Let's imagine what happens with a good spark plug. Sparking occurs due to the high impulse voltage transmitted from the ignition coil (module) through the armored wire to the central electrode of the spark plug (core). This spark ignites the compressed air-fuel mixture in the combustion chamber. An extremely short duration discharge (1/1000 of a second) is generated. The applied voltage range varies from 4,000 to 28,000 volts. A large gap, the operation of the motor "in tightness", the state of compression affect the magnitude of the sparking voltage between the electrodes.
The main role of the spark plug is to generate a strong spark at exactly the right time.
Ignition
The ignition process occurs from fuel particles located between the electrodes when creating a spark. As a result of a chemical reaction (oxidation) and the formation of a spark, a thermal reaction is formed, which turns into a flame. This heat activates the surrounding air-fuel mixture, spreading combustion throughout the combustion chamber. In the case of a weak spark, there is insufficient flame formation and heat generation, the flame goes out and stops burning. With a larger gap, more voltage is required to form a spark, which can reach the limits of the ignition coil performance, reducing the performance of the spark plug (igniter).
To determine the time of occurrence of a spark discharge, the piston is set to the top point of the compression stroke of the air-fuel mixture and the ignition is set slightly ahead. If the mixture is ignited before a certain time, the pressure will increase until the piston passes through the compression cycle, the power of the motor will be lost, the engine will be damaged during prolonged operation, detonation is the moment when the spark jumps until the piston reaches the top point, where the pressure peak of the working mixture in the compression stroke is not created, which leads to unstable operation of the engine. The time of formation of a spark discharge on candles is determined by a computer or an ignition coil.
Figure 1. Discharge voltage change
- voltage increase
- sparking
- capacitive spark
- induction spark
- one millisecond
- voltage graph, T - time graph
The transition of the primary voltage at point "a" to an increase in the secondary (1).
At point "b" there is a partial increase in voltage, sufficient to form a discharge and spark (2).
In the interval "b" and "c" the spark capacity is set. At the beginning of the discharge moment, the spark is generated by the electrical energy stored in the secondary circuit. The current is large, the duration is short (3).
Between "c" and "d" there is an induction spark (4). The spark is generated by the electromagnetic energy of the coil. The current is small, but the duration is longer. The time interval from point "c" continues for about 1 millisecond (5), at point "d" the discharge ends.
Operating modes
The choice of the type and model of a candle is influenced by various circumstances, such as the technical condition of the engine, driving conditions, driving style. For example, during monotonous movement for a long time with ordinary candles, the candle body and electrodes will overheat. Therefore, it is important to choose candles according to the mode of operation.
spark plug gap. The discharge voltage rises in proportion to the spark plug gap. During operation, the plug gap increases, the core wears out, so a high voltage is required, which inevitably leads to misfiring.
Electrode shape. The spark discharge slips more easily on the angular, sharp parts of the electrode. Older spark plugs with rounded electrodes are less prone to sparking and more likely to misfire.
Compression ratio. The discharge voltage rises in proportion to the compression ratio. Compression is higher at low speed and increased engine load.
Air-fuel mixture temperature. The discharge voltage decreases as the temperature of the air-fuel mixture rises. The lower the engine temperature, the higher the voltage must be, so misfiring is more likely to occur in cold weather.
electrode temperature. The discharge voltage decreases as the electrode temperature rises. The temperature rises in proportion to the engine speed. Misfires are more likely to occur at low speeds.
Humidity. As the humidity increases, the temperature of the electrode decreases, so a higher discharge voltage is required.
The ratio of fuel and air. The discharge voltage depends on the volume of the air-fuel mixture, the smaller the volume, the more voltage is required. If the air-fuel mixture decreases due to a fuel system problem, misfiring may occur.
The degree of heating of the candle (glow number). The heat transferred to the igniter electrodes as a result of fuel combustion is dispersed along the path shown in Figure 2.
Figure 2. Heat distribution of a spark plug during fuel combustion
- coolant
- cooling when the air-fuel mixture is supplied through the intake valve
The degree at which the heat received by the candle is dissipated is called the degree of heating (Figure 3). Candles with a high degree of heat dissipation are called "cold", those with a low degree of heat dissipation are called "hot". This is largely determined by the temperature of the gas inside the combustion chamber and the design of the spark plug.
