1. Introduction. 2. Dynamometer.

1. Types of dynamometer.

2. Hydraulic dynamometer.

3. Sensors. 1. Sensors

properties. 2. Types of

sensors. 4. Other

measurements devices.

Chapter 5 Testing Apparatuses

5.1. Introduction:

Engine testing is very important to ensure that the

engine is operate correctly at high efficiency.

The classic engine test was essentially achieved by

mechanical engineer skills or by using simple device

and the engine failed was detected in obvious ways. A

few simple tests were enough to establish the source of

the difficulty. Newer engine test is achieved by

accurate devices which controlled by a computer.

Sensors provide the computer with data engine and

environmental conditions, then the computer deals with

C

H

A

P

T

E

R

5 Testing

Apparatuses

this data and shows it in numerical values or illustrates it in graphical chart.

There are many different apparatuses that are used in test engine experiment. These

apparatuses vary in function, properties and operation methods. This chapter discusses

these apparatuses and mentions their types, functions, operation methods and accessories.

5.2. Dynamometer:

A dynamometer is designed to control engine speed and torque through the process of

converting rotating mechanical energy from loaded output shaft of the test engine into

electrical or thermal energy. Engine power is calculated from the product of rotating

speed and the braking or driving torque seen by the dynamometer. For the measurement

of the engine's mechanical parasitic losses or for the simulation of road load dynamics,

dynamometers should not only be able to absorb the engine's power output but also to

drive the engine.

5.2.1. Types of dynamometer:

There are many types of dynamometers each type has specific characteristic. A

dynamometer for testing must include the following four essential elements:

A means for controlling torque.

A means for measuring torque.

A means for measuring speed.

A means for dissipating power.

The main types of dynamometer are:

Prony Brake

One of the simplest methods of measuring brake power (output) is to attempt to stop the

engine by means of a brake on the flywheel and measure the weight which an arm

attached to the brake will support, as it tries to rotate with the flywheel. This system is

known as the prony brake and forms its use; the expression brake power has come. The

Prony brake shown in Figure 5.1, works on the principle of converting power into heat by

Figure 5.1 Porny Brake.

Figure 5.2 Rope Brake.

dry friction. It consists of wooden block mounted on a flexible rope or band the wooden

block when pressed into contact with the rotating drum takes the engine torque and the

power is dissipated in frictional resistance. Spring-loaded bolts are provided to tighten the

wooden block and hence increase the friction. The whole of the power absorbed is

converted into heat and hence this type of dynamometer must the cooled. The brake

horsepower is given by:

Where, T = W l , W being the weight applied at a radius l.

Rope Brake

The rope brake as shown in Figure 5.2, is another

simple device for measuring BP of an engine. It

consists of a number of turns of rope wound around

the rotating drum attached to the output shaft. One

side of the rope is connected to a spring balance

and the other to a loading device. The power is

absorbed in friction between the rope and the

drum. The drum therefore requires cooling.

Rope brake is cheap and easily constructed but not

a very accurate method because of changes in the

friction coefficient of the rope with temperature.

The BP is given by

where, D is the brake drum diameter, W is the weight in Newton and S is the spring scale

reading.

Hydraulic Dynamometer

Hydraulic dynamometer shown in Figure

5.3, works on the principle of dissipating

the power in fluid friction rather than in dry

friction. More details about this type are

discussed later in this chapter.

Figure 5.3 Hydraulic Dynamometer.

Eddy-current Dynamometer

Eddy-current dynamometers are an absorbing

type dynamometer which converts internally

generating eddy current energy into heat. Eddy-

current dynamometers shown in Figure 5.4,

consist of a disc-type rotor and stator, which are

constructed in a way that are supported by

bearings set outside of cooling chambers. The

dynamometers are suitable for operation in both

directions of rotation with a wide range of power

absorption and control. Due to its ability to cover

a the wide range of applications from steady state

to transient test stands, it is used not only in the

engine development stage but also in various

engine assembly lines.

