NGKGlow Plugs:20Questions & Answers

21. Why are glow plugs fitted? 3

2. What are the benefits of NGK glow plugs? 4

3. Why do glow plugs need to preheat? 5

4. What is post-glow? 5

5. How do I select the correct glow plug? 6

6. How do I interpret the NGK code? 7

7. What different types of glow plug does NGK manufacture? 8

8. How is a glow plug constructed? 8

9. What is a ceramic glow plug? 9

10. What are the benefits of ceramic glow plugs? 9

11. What is SRM-technology? 10

12. What is QGS-technology? 10

13. What is AQGS-technology? 11

14. How do I fit a glow plug? 11

15. Why are glow plugs so engine specific? 12

16. When are glow plugs required? 12

17. What can I expect from a glow plug? 13

18. How do I test glow plugs? 14

19. What technological advances are on the horizon? 15

20. What significance does the use of modern glow plug technology have for the environment? 15

Contents

20Questions & Answers

3DIESEL ENGINES have spontaneous ignition, whichmeans that the injected fueldoes not require a spark to ignite it. The high temperature, which occurs as a result of compressingintake air, is sufficient toignite the fuel. However, in cold conditions, moreenergy is required to help ignitionat start because both the intake airand the engine itself are colder andcompression and pumping lossesare higher too. Therefore, in dieselengines, glow plugs are a key factor for every cold start. At lowambient temperatures they heat thecombustion chamber sufficiently toallow stable combustion conditionsfor the injected fuel.

The 'glow pencil' (rod-like heatingelement) of the glow plug (which fits in the cylinder head)protrudes into the glow chamber orpre-combustion chamber. It is mosteffective when positioned on theedge of the mixing vortex. If it protrudes too far into thecombustion chamber, it impedesthe preparation and formation of an ignitable fuel/air mixture.

NGK glow plugs set the higheststandards in diesel technology,always incorporating the latesttechnological advances. To ensurethat this continues into the future,NGK invests a great deal of time,expertise and money in intensiveresearch and development.

Indirect-injection engine Swirl chamber engine Direct-injection engine

1 Fuel injector2 Sheathed

glow plug3 Prechamber4 Swirl chamber5 Combustion

chamber

1

3 2 4 22

1

1

5

Why are glow plugs fitted?1

4The NGK brand is synonymous with quality across the board. NGK glow plugs:

Start engines quickly and smoothly.

Offer an excellent post-glowfunction.

Have a long service life. Offer the latest in high-

technology for today and tomorrow:

NGK is constantly developinginnovative concepts for the engines of the future.

With NGK glow plugs, engines run quietly and smoothly. They are kinder on the environmenttoo, thanks to the promotion ofclean combustion and lower toxicemissions.

What are the benefits of NGK glow plugs?2

5Before the engine is started,the components of the engine- the cylinder, pistons andvalves for instance - are cold.They take heat out of the intake air. This effect isintensified if the intake air isalso extremely cold; i.e. atlow ambient temperatures.

However, in order to generatecompression ignition successfully,diesel engines require the ambienttemperature inside the combustionchamber to be warm enough. Glow plugs compensate for the heatloss caused by the cool components and cold air and ensure thattemperatures are optimal beforeignition.

To do this, the plug is energisedbefore the engine is started. The temperature of the heater tube rises rapidly to over 800C,ensuring quick ignition and thus environmentally friendlycombustion.

The post-glow switching principle

Battery

Key switch

Starter

Signallamp

Electronic control unit

Relay

Glow plugs

Why do glow plugs need to preheat?

What is post-glow?

Post-glow takes place afterignition when the engine isrunning - possibly the firstfew hundred meters with SRMtravelled by the car. It isrequired to prevent heat losswhilst the engine is warmingup to its normal operatingtemperature.

Without it, there would be aconsiderably greater level of toxicemissions and white and bluesmoke from the exhaust. Theengine would not run smoothlyeither, displaying the characteristiccold-start knocking.

Post-glow helps to keep the combustion chamber at a constanttemperature until the engine reaches a reasonable operatingtemperature.