Figure 3. The degree of heating of the candle
- cold candles
- "Hot" candles
- gas pocket
"Cold" candles have a long metal base and a larger area of the cooled surface exposed to the flame and gas. Good heat dissipation. Spark plugs with a low degree of dissipation have a short base and a small area of the cooled surface.
The relationship between igniter temperature and vehicle speed is graphed in Figure 4. There are temperature limits at which spark plugs should not be operated: the lowest self-cleaning temperature and the highest drip ignition temperature. Good operation is ensured when the central electrode is heated from 500 °C to 950 °C.
Figure 4. Influence of the speed of movement on the degree of heating of the candle
- Low degree of heating of the candle
- normal spark plug operation
- High degree of heating of the candle
S - Vehicle speed
T - Candle temperature
Candle self-cleaning temperature
When the core temperature is 500°C or lower, during the ignition and combustion of the air-fuel mixture, free carbon is released, the fuel does not burn completely and is deposited on the surface of the insulator and the metal base, creating "bridges" of soot between the insulator and the housing. Electricity leaks, incomplete sparking occurs, causing ignition failures. A temperature of 500°C is called the spark plug self-cleaning temperature, as at higher temperatures the carbon burns out completely.
Temperature of glow ignition formation
When the core is heated above 950 °C, glow ignition occurs. This means that the electrode acts as a heat source and the ignition of the fuel occurs without a spark. Thus, the engine power drops, which leads to increased wear of the electrodes and damage to the insulator.
Degree of heating
Spark plugs with low heat dissipation are equipped with a core that is kept warm even at low travel speeds. Therefore, they easily reach the self-cleaning temperature without allowing carbon to be deposited on the insulator.
On the other hand, the highly heated center electrode is not easily heated, which prevents them from reaching the glow ignition temperature even at high speed and high load. This type of spark plug is used on high-speed and powerful motors. Selecting a spark plug with the appropriate heat range should be based on engine performance and operating conditions.
The degree of heating of the candle depends on the season of use.
When the air temperature is high in summer, the inlet air temperature is higher, which increases the load on the engine. At such times, it is better to choose candles with a higher heating range.
Higher engine power requires the installation of candles with a higher heating range.
If the power has been increased due to tuning, there will be an increase in temperature in the cylinder, a precursor to glow ignition. To avoid this, increase the glow number and heat resistance level.
Summarize
The glow number means that the candle matches the conditions of normal operation. The temperature of the fuel mixture during combustion exceeds 1,800 - 2,000°C. If the spark plug is correctly matched to a certain type of engine, then the ignition process of the fuel mixture will be optimal for fuel combustion and combustion of deposits formed:
there will be no overheating of the candle and premature ignition, called glow ignition, when the mixture of air and fuel ignites from the ignited surfaces of the combustion chamber (spark plug electrodes, exhaust valve, thick soot);
there will be no detonation, a specific knocking that manifests itself when operating on low-octane fuel with an increase in engine load, when part of the mixture burns out faster than usual, forming a shock wave in the combustion chamber.
With the optimal functioning of all components of the motor, the lower part of the candle heats up to 600 degrees, the oil and excess fuel that fall on the electrodes burn out, performing a self-cleaning procedure. If the incandescent number does not correspond to the characteristics of operation, deposits on the elements of the cylinder occur more actively than they burn out.
However, there may be situations of using a heat number different from the recommended one. Increasing the number will burn off carbon deposits in a worn out engine idling most of the time or a car used for short runs. In the absence of problems with engine carbon deposits, hot plugs are contraindicated, there is a risk of pre-ignition, detonation.
Special cars (racing, running at high loads, high speeds for a long time) prefer “cold” candles, with a minimum likelihood of glow ignition. Idling and low speed will lead the fireballs to the formation of deposits on the piston group.
To date, many manufacturers produce candles with an extended heating interval, introducing a core made of copper or platinum. Copper is an excellent conductor of heat, allowing the insulator to withstand increased heat by burning contaminant deposits to a pre-ignition state. Platinum is also excellent at dissipating heat from the core.
Helpful information
Did you know that there is more iridium on spark plugs than anywhere else! The iridium alloy is applied to the center electrode by laser welding to reduce electrical erosion.
