temperature sensor

The Seven Basic Types of Temperature Sensors

PT 100 ohm Temperature sensor with a range of 50 - 700 deg

Temperature is defined as the energy level of matter which can be evidenced by some change in that matter. Temperature sensors come in a wide variety and have one thing in common: they all measure temperature by sensing some change in a physical characteristic.

The seven basic types of temperature sensors to be discussed here are

1. Thermocouples
2. Resistive temperature devices (RTDs, thermistors)
3. Infrared radiators
4. Bimetallic devices
5. Liquid expansion devices
6. Molecular change-of-state and
7. Silicon diodes.

Thermocouples

Thermocouples are voltage devices that indicate temperature by measuring a change in voltage. As temperature goes up, the
output voltage of the thermocouple rises - not necessarily linearly.

Often the thermocouple is located inside a metal or ceramic shield that protects it from exposure to a variety of environments.
Metal-sheathed thermocouples also are available with many types of outer coatings, such as Teflon, for trouble-free use in acids and strong caustic solutions.

Resistive Temperature Devices

Resistive temperature devices also are electrical. Rather than using a voltage as the thermocouple does, they take advantage of
another characteristic of matter which changes with temperature - its resistance. The two types of resistive devices are metallic, resistive temperature devices (RTDs) and thermistors.

In general, RTDs are more linear than are thermocouples. They increase in a positive direction, with resistance going up as temperature rises. On the other hand, the thermistors has an entirely different type of construction. It is an extremely nonlinear semi conductive device that will decrease in resistance as temperature rises.

Infrared Sensors

Infrared sensors are noncontacting sensors. As an example, if you hold up a typical infrared sensor to the front of your desk without contact, the sensor will tell you the temperature of the desk by virtue of its radiation - probably 68°F at normal room temperature.

In a noncontacting measurement of ice water, it will measure slightly under 0°C because of evaporation, which slightly lowers
the expected temperature reading.

Bimetallic Devices

Bimetallic devices take advantage of the expansion of metals when they are heated. In these devices, two metals are bonded
together and mechanically linked to a pointer. When heated, one side of the bimetallic strip will expand more than the other. And when geared properly to a pointer, the temperature is indicated.

Advantages of bimetallic devices are portability and independence from a power supply. However, they are not usually quite as
accurate as are electrical devices, and you cannot easily record the temperature value as with electrical devices like thermocouples or RTDs; but portability is a definite advantage for the right application.

Thermometers

Thermometers are well-known liquid expansion devices. Generally speaking, they come in two main classifications: the mercury
type and the organic, usually red, liquid type. The distinction between the two is notable, because mercury devices have certain limitations when it comes to how they can be safely transported or shipped.

For example, mercury is considered an environmental contaminant, so breakage can be hazardous. Be sure to check the current
restrictions for air transportation of mercury products before shipping.

Change-of-state Sensors

Change-of-state temperature sensors measure just that - a change in the state of a material brought about by a change in temperature, as in a change from ice to water and then to steam. Commercially available devices of this type are in the form of labels, pellets, crayons, or lacquers.

For example, labels may be used on steam traps. When the trap needs adjustment, it becomes hot; then, the white dot on the label will indicate the temperature rise by turning black. The dot remainsblack, even if the temperature returns to normal.

Change-of-state labels indicate temperature in °F and °C. With these types of devices, the white dot turns black when exceeding
the temperature shown; and it is a non-reversible sensor which remains black once it changes color. Temperature labels are useful when you need confirmation that temperature did not exceed a certain level, perhaps for engineering or legal reasons during shipment. Because change-of-state devices arenonelectrical like the bimetallic strip, they have an advantage in certain applications. Some forms of this family of sensors (lacquer, crayons) do not change color; the marks made by them simply disappear. The pellet version becomes visually deformed or melts away completely.

Limitations include a relatively slow response time. Therefore, if you have a temperature spike going up and then down very quickly, there may be no visible response. Accuracy also is not as high as with most of the other devices more commonly used in industry. However, within their realm of application where you need a nonreversing indication that does not require electrical power, they are very practical.

Other labels which are reversible operate on quite a different principle using a liquid crystal display. The display changes from black colour to a tint of brown or blue or green, depending on the temperature achieved.

For example, a typical label is all black when below the temperatures that are sensed. As the temperature rises, a colour will appear at, say, the 33°F spot - first as blue, then green, and finally brown as it passes through the designated temperature. In any particular liquid crystal device, you usually will see two colour spots adjacent to each other - the blue one slightly below the temp indicator, and the brown one slightly above. This lets you estimate the temperature as being, say, between 85° and 90°F.