The working principle of eddy current dynamometer is shown in Figure 5.5. It consists of

a stator on which are fitted a number of

electromagnets and a rotor disc made of copper or

steel and coupled to the output shaft of the engine.

When the rotor rotates eddy currents are produced

in the stator due to magnetic flux set up by the

passage of field current in the electromagnets.

These eddy currents are dissipated in producing

heat so that this type of dynamometer also

requires some cooling arrangement. The torque is

measured exactly as in other types of absorption

dynamometers, i.e. with the help of a moment

arm. The load is controlled by regulating the

current in the electromagnets.

Fan Dynamometer

It is also an absorption type of dynamometer in that when driven by the engine it absorbs

the engine power. Such dynamometers are useful mainly for rough testing and running in.

The accuracy of the fan dynamometer is very poor. The power absorbed is determined by

using previous calibration of the fan brake.

Transmission Dynamometers

Transmission dynamometers, also called torque meters, mostly consist of a set of strain-

gauges fixed on the rotating shaft and the torque is measured by the angular deformation

of the shaft which is indicated as strain of the strain gauge. Usually, a four arm bridge is

used to reduce the effect of temperature to minimum and the gauges are arranged in pairs

Figure 5.4 Eddy-current Dynamometer

Figure 5.5 working principle of Eddy-current

Dynamometer

such that the effect of axial or transverse load on the strain gauges is avoided. Figure

5.6, shows a transmission dynamometer which employs beams and strain-gauges for a

sensing torque. Transmission dynamometers are very accurate and are used where

continuous transmission of load is necessary. These are used mainly in automatic units.

Tandem Dynamometer

Tandem Dynamometers shown in Figure 5.7, are the combination of an absorbing type of

dynamometer such as a hydraulic dynamometer or eddy-current dynamometer and an

electrical machine dynamometer such as an AC dynamometer. With their large absorbing

power, Tandems characteristics include lower inertia, high speed and high torque.

Consequently, they are suitable for heavy duty engine testing for engines larger than

500kW.

Figure 5.6 transmission dynamometer.

Figure 5.7 Tandem Dynamometer

5.2.2. Hydraulic dynamometer:

The water brake absorber is sometimes mistakenly called a "hydraulic dynamometer".

Invented by British engineer William Froude in 1877 in response to a request by the

Admiralty to produce a machine capable of absorbing and measuring the power of large

naval engines, water brake absorbers are relatively common today. They are noted for

their high power capability, small size, light weight, and relatively low manufacturing

costs as compared to other, quicker reacting, "power absorber" types.

Their drawbacks are that they can take a relatively long period of time to "stabilize" their

load amount, and that they require a constant supply of water to the "water brake

housing" for cooling. In many parts of the country, environmental regulations now

prohibit "flow through" water, and so large water tanks must be installed to prevent

contaminated water from entering the environment. (Wikipedia is a registered

trademark of the Wikimedia Foundation, Inc., a non-profit organization.)

For more than a century hydraulic dynamometers have been used as power absorbers

for engine test purposes. Development work has been mainly experimental, although

much theoretical work has been done on the closely related fluid coupling and fluid

torque converter.

This latter work has been predominantly on the prediction of steady state performance

maps. As transient testing has increased with the requirements of exhaust emissions

driving cycle tests and the advent of computer control, the dynamic characteristics

of the dynamometer must be studied more closely. particularly the phenomenon of

self-emptying in open loop control mode. From this study the control requirements

around the operating envelope can be determined.((2)) (Hodgson, 1991)

The hydraulic dynamometer operates like a hydraulic turbine/pump. The working

medium, usually water, is circulated within the housing creating frictional resistance to

turbine rotation.