Spark plug serves to transfer high voltage to the engine cylinder in order to create an ignition spark and ignite the working mixture. In addition, the candle must isolate the high voltage supplied to it (more than 30 kV) from the cylinder block, reduce breakdowns and breakthroughs, and also hermetically close the combustion chamber. In addition, it must provide an appropriate temperature range to avoid contamination of the electrodes and the occurrence of glow ignition. The device of a typical spark plug is shown in the figure.
Rice. Bosch spark plug
Terminal rod and center electrode
The terminal shaft is made of steel and protrudes from the spark plug housing. It serves to connect a high voltage wire or a directly mounted rod ignition coil. The electrical connection between the terminal rod and the central electrode is made with the help of a glass melt located between them. A filler is added to the glass melt to improve the burn rate and interference resistance properties. Since the center electrode is located directly in the combustion chamber, it is subject to very high temperatures and severe corrosion due to contact with exhaust gases, as well as with combustion residues of oil, fuel and impurities. High sparking temperatures lead to partial melting and evaporation of the electrode material, so the central electrodes are made of a nickel alloy with chromium, manganese and silicon additives. Along with nickel alloys, silver and platinum alloys are also used, as they burn slightly and dissipate heat well. The central electrode and terminal rod are hermetically fixed in the insulator.
Insulator
The insulator is designed to separate the terminal rod and the central electrode of the spark plug from its body so that there is no breakdown of high voltage to the car's ground. To do this, the insulator must have a high electrical resistance, so it is made of aluminum oxide containing vitreous additives. To reduce leakage currents, the neck of the insulator has ribs.
In addition to mechanical and electrical loads, the insulator is also subjected to high thermal loads. When the engine is running at maximum speed, the temperature at the insulator support reaches 850 °C, and at the insulator head - about 200 °C. These temperatures occur due to cyclic processes of combustion of the working mixture in the engine cylinder. In order for temperatures in the area of the support not to become high, the insulator material must have good thermal conductivity.
General spark plug arrangement
The spark plug has a metal housing that screws into a matching hole in the cylinder head. An insulator is built into the spark plug body and special internal seals are used to seal it. The insulator contains inside the central electrode and the terminal rod. After assembling the spark plug, the final fixation of all parts is carried out by heat treatment. The side electrode, made of the same material as the central one, is welded to the candle body. The shape and location of the ground electrode depends on the type and design of the engine. The gap between the central and side electrodes is adjustable depending on the type of engine and ignition system.
There are many possibilities for the location of the ground electrode, which affects the size of the spark gap. A clean spark is formed between the central electrode and the side, L-shaped. In this case, the working mixture easily enters the gap between the electrodes, which contributes to its optimal ignition. If the ring-shaped side electrode is installed flush with the central one, then a spark can slide over the insulator. In this case, it is called a sliding spark discharge, which allows you to burn deposits and residual deposits on the insulator. The ignition efficiency of the working mixture can be improved either by increasing the duration of sparking, or by increasing the energy of sparking. A combination of sliding and ordinary spark discharges is rational.
Rice. Air Glide Spark Plug Types
To reduce the need for voltage on the spark plug with a sliding spark charge, an additional control electrode can be installed. With an increase in the temperature of the insulator, sparking is able to occur at a lower voltage. With a long spark gap, ignition improves for both lean and rich fuel-air mixtures.
For engines with fuel injection into the intake manifold, a spark plug with a spark discharge path "stretched" in the combustion chamber is preferred, while for engines with direct fuel injection into the combustion chamber and stratification, a spark plug with a surface discharge has advantages due to a better ability self-purification.
When choosing a spark plug suitable for the engine, its heat value plays an important role, with the help of which it is possible to judge the thermal load on the insulator support. This temperature should be approximately 500°C higher than the temperature required for the spark plug to self-clean from deposits. On the other hand, the maximum temperature of about 920 °C must not be exceeded, otherwise glow ignition may occur.
If the temperature required for the spark plug to self-clean is not reached, fuel and oil particles accumulating at the insulator support will not burn, and conductive stripes may form between the electrodes on the insulator, which can lead to misfires.
If the insulator support is heated above 920°C, it will cause uncontrolled combustion of the fuel mixture due to the heating of the insulator support during compression. Engine power is reduced and the spark plug may be damaged due to thermal overload.
