What Is A Spark Plug? How Do Spark Plug Works? - SKengineers
WHAT IS A SPARK PLUG? HOW DO SPARK PLUG WORKS?
A spark plug is an electrical device that is used in
internal combustion engines to ignites compressed aerosol gasoline using an
electric spark. The electrical component is highly used to perform mechanical
jobs.
In simple term, spark plugs turn an energy source (gasoline) into movement. For instance, we have petrol which is highly flammable and also air, that could cause an explosion when mixed. The plug is like lighting fire to the compressed gas.
Spark plugs are either regular (replacement) or performance.
The performance spark plugs are tougher, having the ability to withstand a
greater change in temperatures and mechanical stresses. However, regular types
can’t. well, we’ll further look into them below this article.
Functions of Spark Plugs -
A spark
plug has two major functions in internal combustion engines which include -
Igniting
fuel/air mixture -
as electrical energy is transmitted through the component,
it ignites the gasoline/air mixture in the combustion chamber.
Removing
of heat -
spark plugs cannot create heat, but they can only be used to
remove heat. The temperature of the end of the plugs firing end must be low
enough to prevent pre-ignition but should be high enough to prevent fouling.
Spark plugs can serve as a heat exchanger by eliminating the unwanted thermal
energy from the combustion chamber. The heat is then transferred to the engines
cooling system.
Another discovered function of spark plugs is in Saab direct
ignition. When they are not firing, the device is used to measure ionization in
the cylinders. This ionic current measurement is used to replace the ordinary
cam phase sensor, knock sensor and misfire measurement function.
Why Are Spark Plugs So Important To Your Engine?
Most people don’t think twice about their spark plugs, yet
these small parts play an incredibly important role in how your car functions.
In fact, without properly working spark plugs, your car more than likely
wouldn’t be able to run at all. In this blog, our auto repair experts will take
a closer look at why your spark plugs are so important, including what they do
and how to know when it may be time to replace them.
Spark plug construction -
A spark plug is composed of a shell, insulator and the central
conductor. It passes through the wall of the combustion chamber and therefore
must also seal the combustion chamber against high pressures and temperatures
without deteriorating over long periods of time and extended use.
Spark plugs are specified by size, either thread or nut
(often referred to as Euro), sealing type (taper or crush washer), and spark
gap. Common thread (nut) sizes in Europe are 10 mm (16 mm), 14 mm (21 mm;
sometimes, 16 mm), and 18 mm (24 mm, sometimes, 21 mm). In the United States, common
thread (nut) sizes are 10mm (16mm), 12mm (14mm, 16mm or 17.5mm), 14mm (16mm,
20.63mm) and 18mm (20.63mm).
Parts of
the plug -
Terminal -
The top of the spark plug contains a terminal to connect to
the ignition system. Over of the years variations in the terminal configuration
have been introduced by manufacturers. The exact terminal construction varies
depending on the use of the spark plug. Most passenger car spark plug wires
snap onto the terminal of the plug, but some wires have eyelet connectors which
are fastened onto the plug under a nut. The standard solid non-removable nut
SAE configuration is common for many cars and trucks. Plugs which are used for
these applications often have the end of the terminal serve a double purpose as
the nut on a thin threaded shaft so that they can be used for either type of
connection. This type of spark plug has a removable nut or knurl, which enables
its users to attach them to two different kinds of spark plug boots. Some spark
plugs have a bare thread, which is a common type for motorcycles and ATVs.
Finally, in very recent years, a cup-style terminal has been introduced, which
allows for a longer ceramic insulator in the same confined space.
Insulator
-
The main part of the insulator is typically made from sintered
alumina (Al2O3), a very hard ceramic material with high dielectric strength,
printed with the manufacturer's name and identifying marks, then glazed to
improve resistance to surface spark tracking. Its major functions are to
provide mechanical support and electrical insulation for the central electrode,
while also providing an extended spark path for flashover protection. This
extended portion, particularly in engines with deeply recessed plugs, helps
extend the terminal above the cylinder head so as to make it more readily
accessible.
Dissected modern spark plug showing the one-piece sintered
alumina insulator. The lower portion is unglazed.
A further feature of sintered alumina is its good heat
conduction – reducing the tendency for the insulator to glow with heat and so
light the mixture prematurely.
Ribs -
By lengthening the surface between the high voltage terminal
and the grounded metal case of the spark plug, the physical shape of the ribs
functions to improve the electrical insulation and prevent electrical energy
from leaking along the insulator surface from the terminal to the metal case.
