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Spark plugs - what are they for and how do they work

Spark plug

No gasoline internal combustion engine can be started without a spark plug. In our review, we will consider the device of this part, how it works and what needs to be considered when choosing a new replacement kit.

What are spark plugs

A candle is a small element of a car ignition system. It is mounted above the engine cylinder. One end is screwed into the engine itself, a high-voltage wire is put on the other (or in many engine modifications a separate ignition coil).

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Although these parts are directly involved in the movement of the piston group, it cannot be said that this is the most important element in the motor. The engine will not be possible to start without other components, such as a gasoline pump, carburetor, ignition coil, etc. Rather, the spark plug is another link in the mechanism that contributes to the stable operation of the power unit.

What are candles for in a car?

They provide a spark to ignite gasoline in the combustion chamber of the engine. A bit of history.

The first ICEs were equipped with open flame tubes. In 1902, Robert Bosch invited Karl Benz to install his development in his engines. The part had almost the same design and worked on the same principle as modern counterparts. Throughout history, they underwent minor changes that related to materials for the conductor and dielectric.

Spark plug device

At first glance, it seems that the spark plug (SZ) has a simple design, but in fact its design is much more complicated. This element of the engine ignition system consists of the following elements.

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  • Contact tip (1). The upper part of the SZ, on which a high-voltage wire is put, coming from the ignition coil or individual. Most often, this element is made with a thickening at the end, for fixing according to the latch principle. There are candles with thread on the tip.
  • Insulator with external ribs (2, 4). The fins on the insulator form a current barrier, preventing breakdowns from the rod to the surface of the part. It is made of ceramic with alumina. This unit must withstand temperature jumps of up to 2 degrees (formed during the combustion of gasoline) and at the same time maintain dielectric properties.
  • Case (5, 13). This is the metal part on which the ribs are made for fixing with a wrench. A thread is cut on the lower part of the body, with the help of which the candle is screwed into the spark plug of the motor. The body material is high alloy steel, the surface of which is coated with chrome to prevent the oxidation process.
  • Contact rod (3). The central element through which the electric discharge flows. It is made of steel.
  • Resistor (6). Glass sealers are equipped with most modern SZ. It suppresses radio interference arising from the power supply. It also serves as a seal for the contact rod and electrode.
  • Sealing washer (7). This part can be in the form of a cone or a regular washer. In the first case, this is one element, in the second an additional gasket is used.
  • Heat Sink (8). Provides fast cooling of SZ, expanding the heating range. The amount of carbon deposits formed on the electrodes and the durability of the candle itself depend on this element.
  • Central electrode (9). Initially, this part was made of steel. Today, bimetallic material is used with a conductive core coated with a heat-releasing composition.
  • Thermal cone of the insulator (10). Serves for cooling the central electrode. The height of this cone affects the glow number of the candle (cold or warm).
  • Working chamber (11). The space between the housing and the cone of the insulator. It facilitates the process of burning petrol. In the "torch" candles, this camera is expanded.
  • Side electrode (12). A discharge occurs between it and the core. This process is similar to an arc discharge to mass. There are SZ with several side electrodes.

The photo also shows the value of h. This is a spark gap. Sparking more easily occurs with a minimum distance between the electrodes. However, the spark plug must ignite the air-fuel mixture. And this requires a "fat" spark (at least one millimeter long) and, accordingly, a larger gap between the electrodes.

More about gaps is described in the following video:

Iridium candles - is it worth it to put or not?

To save battery life, some manufacturers use innovative technology to create SZ. It consists in making the central electrode thinner (less energy is required to overcome the increased spark gap), but at the same time so that it does not burn out. For this, an alloy of inert metals (such as gold, silver, iridium, palladium, platinum) is used. An example of such a candle is shown in the photo.

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How spark plugs work in a car

When the engine starts, a high voltage current is supplied from the ignition coil (it can be one for all candles, one for two candles, or individual for each SZ). At this moment, a spark is formed between the electrodes of the plug, igniting the air-fuel mixture in the cylinder.

What loads are they experiencing

During the operation of the engine, each spark plug experiences different loads, so they are made of materials that can withstand such loads for a long time.

Thermal loads

The working part of the spark plug (both of its electrodes) is located inside the cylinder. When the intake valve (or valves, depending on the engine design) opens, a fresh portion of the air-fuel mixture enters the cylinder. In winter, its temperature can be negative or close to zero.

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On a heated engine, when the HTS is ignited, the temperature in the cylinder can rise sharply to 2-3 thousand degrees. Due to such sharp and critical changes in temperature, the electrodes of the plug can deform, which over time affects the gap between the electrodes. In addition, the metal part and the porcelain insulator have different thermal expansion coefficients. Such sudden changes can also destroy the insulator.