The spark plug for the engine is selected according to its glow number. A low glow number plug has a low heat absorption surface and is suitable for engines with high loads. If the engine is lightly loaded, a spark plug with a high glow number is installed, which has a large heat absorption surface. Structurally, the glow number of a spark plug is adjusted during its manufacture, for example, by changing the length of the insulator support.
Rice. Determining the glow number of a spark plug
When using a combined electrode comprising a nickel-based electrode with a copper core, the thermal conductivity and, consequently, the removal of heat from the electrode is improved.
An important challenge in spark plug development is extending maintenance intervals. Due to corrosion associated with the spark discharge, during operation, the gap between the electrodes increases, and at the same time, the need for voltage in the secondary circuit of the ignition system also increases. If the electrodes are severely worn, the spark plug must be replaced. Today, the service life of spark plugs, depending on their design and materials, ranges from 60,000 km to 90,000 km. This is achieved by improving the material of the electrodes and using more ground electrodes (2, 3 or 4 ground electrodes).
During engine operation, spark plugs are subjected to electrical, thermal, mechanical and chemical loads. Let's figure out how car spark plugs work.
What stresses do the spark plugs experience?
Thermal loads. The candle is installed in the cylinder head so that its working part is in the combustion chamber, and the contact part is in the engine compartment. The temperature of the gases in the combustion chamber varies from several tens of degrees at the inlet to two to three thousand during combustion. The temperature under the hood of a car can reach 150°C. Due to uneven heating, the temperature in different sections of the candle can differ by hundreds of degrees, which leads to thermal stresses and deformations. This is aggravated by the fact that the insulator and metal parts differ in the value of the coefficient of thermal expansion.mechanical loads. The pressure in the engine cylinder varies from a pressure below atmospheric at the inlet to 50 kgf/cm2 and higher during combustion. In this case, the candles are additionally subjected to vibration loads.
chemical loads. During combustion, a whole "bouquet" of chemically active substances is formed that can cause oxidation of even very resistant materials, especially since the working part of the insulator and electrodes can have a working temperature of up to 900 ° C.
electrical loads. During sparking, the duration of which can be up to 3 ms, the candle insulator is under the influence of a high voltage pulse. In some cases, the voltage can reach 20-25 kV. Some types of ignition systems can produce much higher voltages, but this is limited by the breakdown voltage of the spark gap.
Deviations from the normal combustion process
Under certain conditions, the normal combustion process may be disturbed, which affects the reliability and service life of the candle. Such violations include the following:
Misfires. May be due to a lean mixture, misfiring or insufficient spark energy. This intensifies the process of carbon deposits formation on the insulator and electrodes.
Hot ignition. Distinguish premature accompanied by the appearance of a spark and delayed- caused by overheated areas of the surfaces of the exhaust valve, piston or spark plug. With premature glow ignition spontaneously increases the ignition timing. This leads to an increase in temperature, engine parts overheat and the ignition timing increases even more. The process takes on an accelerating character until the moment when the ignition timing becomes such that the engine power begins to fall.
Pre-ignition is likely to damage the exhaust valve, piston, piston rings and cylinder head gasket. The candle may burn the electrodes or melt the insulator.
Detonation- occurs when the detonation resistance of the fuel is insufficient in the place most remote from the candle, as a result of compression of the combustible mixture that has not yet burned out. Detonation propagates at a speed of 1500-2500 m/s, which exceeds the speed of sound and causes local overheating of the cylinder, piston, valves and spark plugs. Chips and cracks can form on the spark plug insulator, the electrodes can melt and burn out completely.
Typical signs of detonation are metallic knocking, vibration and loss of engine power, increased fuel consumption and the appearance of black smoke.
A feature of detonation is the time delay from the moment the necessary conditions occur to its occurrence. In this regard, detonation is most likely at relatively low engine speeds and full load, for example, when the car is moving uphill with the gas pedal fully depressed. If the engine power is insufficient, the vehicle speed and engine speed are reduced. With an insufficient octane number of fuel, detonation occurs, accompanied by a ringing metallic knock.
Dieseling. In some cases, uncontrolled operation of a gasoline engine with the ignition off occurs at a very low engine speed. This phenomenon occurs due to self-ignition of the combustible mixture during compression, similar to how it occurs in diesel engines.