Basic Parts of Hydraulic Dynamometer

The basic parts of hydraulic dynamometer are:

1) Stator

2) Rotor

3) Casing

4) Strain Gauge Load Cell

5) Coupling

6) Water Outlet Valve

7) Water inlet

8) Flow Straightener

Principle of working

An hydraulic dynamometer has a working compartment shaped as an elliptic torus

containing two sets of oppositely angled vanes. One set is mounted on a rotor driven

by the engine under test, the other on the stator which is held stationary by the

machine casing. These can be seen in Figure 5.8, illustrating typical Froude F type

machine internals with water outlet holes are at the back of the rotor cups and the

drain annulus between the rotor backs. The double sided rotor eliminates axial thrust

loading. There are holes in the stator vanes to allow water inflow and atmospheric

air venting. later machines have the outlet holes in the stator cup for greater

hydrodynamic stability. When rotating. the rotor vanes pump the fluid from the

inner radius to the outer radius where it passes into the stator. From here it flows

from the outer to the inner radius of the stator transmitting torque and returning to

the inner radius of the rotor. This circuit flow is superimposed on the rotational flow

resulting in a helical flow path, as illustrated in Figure 5.9. Passing of the vanes

disturbs this ideal flow pattern, generating turbulence. This combined with wall

friction, fluid friction, incidence losses between rotor and stator, and eddies caused

by the curved flow path. results in power being transferred to the internal energy of

the working fluid. Hence it is necessary to maintain a sufficient fluid through-flow

to limit the resultant temperature rise.

Figure 5.8 components of hydraulic dynamometer.

The amount of torque produced by the machine is usually adjusted by either the use

of a sluice gate between rotor and stator to reduce the area for fluid mass transfer, or

by reducing the mass of fluid in the working compartment. Due to their superior

transient response and reduced bulk, variable fill machines have superseded the sluice

gate variety. The higher torque capacity to rotational inertia ratio of variable fill

dynamometers also makes their performance superior to most electrical dynamometers

in transient testing.

However when running under open-loop control the variable fill dynamometers

display a torque characteristic. Initially torque increases with speed, but the pressure

generated in the working compartment increases rapidly with speed until the fluid

outflow rate is greater than the inflow and the machine begins emptying. As the

volume of fluid in the working compartment is only a small fraction of the through-

flow, a small difference in flow rates can produce dramatic effect on the torque

developed. At higher speeds the torque begins increasing again, but this is shown

later to be a dynamic effect of the machine accelerating and the rate of emptying

decreasing, rather than increasing fluid fill.

When this characteristic is combined with a typical engine torque curve. as in Figure

5.10, the resultant problems become apparent.

Figure 5.9 water flow path.

At set point A, where the torque gradient is greater for the dynamometer, a positive

engine torque perturbation would increase the speed resulting in a greater

dynamometer torque increase. which would slow the system back towards the set

point. That is, the combination is self-correcting. Where the dynamometer gradient is

more negative. for example set point B, the increase in speed leads to decreased

dynamometer torque, thus augmenting the accelerating torque and moving the system

away from the desired set point.

Similarly, a negative torque perturbation leads to a decrease in system speed, an

increase in dynamometer torque, and possible engine stall Hence an increasing torque

characteristic is desirable.

There are two methods of overcoming this problem; increase water inflow rate as

speed increases, or provide rapidly increasing resistance to water outflow as speed

increases. The former method involves: an inlet valve, which is controlled by rotor

speed; or, an electrical or mechanical pump to increase inflow with speed. Outflow

resistance methods include: a water outlet valve closed manually, by working

compartment pressure feedback, or by shaft speed feedback (hydraulic or

electrohydraulic); or, impellers on the back of the rotors to generate back pressure. It

is desirable to study this self-emptying phenomenon and some methods of dealing

with it so that improvements in dynamometer control can be made The water brake is

available in various different configurations, three of which are described in more detail

below (3)

types of hydraulic dynamometer

The first and most popular water brake dynamometer is commonly referred to as a

variable fill machine. As the name imp lies, the load is controlled by changing the

amount of water that is inside of the casing. The change is typically controlled with a

valve on the inlet and a separate valve on the outlet side. Needle valves are used instead

of ball valves due to their ability to change the flow rate in minute increments. Loading

is slowly changed by opening or closing the inlet valve, and quick ly changed by

opening or closing the outlet valve. This allows small changes in torque resistance by

only changing the inlet valve. This process is fairly simple and can be done manually by

a person or controlled by a computer to hold back the desired amount of torque.

