark timing may

be varied (fig. 11).”

(from the manufacture catalogue)

Figs. 10 & 11 – Carburettor and magneto

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- Engine testing -

Bore and stroke are, respectively, 85.0 mm and

82.5 mm, and the compression ratio can be set

(continuously) between 4.0 and 10,0. Maximum

engine speed is 2000 rpm, Minimum velocity

depends on engine settings, usually being

between 800 and 1000 rpm.

The cooling water is supplied by an external

electric driven pump. The water flow is regulated

by a valve and its flow rate measured with a

rotameter flowmeter (fig. 12). The rotameter has

two scales. The scale to use is in the metal side.

The water inlet and outlet temperatures are

measured by analogue thermometers (fig. 13).

Hourly fuel consumption hC is measured by

measuring the time needed to consume a given

volume of fuel and knowing the fuel’s density fρ .

The density should be measured with a

densimeter, but in the present academic year a

typical value for the density of petrol should be

assumed (see the Annex). Time is measured

with a dedicated chronometer. The volume of

fuel is measured using a cylindrical glass tube

fuel consumption gauge with spacers (fig. 14).

The spacers are machined to a knife edge for

part of their circumference and are positioned so

that a measured volume of fuel is contained

between successive spacers. The volume

between them is 25.0 cm3, 25.0 cm

3, and

50.0 cm3.

Engine speed is computed from a counter and

the above mentioned chronometer. The number

of rotations is counted only while the

chronometer is running. The pair (no. of

rotations - time) then allows calculating the

average engine speed during the time interval

measured. The dedicated counter/chronometer

(fig. 15) has also a tachometer to allow an easy

verification of the engine speed, but it should not

be used to provide values for calculations.

Fig. 12 – Cooling water rotameter flowmeter

Fig. 13 – Inlet and outlet water thermometers

Figs. 14 & 15 - Fuel consumption gauge and

counter/chronometer/ tachometer

Fig. 16 – Air consumption meter

The air flow rate is measured by means of an air consumption meter (fig. 16). This unit consists of a

large plenum chamber upstream of the engine air filter. The air exits the plenum chamber

intermittently to the engine, but due to the large volume of that chamber, the air is virtually quiescent

inside the chamber. Thus the air enters the chamber at a steady rate, making it possible to calculate

the flow rate by measuring the pressure loss at the chamber’s inlet with a manometer and by knowing

the pressure loss coefficient of the inlet. The diameter of the inlet to the plenum chamber is 19,9 mm

and the inlet pressure loss coefficient is 0.60.

The air temperature and pressure upstream of the inlet have to be known. With these two values, with

the diameter D and the pressure loss coefficient K, and the pressure drop p∆ across the inlet, the air

flow rate am& can be computed:

5


p

Tp

p

TRpKAma ∆∆ 310472.42 −==& (2)

with am& in kg·s-1

, ∆p and p in Pa, and T in K.

Exhaust temperature is measured by a thermocouple located at

near downstream of the exhaust valve, and the temperature is

directly read in a digital display (fig. 17).

The brake (fig. 18) is an electrical DC one with a nominal output

of 3500 W at 220 V and 2000 rpm, and a speed range up to

3600 rpm. The machine is shunt wound and separately excited

by a DC electrical generator (fig. 19). The electrical output is

absorbed in a separately mounted load unit with ten electrical

resistances (fig. 20). The electrical load is controlled by a

separate free standing electrical control cabinet (fig. 21).

Figs. 19 & 20 – DC electrical generator and electrical resistances

The brake torque is measured by measuring the force F

necessary to prevent the brake to rotate, keeping it balanced.

The force F is measured with a dynamometer and acts at the end

of a lever. To reach the balance of the brake the wheel that

controls the dynamometer needs to be adjusted.

Power is obtained from the torque and from the brake (and

therefore engine) speed. The length of the lever is 265 mm.

Therefore, brake torque and power are:

FBe 265.0= (3)

04.36

nFPe = (4)

with eB in N·m, F in N, eP in W, and n in rpm.

The electrical brake may enforce resistant torque to the engine

(and allowing to measure it) or motor torque (allowing to start the

engine, as well as to measure mechanical losses by the method

of engine motoring).

Fig. 17 – Exhaust temperature

display

Fig. 18 – DC electric brake

Fig. 21 – Brake’s control cabinet

The formulae for the mechanical losses are eq. 3 and 4 (with the index m instead of e) above, but with

F measured when the engine is being motored. The methodology to measure F when the

dynamometer is generating a motored torque is somehow peculiar, and will be explain in loco by the

lecturer.

Although there is equipment to measure engine emissions, those will not be measured in the present

academic year.

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- Engine testing -

2.3 - Miscellaneous

When testing engines, ambient pressure and temperature should always be

measured, thus allowing corrections to be made. These corrections are meant to

present the results in terms of standard atmospheric conditions, and hence to have

results that are independent of the local conditions.