Although it is not perfectly precise, it does have the advantages of being a small, rugged, nonelectrical indicator that continuously updates temperature.

Silicon Diode

The silicon diode sensor is a device that has been developed specifically for the cryogenic temperature range. Essentially, they
are linear devices where the conductivity of the diode increases linearly in the low cryogenic regions.

Whatever sensor you select, it will not likely be operating by itself. Since most sensor choices overlap in temperature range and accuracy, selection of the sensor will depend on how it will be integrated into a system.
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Viscosity Meter and Viscosity Controller Used on Ships

Viscosity Meter and Viscosity Controller Used on Ships

As the fuel prices go sky high, ships are using lower grades of fuel for saving its operational cost. The fuel used for burning in auxiliary engine and main propulsion plant is normally heavy fuel oil. Along with other properties, viscosity is an important property which determines the efficiency of fuel combustion and of the marine engine.

Viscosity of fuel oil depends on the grade of oil. If the viscosity of the fuel oil and its viscosity index are on the higher side, it would lead to more difficulty in achieving atomization state and poor combustion inside the engine cylinder.

Understanding the Important Definitions

Viscosity

In simple term, it can be defines as ‘resistance to the flow of the fluid offered by its internal layers due to internal frictions’. It is measured in centi-stokes (cst).

Less the viscosity, lesser the resistance to flow and the fuel can be easily atomized.

Viscosity index

 

It is an important factor in selecting any kind of oil, fuel or lube oil. It’s the measure of change of viscosity of oil with variation in temperature.

Since fuel oil is heated to achieve proper atomization, it should have proper VI. If it’s on the higher side, it will be difficult to alter the viscosity of oil by heater.

 

Atomisation

It is the process of breaking the fuel particle into fine mist spray under high pressure to improve the surface area of contact of fuel and air for proper combustion.

Viscometer or Viscotherm

 

The viscosity of the marine bunker HFO fuel when supplied at 50 ̊deg C varies from 180cst to 380 cst. The fuel is heated and the viscosity of the fuel is reduced to 13~15 cst at the time of injection in the engine by means of electrical or steam heaters or both.

The viscosity to the high pressure fuel oil pump has to be maintained approximately at 13 cst to achieve efficient combustion.

A viscotherm or viscometer is used to measure the viscosity of fuel oil at the fuel injection system of the engine.

Construction and Working of Viscosity meter

It consists of a capillary tube inside of which a gear pump is fitted which rotates at very slow rpm (say 40 rpm). There is an out side casing provided for the capillary tube.

When the oil passes through the casing, some part of the oil pass through the gear pump and its capillary, and some part of the oil passes over the capillary tube. Hence a flow difference occurs inside the casing. The oil inside the tube maintains a laminar flow and outside the tube maintains a turbulent flow.

The pressure difference between outside and inside of the tube is measured which is directly proportional to the viscosity of the oil. Hence oil viscosity is maintained.

Viscosity Controller

The viscosity controllers acts as the controller of the 3 way valve from which steam is passed into the heater or bypassed from the heater as per the position of the control valve.

Construction and working

Normally pneumatic control system is used with bellows, flapper and nozzle. The output signal from the viscometer is connected to measured value bellow of the viscosity controller.

Another bellow is supplied with set point of the required viscosity and both the bellows are connected opposite to each other to complete a flapper nozzle control system. The output of flapper nozzle is the controlling signal of fuel oil heater 3 way valve.

A 3-way valve has 2 openings in which one is inlet and 2 are outlet. One outlet goes through the heater and one outlet is connected to a bypass line of heater.

When the set value and measured values are same, no signal is given to control valve and valve position remains same. More of the steam bypasses the heater.

When the measured value decreases, the output signal opens the control valve to steam side so that more steam is supplied and viscosity can be brought down.

It is important to have a better grade of marine fuel oil with proper viscosity index for maintaining proper efficiency of engine and to reduce wear down of the fuel injection parts.

link: http://www.mariners.page4.me/83.html

Fuel injector

Image Credit: www.riceweightloss.com

Older loop scavenged engines may have a single injector mounted centrally in the cylinder head. Because the exhaust valve is in the centre of the cylinder head on modern uniflow scavenged engines the fuel valves (2 or 3) are arranged around the periphery of the head.
The pressure at which the injector operates can be adjusted by adjusting the loading on the spring. The pressure at which the injectors operate vary depending on the engine, but can be as high as 540bar.