A second type of water brake dynamometer is called the constant fill machine, or the

classical Froude or sluice plate design. [1] With this machine, the load is not changed

by varying the amount of water, but by inserting pairs of thin plates between the rotor

and casing. This reduces the clearance between the rotor and casing therefore increasing

the amount of torque that can be absorbed. The opposite will occur if you remove a pair

of the sluice plates. Each setup is not capable of controlling a large variation in torque,

and to change the amount of torque that it can handle, the unit must be disassembled,

and then reassembled with more plates added, or removed. This is a tedious, manual

process that could take a significant amount of time.

A third type of water brake dynamometer is called a disc dynamometer. The loading on

this machine is controlled by a combination of plates and the amount of water inside of

the casing, similar to the variable fill machine described above. The small clearance

between the plates results in intensive shearing of the water which will resist the applied

torque, and by changing the amount of water with the needle valves; more or less torque

can be absorbed. A small variation in this machine is to have perforated discs instead of

solid discs. This will enable the machine to absorb more torque. Each setup is not

capable of controlling a large variation in torque; however it is more adjustable than the

constant fill machine due to the variable amount of water in the casing. Similar to the

constant fill machine, disassembly and reassembly with inserted plates are required to

change the range of torque that the machine can absorb. Again, this is tedious and time

consuming. (Kim, Date: October 31, 2006 )

Application

Hydraulic dynamometers are used as loading units in engine test rigs. They cover a wide

range of dynamometer power and torque values, and are therefore well suited for:

Testing of passenger car and commercial vehicle Diesel engines

Testing of large railway- and marine engines

Engine testing in tandem configuration with asynchronous motor

Testing in research and development

Testing in production and quality assurance 5 (www.technogerma.com)

Cooling system of hydraulic dynamometer:

The cooling water system for any heat engine test facility has provided water of suitable

quality, temperature and pressure to allow sufficient volume to pass through the

equipment in order to have adequate cooling capacity.

The pressure and flow rates have to be sufficiently constant to enable the devices

supplied to maintain control. A common fault of badly designed cooling water systems is

cross talk, where control of one process changes because of sudden supply pressure or

temperature changes caused by external events occurring within a shared supply. It is

essential for purchasers of water-cooled plant to carefully check the inlet water

temperature specified for the required performance, since the higher the cooling water

inlet temperature supplied by the factory, the less work the device will be capable of

performing before the maximum allowable exit temperature is reached.

Types of test cell cooling water circuits

Engine coolant control systems and cell cooling water circuits may be classified as

follows, with increasing levels of complexity:

1. Direct mains water supplied systems containing service modules and cooling

columns that allow heated water to run to waste.

2. Sump or tank stored water systems that are open, meaning at some point in the

circuit water runs back into the sump via an open pipe. These systems normally

incorporate self-regulating water/fluid cooling modules for closed engine cooling

systems filled with special coolant/water mix and, if required, for lubricant

cooling. They commonly have secondary pumps to circulate water from the sump

through evaporative cooling towers when required.

3. Closed pumped circuits with an expansion, pressurization and make-up units in

the circuit. Such systems have become the most common as most modern

temperature control devices and eddy-current or electrical dynamometers, unlike

water-brakes, do not require gravitational discharge. Closed water cooling

systems are less prone to environmental problems such as Legionnaires disease.

4. Chilled water systems (those supplying water below ambient) are almost always

closed.

Open water cooling circuits

The essential features of these systems are that they store water in a sump lying below

floor level from which it is pumped through the various heat exchangers and a cooling

tower circulation system. The sump is normally divided into hot and cold areas by a

partition weir wall (see Fig. 6.1). Water is circulated from the cool side and drains back

into the hot side. When the system temperature reached the control maximum, it is

pumped through the cooling tower before draining back into the cool side.

