The article will provide information about spark plugs, their markings, characteristics, interchangeability and how they work. The main causes of malfunctions associated with spark plugs and methods for their elimination will also be considered.
Spark plugs in a car should be given special attention, because because of such an essentially inexpensive element, we can lose much more: on gasoline, power loss, increased soot formation in the combustion chamber, which will also affect engine life. So, let's go in order.
spark plug device
What is it and what main parts and elements does it consist of? A spark plug is, first of all, a spark gap with two contacts; when current flows through these contacts, a high-voltage arc is formed, which ignites the fuel mixture in the combustion chamber.
The average resource of a spark plug is 30 thousand kilometers. The main breakdowns of the spark plug are breakdowns of the dielectric insulator, as well as significant wear of the electrodes, which leads to a change in the gap and their shape. Subsequently, these malfunctions affect the stable operation of the engine, traction, its start, and the formation of soot in the combustion chamber. However, some spark plugs work out much longer, because it all depends on the quality of workmanship, the materials used, about all this later.
Spark plugs appeared a long time ago, in the days of the first cars and internal combustion engines. Previously, candles were different. Take a look at the picture, which shows a spark plug from Pobeda (1949). Yes, it looks somewhat clumsy, but its main elements and principles of work have remained unchanged since those times.
And this is what modern candles look like.
1 - contact (plug) nut; 2 - insulator; 3 - insulator ribs (current barriers); 4 - contact rod; 5 - candle body; 6 - conductive glass sealant; 7 - sealing ring; 8 - central electrode with a copper core (bimetallic); 9 - heat sink washer
The figure shows the design of a classic modern spark plug. The main elements of any modern spark plug are a metal case, a ceramic insulator, electrodes and a contact rod. A thread is cut on the body of the spark plug, which is screwed into the head of the engine block, the hexagon is a turnkey type "head". The bearing surface (the surface of the spark plug that limits the stroke of the spark plug when screwed into the head of the engine block) can be flat or conical.
For reliable sealing of the candle hole, an o-ring or a conical surface is used, which itself seals the connection of the candle with the head of the cone-to-cone block. The material of the insulator is high-strength technical ceramics. To prevent leakage of electricity on its surface (in the "upper" part of the insulator), annular grooves (current barriers) are made and a special glaze is applied, and part of the insulator from the side of the combustion chamber is made in the form of a cone (called thermal). Inside the ceramic part of the candle, a central electrode and a contact rod are fixed, between which a resistor can be located that suppresses radio interference. Sealing the connection of these parts is carried out with conductive glass mass (glass sealant). The side electrode ("mass") is welded to the body. Electrodes are made of heat-resistant metal or alloy. To improve heat removal from the thermal cone, the central electrode can be made of two metals (bimetallic electrode) - the central part of copper is enclosed in a heat-resistant shell. The bimetallic side electrode has an increased resource due to the fact that the good thermal conductivity of copper prevents its excessive heating.
Spark plug electrode material
The main elements of the spark plug that wear out are the electrodes.
Central electrode
The service life depends on the material used, usually in our time the following materials are used for this electrode:
- copper with heat-resistant nickel coating;
- nickel alloy;
- iridium alloy;
- with platinum welding;
- silver coating;
- gold plating;
- palladium-gold alloys (used for racing cars);
Spark plug electrodes must meet the following requirements:
High corrosion and erosion resistance;
- heat resistance;
- sufficient thermal conductivity;
- plasticity.
In addition, the material of the spark plug electrodes must be technologically advanced and inexpensive in order to be able to launch this design into mass production. As a result, the most common spark plug electrode materials are iron-chromium-titanium, nickel-chromium-iron and nickel-chromium.
Now consider all the pros and cons of using one or another material for spark plug electrodes.
The copper spark plug electrode improves heat dissipation, reduces spark plug deposits at idle, and thereby extends the life of the spark plug.
The platinum coating of the electrode is completely similar to copper, but more wear-resistant, which allows you to reduce the diameter of the central electrode from 2.5 mm (ordinary candle) to 1.1 mm. In this regard, the beam of the discharge passing through the spark plugs is more collected (point-like), which improves the cold start of the engine, increases the service life of the spark plug and, as a result of better ignition, reduces the toxicity of exhaust gases, since their more complete combustion occurs.