Type of glow plug Preheating times Sheathed type glow plug with single coil Standard e.g. Y-103-2, Y-173 20-25 Sec. to 800C

QGS glow plug e.g. Y-103 V, Y-106 V 15-17 Sec. to 800Ce.g. Y-128 T, Y-204 T S1 13-14 Sec. to 800C

QGS glow plug e.g. Y-112 M 1 approx. 10 Sec. to 900Ce.g. Y-107 R, Y-112 R 1 approx. 6 Sec. to 900C

with double coil QGS glow plug e.g. Y-707 RS, Y-702 U approx. 6 Sec. to 900Cself-regulating e.g. Y-701 J, Y-515 J approx. 4 Sec. to 900C

3

4

6Simply take a look at the NGK catalogue, where our full listof diesel vehicle applicationsis provided, showing the correct glow plug for eachengine.

This information is also availableon our website. Go to www.ngkntk.co.uk and selectPart Finder.

5 How do I select the correct glow plug?

7Y, YS: Body earth type YD: Insulated type

Thread size and number of coils: 1:10 mm 2:12 mm 3:10 mm 4:14 mm 5:10 mm (Double coil)7:10 mm (Double coil) 8:18 mm 9:12 mm (Double coil)

Note:Y-109, Y-159 and Y-171 for Caterpillar have a thread size of 3/8 (= approx. 9,5 mm)

Battery voltage: 0-4: 12 V5-9: 24 V

Serial number Special tubematerials

Revisions numberTemperature rise time: V: Rapid glow plug T: Rapid glow plug

(except YS-871T,it is a sheathedtype glow plug)

R, M: QGS (also Y-117SSand Y-204SS)

J: SRM K or no letter:

Standard B: Change U: QGS AS: AQGS

Sheathed heated glow plugs

Y - 2 0 4 T S 1

Y: Sheathed typeglow plug

E: 8 mm (QGS or SRM)

The two last figures build the serial number

Y E 0 1

C: Ceramic glow lug Y: SRC Z: QGS X: QGS with

double isolators

The last two figures build the serial number

Ceramic glow plugs

C Y 0 1

If you thought all glow plugswere the same, you'd betterthink again: on closer inspection,you'll see that glow plugs come ina variety of guises and also differin terms of properties and constituent materials.

With the standard alpha-numericalcode on the NGK glow plugs, youcan classify every glow plug quicklyand easily.

How do I interpret the NGK code?6

MetalHeatingCoil

MagnesiumOxideInsulatingpowder

Metal housing

Caulked nut

Terminal

Regulating coil Thread

Central electrodeHeater tube

8

NGK manufactures suitableglow plugs for a wide varietyof engines and ECUs. NGKglow plugs can be broadlyclassified into two groupswhich are outlined below.

Sheathed-type metal glow plugsThese glow plugs have a heatingcoil enclosed within a tube that is made of heat-resistantmaterial.

Ceramic glow plugs: The heating element of theseglow plugs is completely encasedin a ceramic material.

There are a number of further glowplug varieties which fall withinthese two main categories:

Sheathed-type metal glow plugs

There are four types of sheathedmetal glow plugs available:

Standard sheathed-type glowplugs

Fast heat glow plugs QGS sheathed-type glow plugs Self-regulating sheathed-type

glow plugs

Ceramic glow plugs

There are two types of ceramic glowplug available:

QGS glow plugs Self-regulating glow plugs

7 What different types of glow plug do NGK manufacture?

How is a glow plug constructed?

Structure of a self-regulatingceramic glow plug

Metal sleeve Metal shell Insulator Tightening nut

Caulked nutRegulating coilMetal heating coil Terminal

Structure of a self-regulatingmetal glow plug

8

9Ceramic glow plugs are engineered to perform underthe most extreme conditions.Compared to a metalsheathed plug they have amore robust heating elementwhich is made from a specialhigh melting point material.

This is encased in New Ceramic(Silicon Nitride) which has extremely good thermal conductivityproperties and can withstand veryrapid heating times over extendedservice periods.

What is a ceramic glow plug?