Relative humidity should also be measured, although corrections are not usually

made to take it into account.

Fig. 22 – Ambient thermometer, barometer, and hygrometer

3 - Experimental procedure

3.1 - General description

Start by familiarizing yourself with the laboratory, particularly with the safety conditions and

procedures and learn how to stop the engine in case of an emergency. Familiarize yourself with the

experimental facility that you are going to use and its equipment.

Turn on the ventilation system of the laboratory (or check that it is already on). Check whether the

exhaust system of the combustion products (tail-pipe engine exhaust) is set to the engine that you are

going to test.

Verify whether all the systems concerning the engine that you are going to use are set in place and

ready (e.g., the weights of the de Prony Brake, tachometer for the Diesel engine and that the

counter/chronometer and tachometer for the SI engine is on, fuel in the fuel tanks, the protection of the

pressure manometer of the plenum chamber removed and the liquids’ level correctly set, etc, etc).

Since none of the engines has an autonomous cooling system, open the cooling water valve before

starting the engine.

The engines will be started by the lecturer and the laboratory’s technician. Be attentive to the starting

procedure and try to learn as much as possible from that procedure.

After the start of the engine, load it with a light load. Never let an engine warm up with no load.

But never load the engine too much when it is cold, and, especially, never rev the engine to

high engine speeds in the initial seconds of running the engine.

Before starting to make measurements, register the air temperature, pressure, and relative humidity.

Repeat these registrations immediately after the last measurements of engine performance, prior to

switching the engine off.

Throughout the test (especially when some modification of the settings is carried out) listen attentively

the engine noise, feel its vibrations, its heat release and surface’s temperature (be careful not to touch

the exhaust manifold and pipe !), its smell. This sensorial awareness is one of the reasons to perform

the laboratorial engine tests ! Register the alterations (or the evolutions) that seem more relevant !

After carrying the tests (described in § 3.2 and 3.3), prepare to switch the engine off. Most likely the

engine is very hot (in most tests high engine loads are used towards the end of the test). Reduce the

load (and engine speed, if possible) to very low values and let the engine cool down. Never switch

off an engine when it is very hot.

Once the test is finished, switch off the system. To this end, close the valves of the fuel feeding

system, switch off the electrical systems (SI engine) and equipment, put back in place the cover of the

manometer of the plenum chamber (SI). Do not switch of immediately the engine exhaust extractor,

and let the cooling water run for some minutes.

Clean and tidy up the material.

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3.2 - Diesel engine

3.2.1 - Influence of load at constant speed – test (2)

Start the test complying with the initial description in § 3.1.

While the engine is warming up (with some light load), verify all the systems with the engine running.

Check how the tachometer works, check the exhaust temperature readings (and use it to understand

when the temperature stabilizes). Check the fuel system, learn how it works, and make some

readings of fuel consumption time to get used to the measurement technique and particularities.

Because the fuel feeding system is influenced by the return of the fuel to the fuel tank, the level of the

fuel in the pipettes will oscillate, rendering the reading slightly tricky. Learn how to cope with this

difficulty.

Once the engine has warmed up (it will take some minutes), remove the (low) load from the brake and

equilibrated it for F = 0. Let the engine stabilize for this new load (1 min, say), and start the

measurements. Start the measurement of the fuel consumption with the smaller pipette.

While the time to empty the pipette is being measured, measure the engine speed and keep checking

the exhaust temperature. Register its value towards the end of the measuring period of the fuel

consumption. During this period keep checking the balance of the lever of the brake and adjust the

tightening of the wooden brake blocks if necessary.

Once the fuel reaches the bottom of the pipette, stop the chronometer, register the time measured,

and immediately load the brake with a new force F. Let the engine stabilize for this new load (1 min,

say), and start the new measurements. Repeat this procedure up to the highest value of F. In this

test the maximum value of F, corresponding to the onset of black smoke emission, should be around

fkg23 (≈ 225 N) or fkg24 (≈ 235 N).

When the time required to empty the small pipette becomes less than 60 s, switch to the large pipette.

Make 8 to 12 measurements from F =0 up to maximum F. Decide how to distribute those 8 to 12

measurements in the interval F – 0.

After finishing the last measurement release completely the load, as instructed in § 3.1. Switch off the

engine when the temperature of the exhaust is not very far from the value corresponding to F = 0.

3.2.2 - Influence of load at constant speed with retarded injection – test (3)

The procedure for this is exactly like the one of § 3.2.1. The only difference is the maximum value of

F, that should now be around fkg21 (≈ 206 N) or fkg22 (≈ 216 N).

3.3 - Spark ignition engine


Start the test complying with the initial description in § 3.1. The lecturer will have already set the

compression ratio, ignition timing, and carburettor setting to the required values. Decide which engine

speed will be used for the test.