The disrupted and longer path makes the electricity encounter more resistance
along the surface of the spark plug even in the presence of dirt and moisture.
Some spark plugs are manufactured without ribs; improvements in the dielectric
strength of the insulator make them less important.
Insulator
tip -
Two spark plugs in comparison views in multiple angles, one
of which is consumed regularly, while the other has the insulating ceramic
broken and the central electrode shortened, due to manufacturing defects and /
or temperature swing
On modern (post 1930s) spark plugs, the tip of the insulator
protruding into the combustion chamber is the same sintered aluminium oxide
(alumina) ceramic as the upper portion, merely unglazed. It is designed to
withstand 650 °C (1,200 °F) and 60 kV.
Older spark plugs, particularly in aircraft, used an
insulator made of stacked layers of mica, compressed by tension in the centre
electrode.
With the development of leaded petrol in the 1930s, lead deposits on the mica became a problem and reduced the interval between needing to clean the spark plug. Sintered alumina was developed by Siemens in Germany to counteract this. Sintered alumina is a superior material to mica or porcelain because it is a relatively good thermal conductor for a ceramic, it maintains good mechanical strength and (thermal) shock resistance at higher temperatures, and this ability to run hot allows it to be run at "self cleaning" temperatures without rapid degradation. It also allows a simple single piece construction at low cost but high mechanical reliability. The dimensions of the insulator and the metal conductor core determine the heat range of the plug. Short insulators are usually "cooler" plugs, while "hotter" plugs are made with a lengthened path to the metal body, though this also depends on the thermally conductive metal core.
Seals -
Because the spark plug also seals the combustion chamber of
the engine when installed, seals are required to ensure there is no leakage
from the combustion chamber. The internal seals of modern plugs are made of
compressed glass/metal powder, but old style seals were typically made by the
use of a multi-layer braze. The external seal is usually a crush washer, but
some manufacturers use the cheaper method of a taper interface and simple
compression to attempt sealing.
Metal
case/shell -
The metal case/shell (or the jacket, as many people call it)
of the spark plug withstands the torque of tightening the plug, serves to
remove heat from the insulator and pass it on to the cylinder head, and acts as
the ground for the sparks passing through the central electrode to the side
electrode. Spark plug threads are cold rolled to prevent thermal cycle fatigue.
It's important to install spark plugs with the correct "reach," or
thread length. Spark plugs can vary in reach from 0.095 to 2.649 cm (0.0375 to
1.043 in), such for automotive and small engine applications. Also, a marine
spark plug's shell is double-dipped, zinc-chromate coated metal.
Central
electrode -
Central
and lateral electrodes -
The central electrode is connected to the terminal through
an internal wire and commonly a ceramic series resistance to reduce emission of
RF noise from the sparking. Non-resistor spark plugs, commonly sold without an
"R" in the plug type part number, lack this element to reduce
electro-magnetic interference with radios and other sensitive equipment. The
tip can be made of a combination of copper, nickel-iron, chromium, or noble
metals.
In the late 1970s, the development of engines reached a
stage where the heat range of conventional spark plugs with solid nickel alloy
centre electrodes was unable to cope with their demands. A plug that was cold
enough to cope with the demands of high speed driving would not be able to burn
off the carbon deposits caused by stop–start urban conditions, and would foul
in these conditions, making the engine misfire. Similarly, a plug that was hot
enough to run smoothly in town could melt when called upon to cope with
extended high speed running on motorways. The answer to this problem, devised
by the spark plug manufacturers, was to use a different material and design for
the centre electrode that would be able to carry the heat of combustion away
from the tip more effectively than a solid nickel alloy could. Copper was the
material chosen for the task and a method for manufacturing the copper-cored
centre electrode was created by Flow-form.
The central electrode is usually the one designed to eject
the electrons (the cathode, i.e. negative polarity relative to the engine
block) because it is normally the hottest part of the plug; it is easier to
emit electrons from a hot surface, because of the same physical laws that increase
emissions of vapor from hot surfaces (see thermionic emission). In addition,
electrons are emitted where the electrical field strength is greatest; this is
from wherever the radius of curvature of the surface is smallest, from a sharp
point or edge rather than a flat surface (see corona discharge). Using the
colder, blunter side electrode as negative requires up to 45 percent higher
voltage, so few ignition systems aside from wasted spark are designed this way.