The iridium spark plug electrode has a greater wear resistance than the platinum coating, which also makes it possible to reduce the diameter of the central electrode to 0.7 mm and even to 0.4 mm. At the same time, the electrical conductivity of this electrode is very high, which makes it possible to ignite the mixture at a low on-board voltage (20% lower than normal), and also allows igniting lean fuel-air mixtures. In addition, these spark plugs have a long service life.
Spark plug side electrode (ground electrode)
In addition to the requirements that are put forward to the central electrode, this electrode must be well welded with the candle body, which, as a rule, is made of ordinary steel, and it must also be plastic so that the gap between the electrodes can be adjusted. There are candles in which not only the central electrode is covered with platinum, but also the side one. This improves combustion properties and increases service life. There are candles in which the central electrode is almost completely made of silver (99.9%) and is designed for a service life of 50,000 thousand kilometers. The number of side electrodes changed over time: one, two, three, four. The advantage of multi-electrode spark plugs is a longer resource.
In some cases, spark plugs are used without a ground electrode at all. In them, the role of the side electrode is played by the entire lower side edge of the candle body. The advantage is a longer spark plug resource, high reliability of sparking. But these candles require a specialized ignition system. Since an increase in the area entails an increase in the discharge voltage. Used in sports racing cars. The shape of the ground electrode affects the propagation of the flame front.
Flame front development schemes for single-electrode (a) and multi-electrode (b) candles.
In the second case, due to the "open" spark gap, the combustion of the mixture begins more intensively than in the first case - the flame front of a single-electrode spark plug loses time to exit the interelectrode space.
spark plug insulator
In the first spark plugs, ordinary clay was an insulator. However, specialized porcelain was later used to provide the following:
High resistivity at temperatures close to 800°C;
- high mechanical strength;
- high thermal conductivity and heat resistance;
- good endurance at big temperature drops;
- chemical neutrality to combustion products;
- small temperature coefficient of linear expansion.
But porcelain did not hold this niche for a long time, since at 400 ° C it lost its dielectric properties. Porcelain was replaced by glass, more precisely mica, but this material was low-tech and expensive. Steatite (a material based on talc) became a more popular material in the 30-40s of the last century. Steatite was replaced by aluminum-based ceramics.
At the same time, in the North American continent, the insulator was made from sillimanite, a mineral that was mined in the United States. Sillimanite insulators (85% sillimanite and 15% kaolin) outperformed steatite insulators and worked better under sudden temperature changes. The production was monopolized by the CHAMPION company, which at that time satisfied 70% of the world's demand for candles. That is the brand with history!
Some other firms produced zirconium-beryllium insulators (15% zirconium, 35% beryllium and 50% plastic clays and kaolin). Such insulators had better electrical and thermal properties than sillimanite and steatite, but were fragile and expensive. It is now customary to keep silent about the composition of ceramics in modern spark plugs, referring to a technical and commercial secret and a company secret.
The shape of the insulator has not changed much over the past 100 years.
Spark plugs work in rather difficult conditions. The temperature in the combustion chamber where they are installed varies in the operating mode from 70 to 2500 ° C, the gas pressure reaches 50 - 60 bar, and the voltage on the electrodes is about 20,000 volts.
Main characteristics of spark plugs
To provide the entire range of gasoline engines with spark plugs, the latter are produced with various parameters, which are reflected in the symbol of the spark plug (given below).
Overall and connecting dimensions- this is the diameter and pitch of the thread, the length of the threaded part and the size of the "turnkey" hexagon (21 mm or 16 mm). All of them are strictly defined for each engine, since the wells for candles have a limited design diameter.
heat number- is an indicator of the thermal properties of the candle (its ability to heat up under various thermal loads of the engine). It is proportional to the average pressure at which, during the testing of a spark plug on a motor calibration unit, glow ignition (an uncontrolled process of ignition of the working mixture from the hot elements of the spark plug) begins to appear in its cylinder. Candles with a small incandescent number are called hot. Their thermal cone heats up to a temperature of 900°C (the temperature of the start of glow ignition) with a relatively small thermal load. Such candles are used on low-forced engines with low compression ratios. For cold plugs, glow ignition occurs at high thermal loads, and they are used on highly accelerated engines.
Until the thermal cone is heated to 400°C, deposits form on it, leading to current leakage and disruption of sparking. Upon reaching this temperature, it (soot) begins to burn out, the candle is cleaned (self-cleaning).