While the engine is warming up (with some light load but low speed), verify all the systems with the

engine running. Check how the counter/chronometer works, check the exhaust temperature readings

(and use it to understand when the temperature stabilizes), and check the fuel system. Learn how to

use it, and make some readings of fuel consumption time to get used to the measurement technique

and particularities. Check how to control the load in the brake’s control cabinet, how to equilibrate the

electric brake and read F. Check the response (sensibility) of the cooling water valve and how to read

the water flow rate. Regulate the flow rate to a value in the range of 1.7 to 2.3 l·min-1

. Check the

reading of the water thermometers (the outlet one may prove to be tricky to read). Check the reading

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- Engine testing -

of the manometer of the air consumption meter. Check the operation of the throttle (and be caution

because the throttle command is very near the exhaust, which is very hot !).

Once the engine has warmed up (it will take some minutes), set the throttle to obtain the required

engine speed with a load as low value as possible (if it is possible to set it to 0, the better). Let the

engine stabilize for this new running conditions (1 min, say), and start the measurements. Start the

measurement of the fuel consumption.

While the time to use one volume between spacers is being measured, measure all the values that are

needed:

- equilibrate the brake and read the value of F;

- read the water flow rate (and correct the flow rate, if necessary, trying to keep a value as close to

constant as possible);

- read the thermometers, register the value of the inlet water temperature, and, near the end of this

measurement point, register the value of the outlet water temperature;

- read the manometer of the air consumption meter;

- read the value of the throttle position; and

- read the value of the exhaust temperature and register its value towards the end of this

measurement point.

If the fuel is consumed in less than 60 s, continue to the second volume of fuel. Once the fuel reaches

the spacer (the second if only one volume is used, the third if two volumes are used), stop the

chronometer and register the time and the number of rotations that the engine performed during that

time. Reset both values to zero.

Immediately set the engine to a new condition. Open slightly the throttle and increase the load in a

way such that the engine speed is the chosen one, and the load increase by a required amount (see

below). Let the engine stabilize for this new condition (1 min, say), and start the new measurements.

Repeat this procedure up to the highest value of F. In this test the maximum value of F depends

strongly on the settings of the engine, but very likely it should be around 50 to 70 N.

Make 8 to 12 measurements from Fmin up to Fmax. Decide how to distribute those 8 to 12

measurements in that interval.

After finishing the last measurement measure the mechanical losses by the method of engine

motoring. This measurement is slightly tricky, and will be explained by the lecture at that moment.

After finishing the mechanical losses measurement, release completely the load, as instructed in

§ 3.1. Switch off the engine when the temperature of the exhaust is not very far from the value

corresponding to Fmin.

3.3.2 - Influence of engine speed for constant throttle position – test (5)


compression ratio, ignition timing, and carburettor setting to the required values. Decide which throttle

position will be used for the test.

The initial procedures are identical to those of § 3.3.1 (read it). Once the engine has warmed up (it will

take some minutes), set the load to allow value that, for the chosen throttle position, leads to the

maximum allowed engine speed (1900 rpm – be careful not to exceed it !). Let the engine stabilize for

this new running conditions (2 or 3 min, say), and start the measurements. Start the measurement of

the fuel consumption. While the time to use one volume between spacers is being measured,

measure all the values as indicated in § 3.3.1 (and do not forget the “60 s rule” for the fuel

measurement).

After resetting the counter and chronometer values to zero, immediately set the engine to a new

condition. Increase slightly the load in a way such that the engine speed drops by 80 to 120 rpm. Let

the engine stabilize for this new condition (1 min, say), and start the new measurements. Repeat this

9


procedure up to the highest value of F attainable or to an engine speed where the engine begins to

run irregularly.

An engine speed drop of 80 to 120 rpm between points should allow you to make 8 to 12

measurements from nmax down to nmin.



After finishing the mechanical losses measurement, release completely the load, as instructed in

§ 3.1. Switch off the engine when the temperature of the exhaust seems to be stabilizing.

3.3.3 - Influence of ignition timing at constant speed and throttle position – test (7)


compression ratio and carburettor setting to the required values. Decide which throttle position and

engine speed will be used for the test, and set the ignition timing to the maximum possible value.


take some minutes), set the load to the value that leads the engine to run (for the chosen throttle

position) at the chosen engine speed. Let the engine stabilize for this new running conditions (1 min,

say), and start the measurements. Start the measurement of the fuel consumption. While the time to

use one volume between spacers is being measured, measure all the values as indicated in § 3.3.1

(and do not forget the “60 s rule” for the fuel measurement).


condition. Decrease the ignition advance by 3º (say), and adjust the load to bring the engine speed

back to the prescribed value. Let the engine stabilize for this new condition (1 min, say), and start the

new measurements. Repeat this procedure down to the lowest value of ignition timing attainable or

stop if the engine begins to run irregularly.