A rough rule for deciding sump capacity is that the water should not be turned over more

than once per minute. Within the restraints of cost, the largest available volume gives the

best results. Sufficient excess sump capacity, above working level, should be provided to

accommodate drain-back from pipework, engines and dynamometers upon system

shutdown.

There is a continuous loss of water due to evaporation plus the small drainage to waste

mentioned above and make-up is supplied by way of a float valve fitted to a mains water

supply. To minimize air entrainment the pump suction should be located close to a

corner; return flow should be by way of a submerged pipe with air vent.

This is a classic arrangement with thousands of similar systems installed worldwide, but

care has to be taken to keep debris such as leaves or flood water wash-off from entering

the system via the sump lip or the cooling tower collector.

A sensible design feature at sites where freezing conditions are experienced is to use

pumps submerged in the sump so it can be ensured that, when not being used, the

majority of pipe work will be empty.

Closed water cooling circuits

Essentially, the system uses one or more pumps to force water through the circuit load

where it picks up heat which is then dispersed, usually in the air, via closed cooling

towers, then the water is returned directly to the pump inlet.

It is vital that air is taken out and kept out of the system and that the whole pipe system

be provided with the means of bleeding air out at high points or any trap points in the

circuit. To achieve proper circulation, to cope with thermally induced changes of system

volume and to make up for any leakage, the closed system has to be fitted with an

expansion tank and means of pressurization. Both these requirements can be met by using

a form of compressed air/water accumulator connected to a make-up supply of treated

water. Balancing water systems is the means by which the required flow, through discrete

parts of the circuit having their own particular resistance to flow, is fixed by use of flow

regulation valves having test points fitted for setting purposes. The balancing of closed

cooling systems can be problematic, particularly if a facility is being brought into

commission in several phases meaning that the complete system will have to be

rebalanced at each significant change.

None of the devices fitted within a closed and balanced plant water system should have

valves that change the flow of the plant water (economizer valves) since that variation

will continually unbalance the whole system.

Closed systems are often filled with an ethylene glycolwater mix to cope with freezing

weather conditions or have any external pipe work trace heated.

Engine coolant temperature control modules

Whether or not the engine under test is fitted with its own thermostat, precise control of

coolant temperature is not easily achieved unless the service module used is designed to

match the thermal characteristics of the engine with which it is associated; even here it

may be difficult to achieve stable temperatures at light load.

The instability of temperature control is increased if the engine is much smaller than that

for which the cooling circuit is designed. The capacity of the heat exchanger is the

governing factor and it may be advisable, when a wide range of engine powers is to be

accommodated, to provide several coolers with a range of capacities.

There are many closed system engine coolant temperature control units on the market,

most working on the principle of a closed loop control valve controlling flow of coolant

through a heat exchanger and they can be broken down into the following types:

1. mobile pedestal type;

2. special engine pallet-mounted systems;

3. user-specific, wall-mounted systems;

4. complex fixed pedestal type.

Figure 6.2 is an illustration of a typical service module incorporating heat exchangers for

jacket coolant and lubricating oil, while Fig. 6.3 shows a simplified schematic of the

circuit. The combined header tank and heat exchanger is a particularly useful feature.

This has a filler cap and relief valve and acts in every way as the equivalent of a

conventional engine radiator, ensuring that the correct pressure is maintained.

If some engines are to be tested without their own coolant pumps the module must be

fitted with a circulating pump, commonly of the type used in central heating systems. For

ease of maintenance, it should be possible to withdraw exchanger tube stacks without

major dismantling of the system and a simple means for draining both oil and a coolant

circuits should be provided.

The most usual arrangement is to control the temperature by means of a three-way

thermostatically controlled valve in the engine fluid system. The alternative, where

temperature is controlled by regulating the primary cooling water flow, will work but

gives an inherently lower rate of response to load changes.