Waste spark systems place a greater strain upon spark plugs since they
alternately fire electrons in both directions (from the ground electrode to the
central electrode, not just from the central electrode to the ground
electrode). As a result, vehicles with such a system should have precious
metals on both electrodes, not just on the central electrode, in order to
increase service replacement intervals since they wear down the metal more
quickly in both directions, not just one.
It would be easiest to pull electrons from a pointed
electrode but a pointed electrode would erode after only a few seconds.
Instead, the electrons emit from the sharp edges of the end of the electrode;
as these edges erode, the spark becomes weaker and less reliable.
At one time it was common to remove the spark plugs, clean
deposits off the ends either manually or with specialized sandblasting
equipment and file the end of the electrode to restore the sharp edges, but
this practice has become less frequent for three reasons:
cleaning with tools such as a wire brush leaves traces of
metal on the insulator which can provide a weak conduction path and thus weaken
the spark (increasing emissions).
plugs are so cheap relative to labour cost, economics
dictate replacement, particularly with modern long-life plugs.
iridium and platinum plugs that have longer lifetimes than
copper have become more common.
The development of noble metal high temperature electrodes
(using metals such as yttrium, iridium, tungsten, or palladium, as well as the
relatively high value platinum, silver or gold) allows the use of a smaller
centre wire, which has sharper edges but will not melt or corrode away. These
materials are used because of their high melting points and durability, not
because of their electrical conductivity (which is irrelevant in series with
the plug resistor or wires). The smaller electrode also absorbs less heat from
the spark and initial flame energy.
Polonium spark plugs were marketed by Firestone from 1940 to
1953. While the amount of radiation from the plugs was minuscule and not a
threat to the consumer, the benefits of such plugs quickly diminished after
approximately a month because of polonium's short half-life, and because build-up
on the conductors would block the radiation that improved engine performance.
The premise behind the polonium spark plug, as well as Alfred Matthew Hubbard's
prototype radium plug that preceded it, was that the radiation would improve
ionization of the fuel in the cylinder and thus allow the plug to fire more
quickly and efficiently.
Side
(ground, earth) electrode -
The side electrode (also known as the "ground
strap") is made from high nickel steel and is welded or hot forged to the
side of the metal shell. The side electrode also runs very hot, especially on
projected nose plugs. Some designs have provided a copper core to this
electrode, so as to increase heat conduction. Multiple side electrodes may also
be used, so that they don't overlap the central electrode. The ground electrode
can also have small pads of platinum or even iridium added to them in order to
increase service life.
Spark
plug gap -
Gap gauge
–
A disk with a tapered edge; the edge is thicker going
counter-clockwise, and a spark plug will be hooked along the edge to check the
gap.
Spark plugs are typically designed to have a spark gap which
can be adjusted by the technician installing the spark plug, by bending the
ground electrode slightly. The same plug may be specified for several different
engines, requiring a different gap for each. Spark plugs in automobiles
generally have a gap between 0.6 and 1.8 mm (0.024 and 0.071 in). The gap may
require adjustment from the out-of-the-box gap.
A spark plug gap gauge is a disc with a sloping edge, or
with round wires of precise diameters, and is used to measure the gap. Use of a
feeler gauge with flat blades instead of round wires, as is used on distributor
points or valve lash, will give erroneous results, due to the shape of spark
plug electrodes. The simplest gauges are a collection of keys of various
thicknesses which match the desired gaps and the gap is adjusted until the key
fits snugly. With current engine technology, universally incorporating solid
state ignition systems and computerized fuel injection, the gaps used are
larger on average than in the era of carburettors and breaker point
distributors, to the extent that spark plug gauges from that era cannot always
measure the required gaps of current cars. Vehicles using compressed natural
gas generally require narrower gaps than vehicles using gasoline.
The gap adjustment can be crucial to proper engine
operation. A narrow gap may give too small and weak a spark to effectively
ignite the fuel-air mixture, but the plug will almost always fire on each
cycle. A gap that is too wide might prevent a spark from firing at all or may
misfire at high speeds, but will usually have a spark that is strong for a
clean burn. A spark which intermittently fails to ignite the fuel-air mixture
may not be noticeable directly, but will show up as a reduction in the engine's
power and fuel efficiency.