A reduction of ignition timing around 3º between points should allow you to make 8 to 12

measurements from the maximum to the minimum of ignition timing.



After finishing the mechanical losses measurement, reset the ignition timing to around 20º and release

completely the load, as instructed in § 3.1. Switch off the engine when the temperature of the exhaust

seems to be stabilizing.

3.3.4 - Influence of air/fuel ratio at constant speed and throttle position – test (8)


compression ratio and ignition timing setting to the required values. Decide which throttle position and

engine speed will be used for the test, and set the carburettor setting to the maximum possible value.



position) at the chosen engine speed. Let the engine stabilize for this new running conditions (1 to

2 min, say), and start the measurements. Start the measurement of the fuel consumption. While the

time to use one volume between spacers is being measured, measure all the values as indicated in

§ 3.3.1 (and do not forget the “60 s rule” for the fuel measurement).


condition. Decrease the carburettor setting and adjust the load to bring the engine speed back to the

prescribed value. Let the engine stabilize for this new condition (1 min, say), and start the new

measurements. Repeat this procedure down to the lowest value of carburettor setting attainable or


10

- Engine testing -

Note that the variation of λ with the position of the needle valve of the carburattor (i.e., the carburettor

setting) is clearly non-linear. Hence, it is advisable to reduce that setting by smaller and smaller

amounts from the maximum (probably 10) to the minimum (it depends a lot on the engine speed, load,

ignition timing, and compression ratio chosen, but a value around 0.5 can be expected). Make 8 to 12

measurements from the maximum to the minimum value.



After finishing the mechanical losses measurement, reset the carburettor setting to around 2.5 and

release completely the load, as instructed in § 3.1. Switch off the engine when the temperature of the

exhaust seems to be stabilizing.

3.3.5 - Influence of compression ratio at constant speed and throttle position – test (9)


carburettor and ignition timing settings to the required values. Decide which throttle position and

engine speed will be used for the test, and set the compression ratio to the maximum possible value.



position) at the chosen engine speed. If the engine starts to knock heavily, reduce the

compression ratio until it no longer knocks. Let the engine stabilize for this new running conditions

(1 min, say), and start the measurements. Start the measurement of the fuel consumption. While the

time to use one volume between spacers is being measured, measure all the values as indicated in

§ 3.3.1 (and do not forget the “60 s rule” for the fuel measurement).


condition. Decrease the compression ratio and adjust the load to bring the engine speed back to the

prescribed value. Let the engine stabilize for this new condition (1 min, say), and start the new

measurements. Repeat this procedure down to the lowest value of the compression ratio attainable or


A reduction of the compression ratio of around 0.5 between points should allow you to make 8 to 12

measurements.



After finishing the mechanical losses measurement, reset the compression ratio to around 8.5 and

release completely the load, as instructed in § 3.1. Switch off the engine when the temperature of the

exhaust seems to be stabilizing.

4 - Data processing

NOTES - The general formulae necessary is not given in this Guide. The students are supposed to

know them. Only the particular formulae concerning the test benches will be given here.

The nomenclature used is the one used in the notes of Mendes-Lopes in the ICE course.

4.1 - General calculations

Calculate de engine cylinder capacity and the mean piston speed for the engine speed of your test

(except in test n. 5 - in this case calculate the minimum and maximum mean piston speed used).

Usually, engine tests are performed according to a specified standard (e.g. DIN 70 020, ISO 1585,

SAE J 1349), and that standard specifies a correction for effective power and torque to take into

account the differences between the atmospheric conditions of the actual test and those defined in the

standard. The test that you performed is does not comply with any standard, but nevertheless it is

11


interesting to check the value of the correction if it did. Assuming, for example, that the standard was

DIN 70 020, the specified absolute pressure is refp = 0.1013 MPa, the temperature is refT = 293 K,

the correction for pressure is testref ppA /= , the one for temperature is reftest TTB /= , and the

correction for power is 5.0BA .

Calculate the corrections A and B0.5

and the overall correction for power.

4.2 - Diesel engine


Comply with the calculations indicated in § 4.1.

For each point that you measured, do the following calculations:

−−−− from the characteristics of the De Prony brake (b = 1.200 m and W = 73.5 N) and of the

weight used (F) calculate the engine brake torque eB (the engine effective torque) – eq. 1;

−−−− calculate the engine brake power eP (effective power);

−−−− calculate the mean effective pressure ep (bmep);

−−−− from the volume of the fuel (100.0 or 250.0 cm3) and time ∆t measured, as well as from the

fuel density fuρ calculate the hourly fuel consumption hC ;

−−−− calculate the specific brake fuel consumption eC (bsfc or specific effective fuel consumption);

−−−− from the hourly fuel consumption hC and the mean effective pressure ep calculate the mean

pressure of mechanical losses mp by the method of Willan (or from hC and eP calculate

the power of mechanical loss mP );

−−−− calculate mP (or calculate mp );

−−−− calculate the mean indicated pressure ip and the indicated power iP ;

−−−− calculate the mechanical efficiency mη ;

−−−− calculate the engine’s efficiency eη ;

−−−− calculate the indicated efficiency iη ;

−−−− assume a value for the volumetric efficiency vη (the same for all points, or varying with load

– justify your option), and from that(those) value(s) calculate am& ;

−−−− from am& and hC calculate λ. From the value of λ evaluate your choice of vη . Correct it if

necessary until you feel that the pair (λ, vη ) is acceptable.