Mechanical loads

Depending on the type of engine, when a mixture of fuel and air is ignited, the pressure in the cylinder can change sharply from a vacuum state (negative pressure relative to atmospheric) to exceeding atmospheric pressure by 50 kg / cm XNUMX. and higher. In addition, when the motor is running, it creates vibrations, which also negatively affect the condition of the spark plugs.

Chemical load

Most chemical reactions are possible at high temperatures. The same can be said about the processes occurring during the combustion of carbon fuels. At the same time, a large amount of chemically active substances are released (thanks to this, the catalytic converter works - it enters into a chemical reaction with these substances and neutralizes them). Over time, they act on the metal part of the candle, forming various kinds of carbon deposits on it.

Electrical loads

When a spark is generated, a high voltage current is applied to the center electrode. Basically, this figure is 20-25 thousand volts. In some power units, ignition coils generate a pulse above this parameter. The discharge lasts up to three milliseconds, but this is enough for such a high voltage to affect the state of the insulator.

Deviations from the normal combustion process

Spark plug life can be reduced if the combustion process of the air / fuel mixture changes. This process is influenced by various factors, for example, poor fuel quality, early or late ignition, etc. Here are some of these factors that will shorten the life of new spark plugs.

Misfire

This effect occurs when a lean mixture is supplied (there is much more air than the fuel itself), when insufficient current power is generated (this happens due to a malfunction of the ignition coil or due to poor-quality insulation of high-voltage wires - they break through) or when a spark gap occurs. If the motor suffers from this malfunction, deposits will form on the electrodes and insulator.

Glow ignition

There are two types of glow ignition: premature and retarded. In the first case, the spark is triggered before the piston reaches top dead center (there is an increase in the ignition timing). At this point, the motor heats up a lot, which leads to an even greater increase in SPL.

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This effect leads to the fact that the air-fuel mixture can ignite arbitrarily when it enters the cylinder (it ignites due to the hot parts of the cylinder-piston group). When glow ignition occurs, valves, pistons, cylinder head gasket and piston rings can be damaged. As for the damage to the plug, in this case, the insulator or electrodes may melt.

Detonation

This is a process that also occurs due to the high temperature in the cylinder and the low octane number of the fuel. When detonating, the not yet compressed VTS begins to ignite from a red-hot part in the part of the cylinder farthest from the intake piston. This process is accompanied by a sharp combustion of the air-fuel mixture. The released energy does not propagate from the block head, but from the piston to the head at a speed exceeding the speed of sound.

As a result of detonation, the cylinder overheats in one part, the pistons, valves and the candles themselves overheat. Plus the candle is experiencing increased pressure. As a result of this process, the SZ insulator may burst or part of it may break off. the electrodes themselves may burn out or melt.

Engine knocking is determined by characteristic metallic knocks. Also, black smoke may appear from the exhaust pipe, the engine will start to consume a lot of fuel, and its power will become noticeably less. For the timely detection of this destructive effect, a knock sensor is installed in modern engines.

Dieseling

Although this problem is not related to the incorrect operation of the spark plugs, it still affects them, subjecting them to a lot of stress. Dieseling is self-ignition of gasoline when the engine is turned off. This effect occurs due to the contact of the air-fuel mixture with the hot parts of the engine.

This effect appears only in those power units in which the fuel system does not stop working when the ignition is turned off - in carburetor ICEs. When the driver turns off the engine, the pistons continue to suck in the air-fuel mixture by inertia, and the mechanical fuel pump does not stop the supply of gas to the carburetor.

Dieseling is formed at extremely low engine speeds, which is accompanied by very unstable engine operation. This effect stops when the parts of the cylinder-piston group are not sufficiently cooled. In some cases, this takes a few seconds.

Carbon deposits on a candle

The type of carbon deposits on candles can be very different. According to it, you can conditionally determine some problems with the engine. Hard carbon deposits appear on the surface of the electrodes when the temperature of the combustion mixture exceeds 200 degrees.

Spark plugs - what are they for and how do they work

If there is a large carbon deposit on the candle, in most cases it interferes with the performance of the SZ. The problem can be resolved by cleaning the spark plug. But cleaning does not eliminate the cause of the unnatural carbon deposits, so these causes must be addressed anyway. Modern candles are designed to be self-cleaning.

Candle resource

Spark plug life does not depend on one factor. The period for replacing SZ is influenced by:

If we take classic nickel candles, then they usually run up to 15 kilometers. If the car is operated in a megalopolis, then this figure will be lower, because although the car does not drive, when it is in a traffic jam or a jam, the engine continues to work. Multi-electrode analogs last approximately twice as long.

When installing candles with iridium or platinum electrodes, as indicated by the manufacturers of these products, they can move up to 90 thousand kilometers. Of course, the technical condition of the motor also affects their performance. Most automotive services recommend replacing spark plugs every 30 thousand kilometers (as part of every second scheduled maintenance).