On engines where the possibility of supplying fuel to the cylinder with the ignition off is not ruled out, dieseling occurs when you try to stop the engine. When the ignition is turned off, the engine continues to run at very low speeds and is extremely uneven. This may last for a few seconds, then the engine will spontaneously stop.
The reason for dieseling is in the design features of the combustion chamber and in the quality of the fuel. Candles cannot be the cause of this phenomenon, since their temperature at low speeds is clearly insufficient to ignite the combustible mixture.
Nagar on a candle is a solid carbonaceous mass formed at a surface temperature of 200°C and above. The properties, appearance and color of carbon deposits depend on the conditions of its formation, the composition of the fuel and engine oil. If the candle is cleaned of soot, then its performance is restored. Therefore, one of the requirements for a candle is the ability to self-clean from carbon deposits.
Removal of carbon deposits, if there are no non-combustible substances in the combustion products, occurs at a temperature of 300-350 ° C - this is the lower limit of the candle's performance. The effectiveness of self-cleaning from carbon deposits depends on how quickly the insulator heats up to this temperature after starting the engine.
Undoubtedly, any element of the vehicle is its integral part, which is assigned certain functions. If everything is more or less clear with large units (motor, generator, battery, etc.), then the issue of the purpose of small parts is sometimes difficult to figure out. It is these small components of a large car design that are spark plugs, which will be discussed later.
What are spark plugs for in a car?
If we draw an analogy with an ordinary wax candle, then an automobile spark plug is also capable of burning, only its flame is presented in the form of a short-term spark, which is responsible for igniting the air-fuel mixture in various types of thermal engines. As for gasoline power units, the ignition of the fuel liquid is preceded by an electrical discharge, the voltage of which corresponds to several thousand or even tens of thousands of volts. Such a discharge appears between the electrodes of a spark plug that fires at each cycle at a particular moment in the operation of the power unit.
It turns out that if this element is removed from the general working chain, then the ignition of the mixture will not occur, and the motor will not be able to start its work. We will pay attention to how spark plugs work, but a little later.
The device and principle of operation of spark plugs
The main structural elements of automotive spark plugs include an insulator, a central electrode, a contact rod and, in fact, the body itself, in which all this is placed. The contact rod acts as a connecting element between the spark plug and the coil, or the spark plug and the high-voltage wire. The central electrode plays the role of a cathode made of alloyed steel. The electrode diameter is in the range of 0.4-2.5 mm.
Today, to create this element, two metals are used at once: copper (the core is made from it) and steel (a bimetallic electrode). The steel shell heats up well, thereby ensuring a reliable and quick start of the power plant, and the copper core quickly removes heat.
To increase the service life of spark plugs, increase the resistance of parts to corrosion and damage under the influence of electrochemical processes, the core is made of a noble or rare earth steel alloy (iridium, platinum, yttrium, tungsten or palladium). It was this fact that contributed to the appearance of additions to the name of the parts:, platinum, etc.
The center electrode and the contact rod are connected using a conductive sealant, which is simply necessary to protect the electrical equipment of the motor from problems arising from sparking. Conductive glass mass often becomes such a sealant. The insulator serves as a connecting link that connects the contact rod to the central electrode. It is this element that provides electrical insulation and the set temperature of the spark plug.
All of these elements are enclosed in a metal case made of nickel alloy. It is complemented by a thread for screwing the spark plug into the cylinder head and holding it there. The lower part of the candle is presented in the form of a side electrode made of nickel alloy. There is a gap between the central and side electrodes, the dimensions of which affect the ignition quality of the fuel-air mixture.
The use of a spark plug with a large gap requires the use of a higher breakdown voltage, which increases the likelihood of misfire. As a result, we get an increase in fuel consumption and harmful exhaust gases. At the same time, too small a gap creates a small spark, as a result of which the efficiency of fuel assembly ignition is significantly reduced.
The principle of operation of a spark plug is quite simple: the air-fuel mixture is ignited by an electric discharge, the voltage of which reaches several thousand or even tens of thousands of volts. This voltage appears between the electrodes of the spark plug at a particular moment of each working cycle of the power plant of the machine.
Types of spark plugs
One of the main criteria for dividing spark plugs into types is their design. So, given the device of such "lighters", they are divided into:
two-electrode (the classic version, in which there is one central and one side electrode);
multielectrode (they provide for the presence of one central and several side electrodes).