If there is anything else that you believe that should be calculated, do it !


The calculations are exactly the same as those referred to in § 4.2.1.




From the values of F measured for the mechanical losses (motoring method – dragged engine),

calculate the mechanical losses power Pm (eq. 4) and define a curve of Pm vs throttle position. From

that curve extract the values of Pm corresponding to each throttle position that you used when the

engine was running.

12

- Engine testing -

For each point that you measured, do the following calculations:

−−−− from the characteristics of the brake and the force F measured with a dynamometer

calculate the engine brake torque eB (the engine effective torque) – eq. 3;

−−−− calculate the engine brake power eP (effective power) – eq. 4;

−−−− calculate the mean effective pressure ep (bmep);

−−−− from the volume of the fuel used and time ∆t measured, as well as from the fuel density fuρ

calculate the hourly fuel consumption hC ;

−−−− calculate the specific brake fuel consumption eC (bsfc or specific effective fuel consumption);

−−−− although the Willan method is very questionable when engine load is controlled by throttling

of the air, use it nonetheless, and compare its single result (constant mechanical losses) with

the mean value of mechanical losses that you obtained with the motoring method. Hence,

from the hourly fuel consumption hC and the power eP calculate the power of mechanical

loss mP by the Willan method. From that comparison, decide whether to use the single value

of the Willan method or the curve from the motoring method (and justify your decision !) and

stick to your decision

−−−− calculate mp (from the mP that you decided to use);

−−−− calculate the mean indicated pressure ip and the indicated power iP ;

−−−− calculate the mechanical efficiency mη ;

−−−− calculate the engine’s efficiency eη ;

−−−− calculate the indicated efficiency iη ;

−−−− from the characteristics of the air consumption meter and the ∆p measured calculate the air

flow rate am& ;

−−−− calculate de volumetric efficiency vη

−−−− calculate λ ;

−−−− from the water flow rate am& and the in and out temperatures of the cooling water calculate

the power removed by the cooling system coolingP ;

−−−− from the fuel and the air flow rates, respectively hC and am& , the exhaust and ambient

temperatures exhT and ambT , calculate the heat power lost through the exhaust exhP ;

−−−− from eP , coolingP , exhP , and the energy per unit time introduced into the engine ( LHVCh

3600),

calculate the power that was not accounted for closureP (closure term).




From the values of F measured for the mechanical losses (motoring method – dragged engine),

calculate the mechanical losses power Pm (eq. 4) and define a curve of Pm vs n. From that curve

extract the values of Pm corresponding to each engine speed that you used when the engine was

running.

For each point that you measured, do the calculations mentioned in § 4.3.1, with the following

exception:

−−−− do not use the Willan method. Stick to the values of Pm extracted from the curve mentioned

just above.


13




It is assumed that mechanical losses do not vary with ignition advance (or that their variation can be

neglected compare with the precision of the experimental measurements in your test). Hence, you

measured just one value F. If you measured more than one, use an averaged value of your

measurements. From the value of F measured (by the motoring method – dragged engine), calculate

the mechanical losses power Pm (eq. 4).


exception:

−−−− do not use the Willan method. Stick to the value of Pm mentioned just above;

−−−− from coolingP , exhP ,and closureP compute the correspondent energy losses per cycle coolingE ,

exhE ,and closureE .




It is assumed that mechanical losses do not vary with the air / fuel ratio (or that their variation can be

neglected compare with the precision of the experimental measurements in your test). Hence, you

measured just one value F. If you measured more than one, use an averaged value of your

measurements. From the value of F measured (by the motoring method – dragged engine), calculate

the mechanical losses power Pm (eq. 4).


exception:

−−−− do not use the Willan method. Stick to the value of Pm mentioned just above.




It is assumed that mechanical losses almost do not vary with the compression ratio (or that their

variation can be neglected compare with the precision of the experimental measurements in your test).

Hence, you measured just one value F. If you measured more than one, use an averaged value of

your measurements. From the value of F measured (by the motoring method – dragged engine),

calculate the mechanical losses power Pm (eq. 4).


exception:

−−−− do not use the Willan method. Stick to the value of Pm mentioned just above;

−−−− for each compression ratio assume an average temperature of the entire cycle (justify your

options), and a corresponding value for γ, and calculate then the efficiency of the ideal cycle

idη ;

−−−− calculate the efficiency of implementation of the indicated cycle ψ.