Variations
on the basic design -
Spark
plug with two side (ground) electrodes -
Over the years variations on the basic spark plug design
have attempted to provide either better ignition, longer life, or both. Such
variations include the use of two, three, or four equally spaced ground
electrodes surrounding the central electrode. Other variations include using a
recessed central electrode surrounded by the spark plug thread, which
effectively becomes the ground electrode (see "surface-discharge spark
plug", below). Also there is the use of a V-shaped notch in the tip of the
ground electrode. Multiple ground electrodes generally provide longer life, as
when the spark gap widens due to electric discharge wear, the spark moves to another
closer ground electrode. The disadvantage of multiple ground electrodes is that
a shielding effect can occur in the engine combustion chamber inhibiting the
flame face as the fuel air mixture burns. This can result in a less efficient
burn and increased fuel consumption. They also are difficult or nearly
impossible to adjust to another uniform gap size.
Surface-discharge
spark plug -
A piston engine has a part of the combustion chamber that is
always out of reach of the piston; and this zone is where the conventional
spark plug is located. A Wankel engine has a permanently varying combustion
area; and the spark plug is inevitably swept by the rotor's apex seals. If a
spark plug were to protrude into the Wankel's combustion chamber it would be
hit by the passing apex seal, but if the plug were recessed to avoid this,
mixture access to the spark would be reduced, leading to misfire or incomplete
combustion. So a new type of "surface discharge" plug was developed,
presenting an almost flat face to the combustion chamber. A stubby centre
electrode projects only very slightly, and the entire earthed body of the plug
acts as the side electrode. The electrodes thus sit just beyond the reach of
the passing apex seal, while the spark is accessible to the fuel/air mixture.
The arc gap remains constant throughout the entire service life of a
surface-gap spark plug, and the spark path will continually vary (instead of
darting from the centre to the side electrode as in a conventional plug). A
further advantage of the surface-gap design is that the side electrode cannot
break off and potentially cause engine damage, though this also doesn't often
happen with conventional spark plugs.
Sealing
to the cylinder head -
Old spark plug removed from a car, new one ready to install.
Most spark plugs seal to the cylinder head with a single-use
hollow or folded metal washer which is crushed slightly between the flat
surface of the head and that of the plug, just above the threads. Some spark
plugs have a tapered seat that uses no washer. The torque for installing these
plugs is supposed to be lower than a washer-sealed plug. Spark plugs with
tapered seats should never be installed in vehicles with heads requiring
washers, and vice versa. Otherwise, a poor seal or incorrect reach would result
because of the threads not properly seating in the heads.
Tip
protrusion -
Different spark plug sizes. The left and right plug are
identical in threading, electrodes, tip protrusion, and heat range. The centre
plug is a compact variant, with smaller hex and porcelain portions outside the
head, to be used where space is limited. The rightmost plug has a longer
threaded portion, to be used in a thicker cylinder head.
The length of the threaded portion of the plug should be
closely matched to the thickness of the head. If a plug extends too far into
the combustion chamber, it may be struck by the piston, damaging the engine
internally. Less dramatically, if the threads of the plug extend into the
combustion chamber, the sharp edges of the threads act as point sources of heat
which may cause pre-ignition; in addition, deposits which form between the
exposed threads may make it difficult to remove the plugs, even damaging the
threads on aluminium heads in the process of removal.
The protrusion of the tip into the chamber also affects plug
performance, however; the more centrally located the spark gap is, generally
the better the ignition of the air-fuel mixture will be, although experts
believe the process is more complex and dependent on combustion chamber shape.
On the other hand, if an engine is "burning oil", the excess oil
leaking into the combustion chamber tends to foul the plug tip and inhibit the
spark; in such cases, a plug with less protrusion than the engine would normally
call for often collects less fouling and performs better, for a longer period.
Special "anti-fouling" adapters are sold which fit between the plug
and the head to reduce the protrusion of the plug for just this reason, on
older engines with severe oil burning problems; this will cause the ignition of
the fuel-air mixture to be less effective, but in such cases, this is of lesser
significance.
Major
Parts of a Spark Plug -
Below are
the various parts of a spark plug and their functions -
Insulator
-
This part insulates the terminal, centre shaft and centre
electrode from the housing. it helps to prevent the escape of high voltage from
the electrodes. Because the bottom part of the insulated is inserted into the
combustion chamber, high purity alumina with great heat-proof characteristic,
mechanical strength, excellent insulation and thermal conductivity at high
temperature must be used.