OPERATION

– Fuel injectors achieve this by making use of a spring loaded needle valve.
– The fuel under pressure from the fuel pump is fed down the injector body to a chamber in the nozzle just above where the needle valve is held hard against its seat by a strong spring.
– As the fuel pump plunger rises in the barrel, pressure builds up in the chamber, acting on the underside of the needle as shown. When this force overcomes the downward force exerted by the spring, the needle valve starts to open.
– The fuel now acts on the seating area of the valve, and increases the lift.
– As this happens fuel flows into the space under the needle and is forced through the small holes in the nozzle where it emerges as an “atomised spray”.

Image Credit: www.marinediesels.co.uk

At the end of delivery, the pressure drops sharply and the spring closes the needle valve smartly.

ATOMIZATION

It is the break-up of the fuel change into a very small particles when it is injected into the cylinder
Proper atomization facilitates the starting of the burning and ensures that each minute particle of fuel is surrounded by oxygen particles which it can combine

Image Credit: www.marineinsight.com

PENETRATION

It refers to the distance that the fuel particles travel or penetrate into combustion chamber

TURBULENCE or SWIRL

– It refers to the aim movement pattern within the combustion chamber at the end of compression.
The spray pattern of the fuel is cone-shaped.

– These occurs when there is an excess velocity of fuel spray during injection, causing contact with metallic engine parts and one result is flame burning

INJECTOR NOZZLE:

The body of a fuel injector valve is normally flanged at the upper end and the lower end is threaded to accommodate the nozzle body and nozzle cap nut
The nozzle body contains four holes. One is for the fuel inlet and another for the fuel priming valve, these two holes are connected through a common space within the fuel nozzle or by annular space

Image Credit: DieselNet

The valve needle which has been lapped into a very accurately machine guide into the nozzle body, is held on the conical seat immediately above the atomization holes
Slightly clearance between needle and nozzle body to allow for temperature changes when working with heated fuel.

COOLING OF FUEL INJECTION VALVE:

Some injectors have internal cooling passages in them extending into the nozzle through which cooling water is circulated. This is to prevent overheating and burning of the nozzle tip.
Injectors on modern 2 stroke crosshead engines do not have internal water cooling passages. They are cooled by a combination of the intensive bore cooling in the cylinder head being close to the valve pockets and by the fuel which is recirculated through the injector when the follower is on the base of the cam or when the engine is stopped.

As well as cooling the injector, recirculating the fuel when the engine is stopped keeps the fuel at the correct viscosity for injection by preventing it from cooling down.
The animation opposite shows the principle on which one system operates.
Fuel injectors must be kept in good condition to maintain optimum efficiency, and to prevent conditions arising which could lead to damage within the cylinder. Injectors should be changed in line with manufacturers recommendations, overhauled and tested. Springs can weaken with repeated operation leading to the injector opening at a lower pressure than designed. The needle valve and seat can wear which together with worn nozzle holes will lead to incorrect atomisation and dribbling

FAULTS OF FUEL INJECTORS:

1. Over heating OR under cooling:
If cooling of the injector is reduced, either by fuel valve cooling system or poor heat transfer to the cylinder head, then the working temperature of the injector will rise. This can cause:-
– Softening of the needle and seat which increases the possibility of nozzle leakage and/or,
– Fuel to expand/boil out of the fuel sac, leading to carbon trumpet formation, and increased levels of HC and smoke in the exhaust gases.

2. Over cooling:
More common on older vessels with separate fuel valve water cooling systems. When the injector is over cooled, the tip of the injector falls below the condensation temperature and acid corrosion due to the sulphur in the fuel oil occurs. This can severely corrode the injector tip, causing the spray pattern to be affected.

3. leakage from Nozzle:
This fault will produce carbon trumpets as the dribble of fuel burns close to the tip and the carbon deposits remain. The formation of the trumpets will have a progressive affect by influencing the spray pattern of the fuel, and this can be detected in the increased exhaust gas temps and smoke levels.
Nozzle leakage can sometimes be identified by a seat defect(the seat is no longer narrow in appearance, and is caused by):-
– Insufficient cooling,
– Dirt within the fuel damaging/abrading the seating area,
– Excessive needle valve hammering, due to excessive time in service, excessive needle lift or spring force.

4. Weak spring:
This will cause the injector to open and close at a lower pressure. Thus the size of the fuel droplets will increase during these injection periods.
Increased droplet size at the start of combustion will decrease the maximum cylinder pressure (late combustion), whilst increased droplet size at the end of combustion will increase the exhaust temperature and smoke (afterburning).
Causes of a weak spring are usually metal fatigue, due to an excessive number of operations.