14

- Engine testing -

5 - Presentation and discussion of the results

5.1 - General considerations

Present all the data on the engine (including what is referred to in § 4.1), on the fuel, and on the

ambient conditions.

Present a table with all the measured (unprocessed !) values (including, when applicable, throttle

position, ignition advance, carburettor setting, compression ratio, for the SI tests).

Present a table with all the processed results (as defined in § 4.2 or § 4.3). Include in that table the

single values that you obtained and considered constant for all the points (e.g. mechanical losses –

except in test 5, and, depending on your decision, test 4).

Having processed the date (§ 4) you should consider how to present the results in order to extract as

much relevant information as possible from your test. That presentation should highlight the engine

performance and how that performance is affected by the variations imposed. Coherence in the

results should be shown up, and whenever incoherencies are present they should be discussed and

an explanation (or tentative explanation) should be presented.

Comply with the requests in § 5.2 or § 5.3, but feel free to add whatever you believe may help to

achieve the objectives expressed in § 1 (in particular the objective b)).

You should present the diagrams requested in § 5.2 or § 5.3 (and others, as just mentioned). In those

diagrams:

−−−− represent all the points that you measured and/or processed, including those that you believe

are subjected to errors;

−−−− draw a smooth curve that you feel that best describes the tendency shown by your results.

That curve should not consider the points that you believe not to be correct.

Note – there are usually four options to present points and the corresponding curve, as

shown in figure 23. Although they are all valid and the best choice depends on the objectives

of the diagram and of the document that the diagram is included in, in this report you are

requested to use option D of the figure:

0.0

1.0

2.0

3.0

4.0

0 10 20 30 40

incorrect value

0.0

1.0

2.0

3.0

4.0

0 10 20 30 40

incorrect value

0.0

1.0

2.0

3.0

4.0

0 10 20 30 40

incorrect value

0.0

1.0

2.0

3.0

4.0

0 10 20 30 40

incorrect value

A – No line B – Straight line linking all points

C – Smooth line through all points

D – Trend line of the correct points

Fig. 23 – Four options to represent points and corresponding curve

In your test identify the most important numerical results, and state them wherever you believe it is

appropriate (abstract and/or discussion of results and – specially – conclusions). Here are some

examples (list not exhaustive and not applicable to all tests):

−−−− maximum value of pe measured and the corresponding eC ;

−−−− value of engine speed or of ignition advance or of λ or of rc that led to the maximum value of

pe measured and the corresponding eC ;

−−−− value of engine speed or of ignition advance or of λ or of rc that led to the minimum value of

eC measured and the corresponding pe;

−−−− value of pe measured at the smoke limit;

−−−− … (etc, etc, etc – this list is just an example).

15


5.2 - Diesel engine


Comply with the instructions in § 5.1.

Present the following diagrams:

−−−− hC and iη vs ep . In that diagram draw the line that allowed you to obtain mp ;

−−−− eC and eη vs ep ;

−−−− iη , eη and mη vs ep . Use an appropriate scale for iη , eη and another for mη ;

−−−− vη vs ep if you did not consider vη constant;

−−−− ep vs λ ;

−−−− exhaustT vs ep .

Explain/justify the various curves of the diagrams. Justify your decision on the assumed variation

of vη vs ep .

Explain the relation between the curve iη vs ep and the points of hC vs ep that you used in the

Willan method.

Compare/discuss/justify the relation between the curves of eC and of eη , both as a function of ep .

Compare/discuss/justify the relation between the curves of iη , of eη , and of mη , all three as a

function of ep .

Describe you sensations concerning the noise, heat, vibrations, etc, of the engine, in particular how

they changed with the variation of load.

Add whatever you believe to be worthwhile mentioning about the engine performance and how this

was influenced by the load.


The instructions are exactly the same as those referred to in § 5.2.1 with the following difference: in

each diagram add the curve(s) corresponding to the engine working with the correct injection

advance. The values of a test equivalent of yours with the correct injection advance will be given to

you by the lecturer.

As in test 2 explain/justify the various curves of the diagrams, but put special emphasis on the

comparison and explanation of the differences between each curve of the test with the retarded

injection and the corresponding curve of the test with the correct injection advance.





−−−− ep and vη vs positionthrottle

−−−− hC and iη vs ep . In that diagram draw the line that allowed you to obtain mp ;

−−−− eC and eη vs ep ;

−−−− eC and hC vs ep ;

−−−− iη , eη and mη vs ep . Use an appropriate scale for iη , eη and another for mη ;

−−−− vη vs ep ;

16

- Engine testing -

−−−− λ vs ep ;

−−−− coolingP , exhP , and closureP vs ep ;

−−−− exhaustT vs ep .