Terminal
-
A terminal is attached to a high-tension cord which allows
high-voltage current to flow through the ignition system. It contained a
terminal nut that supports almost any high-tension cord available. For some
vehicles that do not require a terminal nut, the terminal can be removed.
Ring,
Parking Washer -
This spark plug component helps the insulator and the
housing tightly fit each other and maintain air-tightness.
Gasket -
The gasket makes the housing and the engine perfectly fit
each other and also maintain the airtightness of the combustion chamber.
Although, there is a procedure for tightening and the suitable locking margin
must be secured.
Centre
Shaft (stem) -
The centre shaft connects the terminal and the centre
electrode. The part is made of steel and contains a role that allows
high-voltage current to flow from the terminal to the centre electrode without
loss.
Glass
Seal -
The glass seal is located between the centre shaft and
insulator to main the airtightness. It is made from a special mixture of glass
powder and copper powder. They are charged in the installation section of the
shaft and centre shaft and centre electrode and then melted at high
temperature. This bond the centre shaft and the centre electrode and fuses the
insulator and the metal. Their sealing is good and the thermal ratio of
expansion is perfect. Because of this, even under harsh conditions gaps do not occur
and good airtightness can be protected.
Electrode
with Copper -
A special nickel alloy is employed at the centre electrode
to reduce electrode wear and copper is sealed into the centre section to
enhance its thermal conductivity.
Housing -
The housing creates an outer shell that surrounds and
supports the insulator. It also allows the spark plug to be installed to the
engine. at the bottom part, there is a ground electrode that makes current flow
through the engine itself to the centre electrode over the gap.
U-groove
Ground Electrode -
This component serves a very important purpose as it allows
large ignition energy to be obtained, widen the flame core (flame size) easily.
The surface contacted by the air-fuel mixture is large and there is much edge
section, and sparks easily occur. Finally,
Tapered
Cut Ground Electrode -
In this part, the electrode tip is cut to a finely tapered
shape. The purpose is to reduce the quenching effect, which enriches the
ignition performance.
Types of
Spark Plugs -
Below are
the various types of spark plugs available out there -
Copper
Spark Plugs -
In these types of the spark plug, the centre electrode is
copper core coated with a nickel alloy. There is a need for more voltage to
produce sparks because the centre electrode has the largest diameter compared
to others. Because nickel alloys are a soft material and not very durable,
copper spark plugs need to be replaced more frequently than other types. Some
cars are designed to use the plug despite their shorter lifespan. Although some
manufacturers see installing expensive spark plugs may be a waste of money.
Iridium
Spark Plugs -
The iridium types of spark plug last longer since iridium is
harder and more durable material than platinum. The centre electrode is designed
to be small which makes it requires less voltage to generate a spark. This is
why it’s of the high cost compared to the first type. Nowadays, most vehicle
features the iridium spark plug because it minimizes the amount of car
breakdown.
Single
Platinum Spark Plugs -
These types of the spark plug are similar to the
copper/nickel version, only that, its centre electrode contains a platinum
disc. this disc is welded to the tip rather than nickel alloy. Single platinum
plugs are expensive but last longer than nickel alloy before it has worn away.
It generates more heat, which reduces carbon build-up. The plug is recommended
for new cars with a coil-on-plug ignition system.
Double
Platinum Spark Plugs -
In these types, there is a platinum coating both at the centre
and ground electrodes, which makes them more efficient and last longer. It is a
great choice for a wasted spark ignition system that exerts more wear on both
electrodes.
In a wasted spark ignition system, each ignition coil
ignites two spark plugs at a time. One in the compressor stroke’s cylinder and
the other in the exhaust stroke’s cylinder. At last, the spark gets wasted
because the air/fuel mixture is already burnt in the previous stroke. this
ignition system is not much affected by rain or debris.
Silver
Spark Plugs -
Because the material of silver spark plug is less durable,
it does not last long as iridium or platinum spark plug. But it has beat
thermal conductivity, it’s often used I older European performance cars and
motorcycles.
Working
Principle of a Spark Plug -
The working of a spark plug can be quite complex in some
stage but can be very interesting to learn. As earlier mentioned, its purpose
is to ignite the compressed air/fuel mixture of gasoline engines.
The device contains an insulated centre electrode that runs
its length and there are one or more ground electrodes on the bottom end. This
part is separated from the exposed end of the centre electrode which is called
“spark gap”. Whenever voltage is supplied from the ignition coil to the spark
plug, it is high enough, causing the electrical energy to jump the gap and
produce a spark.