5. Slack needle:
Slight leakage between the needle valve and its body is required to provide lubrication of the moving parts. However excess leakage due to a slack needle will allow a greater quantity, and larger size of fuel particle to pass between the valve and body.
The quantity of leakage should not influence injector performance unless excessive, but dirt particles between the needle and body can increase friction and make the needle action sluggish.
The cause of a slack needle is usually poor filtration of the fuel causing wear between needle and body.

6. Poor atomisation:
This will increase the size of the fuel droplets, which will increase the time required for combustion. Thus engine noise, exhaust smoke, exhaust temperatures, etc will increase. Poor atomisation can be caused by low injection pressure (fuel pump wear), high fuel viscosity and nozzle hole obstruction such as carbon trumpets.

7. Poor penetration
This will reduce the mixing which occurs between the fuel and air, and will increase the over-rich areas in the centre area of the cylinder. Thus only following combustion in the centre area will the expanding gases move the fuel charge into the air rich outer ring of the cylinder where the greatest mass of air is present.
This will increase the time required for combustion as the fuel/air mixture is not correct in many areas, and hence afterburning, exhaust temps, and smoke will increase.
Causes of poor penetration is reduced injection pressure, and nozzle hole blockage such as trumpets or sac deposits.

8. Over penetration
This will occur when the air density within the cylinder is reduced, or with over-size holes. The liquid stream travels too far into the cylinder, so that a high level of liquid impingement on the liner wall takes place. This will remove the liner lubrication, and once burning will greatly increase the liner wall temperature, and its thermal stress.
If this over penetration is caused by prolonged low power operations, then “slow speed” nozzles should be fitted.

Slow steaming nozzles can be used when regular and prolonged engine operation is required between 20-50% power.
The nozzle hole diameter is reduced to
i. Reduce the penetration that will occur into the less dense cylinder air
ii. Keep the atomisation level and injection pressure sufficient, as mass flow rate is reduced.

If the engine is operated for long period on low levels of power/speed with `normal’ size injector nozzles, then the atomisation will reduce, thus engine noise, mechanical loading, exhaust smoke, exhaust temps, and fuel consumption will increase.

EFFECT OF FAULTY FUEL INJECTORS:

1. Greatly enlarged holes cause overheating, perhaps burning of piston upper surface, also cause carbon deposits in the piston cooling space, if oil cooled. It may also cause increased cylinder and piston ring wear

2. If the holes are chocked, the fuel sprays will be effected to the extent that imperfect combustion will result. This in turn may reduce the power output quite considerably and bring about all the mechanical troubles usually associated with after burning.
3. If the injectors leaky or spring is damaged, burning of piston upper surface, also cause carbon deposits in the piston cooling space, if oil cooled. It may also cause increased cylinder and piston ring wear and can lead to scavenge fire.

INDICATION OF FAULTS:

1. Early injection is usually evidenced by knocking in the cylinder. On the power diagram the maximum pressure will be considerably in excess. Exhaust temperature will be low.

2. Leaky valve can be detected through indicator diagram, which show reduced combustion pressure. This will be some reduction in power output, increasing in exhaust temperature about 10oC and smoky gases. Chocking of atomizer and exhaust ports. Surging in turbo-blower are also some of the indication

3. After burning will cause higher exhaust temperature and pressure. The maximum height of both the power and draw diagram would be reduced. Other indications are smoky exhaust, possible fires in uptake, fouling of exhaust system, surging of turbo-blower

4. Choked fuel injectors – combustion efficiency of an engine depends on fuel atomization, shape and direction of the fuel sprays. So the holes should be clear and clean. First outward indication of accumulation of carbon deposits will be increase in the exhaust temperature due to fuel not mixing properly with the air, consequently not burning completely in the allocated time. Power output is reduced and the exhaust is smoky.

MAINTENANCE

• Fuel injectors must be kept in good condition to maintain optimum efficiency, and to prevent conditions arising which could lead to damage within the cylinder.
• Injectors should be changed in line with manufacturers recommendations, overhauled and tested.
• Springs can weaken with repeated operation leading to the injector opening at a lower pressure than designed.
• The needle valve and seat can wear which together with worn nozzle holes will lead to incorrect atomization and dribbling.
• Proper cooling should be made during operation. Cooling passages to be cleaned during overhaul.
• Proper grade of fuel oil should be used and it should be used after proper purification to prevent atomized holes become enlarged, conical and oval due to abrasive materials.
• The valve body and valve needle should always be considered as a unit, not as two separate pieces and they should be renewed together.
• The holes should be cleaned and cleared properly without damaging by blown with compressed air.
• The valve needle must be perfectly fluid tight when in the closed position and must open and close smartly.
• The cam operating the fuel valves or the fuel pump, as the case may be, should effect opening and closing in the shortest time practicable.