The combination of heatingcoil and ceramic coatingallows ceramic glow plugs toreach higher temperaturesthan metal sheathed-type glow plugs, thus enabling theengine to reach operating temperature particularlyquickly, even at temperatureswell below freezing.

Due to the robust nature of theheating coil and the ceramicmaterials, post-glow times of up toten minutes can be employed.

A further advantage of ceramicglow plugs is that the cross sectional area heating portion canbe made a much smaller. This is amajor advantage to modern dieselengines where space is severelyrestricted around the combustionchamber.

10 What are the benefits of ceramic glow plugs?

First generation SRC (SelfRegulating Ceramic glow plug)

Regulating coil

Second generation HTC (HighTemperature Ceramic glow plug)

Third generation NHTC (New-High Temperature Ceramicglow plug

Metal heatingcoil

Ceramic heatingelement

All-ceramic-heater

9

10

QGS is an abbreviation ofQuick Glow System. QGS metal sheathed-typeglow plugs heat up extremelyquickly. This means that theyare very quick to preheat andimprove cold-start behaviour.

This type of glow plug is only usedin conjunction with a special QGScontroller that regulates the energysupplied and thus the heating ofthe glow plug. There are two typesof quick-start glow plugs. They are not interchangeable as they differ in internal design andconstruction.

The following types are available:

QGS glow plug withone heating coil

QGS glow plug with one heatingand one regulating coil

The heater coil in the first type has a very low resistance which allowsan extremely large current flowproviding the very rapid warm upcharacteristic. The second type hasan additional regulating coil whichincreases its resistance as thetemperature rises.This provides a certain degree ofcontrol for the heating coil.As QGS glow plugs are designed to consume very large amounts ofcurrent it is very important thatthey are only used where the vehicle is designed with a specificQGS control system.

SRM is an abbreviation ofSelf Regulated Metal.Similar to QGS glow plugswith two heating coils, SRM sheathed-type glowplugs have a heating coil and a regulating coil.

The heating coil heats up very quickly and as the temperature of the control coil rises so the resistance increases, thus regulating the current flow.

The self regulation provided by the control coil allows SRM glowplugs to be run with almost noexternal control or monitoring, thus providing excellent preheatingand post-glow properties.

What is SRM technology?

What is QGS technology?

11

12

11

Before fitting a glow plug,you should always make surethat the thread is clean.Once you have done this, screw inthe glow plug by hand until theseating comes into contact withthe cylinder head. It can then be tightened using theappropriate tightening torque (see below).

PLEASE NOTE:Ceramic glow plugs are very robustagainst combustion conditionshowever, ceramic materials are by their very nature, brittle andmust be handled accordingly.Careless handling during installation or removal could damage the ceramic probe rendering the plug unserviceable.

How do I fit a glow plug?

Tightening torques of terminal nutsThread diameter Appropriate

tightening torques4 mm (M4) 0,81,5 Nm5 mm (M5) 3,04,0 Nm

Tightening torques of glow plugs:Thread diameter Appropriate

tightening torques8 mm 815 Nm

10 mm 1520 Nm12 mm 2025 Nm14 mm 2025 Nm18 mm 2030 Nm

14

What is AQGS technology?13An evolution of the QGS type,AQGS is an abbreviation ofAdvanced Quick GlowSystem. Their very high performance characteristicsallow even faster heatingtimes than either the SRM or QGS types.

These double coil glow plugs are designed to operate at battery voltage at the very shortpre heating stage, approximately6.5 volts during cranking and 5.0 volts in the post glow period.Due to the high in rush current and the specific stages of applied voltage they require very precisecontrol by PWM (pulse width modulation) via the ECU. Thisstrategy enables strict control oftheir long post glow performance

as the ECU can take data from various sensors around the engineensuring that the glow plug performance is at its optimumallowing further reduction of harmful emissions.

Except at very low ambient temperatures the glow plug is primarily used to control smoke andother emissions after the start upand just as importantly for the driver, good performance from cold.

1100

1000

900

800

700

600

500

400

300

200

100

010 20 30 40

Glow plugs are required when the temperature insidethe combustion chamber isnot high enough to ignite bythe heat generated fromcompression of the intake air;e.g. under cold start conditions.Some older engine designs evenrequire a preheating period after arelatively brief period of rest.