The electrodes were traditionally made of copper but it’s
improve using high metals like iridium and platinum. The modern spark plugs are
designed with smaller centre electrodes so that lower voltage will be required
to generate sparks. This is because less voltage will make a more efficient
ignition system.
The plug is installed to a high voltage generated by
ignition or magneto. A voltage difference is developed between the centre
electrode and side electrode when the electrons flow from the coil. At this
stage, no current can flow because the air and fuel in the gap is an insulator,
but as the voltage rises, the structure of the gas between the electrodes
begins to change. Once the voltage exceeds the dielectric strength of the
gases, it becomes ionized.
Hot and
Cold Plugs -
The heat range of spark plugs is the temperature of the tip
in the spark gap. The component is considered hot or cold depending on the
temperature. The hot spark plugs are good insulators because more heat is
stored in the tip, and therefore in the combustion chamber. It tends to last
longer than the cold type because the temperature is high enough to burn off
carbon deposits. This is why hot plugs work well on standard vehicles.
Cold spark plugs are much less insulated which is why more
heat is conducted out of the tip and away from the chamber. This keeps the
combustion chamber cooler. However, too much hot cylinder chambers for perfect
function can result in pre-ignition or knocking (uneven fuel burn) which can
cause permanent damage to the engine. Cold plugs are ideal for high-performance
vehicles with high-temperature engines, those with high horsepower, high rpm,
prolonged acceleration or high-speed driving, or forced induction.
Symptoms
of Bad or Failing Spark Plug -
Below are
the symptoms of bad or failing spark plug and their prevention -
Slow acceleration
-
When spark plugs begin to fail, you begin to noticed poor
acceleration on your car. Though in modern vehicles where the sensor is telling
the most condition of the engine ignition system. The issue can be easily
noted. Sometimes the issue can be from a faulty sensor, but in most cases, it’s
a worn-out plug. Slow acceleration can be caused by several factors in the
engine such as bad fuel filters, dirty or clogged fuel injector, or faulty
oxygen sensor. This is why an expert needs to examine the situation as soon as
it started.
Poor Fuel
Economy -
A bad spark plug could make you spend more money on fuel. A
good spark plug helps to burn fuel efficiently in the combustion cycle, which
helps to achieve more than the average fuel economy. The problem occurs on the
spark plug either because the gap between the electrodes is either too close or
their much gap in-between. In most cases, mechanics adjust the gap when you
complain of a similar issue. Well, it is better to change the plug instead to
avoid such in the future.
Difficult
Start-up -
The issue is common as you find a DIY driver going straight
losing his spark plug when he/she have trouble starting their car. In most time
the device seems to be worn. But, different symptoms can affect an engine’s ignition
system, an expert should be involved.
When Do I
Need to Change My Spark Plugs?
Most manufacturers these days will install “extended-life”
spark plugs at the factory. They’re only marginally more expensive than a
standard plug, and it sounds really good to the consumer. Extended-life spark
plugs are usually rated for a lifespan of around 100,000 miles. As these plugs
approach the end of their life, the gap between the two leads begins to widen,
which leads to reduced efficiency and the possibility of misfiring. If your
plug corrodes to the point where it breaks, it could do serious damage to the
interior of your engine cylinder, which leads to an extremely expensive repair
to get it fixed.
Be sure to consult your vehicle’s owner’s manual to see how
long of a lifespan your spark plugs are rated for. Never let your spark plugs
go past their rated mileage.
Engine
Misfiring -
Misfiring of engines is an issue from the ignition system,
often time in modern cars it’s a fault from a sensor. But it’s also caused by
the spark plug wire or if the tip of the spark plug that connects the wire got
damaged. If an engine misfire the driver will experience intermittent stumbling
or sputtering sounds in the engine. if care is not taken and the misfiring
continues, exhaust emissions will increase, fuel economy will drop, and engine
power will decrease. So, a different problem is related to misfiring, consider
seeing a mechanic immediately you notice misfire in the engine.
In conclusion, a spark plug is a great component which we’ve
seen effective working on gasoline engines. We’ve also examined two functions
it offers which include igniting and removing heat from the chamber. Various
spark plug parts and functions were revealed and also types as well as bad
symptoms.