References:

1. www.marineengineering.co.uk
2. The Running and Maintenance of Marine Machinery – Cowley
3. Reeds Marine Engineering Series, Vol. 12 – Motor Engineering Knowledge for Marine Engineers
4. Lamb’s Question and Answers on Marine Diesel Engines – S. Christensen
5. Principles and Practice of Marine Diesel Engines – Sanyal

Written by Mohammud Hanif Dewan, IEng, IMarEng, MIMarEST, MRINA

MAN B&W Reversing Operational Information - Inverted cam & cylinder actuated

The fuel pump cam on the MAN B&W MC series engine is designed to raise the plunger on the injection stroke and then keep the plunger at the top of its stroke while the follower stays on the peak of the cam until just before the next delivery stroke when the follower returns to the base circle of the cam, and the fuel pump plunger moves down on its suction stroke.

The animation shows the cam follower just beginning to move up the slope of the cam with the camshaft rotating in anticlockwise direction. (i.e. start of injection)

If the engine direction is reversed at this point, then air will enter the pneumatic cylinder as shown and will move the piston to the right. The cam follower will be moved across and would finish in the position shown which would be at the correct fuel pump timing for running astern.

It should be noted that the reversal of the follower only takes place while the engine is rotating. If the engine had been stopped from running ahead, and then started astern, the fuel pump followers would move across as the engine starts to rotate, and before the fuel is admitted by venting the fuel pump puncture valves.

A micro switch shown on the LHS detects whether the follower has moved across. If not, an indicator light is lit in the control room, However the engine will still start if a follower fails to move, perhaps due to corrosion in the servo cylinder. A high exhaust temperature deviation alarm would operate within a short time. Allowing the engine to start in this situation could be useful during manoeuvring in confined waters.

The video clip opposite shows a cam follower moving from astern to ahead on a MAN B&W MC engine.

Reversing Servomotor on MAN B&W 2 Stroke Engine

Indicator Lights for Camshaft

AIR EJECTOR THEORY & APPLICATION

HOW DOES AN AIR EJECTOR WORK?

An air ejector or steam ejector is a device which uses the motion of moving fluid (Motive Fluid) to transport another fluid (Suction fluid). It is has a wide range of application in steam ejector in boiler condenser, fresh water generator and in priming the centrifugal pump.

AIR EJECTOR THEORY

It works on the principle of convergent /divergent nozzle as it provides the venturi effect at the point of diffusion as the tube gets narrows at the throat the velocity of the fluid increases and because of the venturi affect it pressure decreases, vacuum will occur in the diffuser throat where the suction line will be provided.

An air ejector which uses the high pressure motive fluid such as air or steam to flow through the convergent nozzle the function of the convergent nozzle is to convert the pressure energy of the motive fluid into the velocity energy.

As in convergent nozzle the following effect takes place,

P1-pressure of the fluid entering the nozzle.

V1- velocity of the fluid entering the nozzle.

P2- pressure of the fluid leaving the nozzle.

V2- velocity of the fluid leaving the nozzle.

By Bernoulli’s theorem:

P1 × V1 = P2 × V2.

As the pressure energy before entering the convergent nozzle is greater and the velocity is less for the fluid. At the point of discharge the pressure energy is converted into the velocity so the velocity will be greater and the pressure will be less during the discharge.

Divergent nozzle the opposite effect takes place velocity energy is convert into pressure energy, at the point of diffusion there is a low pressure or vacuum is created which is used to suck the other fluid for the motion.

In the fig:

C- Convergent Nozzle.

D- Divergent Nozzle.

V- venturi Point or Diffuser Point.

AIR EJECTOR

 APPLICATION OF AIR EJECTORS:

1. Steam Jet Air Ejector:

It is one of the types of air ejector which is used in the steam like near the condenser to remove the non-condensable gases and some vapour entering into main condenser by an air ejector and it is cooled by the main condensate and released in the ejector condenser.