Modern diesel engines also oftenrequire the post-glow function of the glow plugs to help further reduce emissions.

12

Glow plugs are designed to reach their saturation temperature after a specificperiod of time at a given voltage application.

This temperature has to be maintained for a specific period oftime to provide stable combustionconditions.

Diesel engine operation and toxicemissions can only be improved if the glow plug matches or exceedsthe engine manufacturer'sspecification.

Why are glow plugs so engine specific?

When are glow plugs required?

Temperature (C)

Time (Sec.)

SRM-sheathed type glow plugsQGS-sheathed type glow plugsQuick-start glow plugsFast heating type glow plugs

16

15

13

When choosing a glow plug,do not compromise on the following features:

Safe start-up from low ambienttemperatures

Low emissions during warm-upphase

Stable idling running beforeengine reaches operatingtemperature

High quality coating on shell forhigh resistance to corrosion

Unique shell design for excellentheat transfer, perfect gas tightsealing and high resistance todeformation and security of theheating coils.

Many car manufacturers are notprepared to compromise on thesefeatures either - which is why theychoose proven NGK technology.

What can I expect from a glow plug?17

14

To ensure that a sheathed-type glow plug is functioningcorrectly, you should measurethe resistance between the terminal and the metalcasing.

For reliable results, you shouldmake the following preparations:

Ensure that your measuringinstrument is capable of displaying even the most minimaltesting voltages. The reason for this is that a QGS glow plugat ambient temperature only has a resistance of approximately 0.1 1.

Before taking the measurements,remove any rust, dirt, oil or lacquer from the thread of theglow plug.

Ideally, you should check ceramicglow plugs without removing from the engine. This reduces the risk of damage as a result of dismantling.

You evaluate the results of themeasurement as follows:

If a resistance of ' is displayed,the heating coil is broken.

If the resistance is below 5 1,the heating coil is functioning properly.

The resistance of ceramic glowplugs is usually below 1 1.

Please take particular note of thefollowing:

It is not recommended to check a glow plug by applying batteryvoltage until it glows. The heatingcoil temperature can be raised to the point of damage before thetube appears to be well heated;this is especially true for QGStypes. There is also a great risk of personal injury.

Glow plug of type CY, CZ Glow plug of type CXGlow plug of type Y

red =terminal

black/white =metal shell

How do I test glow plugs?18

NGK leads the way in the development of new technologies for this dynamicmarket. Anticipating trendsand developing solutions atan early stage has alwaysbeen an NGK forte.

Taking emissions as an example,the impending EU emissions standards Euro 4 and Euro 5 willsoon make it necessary to lower the comparatively high compressionratio of diesel engines.

In order to guarantee reliableignition for such engines, NGK hasdeveloped NHTC generation ceramicglow plugs.

The secret of these glow plugs istheir longer heating element andnarrow diameter which enable themto increase temperature by up to1,000C in less than two seconds.

They also have a longer post-glowduration and, for the first timeever, offer an intermittent-glowfunction to reduce emissions.

NHTC glow plugs: ground-breakingtechnology from NGK.

What technological advances are on the horizon?

15

Innovative glow plugs are a key component in effectivepollution control. NGK recognised this and investedin ceramic glow plugs as afuture market at a time whenmost people still consideredthe new technology to beuneconomical.

Their success has proven that this was the right strategy: EU emissions standards are becoming increasingly more stringent and, in respect of exhaust emissions, require perfect interaction between all componentsof the engine. They are alsobeneficial for the development ofdiesel engines which operate at alower compression ratio.

What significance does the use of modern glowplug technology have for the environment?

These engines are reliant on high-performance glow plugs, such as the NGK ceramic glowplugs, to meet the stringentrequirements from Brussels.

20

19

For up-to-date information

about glow plugs go to:

www.ngkntk.co.uk

NGK Spark Plugs (UK) LtdMaylands AvenueHemel HempsteadHerts HP2 4SDTel: 01442 281000Fax: 01442 281001www.ngkntk.co.uk