1
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.
Fig. 1 - Diesel engine
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. 2 - Pre-chamber, valves, and injector
- Internal Combustion Engines -
2
engine speed is kept constant.
Hourly fuel consumption C h is measured by measuring
the time needed to consume a given volume of fuel and
knowing the fuel’s density ρ f . 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
3
3
100.0 cm and 250.0 cm .
There is no equipment available to measure gas flow
&a
rates (air or exhaust). Nevertheless, the air flow rate m
can be easily estimated by assuming a value for the
volumetric efficiency η v .
Figs. 3 & 4 – Densimeter and fuel
measuring system
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. 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
drum
wooden
stripe with a series of wooden brake blocks.
brake
stripe
blocks
lever
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
b
certain limits, but when it is steady, the torque
F
wheel
of the friction force between the wooden brake
blocks and the drum is balanced by the
Fig. 6 – De Prony Brake
moment of the lever. The determination of this
moment allows the torque at the drum to be known, and that torque is the engine brake torque Be .
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
Be = b (F + W )
(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 Be 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.
- Engine testing -
Fig. 7 - Tachometer
3
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
- Internal Combustion Engines -
4
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 C h is measured by
measuring the time needed to consume a given
volume of fuel and knowing the fuel’s density ρ f .
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
3
3
between them is 25.0 cm , 25.0 cm , and
3
50.0 cm .
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
& a can be computed:
flow rate m
- Engine testing -
5
&a = AK
m
2 ∆p
RT
= 4.472 10 −3
p
∆p
T
p
(2)
& a in kg·s-1, ∆p and p in Pa, and T in K.
with m
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).
Fig. 17 – Exhaust temperature
display
Figs. 19 & 20 – DC electrical generator and electrical resistances
Fig. 18 – DC electric brake
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:
B e = 0.265 F
Pe =
Fn
36.04
(3)
(4)
with Be in N·m, F in N, Pe 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. 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.
- Internal Combustion Engines -
6
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.
- Engine testing -
7
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
23 kg f (≈ 225 N) or 24 kg f (≈ 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 21 kg f (≈ 206 N) or 22 kg f (≈ 216 N).
3.3 - Spark ignition engine
3.3.1 - Influence of load at constant speed – test (4)
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
-1
the water flow rate. Regulate the flow rate to a value in the range of 1.7 to 2.3 l·min . Check the
reading of the water thermometers (the outlet one may prove to be tricky to read). Check the reading
- Internal Combustion Engines -
8
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.
measurements in that interval.
Decide how to distribute those 8 to 12
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)
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 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
- Engine testing -
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 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 seems to be stabilizing.
3.3.3 - Influence of ignition timing at constant speed and throttle position – test (7)
Start the test complying with the initial description in § 3.1. The lecturer will have already set the
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.
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 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).
After resetting the counter and chronometer values to zero, immediately set the engine to a new
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 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, 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)
Start the test complying with the initial description in § 3.1. The lecturer will have already set the
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.
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 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 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).
After resetting the counter and chronometer values to zero, immediately set the engine to a new
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
stop if the engine begins to run irregularly.
- Internal Combustion Engines -
10
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 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, 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)
Start the test complying with the initial description in § 3.1. The lecturer will have already set the
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.
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 the value that leads the engine to run (for the chosen throttle
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).
After resetting the counter and chronometer values to zero, immediately set the engine to a new
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
stop if the engine begins to run irregularly.
A reduction of the compression ratio of around 0.5 between points should allow you to make 8 to 12
measurements.
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, 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
- Engine testing -
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 pref = 0.1013 MPa, the temperature is Tref = 293 K,
the correction for pressure is A = pref / ptest , the one for temperature is B = Ttest / Tref , and the
correction for power is A B0.5 .
0.5
Calculate the corrections A and B
and the overall correction for power.
4.2 - Diesel engine
4.2.1 - Influence of load at constant speed – test (2)
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 Be (the engine effective torque) – eq. 1;
−
calculate the engine brake power Pe (effective power);
−
calculate the mean effective pressure p e (bmep);
−
from the volume of the fuel (100.0 or 250.0 cm ) and time ∆t measured, as well as from the
fuel density ρ fu calculate the hourly fuel consumption C h ;
−
calculate the specific brake fuel consumption C e (bsfc or specific effective fuel consumption);
−
3
from the hourly fuel consumption C h and the mean effective pressure p e calculate the mean
pressure of mechanical losses p m by the method of Willan (or from C h and Pe calculate
the power of mechanical loss Pm );
−
calculate Pm (or calculate p m );
−
calculate the mean indicated pressure p i and the indicated power Pi ;
−
calculate the mechanical efficiency η m ;
−
calculate the engine’s efficiency η e ;
−
calculate the indicated efficiency η i ;
−
assume a value for the volumetric efficiency η v (the same for all points, or varying with load
&a;
– justify your option), and from that(those) value(s) calculate m
−
& a and C h calculate λ. From the value of λ evaluate your choice of η v . Correct it if
from m
necessary until you feel that the pair (λ, η v ) is acceptable.