A steam is used as the motive fluid to withdraw air and dissolved gases from the condenser by the ejector action. In each stage of the steam jet ejector, high pressure steam is expanded in a convergent /divergent nozzle. The steam leaves the nozzle at a very high velocity in the order of 1220 m/s and a proportion of the kinetic energy in the steam jet transferred by interchange of momentum to the body of air which entrained and passes along with the operating steam through a diffuser in which the kinetic energy of combined steam is re-converted to pressure energy.

The maximum pressure ratio that can be obtained with a single stage is roughly 5:1 and consequently it is necessary to use two or even three stages in series to establish a vacuum in the order of 724mm of Hg with reasonable steam consumption.

Design Feature:

There are a variety of ejectors designed in service which work on the same principle. Older unit have heavy cast steel which serves as a vapour condenser and also contains diffusers. These are arranged vertically the steam entering at the top. More recent design has the diffuser arrangement externally and vapour condenser shell is somewhat lighter in construction.

Horizontal singe element two stage air ejectors this unit comprises a stack u-tubes contained in a fabricated mild steel condenser shell on which is mounted a single element two stage air ejector.

The condensate from the main or auxiliary condenser is used as the cooling medium. High velocity operating steam emerging from the 1 st stage ejector nozzle entrains the non-condensable and vapour from the main condenser and the mix discharge into the inter condenser.

Most of the steam and vapour is condensed when it comes into contact with the cool surface of the tubes, falls to the bottom of the shell and drains to the main or auxiliary condenser.

The remaining air and water vapour are drawn into the second stage ejector and discharged to the steam drain tank and non-condensable gases are at last discharged to the atmosphere through vacuum retaining valve.

2.Fresh Water Generator:

The next main application of the air ejector in marine field is in fresh water generator as it is used to remove the air and non-condensable in the evaporator chamber so as to maintain the vacuum inside the chamber. Thus the efficiency of the generation increases at low temperature of the sea water.

3. Self-Priming of Centrifugal Pumps:

It is also employed in priming of the centrifugal pumps by the air ejector, which removes the air inside the casing of the pump by the suction effect created by the air ejector thus by flooding casing with the liquid so that it helps in stating of the pump.

APPLICATION OF AIR EJECTORS areas:

Freshwater Generator

OWS

mechanical Governor and its types..!!!

Mechanical Governer

Diesel Fuel Systems

Mechanical Governors

This Meeting Guide is the third in a series dealing with the basic

diesel engine fuel system and components. It is about the diesel

governor.

Fig. 01

Each Caterpillar diesel engine is equipped with a governor. Why?

Diesel engines can accelerate-increase speed-at the rate of more

than 2000 revolutions per second. Yes, PER SECOND. Without a

governor a diesel engine can quickly destroy itself.

Fig. 02

GOVERNORS

Never operate a diesel engine without a governor controlling it. If

you were to move the fuel rack of a diesel engine to the full “ON”

position without a load and with the governor not connected, the

engine speed might climb and exceed safe operating limits before

you could shut it down. One second...two seconds...before you

knew what was happening, the engine may have been seriously

damaged by overspeeding.

This warning - never operate a diesel engine without a governor

controlling it - is concerned with one of the purposes of governors:

to prevent engine overspeeding. Governors also keep the engine at

the desired speed and increase or decrease engine power output to

meet load changes.

 WARNING

Fig. 03

This presentation introduces and explains the mechanical governor.

The mechanical governor is the simplest of the various types of

governors and is basic to their operation.

Besides the mechanical governor, Caterpillar engines use: servomechanical

governors, hydraulic governors and electronic

governors. These governors will be discussed in future

presentations.

 MECHANICAL

Fig. 04

This tractor is equipped with a mechanical governor. We can see the

governor control lever, the control linkage, the governor and the fuel

injection pump housing.

Fig. 05.

This is a closeup of the governor, mounted on the rear of the fuel

injection pump housing.

Let’s look at the construction and operation of the mechanical

governor using schematic illustrations.

Fig. 06

Diesel engine mechanical governors consist of two basic

mechanisms: the speed measuring mechanism and the fuel changing

mechanism.

Fig. 07

The speed measuring mechanism senses engine speed changes, and

the . . . .

Fig. 08

. . . fuel changing mechanism increases or decreases the amount of

fuel supplied the engine to correct these changes.

Let’s look at each basic mechanism separately and learn how it

operates.

Fig. 09

The speed measuring mechanism is simple, has few moving parts

and measures engine speed accurately. The main parts are:

1) gear drive from the engine,

2) flyweights, and

3) spring.

Fig. 10

The flyweights and “L” shaped ballarms which pivot are mounted

on the governor drive.

Fig. 11

The flyweights are rotated by the engine.