Types of spark plugs

The main parameters by which all SZ differ:

  1. number of electrodes;
  2. material of the central electrode;
  3. heat number;
  4. case size.

Firstly, candles are single-electrode (classic with one electrode "per mass") and multi-electrode (there can be two, three or four side elements). The second option has a longer resource, because a spark stably appears between one of these elements and the core. Some are afraid to acquire such a modification, thinking that in this case the spark will be distributed among all the elements and therefore will be subtle. In fact, the current always follows the path of least resistance. Therefore, the arc will be one and its thickness does not depend on the number of electrodes. Rather, the presence of several elements increases the reliability of sparking when one of the contacts is burned.

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Secondly, as already noted, the thickness of the central electrode affects the quality of the spark. However, thin metal quickly burns out with strong heating. To eliminate this problem, manufacturers have developed a new type of candle with a core of platinum or iridium. Its thickness is about 0,5 millimeters. The spark in such candles is so powerful that soot is practically not formed in them.

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Thirdly, the spark plug will work properly only with a certain heating of the electrodes (the optimal temperature range is from 400 to 900 degrees). If they are too cold, soot will form on their surface. Excessive temperature leads to cracking of the insulator, and in the worst case, to ignition (when the fuel mixture ignites from the temperature of the electrode, and then a spark appears). And in the first and second case, this adversely affects the entire motor.

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The higher the rate of the glow number, the less SZ will heat up. Such modifications are called “cold” candles, and with a lower rate - “hot”. In conventional motors, models with an average indicator are installed. Industrial equipment often runs at lower speeds, so they are equipped with "hot" candles, which do not cool down so quickly. The engines of sports cars often operate at high speed, so there is a risk of overheating of the electrodes. In this case, “cold” modifications are installed.

Fourth, all NWs differ in the size of the faces for the key (16, 19, 22 and 24 millimeters), as well as the length and diameter of the thread. What size of a candle is suitable for a particular engine can be found in the instruction manual.

The main parameters of this part are discussed in the video:

What you need to know about spark plugs

Marking and service life

On the ceramic insulator of each part there is a marking that allows you to determine whether it is suitable for this motor or not. Here is an example of one of the options:

A - U 17 D V R M 10

Marking positionThe value of the symbolDescription
1Thread TypeA - thread M14x1,25 M - thread M18x1,5 T - thread M10x1
2Abutment surfaceK - conical washer - - flat washer with gasket
3DesignM - small-sized candle U - reduced hexagon
4Heat number2 - the hottest 31 - the coldest
5Threaded Length (mm.)N - 11 D - 19 - - 12
6Features of the thermal coneB - protrudes from the housing - - recessed into the housing
7The presence of glassP - with resistor - - without resistor
8Core materialM - copper - - steel
9Upgrade serial number 

Each manufacturer sets its own timing for replacing spark plugs. For example, a standard single-electrode spark plug must be replaced when the mileage is no more than 30 km. This factor also depends on the indicator of engine hours (how they are calculated is described using an example car oil change). More expensive ones (platinum and iridium) need to be changed at least every 90 km.

The service life of the SZ depends on the characteristics of the material from which they are made, as well as on operating conditions. For example, carbon deposits on the electrodes may indicate malfunctions in the fuel system (supply of an excessively enriched mixture), and a white coating indicates a mismatch in the glow number of the spark plug or early ignition.

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The need for checking spark plugs may arise in the following cases:

  • when you sharply press the accelerator pedal, the motor reacts with a noticeable delay;
  • difficulty starting the engine (for example, for this you need to turn the starter for a long time);
  • lower motor power;
  • significant increase in fuel consumption;
  • engine check on the dashboard lights up;
  • complicated start of the engine in the cold;
  • unstable idling (troit motor).

It is worth noting that these factors indicate not only the malfunction of the candles. Before proceeding with their replacement, you should look at their condition. The photo shows which unit in the engine requires attention in each individual case.

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How to check that the candles are working correctly

In case of incorrect operation of the power unit, first of all, it is necessary to pay attention to the elements that are subject to planned replacement. There are several ways to check if spark plugs are working properly.

Alternating power off

Many motorists take turns removing the wires from the spark plugs on an already running engine. During normal operation of these elements, disconnecting the high-voltage wire will immediately affect the operation of the motor - it will begin to twitch (because one cylinder has stopped working). If the removal of one of the wires did not affect the operation of the power unit, then this candle does not work. When using this method, the ignition coil can be damaged (for long-term operation, it must always be discharged, and if it is removed from the spark plug, the discharge does not occur, so the individual coil can be punctured).