The types 2 and 3 listed above are often designed and built by the user, particularly the

pallet-mounted systems which may use specific ex-vehicle parts for such items as the

header tank and expansion vessel.

Type 4 are the most complex and incorporate a coolant circulation pump, heaters and

complex control strategies to deal with low engine loads and transient testing.

None of these devices will operate satisfactorily if not integrated well with the engine and

cell pipe work. Time and distance lag, between a sensor located at the engine (inlet or

outlet) and the control valve at the cooler, may be significant and the length and volume

of pipe runs between engine and service module should be kept to a minimum. The sum

of these phenomena is often referred to as the thermal inertia of the cooling system and

can be most easily visualized by considering the speed at which heated or cooled fluid is

circulated, detected and diverted within the total engine/cooling system.

To reduce thermal inertia there are two widely used strategies:

1. Reduce the distance and fluid friction head between coolers and engine.

2. Circulate the coolant between engine and coolers with auxiliary pumping (in both

cases the interconnecting pipes should be insulated against heat loss/gain).

Strategy 1 is best served by arranging a pallet-mounted cooling module close to the

engine. In cases such as anechoic cells, where the heat exchanger is inevitably remote

from the engine, strategy 2 is required to speed up the rate of circulation by an auxiliary

pump mounted outside the cell to reduce lag.

Some high-end devices provides a continuous circulation of coolant within its own

system from which the engine draws off the required flow. However, the quality of

control is still dependent on good installation to reduce fluid transit time and heat loss.

5.3. Sensors:

A sensor is a device that measures a particular characteristic of an object or system. Some

sensors are purely mechanical, but most sensors are electronic, returning a voltage signal

that can be converted into a useful engineering unit. A Sensor converts the physical

parameter (for example: temperature, blood pressure, humidity, speed, etc.) into a signal

which can be measured electrically .Sensors take advantage of the mechanical or

electrical response of its components to relate the response to a relevant quantity.

Sensor properties:

Diesel engine sensors must meet the following requirements:

High degree of reliability

Favorable manufacturing costs (i.e. not too expensive)

High degree of accuracy

Remain fully functional even under extreme operating conditions

Compact design

Types of sensor:

There are many types of sensors, some sensors are connected to the engine and others are

connected to the dynamometer. The types of sensors which used in the engine test are:

1. Speed Sensor:

Speed Measurement typically comes from an inductive

(variable reluctance) sensor reading a number (n) of teeth

of a rotating gear (directly connected to the dynamometers

shaft) as they pass. Sinusoidal output is measured for

period. Period is then inverted for frequency, and

converted to rpm. 60-tooth gears are common as the

frequency (in Hz) is equal to the rpm. The Figure 5.,

illustrates the speed sensor.

2. Throttle Position Sensor

Measurement of the throttle position usually comes from a throttle mounted

potentiometer (variable resistor) which is connected between 5V and ground. This gives a

Throttle Position Signal (TPS) as a voltage directly proportional to the throttle position.

As shown in Figure 5.11.

3. Torque Sensor:

Torque is almost always measured with a strain gage instrumented load cell or force

transducer. This is a mechanical member which undergoes significant strain with an

applied force. Semiconductor or wire foil strain gages on the surface are stretched or

compressed, changing their resistance. Often several gages are oriented in a whetstone

Figure 5.10 speed sensor,

Figure 5.11 throttle sensor.

bridge giving greater sensitivity and

reduced susceptibility to temperature

variation effects. Excitation voltage of

bridge is usually 5V to 10V.

Load cells almost always require a specific

amplifier which can be adjusted to zero

the load, and adjust the span (calibration

factor) Figure 5.12, shows torque sensor.

4. Intake Air Temperature Sensor

The Intake Air Temperature Sensor determines the temperature of the incoming air

stream and feeds this data into the Power Dyne data acquisition for graphing against

speed, power and torque figures.