The longer the thermal cone, the larger its area, so it heats up to the self-cleaning temperature with less heat load. In addition, the protrusion of this part of the insulator from the body enhances its blowing with gases, which additionally accelerates heating and improves cleaning from carbon deposits. An increase in the length of the thermal cone leads to a decrease in the glow number (the candle becomes "hot"). To leave it unchanged, bimetallic central electrodes are used in the design, which better remove heat. Such candles (they are called thermoelastic) warm up faster to the self-cleaning temperature (like hot ones), but cause glow ignition at high thermal loads (like cold ones).
The domestic industry produces spark plugs with glow numbers of 8, 11, 14, 17, 20, 23 and 26. There is no single scale of glow numbers abroad.
If you put too “cold” (with a large glow number) candles, the process of their self-cleaning is difficult, and the motor will work intermittently. If it is too “hot”, the so-called glow ignition is possible, which, in its symptoms and destructive consequences, resembles the self-detonation of a diesel engine.
spark gap- is indicated in the car's operating instructions (but can also be indicated on the packaging or in the marking of the candle) and is in the range from 0.5 to 2 mm. Depending on the design of the electrodes, the gap can be adjustable (by bending the side gap). the design of the electrodes, the gap can be adjustable (by bending the side electrode) and unregulated.
On a Russian-made spark plug, the following must be indicated:
Date of manufacture (month or quarter and (or) the last two digits of the year of manufacture);
- trademark (or) name of the manufacturer;
- conventional designation of the type of candle (decoding is given below);
- the inscription "Made in Russia" or RUS.
In addition, the marking with the main characteristics of the spark plug is directly applied according to figure B
Due to the lack of a unified marking system abroad, it is possible to determine the compliance of spark plugs from different manufacturers only with the help of catalogs or interchangeability tables (Table 1). in addition, each manufacturer often has its own labeling system. More details in the section below "Manufacturers of spark plugs Denso (Denso), Bosh (Bosch), Champion (Champion), NGK (NZhK)"
Spark Plug Trends
Currently, more and more spark plugs are produced with a bimetallic electrode. This allows, in addition to improving thermoelasticity, to increase their reliability and durability.
There is a growing production of spark plugs with the protrusion of the thermal cone of the insulator from the metal body, which provides improved self-cleaning from carbon deposits.
In order to increase the service life, which does not require adjustment of the spark gap, spark plugs are produced with several "ground" electrodes.
To improve the process of sparking (igniting ability of a spark), candles with an increased spark gap are being developed, the shape and profile of the electrodes are changed, and platinum is applied to their surface.
There is a growing production of spark plugs using surface discharge (in which there is no "mass" electrode, and the spark goes from the central electrode to the housing along the surface of the insulator).
To reduce radio interference, more and more spark plugs are equipped with a built-in interference suppression resistor.
Table 1. Interchangeability of spark plugs (dash - there is no analogue or no information)
| RUSSIA | AUTOLITE | BERU | Bosch | BRISK | CHAMPION | EYQUEM | MAGNETI MARELLI | NGK | NIPPON DENSO |
|---|---|---|---|---|---|---|---|---|---|
| A11, A11-1, A11-3 | 425 | 14-9A | W9A | N19 | L86 | 406 | FL4N | B4H | W14F |
| A11R | 414 | 14R-9A | WR9A | NR19 | RL86 | - | FL4NR | BR4H | W14FR |
| A14V, A14V-2 | 275 | 14-8B | W8B | N17Y | L92Y | 550S | FL5NR | BP5H | W16FP |
| A14VM | 275 | 14-8BU | W8BC | N17YC | L92YC | C32S | F5NC | BP5HS | W16FP-U |
| A14VR | - | 14R-7B | WR8B | NR17Y | - | - | FL5NPR | BPR5H | W14FPR |
| A14D | 405 | 14-8C | W8C | L17 | N5 | - | FL5L | B5EB | W17E |
| A14DV | 55 | 14-8D | W8D | L17Y | N11Y | 600LS | FL5LP | BP5E | W16EX |