If there is anything else that you believe that should be calculated, do it !
4.2.2 - Influence of load at constant speed with retarded injection – test (3)
The calculations are exactly the same as those referred to in § 4.2.1.
4.3 - Spark ignition engine
4.3.1 - Influence of load at constant speed – test (4)
Comply with the calculations indicated in § 4.1.
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.
- Internal Combustion Engines -
12
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 Be (the engine effective torque) – eq. 3;
−
calculate the engine brake power Pe (effective power) – eq. 4;
−
calculate the mean effective pressure p e (bmep);
−
from the volume of the fuel used and time ∆t measured, as well as from the fuel density ρ fu
calculate the hourly fuel consumption C h ;
−
calculate the specific brake fuel consumption C e (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 C h and the power Pe calculate the power of mechanical
loss Pm 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 p m (from the Pm that you decided to use);
−
calculate the mean indicated pressure p i and the indicated power Pi ;
−
calculate the mechanical efficiency η m ;
−
calculate the engine’s efficiency η e ;
−
calculate the indicated efficiency η i ;
−
from the characteristics of the air consumption meter and the ∆p measured calculate the air
&a ;
flow rate m
−
calculate de volumetric efficiency η v
−
calculate λ ;
−
& a and the in and out temperatures of the cooling water calculate
from the water flow rate m
the power removed by the cooling system Pcooling ;
−
& a , the exhaust and ambient
from the fuel and the air flow rates, respectively C h and m
temperatures Texh and Tamb , calculate the heat power lost through the exhaust Pexh ;
−
from Pe , Pcooling , Pexh , and the energy per unit time introduced into the engine (
Ch
LHV ),
3600
calculate the power that was not accounted for Pclosure (closure term).
If there is anything else that you believe that should be calculated, do it !
4.3.2 - Influence of engine speed for constant throttle position – test (5)
Comply with the calculations indicated in § 4.1.
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 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.
If there is anything else that you believe that should be calculated, do it !
- Engine testing -
13
4.3.3 - Influence of ignition timing at constant speed and throttle position – test (7)
Comply with the calculations indicated in § 4.1.
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).
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 value of Pm mentioned just above;
−
from Pcooling , Pexh ,and Pclosure compute the correspondent energy losses per cycle E cooling ,
E exh ,and E closure .
If there is anything else that you believe that should be calculated, do it !
4.3.4 - Influence of air/fuel ratio at constant speed and throttle position – test (8)
Comply with the calculations indicated in § 4.1.
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).
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 value of Pm mentioned just above.
If there is anything else that you believe that should be calculated, do it !
4.3.5 - Influence of compression ratio at constant speed and throttle position – test (9)
Comply with the calculations indicated in § 4.1.
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).
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 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
η id ;
−
calculate the efficiency of implementation of the indicated cycle ψ.
If there is anything else that you believe that should be calculated, do it !
- Internal Combustion Engines -
14
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:
4.0
4.0
4.0
incorrect value
4.0
incorrect value
incorrect value
incorrect value
3.0
3.0
3.0
3.0
2.0
2.0
2.0
2.0
1.0
1.0
1.0
1.0
0.0
0.0
0.0
0
10
20
A – No line
30
40
0
10
20
30
0.0
0
40
B – Straight line linking all
points
10
20
30
40
C – Smooth line through all
points
0
10
20
30
40
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 Ce ;
−
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 Ce ;
−
value of engine speed or of ignition advance or of λ or of rc that led to the minimum value of
Ce measured and the corresponding pe;
−
value of pe measured at the smoke limit;
−
… (etc, etc, etc – this list is just an example).
- Engine testing -
15
5.2 - Diesel engine
5.2.1 - Influence of load at constant speed – test (2)
Comply with the instructions in § 5.1.