5. Air/Fuel Ratio Exhaust Sensors

Accurately determine exhaust gas mixture over a wide range of engine operating

conditions with ultra-fast response time Seamlessly integrates with your Power

Dyne Controller and Data Acquisition System for graphing AFR against horsepower

torque and engine RPM. Dual channel AFR. Figure 5. , shows air/fuel ratio exhaust

sensor.

6. Pressure Sensors

Designed to provide a highly stable and accurate measurement of fluid and/or gas

pressures. Enables you to graph various pressures against power, torque and engine rpm

curves. (-15 to 15-psi, 30-psi, 60-psi, 100-psi, 0-2,000 psi).

7. Fuel temperature sensor:

Exhaust Gas Temperature Sensor

Developed specially for on track racing and dyno applications, these EGT have an

exposed tip design to provide quick response. Installs using weld type compression

fitting (included). Range: 0- 1000 C.

8. Oil Temperature Sensor

Accurately measure and monitor engine oil temperature. Closely monitoring engine oil

temperature ensures your dynamo runs are comparable and increases repeatability.

9. Cooling water temperature sensor:

Cooling water temperature can be measured directly by sensor on intake manifold. The

coolant temperature value monitored by controller was read from the output data stream

on its serial port interface.

Figure 5.12 torque sensor.

10. Load Cell (dynamometer) Temperature Measurement

Measured by using a coolant temp sensor immersed in the load cell hydraulic fluid

reservoir. The temperature of the hydraulic fluid in the load cell was measured by

submerging a standard GM coolant temperature sensor in the fluid reservoir. A voltage

divider was used to condition the signal and a lookup table for the resistance to

temperature relation of the sensor used to give the temperature.

11. Emissions Sensors Or Measurements

The most common tool is a 5-gas analyzer measuring CO, HC, CO2 with a non-

dispersive Inferred sensor. There is a separate sensor for O2 and NOx. These units are

fairly inexpensive (

5.4. Other Measurements devices:

Fuel Consumption Measurement

Fuel consumption is measured in two ways :

a. The fuel consumption of an engine is measured by determining the volume flow

in a given time interval and multiplying it by the specific gravity of the fuel

which should be measured occasionally to get an accurate value .

b. Another method is to measure the time required for consumption of a given mass

of fuel. Accurate measurement of fuel consumption is very important in engine

testing work .

As already mentioned two basic types of fuel measurement methods are :

Volumetric type

Gravimetric type .

Volumetric type flow meter includes Burette method, Automatic Burette flow meter and

Turbine flow meter.

Gravimetric Fuel Flow Measurement

The efficiency of an engine is related to the kilograms of fuel which are consumed and

not the number of liters. The method of measuring volume flow and then correcting it for

specific gravity variations is quite inconvenient and inherently limited in accuracy.

Instead if the weight of the fuel consumed is directly measured a great improvement in

accuracy and cost can be obtained .

There are three types of gravimetric type systems which are commercially available

include Actual weighing of fuel consumed, Four Orifice Flow meter, etc.

Measurement of Air Consumption

In IC engines, the satisfactory measurement of air consumption is quite difficult because

the flow is pulsating, due to the cyclic nature of the engine and because the air a

compressible fluid. Therefore, the simple method of using an orifice in the induction

pipe is not satisfactory since the reading will be pulsating and unreliable .

All kinetic flow-inferring systems such as nozzles, orifices and venturies have a square

law relationship between flow rate and differential pressure which gives rise to severe

errors on unsteady flow. Pulsation produced errors are roughly inversely proportional to

the pressure across the orifice for a given set of flow conditions. The various methods

and meters used for air flow measurement include: Air box method, and Viscous-flow air

meter.((1))

Barometric Pressure:

The barometric pressure measured by MegaSquirt pressure sensor on power up and

stored. Value only recorded each time MegaSquirt is powered up before cranking. Taken

off live data stream output of MegaSquirt.

Outside Air Temperature:

The outside air temperature can be recorded from local weather website.

Engine Charging Volts:

Measured by MegaSquirt upon each test. Taken off live data stream output of

MegaSquirt.