| A14DVR | 4265 | 14R-8D | WR8D | LR17Y | NR11Y | - | FL5LPR | BPR5E | W16EXR |
| A14DVRM | 65 | 14R-8DU | WR8DC | LR17YC | RN11YC | RC52LS | F5LCR | BPR5ES | W16EXR-U |
| A17B | 273 | 14-7B | W7B | N15Y | L87Y | 600S | FL6NP | BP6H | W20FP |
| A17D | 404 | 14-7C | W7C | L15 | N4 | - | FL6L | B6EM | W20EA |
| A17DV, A17DV-1, A17DV-10 | 64 | 14-7D | W7D | L15Y | N9Y | 707LS | FL7LP | BP6E | W20EP |
| A17DVM | 64 | 14-7DU | W7DC | L15YC | N9YC | C52LS | F7LC | BP6ES | W20EP-U |
| A17DVR | 64 | 14R-7D | WR7D | LR15Y | RN9Y | - | FL7LPR | BPR6E | W20EXR |
| A17DVRM | 64 | 14R-7DU | WR7DC | LR15YC | RN9YC | RC52LS | F7LPR | BPR6ES | W20EPR-U |
| AU17DVRM | 3924 | 14FR-7DU | FR7DCU | DR15YC | RC9YC | RFC52LS | 7LPR | BCPR6ES | Q20PR-U |
| A20D, A20D-1 | 4054 | 14-6C | W6C | L14 | N3 | - | FL7L | B7E | W22ES |
| A23-2 | 4092 | 14-5A | W5A | N12 | L82 | - | FL8N | B8H | W24FS |
| A23B | 273 | 14-5B | W5B | N12Y | L82Y | 755 | FL8NP | BP8H | W24FP |
| A23DM | 403 | 14-5CU | W5CC | L82C | N3C | 75LB | CW8L | B8ES | W24ES-U |
| A23DVM | 52 | 14-5DU | W5DC | L12YC | N6YC | C82LS | F8LC | BP8ES | W24EP-U |
Warranty period for spark plugs
According to the requirements of OST 37.003.081 "Spark plugs", the manufacturer must guarantee the uninterrupted operation of spark plugs for 18 months, provided that the mileage of a car with a classic ignition system does not exceed 30 thousand km, and with an electronic system - 20 thousand km. This is true only if the spark plugs match the engine model and the rules for the operation of the car, their installation, transportation and storage are observed. According to experts, on engines in good technical condition, the actual service life of candles can be 2 times longer.
CARE FOR SPARK PLUGS IN THE CAR. CHECKING AND REPLACING SPARK PLUGS
Every 10-15 thousand kilometers of the car, you should check the condition of the candles and, if necessary, adjust the gap between the electrodes.
Spark plugs for foreign cars or VAZs
I would like to put an end to the question of whether there are spark plugs specialized for foreign cars and for VAZs. In fact, it has always been and always will be, spark plugs recommended by the manufacturer should be used for the car. The desire to choose candles for Samara that are successfully used for foreign cars and do not correspond to performance characteristics and recommendations will not lead to anything good. Manufacturers today are trying to cover the entire market, get the maximum profit and popularity, whether domestic or foreign. Therefore, today you can pick up candles from domestic manufacturers for foreign cars, and imported candles for VAZs or vice versa, everything will depend on your preferences. The most important thing, whether it is a foreign car or a VAZ, is to install candles with the characteristics recommended by the manufacturer.
Dismantling the spark plug from the engine is carried out in the following sequence:
Remove the tip of the high voltage wire (it is unacceptable to pull on the wire);
- unscrew the candle one turn with a special key, then clean the surface in the recess of the cylinder head around it with compressed air or a brush so that dirt particles do not get on the thread or into the combustion chamber;
- turn out the candle;
- check the presence of a sealing ring (for candles with a flat supporting surface);
- carefully inspect the candle for mechanical damage to the insulator, body and electrodes.
Typically, engines are fitted with aluminum cylinder heads, because aluminum expands more when heated than a spark plug, the spark plug can actually be trapped in the threads. Therefore, unscrewing the spark plugs should only be carried out when the engine is completely cool, that is, at the same temperatures at which it was installed. In addition, before installing new candles, it is necessary to apply a thin layer of graphite or copper grease (Cupfer Paste) to the spark plug threads. The lubricant will prevent the threads from oxidizing, and even with a slight change in the shape of the threads under the influence of high temperatures, it will be easy to unscrew the old spark plugs that have expired in the future.