Present the following diagrams:
−
C h and η i vs p e . In that diagram draw the line that allowed you to obtain p m ;
−
C e and η e vs p e ;
−
η i , η e and η m vs pe . Use an appropriate scale for η i , η e and another for η m ;
−
η v vs pe if you did not consider η v constant;
−
p e vs λ ;
−
Texhaust vs p e .
Explain/justify the various curves of the diagrams. Justify your decision on the assumed variation
of η v vs p e .
Explain the relation between the curve η i vs p e and the points of C h vs p e that you used in the
Willan method.
Compare/discuss/justify the relation between the curves of C e and of η e , both as a function of p e .
Compare/discuss/justify the relation between the curves of η i , of η e , and of η m , all three as a
function of p e .
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.
5.2.2 - Influence of load at constant speed with retarded injection – test (3)
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.
5.3 - Spark ignition engine
5.3.1 - Influence of load at constant speed – test (4)
Comply with the instructions in § 5.1.
Present the following diagrams:
−
p e and η v vs throttle position
−
C h and η i vs p e . In that diagram draw the line that allowed you to obtain p m ;
−
C e and η e vs p e ;
−
C e and C h vs p e ;
−
η i , η e and η m vs pe . Use an appropriate scale for η i , η e and another for η m ;
−
η v vs pe ;
- Internal Combustion Engines -
16
−
λ vs pe ;
−
Pcooling , Pexh , and Pclosure vs p e ;
−
Texhaust vs p e .
Explain/justify the various curves of the diagrams. Note that in your test λ was not a function of
p e , 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 η i vs p e and the points of C h vs p e that you used in the
Willan method.
Compare/discuss/justify the relation between the curves of C e and of η e , both as a function of p e .
Compare/discuss/justify the relation between the curves of η i , of η e , and of η m , all three as a
function of p e .
Compare/discuss the curves of Pcooling , Pexh , and Pclosure , and comment on their values (comparing
them also with Pe ).
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.
5.3.2 - Influence of engine speed for constant throttle position – test (5)
Comply with the instructions in § 5.1.
Present the following diagrams:
−
pm 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);
−
pm and Pm vs n . Represent now not the values that you obtain from Fm but those that you
obtained from the curve mentioned just above;
−
p e and Pe vs n ;
−
C e and η e vs n;
−
C e and C h vs n;
−
η i , η e and η m vs n. Use an appropriate scale for η i , η e and another for η m ;
−
η v vs n;
−
λ vs n;
−
Pcooling , Pexh , and Pclosure vs n;
−
E cooling , E exh ,and E closure vs n;
−
Texhaust 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 p m and n, and justify the curve that, taking into account the
values of Fm that you measured, you used to assign the values of p m to each point of the test.
- Engine testing -
17
Compare/discuss/justify the relation between the curves of η i , of η e , and of η m , all three as a
function of n.
Compare/discuss the curves of Pcooling , Pexh , and Pclosure , and comment on their values (comparing
them also with Pe ).
Compare/discuss the curves of E cooling , E exh ,and E closure , and compare their evolution with n with
the corresponding evolution of Pcooling , Pexh , and Pclosure .
Describe you sensations concerning the noise, heat, vibrations, etc, of the engine, in particular how
they changed with the variation of speed.
Add whatever you believe to be worthwhile mentioning about the engine performance and how this
was influenced by the load.
5.3.3 - Influence of ignition timing at constant speed and throttle position – test (7)
Comply with the instructions in § 5.1.
Present the following diagrams:
−
p e vs ignition advance
−
C e and η e vs ignition advance ;
−
C e and C h vs ignition advance ;
−
η i , η e and η m vs ignition advance . Use an appropriate scale for η i , η e and another for
ηm ;
−
η v vs ignition advance ;
−
λ vs ignition advance ;
−
Pcooling , Pexh , and Pclosure vs ignition advance ;
−
Texhaust vs ignition advance .
Explain/justify the various curves of the diagrams. Note that in your test λ was not a function of
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 C e and of η e .
Compare/discuss/justify the relation between the curves of η i , of η e , and of η m , all three as a
function of the ignition advance.
Compare/discuss the curves of Pcooling , Pexh , and Pclosure , and comment on their values (comparing
them also with Pe ).
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.
5.3.4 - Influence of air/fuel ratio at constant speed and throttle position – test (8)
Comply with the instructions in § 5.1.
Present the following diagrams:
−
λ vs carburattor setting
−
p e vs λ
- Internal Combustion Engines -
18
−
C e and η e vs λ;
−
C e and C h vs λ;
−
η i , η e and η m vs λ. Use an appropriate scale for η i , η e and another for η m ;
−
η v vs λ;
−
Pcooling , Pexh , and Pclosure vs λ;
−
Texhaust vs λ.