The latter option is used when there is a desire to get a reliable spark plug with a long service life. The fact is that in the two-electrode version, a spark occurs only between two electrodes, causing their rapid burnout, and a multi-electrode spark plug allows a spark to appear between the central and one of the side electrodes. Given the reduced load on each side electrode, it makes sense that the spark plug will last longer.
In addition, it is possible to divide spark plugs into types based on the material of their manufacture. In this case, classical and platinum products are distinguished. In the first case, most often, the electrodes are made of copper, but there are options in which the electrodes are coated with rare metals (for example, yttrium). Such a coating increases the resistance of the electrodes, but has almost no effect on other characteristics.
Platinum electrodes have high corrosion and temperature resistance, and they can be not only central, but also side elements. The specified type of spark plugs is mounted in turbo engines equipped with a turbo or mechanical supercharger. Compared to classic options, the service life of platinum products is relatively longer, but they are also more expensive.
Relatively recently, another type of spark plugs has appeared - plasma-prechamber. In this case, the role of the side electrode is assigned to the body of the product, and the design itself forms a spark annular gap in which the spark moves in a circle. It is generally accepted that this type of spark plug improves the self-cleaning of parts, thereby increasing their service life.
The central electrode of the spark plug is connected to the contact terminal through a special ceramic resistor, which perfectly reduces interference from a running ignition system. Often, the tip of the central electrode is made of iron-nickel alloys, to which chromium, copper and other rare earth metals are added.
The edges of the central electrode are most susceptible to electronic erosion - burnout, which is why it is necessary to periodically clean off the traces of erosion with emery. However, today the need for such a procedure has disappeared, since alloys with "noble" metals have begun to be used: tungsten, platinum, iridium, etc. There are variants of classic products in which the electrodes are coated with yttrium alloy, which also helps to increase the resistance of the electrodes to negative influences, and is a key feature of such spark plugs.
Another classification of the parts described is based on thermal characteristics, that is, according to the glow number, candles are divided into: hot (heat number ranges from 11 to 14), medium candles (from 17 to 19) and cold (more than 20). There are also unified products, the glow number of which corresponds to 11-20. Each engine requires the installation of candles that are ideally matched to it in terms of thermal characteristics. The type of thread of spark plugs is also the reason for their division into types, both in length and in the size of the turnkey head. All these parameters must be taken into account when choosing parts.
Marking and service life
The main parameters of spark plugs of any kind are the connecting dimensions of the parts (length and diameter of the threaded part), glow number, the presence of a built-in resistor and the position of the thermal cone.
Domestic spark versions of such products, suitable for engines of almost all vehicles (cars and trucks, buses, motorcycles, etc.), fully comply with the requirements of the international standard ISO MS 1919, thereby providing the possibility of replacing them with foreign analogues in terms of characteristics and dimensions.
The difference between the overall and connecting dimensions of spark plugs is explained by the variety of power plants produced. Modern requirements for improving the quality of their operating parameters determine the main direction in the development of spark plugs: the threaded part is lengthening, while the diametrical dimensions are decreasing. Marking of spark plugs, which are produced in Russia, is presented below.
Notes:
* - Spark plugs, threaded part of the body of which corresponds to 9.5 mm. There are only options with a M14x1.25 thread, and a turnkey hexagon size of 19.0 mm.
** - Products with a length of the threaded part of the body of 12.7 mm, which are produced only with a thread size of M14x1.25. In this case, the size of the turnkey hexagon is 16.0 and 20.8 mm.
*** - Sequence number of development. Specifies information about the spark gap value specified by the manufacturer and/or information about other design features that do not affect the overall performance of the spark plug.
He.- the designation is not put.
What to look for when buying
The spark plug device is not the only parameter that you should pay attention to when choosing such parts. However, the most important of them include only two characteristics: glow number And candle size. As for the size, everything is quite simple here: too small a candle will simply fall into the candle well, while a large one will not fit into it.
Pre-ignition is a more serious parameter that determines the temperature range of the spark plug (the temperature at which the air-fuel mixture can ignite from a spark, and not from a hot electrode).
A high calorific value indicates the “coldness” of the candle, which means that such a part is designed to work on motors that can warm up to high temperatures and endure serious loads. A low glow number indicates a "hot" spark plug that may be self-cleaning. For this reason, you should not immediately write down such products in the ranks of "inappropriate".