Installation of spark plugs is carried out in the following sequence
New candles covered with conservation grease must be wiped and washed in a solvent (gasoline). It is permissible to boil candles in water and dry, the candle must be cleaned of any dirt and external coatings, it is possible to wash it with a brush in clean gasoline and blow it with compressed air;
- carefully inspect the candle for mechanical damage, sealing ring, contact nut, it is necessary to inspect and make sure that there is no damage to the insulator and body (chips, cracks, dented threads);
- check and, if necessary, adjust the spark gap (by bending the "ground" electrode) to the value specified in the vehicle operating instructions. When adjusting the gap, it is forbidden to press on the central electrode, as this can lead to breakage of the insulator spout.;
- the candle is wrapped by hand into the candle hole and tightened with a special key with a force of 2 kg * m. (there may be other meanings, this is just the most popular)
It is not recommended to use a candle with a different thread length, because soot on unused threads will make it difficult to turn out the “long” candle or wrap the regular one after the “short” one was standing.
Let's repeat about engine temperatures during dismantling and installation of spark plugs. Engines are equipped with aluminum cylinder heads, since aluminum expands more when heated than a spark plug, the spark plug may not actually turn on the head threads. Therefore, the installation of spark plugs should only be carried out when the engine is completely cool.
Spark Plug Malfunctions
It is important to be able to recognize a malfunction as a result of which the car does not work stably (floating idle, troit, does not develop proper power). Spark plugs are not always the cause of these problems. Other elements are also involved in the ignition of the fuel mixture in the engine: the ignition system, the distributor for supplying voltage to the candles, the high-voltage coil, and various sensors.
The spark must ignite at the right moment. The ideal moment occurs shortly before the piston reaches its highest point and the compression is at its maximum. Too sooner or later, a spark will break the efficiency of the engine, and also lead to increased fuel consumption and increased emissions.
It remains to be noted that the ideal operation of the engine for both foreign cars and VAZs is still ensured under the conditions of serviceable spark plugs and the ignition system itself.
Normal looking spark plugs
The appearance of the spark plug (its electrodes) gives an idea of the mode of operation of the engine and the spark plug.
By the appearance of the electrode and the cone of the spark plug insulator, one can judge the correct mixture formation or problems in the ignition system. Evaluation of the appearance of a spark plug is an essential part of engine diagnostics. In this case, you should perform some actions before checking the candles. Prolonged idling, especially when starting the engine cold, can cause soot to settle on the surface and thus hide the real picture. Before checking, it is necessary that the car has traveled approximately 10 kilometers. In this case, the engine must operate at various speeds and at medium loads. After the engine has stopped, prolonged idling should be avoided. After dismantling the spark plugs, certain conclusions can be drawn. 
.
The color of the thermal cone of the insulator is from gray-white, gray-yellow to brown. The engine is OK. The heat number is correct. The fuel mixture and ignition settings are correct, there are no misfires, and the cold start system is working. There is no sediment from fuel impurities and alloying components of engine oil. There are no thermal loads.
Faulty spark plugs and causes of failure
The most likely causes of spark plug failure are contamination with products of incomplete combustion or an increase in the spark gap due to worn electrodes. Moreover, the technical condition of the engine has a decisive influence on the performance of the candles. If the spark plugs are systematically coated with soot, the cause of the contamination should be found and eliminated. In fact, with this malfunction, the so-called “breakdown” problem of spark plugs fails up to 90% of all spark plugs. During combustion, a conductive layer is formed on the insulator, which is practically not removed. This leads to spark instability and misfiring. A similar phenomenon is especially significant for modern cars that comply with EURO standards in terms of environmental indicators and operate on lean mixtures (requiring a powerful spark to ignite). That is, we can conclude that spark plugs fail due to breakdown, without having time to wear out.
You can clean spark plugs with solvents and a brush (not metal). The following are more specific cases of faulty spark plugs.
WITH the spark plug is excessively sooty.
The thermal cone of the insulator, the electrodes and the body of the spark plug are covered over the entire area with intense black soot.
Cause: Incorrect adjustment of the fuel-air mixture (carburetor, injection system), excessively rich working mixture, heavily clogged air filter, automatic cold start system is out of order or "leakage" for an excessively long time in the extended state, driving mainly for short distances, the glow value of the candle is too small (“cold” candle).
Consequences: Misfiring, poor cold engine behavior.
Remedy: adjust the working mixture and engine starter, check the air filter.
Spark plug too oily.
The thermal cone of the insulator, the electrodes and the body of the spark plug are covered with soot with an oily sheen or oil soot.
Reason: excess oil in the combustion chamber, too high oil level, heavily worn piston rings, cylinders, valve guides. For 2-stroke gasoline engines - excess oil in the fuel.