Fig. 12

As the flyweights rotate, they exert a centrifugal force outward. The

flyweights move outward pivoting the ballarms upward. The amount

of outward force depends on the speed of rotation.

Centrifugal force is the basic operating principle of the speed

measuring mechanism. Now, what is centrifugal force?

Fig. 13

If we tie a ball on a string . . . .

Fig. 14

. . . . . and swing it around and around . . .

Fig. 15

faster and faster, an outward force-centrifugal force- is exerted on

the ball. This centrifugal force swings the ball outward and upward

until the ball is nearly straight out.

And, we can see that the faster we swing it, the greater the pull on

the string and the farther outward it swings.

Fig. 16

This force - centrifugal force - is the basic principle used in the

speed measuring operation of the diesel engine governor. Keep

centrifugal force in mind as we discuss the other parts of the speed

measuring mechanism. Remember, the greater the engine speed, the

greater the centrifugal force and, therefore, the greater the

movement of the flyweights and ballarms.

Fig. 17

We need to control this centrifugal force, so we have the governor

spring. The spring acts against the force of the rotating flyweights

and tends to oppose them. The force exerted by the spring depends

on the governor control setting.

Fig. 18

A lever connected to the governor control pushes on or compresses

the spring. The spring force opposes the flyweights to regulate the

desired engine speed setting.

The governor control, shown here as a simple push-pull knob, may

be a hand operated control lever or a foot operated accelerator

pedal.

Fig. 19

As long as the spring force equals the flyweight centrifugal force,

engine speed remains constant.

Fig. 20

The speed measuring mechanism, then, senses and measures engine

speed changes. The fuel changing mechanism links the speed

measuring mechanism with the fuel injection pumps to control

engine.

Fig. 21

The fuel changing mechanism consists of the:

1) connecting linkage,

2) rack and

3) the fuel injection pump.

Fig. 22

Flyweight movement - outward in this example - due to engine

speed changes, are transferred through the simple linkage to the

rack and, therefore, to the fuel injection pump plunger.

Fig. 23

When the engine load increases - as when a dozer digs in - the

speed decreases. The flyweight force decreases, and the spring

moves the linkage and rack to increase the fuel to the engine. The

increase fuel position is held until the engine speed returns to the

desired setting, and the flyweight force again balances the spring

force.

Fig. 24

When the engine load decreases, the speed increases. The flyweight

force increases, overcoming the spring force, moving the rack to

decrease fuel to the engine. The decrease fuel position is held until

engine speed returns to the governor control setting, and the spring

force again balances the flyweight force.

Fig. 25

In summary, the basic governor consists of the:

drive gears, flyweights, spring, and control lever of the speed

measuring mechanism, and the connecting linkage, rack and fuel

injection pump of the fuel changing mechanism.

Fig. 26

The rack which meshes with the injection pump plunger gear

segments extends from the injection pump housing into the

governor. The rack and fuel injection pumps are parts of the fuel

injection pump housing assembly.

Fig. 27

As you recall, Meeting Guide 43, Fuel Systems: Part 2, explained

fuel injection pump operation and how the fuel injected into each

cylinder is increased or decreased.

Fig. 28

In this cutaway governor and fuel injection pump housing, we see

that the rack extends into the governor. Rack movement controls the

amount of fuel injected in each cylinder.

Let’s look at a closer view of our cutaway governor.

Fig. 29

In this cutaway section of our housing, see the flyweights, spring,

spring seat and thrust bearing. The thrust bearing (not previously

mentioned) is an anti-friction bearing between the flyweight

ballarms which rotate and the spring seat which, of course, does not

rotate.

Fig. 30

The governor is driven by the lower gear bolted to the fuel injection

pump camshaft.

The control lever has been removed from its shaft in the governor

housing and set in place to show how it is positioned.

Fig. 31

Looking closer, we can see (from right to left) the drive gear ,

flyweights , spring, spring seats, control lever and the collar and bolt

which connects to the rack. The purpose of the collar is explained

later.

Fig. 32

This governor cross section illustrates: (1) lever, (2) spring seat, (3)

spring, (4) spring seat and thrust bearing and (5) flyweight

assembly.

The arrows indicate drive gear rotation and rack movement.

Fig. 33

Two adjusting screws limit the travel of the governor control lever

between LOW IDLE position and the HIGH IDLE position.

The low idle stop and high idle stop are simply minimum and

maximum engine rpm settings with no load on the engine.

Fig. 34

The high and low idle adjusting screws are located under the cover

on the governor.