Explain/justify the various curves of the diagrams. Note that in your test λ was not a function of

ep , and, ideally, it should have been constant. Most likely it has not. When discussing the points

calculated and the curves, consider the values of λ for each specific point. Deviations of λ from a

constant value may help (or not !) to understand deviations of the points from expected values.

Explain the relation between the curve iη vs ep and the points of hC vs ep that you used in the

Willan method.

Compare/discuss/justify the relation between the curves of eC and of eη , both as a function of ep .


function of ep .

Compare/discuss the curves of coolingP , exhP , and closureP , and comment on their values (comparing

them also with eP ).








−−−− mp vs n . Include the curve that you used to compute the mechanical losses for the entire

engine speed range (most likely it had to be extrapolated, both to lower and higher engine

speeds);

−−−− mp and mP vs n . Represent now not the values that you obtain from mF but those that you

obtained from the curve mentioned just above;

−−−− ep and eP vs n ;

−−−− eC and eη vs n;

−−−− eC and hC vs n;

−−−− iη , eη and mη vs n. Use an appropriate scale for iη , eη and another for mη ;

−−−− vη vs n;

−−−− λ vs n;

−−−− coolingP , exhP , and closureP vs n;

−−−− coolingE , exhE ,and closureE vs n;

−−−− exhaustT vs n.

Explain/justify the various curves of the diagrams. Note that in your test λ was not a function of n,

and, ideally, it should have been constant. Most likely it has not. When discussing the points

calculated and the curves, consider the values of λ for each specific point. Deviations of λ from a

constant value may help (or not !) to understand deviations of the points from expected values.

Explain the expected relation between mp and n, and justify the curve that, taking into account the

values of mF that you measured, you used to assign the values of mp to each point of the test.

17



function of n.



Compare/discuss the curves of coolingE , exhE ,and closureE , and compare their evolution with n with

the corresponding evolution of coolingP , exhP , and closureP .


they changed with the variation of speed.






−−−− ep vs advanceignition

−−−− eC and eη vs advanceignition ;

−−−− eC and hC vs advanceignition ;

−−−− iη , eη and mη vs advanceignition . Use an appropriate scale for iη , eη and another for

mη ;

−−−− vη vs advanceignition ;

−−−− λ vs advanceignition ;

−−−− coolingP , exhP , and closureP vs advanceignition ;

−−−− exhaustT vs advanceignition .


the ignition advance, and, ideally, it should have been constant. Most likely it has not. When

discussing the points calculated and the curves, consider the values of λ for each specific point.

Deviations of λ from a constant value may help (or not !) to understand deviations of the points from

expected values.

Compare/discuss/justify the relation between the curves of eC and of eη .


function of the ignition advance.










−−−− λ vs settingrcarburatto

−−−− ep vs λ

18

- Engine testing -

−−−− eC and eη vs λ;

−−−− eC and hC vs λ;

−−−− iη , eη and mη vs λ. Use an appropriate scale for iη , eη and another for mη ;

−−−− vη vs λ;

−−−− coolingP , exhP , and closureP vs λ;

−−−− exhaustT vs λ.

Explain/justify the various curves of the diagrams.



function of the ignition advance.










−−−− ep e eP vs cr

−−−− eC and eη vs cr ;

−−−− eC and hC vs cr ;

−−−− idη , ψ and iη vs cr . Use appropriate scales for these efficiencies;

−−−− iη , eη and mη vs cr . Use an appropriate scale for iη , eη and another for mη ;

−−−− vη vs cr ;

−−−− λ vs cr ;

−−−− coolingP , exhP , and closureP vs cr ;

−−−− exhaustT vs cr .


the compression ratio, and, ideally, it should have been constant. Most likely it has not. When

discussing the points calculated and the curves, consider the values of λ for each specific point.

Deviations of λ from a constant value may help (or not !) to understand deviations of the points from

expected values.


Compare/discuss/justify the relation between the curves of idη , of ψ and of iη , all three as a

function of the compression ratio.


function of the compression ratio.



19






6 - Notes on the report

The purpose of the report is the usual for all technical reports relating to experimental studies.

However, this one should give special emphasis to the explanation and interpretation of the verified

and measured performance of the engine.

The structure may vary slightly. For this report, one possibility is the following:

� Summary - short text (max. 300 words) stating the objectives of the test, type of

experimental setup used, experiments carried out, most relevant results and conclusions of a

more general nature.

� Index

� Notation - only if the students think is it justified, which depends on the number of variables,

acronyms, etc. used. If presented, Notation should indicate the Roman characters, followed

by Greek characters, indexes, and abbreviations or acronyms. Within each of these

categories alphabetical order of the characters presented should be used.

� Introduction (or Introduction and objectives) - short text putting the subject of the work in

context and/or defining the objectives of the work.