Consequences: Misfiring, poor starting behavior.
Remedy: engine overhaul, correct gasoline-oil mixture, installation of new spark plugs.
Deposits form on the spark plug.
Reason: lead impurities in leaded gasoline or ferrocene (see section ""). Glaze forms at high engine loads after a long period of partial load.
Remedy: installing new spark plugs, it is useless to clean the old ones.
Lead deposits form on spark plugs.
The thermal cone of the insulator is partially covered with a brownish-yellow glaze, the color of which can sometimes turn into a greenish one.
Reason: lead impurities in leaded gasoline or ferocene (see the section "Octane number of gasoline, methods for increasing the octane number. Features of the use of gasoline with different octane numbers."). Glaze forms at high engine loads after a long period of partial load.
Consequences: under heavy loads, the glaze becomes a conductor of electricity and contributes to misfiring.
Remedy: replace with new spark plugs, it is useless to clean the old ones.
Ash builds up on spark plugs.
Strong deposits of ash from impurities of oil and fuel on the thermal cone of the insulator, the cavity accessible to the working mixture and on the ground electrode. From loose to slag formation.
Cause: Alloying compounds, especially from motor oil, can leave this ash in the combustion chamber and on the screwed-in surface of the spark plug.
Consequences: Can lead to spontaneous ignition from hot ash, loss of power and engine damage.
Remedy: Repair the engine. Replace old spark plugs with new spark plugs and possibly use a different oil.
Molten spark plug center electrode.
The central electrode is welded, the faded softened nose cone of the insulator.
The heat value of the spark plug is too low (“hot plug”).
Consequences: Misfiring, loss of power (engine damage).
Remedy: check the engine, ignition system and the quality of the working mixture. Replace old spark plugs with new spark plugs with the correct glow rating.
Melted center electrode and spark plug insulator.
The central electrode is melted, while the side electrode is badly damaged.
Cause: Thermal overload due to pre-ignition, e.g. pre-ignition, combustion residues in the combustion chamber, burnt valves, ignition distributor and poor fuel quality.
Consequences: Misfiring, loss of power, possible engine damage. It is possible to split the thermal cone of the insulator due to overheating of the central electrode.
Welded both spark plug electrodes.
The electrodes look like cauliflower. It is possible to deposit materials foreign to the candle.
Cause: Thermal overload due to pre-ignition, e.g. pre-ignition, combustion residues in the combustion chamber, burnt valves, ignition distributor and poor fuel quality.
Consequences: before the complete destruction of the engine, there is a significant loss of power.
Remedy: check the engine, ignition system and the quality of the working mixture. Install new spark plugs.
Severe wear of the center electrode of the spark plug.
Cause: The instructions for the interval between spark plug replacements were not observed.
Severe wear of the ground electrode of the spark plug.
Cause: aggressive fuel and oil impurities. Unfavorable turbulence in the combustion chamber, possibly due to deposits, detonation in the engine. There is no thermal overload.
Consequences: Interruptions in ignition, especially during acceleration (the voltage is not enough for the increased interelectrode distance). Bad behavior when starting the engine.
Remedy: Replace with new spark plugs.
Destruction of the thermal cone of the spark plug insulator.
Cause: Mechanical damage due to shock, falling or pressure on the center electrode due to improper handling. In extreme cases, due to the formation of deposits between the insulator and the center electrode or through corrosion of the center electrode - especially during long periods of operation - the thermal cone of the insulator may crack.
Consequences: interruptions in ignition, the spark gets into places where the penetration of a fresh combustible mixture is difficult.
Remedy: Replace with new spark plugs.
Measuring and adjusting the gap of spark plugs
On average, spark plug wear after 15,000 km of run, even on a serviceable engine, is 0.1 mm. This wear affects sparking and, accordingly, the correct operation of the spark plugs and the engine. As a result, it is very important to monitor not only the external condition of the spark plug, but also the location of the electrodes and the gap between them. As a rule, the gap for each car and engine is individual, it is given in the owner's manual for the car. The spark plug gap is easiest to set using dial gauges or templates (shown in the figure below) and a device for adjusting the gap and locating the electrodes shown in the figure below.
Checking spark plugs
After setting the gap and cleaning the spark plugs, it is necessary to check for the formation of the correct spark. The spark on the candle must correspond to the figure (see above), in case of deviation from this spark or its absence, the spark plug is not suitable for further operation. You can check the spark on the engine or using a special simple home-made device - "A device for quickly checking spark plugs"
What spark plugs should be installed for the summer and for the winter.