Heat
range -
Construction of hot and cold spark plugs – a longer insulator
tip makes the plug hotter
The operating temperature of a spark plug is the actual
physical temperature at the tip of the spark plug within the running engine,
normally between 500 and 800 °C (932 and 1,472 °F). This is important because
it determines the efficiency of plug self-cleaning and is determined by a
number of factors, but primarily the actual temperature within the combustion
chamber. There is no direct relationship between the actual operating
temperature of the spark plug and spark voltage. However, the level of torque
currently being produced by the engine will strongly influence spark plug
operating temperature because the maximal temperature and pressure occur when
the engine is operating near peak torque output (torque and rotational speed
directly determine the power output). The temperature of the insulator responds
to the thermal conditions it is exposed to in the combustion chamber, but not
vice versa. If the tip of the spark plug is too hot, it can cause pre-ignition
or sometimes detonation/knocking, and damage may occur. If it is too cold,
electrically conductive deposits may form on the insulator, causing a loss of
spark energy or the actual shorting-out of the spark current.
A spark plug is said to be "hot" if it is a better
heat insulator, keeping more heat in the tip of the spark plug. A spark plug is
said to be "cold" if it can conduct more heat out of the spark plug
tip and lower the tip's temperature. Whether a spark plug is "hot" or
"cold" is known as the heat range of the spark plug. The heat range
of a spark plug is typically specified as a number, with some manufacturers
using ascending numbers for hotter plugs, and others doing the opposite – using
ascending numbers for colder plugs.
The heat range of a spark plug is affected by the
construction of the spark plug: the types of materials used, the length of
insulator and the surface area of the plug exposed within the combustion
chamber. For normal use, the selection of a spark plug heat range is a balance
between keeping the tip hot enough at idle to prevent fouling and cold enough
at maximal power to prevent pre-ignition or engine knocking. By examining
"hotter" and "cooler" spark plugs of the same manufacturer
side by side, the principle involved can be very clearly seen; the cooler plugs
have a more substantial ceramic insulator filling the gap between the centre
electrode and the shell, effectively allowing more heat to be carried off by
the shell, while the hotter plugs have less ceramic material, so that the tip
is more isolated from the body of the plug and retains heat better.
Heat from the combustion chamber escapes through the exhaust
gases, the side walls of the cylinder and the spark plug itself. The heat range
of a spark plug has only a minute effect on combustion chamber and overall
engine temperature. A cold plug will not materially cool down an engine's
running temperature. (A too hot plug may, however, indirectly lead to a runaway
pre-ignition condition that can increase engine temperature.) Rather, the main
effect of a "hot" or "cold" plug is to affect the
temperature of the tip of the spark plug.
It was common before the modern era of computerized fuel
injection to specify at least a couple of different heat ranges for plugs for
an automobile engine; a hotter plug for cars that were mostly driven slowly
around the city, and a colder plug for sustained high-speed highway use. This
practice has, however, largely become obsolete now that cars' fuel/air mixtures
and cylinder temperatures are maintained within a narrow range, for purposes of
limiting emissions. Racing engines, however, still benefit from picking a
proper plug heat range. Very old racing engines will sometimes have two sets of
plugs, one just for starting and another to be installed for driving once the
engine is warmed up.
Spark plug manufacturers use different numbers to denote
heat range of their spark plugs. Some manufacturers, such as Denso and NGK,
have numbers that become higher as they get colder. By contrast, Champion,
Bosch, BRISK, Beru, and ACDelco use a heat range system in which the numbers
become bigger as the plugs get hotter. As a result, heat range numbers need to
be translated between the different manufacturers. The same numbers have very
different meanings between different manufacturers. In this case, plugs with
the same heat range numbers can't be interchanged casually as being equal. To
give an extreme case, NGK's BR2LM is equivalent to Champion's RJ19LM, which is
a common spark plug for many lawnmowers.
When Do I
Need to Change My Spark Plugs?
Most manufacturers these days will install “extended-life”
spark plugs at the factory. They’re only marginally more expensive than a
standard plug, and it sounds really good to the consumer. Extended-life spark
plugs are usually rated for a lifespan of around 100,000 miles. As these plugs
approach the end of their life, the gap between the two leads begins to widen,
which leads to reduced efficiency and the possibility of misfiring. If your
plug corrodes to the point where it breaks, it could do serious damage to the
interior of your engine cylinder, which leads to an extremely expensive repair
to get it fixed.
Be sure to consult your vehicle’s owner’s manual to see how
long of a lifespan your spark plugs are rated for. Never let your spark plugs
go past their rated mileage.
Comments
Post a Comment