Explain/justify the various curves of the diagrams.
Compare/discuss/justify the relation between the curves of C e and of η e .
Compare/discuss/justify the relation between the curves of η i , of η e , and of η m , all three as a
function of the ignition advance.
Compare/discuss the curves of Pcooling , Pexh , and Pclosure , and comment on their values (comparing
them also with Pe ).
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.
5.3.5 - Influence of compression ratio at constant speed and throttle position – test (9)
Comply with the instructions in § 5.1.
Present the following diagrams:
−
p e e Pe vs r c
−
C e and η e vs r c ;
−
C e and C h vs r c ;
−
η id , ψ and η i vs r c . Use appropriate scales for these efficiencies;
−
η i , η e and η m vs r c . Use an appropriate scale for η i , η e and another for η m ;
−
η v vs r c ;
−
λ vs r c ;
−
Pcooling , Pexh , and Pclosure vs r c ;
−
Texhaust vs r c .
Explain/justify the various curves of the diagrams. Note that in your test λ was not a function of
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 C e and of η e .
Compare/discuss/justify the relation between the curves of η id , of ψ and of η i , all three as a
function of the compression ratio.
Compare/discuss/justify the relation between the curves of η i , of η e , and of η m , all three as a
function of the compression ratio.
Compare/discuss the curves of Pcooling , Pexh , and Pclosure , and comment on their values (comparing
them also with Pe ).
- Engine testing -
19
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.
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
- Internal Combustion Engines -
20
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)
CnH1.7n
Formula =
Molecular
weight
CnH1.8n
1
≈ 148 to 170
-1
kg·kmol
1
UHV = 46.1 MJ·kg
LHV = 43.2 MJ·kg
Density
(liquid)
≈ 0.72 to 0.78
kg·dm
-3
(A/F)s m ≈ 14.5
Gasoline
CnH1.69n
Formula =
Molecular
weight
CnH1.88n
1
≈ 106 to 115
-1
kg·kmol
1
UHV = 47.3 MJ·kg
LHV = 44.0 MJ·kg
Density
(liquid)
≈ 0.78 to 0.84
kg·dm
-3
(A/F)s m ≈ 14.6
Properties of water
T (ºC)
ρ (kg·dm-3)
-1
-1
cp (kJ·kg K )
20
30
40
50
60
70
80
0.9982
0.9957
0.9922
0.9881
0.9832
0.9778
0.9718
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)
- Engine testing -
21
Psychometric diagram
100 %
p = 1,01325 bar
0,900 m 3 kg-1
32
90
28
80
70
24
60
0,875 m 3 kg-1
50
20
40
0,850 m 3 kg-1
16
30
12
3
0,825 m kg
20
-1
8
0,800 m 3 kg-1
10
4
0
0
5
10
15
20
25
30
35
40
45
50
temperatura (ºC)
- Internal Combustion Engines -
humidade específica (g água kg-1ar seco)
0,925 m 3 kg-1
22
INTERNAL COMBUSTION ENGINES
Test of the Deutz Diesel engine
Test N. ___________
Date : _______________
Engine →
Bore: 190 mm
Stroke: 320 mm
Fuel →
ρ : ___________________
Report due : _______________
N. of cylinders : 1
LHV : _______________________
Injection advance : _____________________
Engine speed : _________________________
Air →
Initial
T = ______________
p = ______________
RH = _____________
Final
T = ______________
p = ______________
RH = _____________
Point N.
F
(kg)
Volume of fuel
3
(cm )
∆t
(s)
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 : ________________
- Engine testing -
n
(rpm)
Texh
(ºC)
INTERNAL COMBUSTION ENGINES
Test of the Peter-Plint W1 engine
Test N. ___________
Engine →
Air →
Point N.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Date : _______________
Bore: 85.0 mm
Stroke: 82.5 mm
N. of cylinders : 1
Fuel →
Initial
T = ______________
p = ______________
RH = _____________
Final
T = ______________
p = ______________
RH = _____________
Throttle
position
rc
Ignition
advance
(CAD)
Carb.
setting
F
(N)
Volume
of fuel
3
(cm )
∆t
(s)
N. of
rotations
∆pair
(Pa)
ρ : ___________________
Water
flow rate
-1
(l⋅min )
Twater in
(ºC)
Report due : _______________
LHV : ___________________
Twater out
(ºC)
Texh
(ºC)
Fm
(N)