The most appropriate way to select spark plugs, considering their longevity and other important characteristics, is to contact your dealer or consult your vehicle owner's manual. True, its use is not always possible, since the manuals may not be at hand, and the owners of old brands will not always be able to find the candles that the manufacturer advised them 15-20 years ago.
The time has come, dear readers, to talk about the element that crowns the entire ignition system of a car and is without a doubt one of the key in the operation of gasoline. The spark plug is precisely for the sake of the spark that occurs between its electrodes, and all tricks are started with electronics, distributors and other things. Let's take a closer look at this node, consider the design of the spark plug and the nuances that novice drivers need to know about it.
So, as we already know, the heroine of this article is needed in order to ignite the fuel-air mixture in the engine cylinder.
Unfortunately, very often car owners do not pay due attention to these elements, considering them to be simple consumables. In fact, candles, like many other engine components, require a certain amount of attention, because the stability of the power unit depends on them.
In addition, quite high requirements are placed on their reliability. Just imagine the conditions under which candles have to work - high voltage supplied to their electrodes (up to 40,000 Volts), high temperatures reaching 1000 degrees and aggressive chemical processes associated with fuel combustion. All this dictates certain conditions that the spark plug device must meet, and more on that later ...
Despite all the responsibility that lies on the shoulders of candles, their design is quite simple. As they say: "The simpler, the more reliable." It consists of the following parts:
- contact rod (tip);
- central electrode;
- ceramic insulator;
- metal case;
- resistor;
- side electrode.
The contact rod or, as it is also called, the tip is designed to connect to the high-voltage wires of the ignition system.
The other end of the rod through a resistor, which serves to reduce the level of interference from a spark discharge, is connected to the central electrode, and all these elements are placed in a refractory ceramic insulator.
The insulator, as its name implies, serves to prevent a short circuit between the central electrode, which is supplied with voltage up to 40,000 volts, and the body, which has a reliable electrical connection to ground. The insulator has not only an outer part that is visible, but also an inner part (the so-called thermal cone) that goes directly into the combustion chamber of the engine cylinder.
With the correct mode of operation of the power unit and the candle, the thermal cone plays a very important role - soot particles burn out on its surface due to the high temperature, the candle self-cleans from the combustion products of the fuel and deposits do not accumulate.
But if suddenly the temperature of the thermal cone exceeds the permissible one, then the mixture can be heated by ignition - an extremely negative phenomenon in which the fuel ignites not from a spark, but from an insulator heated to very high temperatures.
The metal housing combines the above internal parts and is threaded for screwing into the housing.
Well, the last element is the side electrode. It is welded to the body and is located near the central electrode. It is between them that a spark jumps, reviving the gasoline engine.
What does a car owner need to know?
It is useful for the car owner to know not only the structure of the spark plug, but also its main characteristics. This is the only way to choose the optimal model of this part, which is best suited for the motor. There are several of them:
- glow number is a very important parameter, it depends on it whether the mixture will be ignited in the cylinders, which can lead to serious engine damage. For each motor, the specifications indicate the recommended value of this parameter and it is highly desirable to use the appropriate candles - not with a large, and even less so, with a smaller number;
- spark gap - in fact, this is the distance between the central and side electrode. The smaller it is, the less voltage is needed to form a spark;
- self-cleaning ability - how the candle copes with the products of combustion of fuel and deposits. This parameter does not have any objective scale - you have to take the word of the manufacturer;
- the working temperature of the candle should be in the range of 500 - 900 degrees Celsius;
- candle diameter and thread length - the first parameter is usually 14 mm, but the second depends on the engine power - the more horses under the hood, the longer the thread should be, usually from 12 to 25 mm.
Manufacturers indicate many of these characteristics on the body of the candle in the form of special ciphers, which can be deciphered using tables.
There are also interchangeability tables - which candle model can be replaced with another without problems.
As we can see, friends, the heroine of today's article is not an easy element, and it is important for a motorist to know not only the spark plug structure, but also its parameters so that when replacing there are no problems with the power unit, which can turn into expensive repairs.
This is where the story about the candle comes to an end, and I will start preparing the following articles in which I will tell you about other secrets hiding in the depths of cars.