Fig. 35

Notice that the holes in the cover are shaped to lock the screws and

prevent them from turning after they are adjusted.

Fig. 36

The operators control is positioned at the desired governor setting:

low idle, high idle or fuel off.

Fig. 37

When the lever in the governor is in the LOW IDLE position, a

spring loaded plunger in the lever assembly contacts the low idle

stop of the adjusting screw.

Fig. 38

When the lever in the governor is in the HIGH IDLE position, the

lever contacts the high idle adjusting screw.

Fig. 39

To shut the engine down, the governor control is moved full forward

- past . . . .

Fig. 40

. . . the low idle stop. It is necessary to force the plunger over the

shoulder on the low idle screw . . .

Fig. 41

. . .to move the rack to the FUEL OFF position.

Fig. 42

Looking, again, at the governor cross section see

(1) the high idle adjusting screw and

(2) the low idle adjusting screw. The lever is against the HIGH IDLE screw.

The low idle and high idle screws, then limit minimum and

maximum engine rpm with no load on the engine. What limits

engine power output when the engine is fully loaded?

Fig. 43

A collar and stop bar limit rack travel and, therefore, the power

output. The collar is secured by a bolt connecting the rack linkage.

The stop bar is mounted in the governor housing. With the rack

moved to the FULL LOAD position, the collar just contacts the stop

bar.

Fig. 44

When our engine is operating with the governor at high idle (1) and

picks up a load, the speed decreases, flyweight centrifugal force

lessens, and the spring moves the rack to give the engine more fuel

increasing power. The collar (2) and stop bar (3) limit the distance

the spring can move the rack. As the collar contacts the stop bar,

full load position is reached. This limits the fuel delivered to the

engine so as not to exceed design limitations.

Fig. 45

Returning to the governor cross section, note the location of the:

(1) collar,

(2) stop bar,

(3) bolt and

(4) rack.

Like other diesel engine components, the governor must be

lubricated for long life. Let’s look at a governor lubrication system

schematic.

Fig. 46

The governor is lubricated by the engine lubricating system. Oil

from the diesel engine oil manifold is directed to the governor drive

bearing. All other governor parts are lubricated by splash.

The oil drains from the governor, through the fuel injection pump

housing, back to the engine crankcase.

Fig. 47

In summary, we have discussed the mechanical governor’s primary

components and principle of operation. Remember a governor has

two basic mechanisms: the speed measuring mechanism and the

fuel changing mechanism.

Fig. 48

In our cross section we located the lever, spring, spring seats,

flyweights, thrust bearing, drive gears and rack. We also discussed

the high and low idle settings and the full load stop.

At the beginning of this lesson we warned: NEVER OPERATE A

DIESEL ENGINE WITHOUT A GOVERNOR CONTROLLING

IT. Why are governors so important to a diesel engine?

Fig. 49

Note: The instructor should make clear we are not saying

gasoline engines never have a governor. Some

gasoline engines use a governor for the same reasons as

a diesel: to control engine speed and to regulate engine power output.

First, gasoline engines are self-limiting. Engine speed is controlled

by a butterfly valve in the intake manifold which limits the air

supply Limiting the amount of air taken in for combustion, limits

engine speed.

Fig. 50

Diesel engines, however, are not self-limiting. Engine air intake is

not limited, and the cylinders always have more air than is needed

to support combustion. The amount of fuel injected into the

cylinders controls engine speed.

Fig. 51

And, as the fuel is injected directly into the cylinders rather than

into the air intake manifold, engine response is immediate. This,

resulting greater power stroke, adds up to very rapid acceleration.

As we said earlier, diesel engines can accelerate at a rate of more

than 2000 revolutions per second. Because of this rapid

acceleration, manual control is difficult, if not impossible.

Fig. 52

NEVER OPERATE A DIESEL ENGINE WITHOUT A

GOVERNOR CONTROLLING IT.

Fig. 53

At this point, we have built up the basic diesel mechanical governor.

This governor works fine on engines whose engine speed is held

fairly constant and the governor is controlled by hand. However, on

other engines, the force needed to compress the governor spring or

to move the rack -just operating the governor - could be very tiring

to the operator.

Fig. 54

With the servo-mechanical governor, the work operation of

compressing the governor spring is done with engine oil pressure.

Fig. 55

With the hydraulic governor, the work operation of moving the fuel

injection pump rack is done with engine oil pressure.

These governors are discussed in . . . .

Fig. 56

. . . . Meeting Guide 60, “Servo Mechanical Governors.”

Fig. 57