Some may have such a question, which spark plugs should be put in for the winter and for the summer. Strange as it may seem, the answer to the question about the seasonality of the installed spark plugs is obvious. Spark plugs for summer and for winter are the same, the main criterion is serviceability. It often happens that in the summer we have enough spark plugs and in poor condition, since the average temperatures are much higher and all engine systems work better, in addition, the conditions for igniting the fuel mixture at elevated temperatures are also better. With the advent of the cold season, the fuel mixture ignites much worse, it is in winter that it is much more important to have the same spark plugs recommended by the manufacturer, but serviceable spark plugs, on which the reliable start and operation of the car engine will depend.
Manufacturers of spark plugs Denso (Denso), Bosh (Bosch), Champion (Champion), NGK (NZhK)
Spark plugs Denso (Denso)
Candles Denso (Denso - available only with iridium coating) are standard on new car models of some brands. In particular, Toyota has been cooperating with DENSO for many years. In conditions of tough operation, when ordinary spark plugs simply “flood” at speed, iridium candles work without failures. The complex alloy of iridium provides increased reliability of the Denso spark plug. DENSO iridium spark plugs are used even for racing engines, as they not only provide stable operation, but also improve the car's acceleration characteristics by 0.3-0.5 seconds.
The maximum service interval for replacing a Denso candle is one hundred thousand kilometers, although it must be noted that this indicator directly depends on the driving style, operating conditions and the car itself. Contrary to popular belief, iridium spark plugs, in particular Denso spark plugs, are also suitable for older car models. DENSO spark plugs also work on any gasoline.
Bosh spark plugs (Bosch)
BOSCH also develops and supplies spark plugs to car manufacturers directly to the production line. The main line includes candles with the names Super and Super Plus. Super - these are in most cases copper-nickel candles with the number of ground electrodes from 1 to 4.
SuperPlus are distinguished by the addition of the rare earth element yttrium. Yttrium forms a sticky oxide layer and makes the spark plug remarkably resistant to wear and high temperatures. Using this principle, Bosch creates candles for various car models, differing only in electrode gaps. Another "plus" of the BOSCH Super Plus candles is a point ground electrode - a new design solution in most Super plus candles. As a result, this plug gives a significant increase in injection reliability, and therefore optimal combustion of the fuel mixture using a catalytic afterburner. Premium products include Super4, Platinum candles. The Super 4 uses the latest airborne spark principle and for the first time features 4 thin electrodes combined with a pointed silver plated center electrode. This combination is unique in its kind and has important advantages - depending on the load of the engine and the degree of wear, the spark itself finds the best path for reliable operation. Unlike other spark plugs found on older vehicles, the BOSCH-Super 4 has eight different spark paths. Another important advantage of a candle is that it can be self-cleaning. Platinum plugs have a "pure" platinum center electrode that smoothly transitions into a ceramic insulator. The original design allows you to quickly reach the self-cleaning temperature of the candle. Using a lower ignition voltage, BOSCH Platinum spark plugs provide reliable engine starts in hot and cold conditions, providing a more reliable spark at high RPMs. All BOSCH candles are supplied in packs of 10 and 4. Each candle, in turn, has its own packaging. Ten-digit BOSCH numbers for candles have two ranges - 0 241 XXX XXX (candles without noise suppression resistor) and 0 242 XXX XXX (with noise suppression resistor). The trend is to reduce the number of candles without a noise suppression resistor, and replace them with analogues with a resistor. Spark plugs manufactured by BOSCH are suitable for a wide range of passenger cars around the world - from the Russian car industry (BOSCH produces a series of Yttrium spark plugs especially for Russian cars) to sports Porsche.
Spark plugs Champion (Champion)
Champion has been a leader in spark plug technology since 1908, and not only as the spark plug manufacturer that has chosen the OE series for the most engine modifications.