Spark test

This is a less harmful way for the ignition coil, especially if it is individual (included in the candlestick design). The essence of such a test is that the plug is unscrewed while the engine is not running. A high-voltage wire is put on it. Next, the candle must be leaned against the valve cover with the thread.

Spark plugs - what are they for and how do they work

We are trying to start the engine. If the spark plug is intact, a clear spark will appear between the electrodes. If it is insignificant, then you need to change the high-voltage wire (there may be a leak due to poor insulation).

Tester check

A piezo spark probe or tester is required to complete this procedure. You can buy it at an auto parts store. At the same time, the engine is turned off. Instead of the candlestick of the high-voltage wire, the tip of the tester's flexible connector is put on the candle. The spring loaded probe is firmly pressed against the valve cover body (motor weight).

Then the tester button is pressed several times. In this case, the indicator light should light up, and a spark crackle should appear on the candle. If no light comes on, then the candle is inoperative.

What happens if you don't change the candles in time?

Of course, if the motorist does not pay attention to the condition of the spark plugs, the car will not receive critical damage. The consequences will appear later. The most common outcome of this situation is the refusal of the engine to start. The reason is that the ignition system itself can work properly, the battery is fully charged, and the spark plugs either do not produce a sufficiently powerful spark (for example, due to large carbon deposits), or do not generate it at all.

To prevent this, you need to be attentive to indirect signs indicating problems with candles:

  1. The motor began to triple (twitches at idle or while driving);
  2. The engine began to start poorly, the candles are constantly flooded;
  3. Fuel consumption has increased;
  4. Thicker exhaust smoke due to poorly burning fuel;
  5. The car has become less dynamic.

If the driver is surprisingly calm in the presence of all these signs, and continues to operate his car in the same mode, more serious consequences will soon appear - up to and including engine failure.

One of the most unpleasant consequences is frequent detonation in the cylinders (when the air-fuel mixture does not burn smoothly, but explodes sharply). Ignoring a pronounced metallic sound while the engine is running will lead to the appearance of black smoke from the exhaust pipe, which indicates engine breakdown.

Spark plug malfunctions

A malfunction of the spark plugs is indicated by the complete or partial absence of ignition in one or more cylinders. This effect cannot be confused with anything - if one or two candles do not work at once, the engine will either not start, or it will work extremely unstable (it will "sneeze" and twitch).

Spark plugs do not contain any mechanisms or a large number of elements, therefore their main malfunctions are cracks or chips of the insulator or deformation of the electrodes (the gap between them has melted or changed). Candles will be unstable if carbon deposits are deposited on them.

How to care for candles in winter?

Many experts recommend installing new candles for the winter, even if the old ones are still working normally. The reason is that when starting the engine, which has stood all night in the cold, the temperature of a weak spark will not be enough to ignite cold fuel. Therefore, it is necessary that the candles consistently form greasy sparks. At the end of the winter period, it will be possible to install the old SZ.

Moreover, during the operation of the machine in winter, carbon deposits can form on the candles, which is greater than during the operation of other candles in the other three seasons. This happens during short trips in cold weather. In this mode, the engine does not warm up properly, which is why the candles cannot clean themselves of carbon deposits on their own. In order for this process to be activated, the motor must first be brought to operating temperature, and then driven at higher speeds.

How to choose spark plugs?

In some cases, the answer to this question depends on the financial capabilities of the motorist. So, if the ignition and fuel supply systems are correctly configured, standard spark plugs change only because the manufacturer so requires.

The best option is to buy those candles that are recommended by the engine manufacturer. If this parameter is not specified, then in this case you should focus on the size of the candle and on the parameter of the glow number.

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Some motorists have in stock two sets of candles (winter and summer). Driving short distances and at low speeds requires the installation of a “hot” modification (more often such conditions occur in winter). Long journeys at higher speeds, on the contrary, will require the installation of more “cold” analogues.

An important factor in choosing SZ is the manufacturer. Leading brands take money not only for the name (as some motorists mistakenly believe). Candles from manufacturers such as Bosch, Champion, NGK, etc. have an increased resource, they use inert metal alloys and are more protected from oxidation.

Timely maintenance of the fuel and ignition systems will significantly extend the life of the spark plugs and ensure the stability of the internal combustion engine.

For more information about the operation of spark plugs and which modification is better, see the video:

Related videos

Here is a short video on common mistakes when choosing new spark plugs:

Questions and answers:

What is the candle in the car for? It is an element of the ignition system that is responsible for igniting the air / fuel mixture. The spark plugs are used in engines running on gasoline or gas.

Where is the candle inserted in the car? It is screwed into the spark plug well located in the cylinder head. As a result, its electrode is in the combustion chamber of the cylinder.

How do you know when it's time to change your spark plugs? Difficult starting of the motor; the power of the power unit has dropped; increased fuel consumption; "Pensiveness" when you press the gas sharply; tripping of the engine.

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