� Experimental set-up - brief description of the rig. Detailed descriptions are not needed –

the goal is to give the reader an idea of the type of installation used. The reader can then be

directed to this guide for details. In any case, if the student believes that there is(are) some

detail(s) that is(are) worth mentioning, he/she should draw attention to it(them).

� Experimental procedure - ditto.

� Experimental results - presentation of data on the experimental set-up, ambient conditions,

fuel properties, etc.. Presentation in a table of the measured values for each experimental

condition (points should be numbered). Presentation, in one or more tables, of the values

calculated for each experimental condition (points numbered, maintaining the correspondence

with the table of measured values). Presentation of the results in graphical.

� Discussion of results - discussion of the results (in line with what is indicated in § 5).

� Conclusion - a brief (!) conclusion, both with regard to the objectives of the work and to the

more noteworthy results.

� Bibliography

� Acknowledgements - only if justified

Note - if the student wishes and feel that this is justified, he/she can (should !) include a critical

appraisal of the experimental setup, procedure, etc., and suggestions for improvement. This appraisal

should be placed where this is more appropriate: "Experimental Setup", "Procedure", "Results ...",

"Conclusion" (but in this case it should be a very short text), or in a specific section.

JMC Mendes-Lopes

October 2012

20

- Engine testing -

Annex

Characteristics of the Deutz Diesel engine

Bore = 190 mm

Stroke = 320 mm

Compression ratio = - (unknown)

Maximum engine speed = 450 rpm (currently).

Characteristics of the Peter-Plint W1 engine

Demonstration and instructional engine - spark ignition, naturally aspirated, 4-stroke, side valve,

water-cooled, variable compression ratio, single cylinder engine.

Bore = 85.0 mm

Stroke = 82.5 mm

Compression ratio = variable between 4.0 and 10.0

Maximum engine speed = 2500 rpm (currently restricted to 2000 rpm).

Properties of the fuels

Diesel fuel (light)

Formula = CnH1.7n

CnH1.8n

Molecular

weight

≈ 148 to 170

kg·kmol-1

Density

(liquid)

≈ 0.72 to 0.78

kg·dm-3

UHV = 46.1 MJ·kg1 LHV = 43.2 MJ·kg

1 (A/F)s m ≈ 14.5

Gasoline

Formula = CnH1.69n

CnH1.88n

Molecular

weight

≈ 106 to 115

kg·kmol-1

Density

(liquid)

≈ 0.78 to 0.84

kg·dm-3

UHV = 47.3 MJ·kg1 LHV = 44.0 MJ·kg

1 (A/F)s m ≈ 14.6

Properties of water

T (ºC) 20 30 40 50 60 70 80

ρ (kg·dm-3

) 0.9982 0.9957 0.9922 0.9881 0.9832 0.9778 0.9718

cp (kJ·kg-1

K-1

) 4.1787 4.1755 4.1756 4.1774 4.1810 4.1864 4.1935

Properties of the air

See psychometric diagram in the next sheet (for patm = 1.01325 bar)

21


Psychometric diagram

0 5 10 15 20 25 30 35 40 45 50

temperatura (ºC)

0

4

8

12

16

20

24

28

32

hu

mid

ad

e e

sp

ecífic

a (g

ág

ua kg

-1ar

seco)

100 %

90

80

70

60

50

40

30

20

10

0,800 m3 kg-1

0,825 m3 kg-1

0,850 m3 kg-1

0,875 m3 kg-1

0,900 m3 kg-1

0,925 m3 kg-1

p = 1,01325 bar

22

- Engine testing -

INTERNAL COMBUSTION ENGINES

Test of the Deutz Diesel engine

Test N. ___________ Date : _______________ Report due : _______________

Engine → Bore: 190 mm Stroke: 320 mm N. of cylinders : 1

Fuel → ρ : ___________________ LHV : _______________________

Injection advance : _____________________

Engine speed : _________________________

Air → Initial T = ______________ p = ______________ RH = _____________

Final T = ______________ p = ______________ RH = _____________

Point N. F

(kg)

Volume of fuel

(cm3)

∆t

(s)

n

(rpm)

Texh

(ºC)

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

Value of F at the appearance of black smoke : ________________

INTERNAL COMBUSTION ENGINES

Test of the Peter-Plint W1 engine

Test N. ___________ Date : _______________ Report due : _______________

Engine → Bore: 85.0 mm Stroke: 82.5 mm N. of cylinders : 1 Fuel → ρ : ___________________ LHV : ___________________

Air → Initial T = ______________ p = ______________ RH = _____________

Final T = ______________ p = ______________ RH = _____________

Point N. Throttle

position rc

Ignition

advance

(CAD)

Carb.

setting

F

(N)

Volume

of fuel

(cm3)

∆t

(s)

N. of

rotations

∆pair

(Pa)

Water

flow rate

(l⋅min-1

)

Twater in

(ºC)

Twater out

(ºC)

Texh

(ºC)

Fm

(N)

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

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