Champion Series OE- equivalent to original spark plugs for any car
Technologies Copper Core, Dual Copper Core, Multi-electrode and Platinum
Complete range of automotive, industrial, marine, light duty, motorcycle and racing spark plugs. Champion plugs with a copper core in the center electrode (Copper Core OE) are the industry standard for efficiency today and the best-selling plug type worldwide. Available for OE assembly lines for Nissan, Daewoo, Hyundai, Mazda and Subaru. Champion Plugs with Copper Cores in the Center and Ground Electrodes (Double Copper OE) are a unique technology developed by Champion to produce one of the most advanced plug types ever. They were chosen for installation on the OE conveyor - Chrysler, Renault, Citroen, Fiat, Peugeot and Jeep. Champion OE multi-electrode spark plugs - two and three electrode spark plug designs provide the best choice where manufacturers require this particular technology. Champion supplies multi-electrode spark plugs to manufacturers such as Fiat, Lancia and Volvo. Champion Platinum OE spark plugs are the pinnacle of spark plug technology for the most advanced vehicles that manufacturers install such plugs on the assembly line. Champion Platinum spark plugs are fitted to vehicles manufactured by Land-Rover, Renault, Rover, Skoda and Lotus.
Champion EON Series- the first specially designed to achieve maximum ignition efficiency with extended service life for high compression engines. EON spark plugs combine the best of original OE designs with state-of-the-art racing technology for today's high performance multi-valve engines. Champion is a leading manufacturer of industrial spark plugs for stationary engines, offering extended service life which is an important factor in many industrial applications requiring many thousands of hours of operation under extreme conditions. As a leader in spark plug technology for light duty engines, Champion offers these components for a variety of engines, including those used on lawnmowers, trimmers, snow blowers, chainsaws, snowmobiles, small generators and more. From inflatable boats to powerboats, inboard or outboard motors, and jet skiers, Champion outboard spark plugs are engineered for easy starting, maximum life and total reliability. Champion has long been known as a supplier of spark plugs to some of the world's most famous motorcycle manufacturers. Champion's involvement in motorsports has always contributed to the development of products designed for the public road and has brought additional benefits to ordinary motorcycle users. Champion offers the world's most advanced motorsport spark plug technology and is thus indirectly involved in all racing disciplines from Formula 1 to Superbike, rally and boat racing.
Spark plugs NGK (NZhK)
NGK is registered in Japan. On November 11, 1936, NGK Spark Plug Co., Ltd. was founded with a starting capital of 1 million yen. A year later, the young company delivered its first spark plugs. At the moment, NGK is one of the leaders successfully competing with the manufacturers of spark plugs described above.
The main series of NGK spark plugs are:
V-Line and LPG LaserLine- Excellent equipment for repair service
To make the work of the trade and the workshop more efficient, NGK has developed the V-Line and LPG LaserLine ranges for the car service.
Iridium IX- alternative for higher power
These spark plugs with a middle electrode made of the noble metal iridium are used by many manufacturers as factory equipment. They have been developed specifically for the latest propulsion technology, but also for older models they provide an alternative to the standard types in order to fully utilize the power reserves. The iridium electrode material is almost insensitive to electrospark erosion. Iridium makes it possible to produce particularly thin medium electrodes with a diameter of only 0.6 mm. With thin middle electrodes, more flammable mixture is supplied for the ignition spark. This gives reliable
The type designation for NGK spark plugs consists of:
The combination of letters (1-4) in front of the glow number indicates the thread diameter, hex key opening, and also the design.
The 5th position (number) indicates the glow number.
The 6th letter indicates the length of the thread.
The 7th letter contains information about the special design feature of the spark plug.
The 8th position in the form of a number indicates a special interelectrode gap.
Well, at the end of the article, I also wanted to say about possible fake spark plugs.
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 body. 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).
With all the variety of designs, any spark plug (Fig. 9) includes 8 of itself ceramic insulator, metal case, electrodes and contact head for connection with high voltage wire.
Central electrode installed in an insulator channel having a variable diameter. The electrode head rests on the conical surface of the insulator channel at the point of transition from a larger diameter to a smaller one. The working part of the central electrode protrudes from the insulator by 1.0 to 5.0 mm. The fixing of the electrode in the channel of the insulator and the sealing of this connection is carried out using glass sealant. It is a mixture of special technical glass and metal powder. Glass must have a thermal expansion coefficient equal to that of ceramics. In this case, the sealing plug will not be destroyed by temperature changes during operation. Mogall powder (copper or lead) is added to glass to make it electrically conductive.
The assembly of the core (insulator assembly with the central electrode and the contact rod) is carried out in the following order. The electrode is installed in the channel of the insulator and a powdered glass sealant is poured on top or placed in the form of a tablet. Then, a contact head is installed in the channel of the insulator. Before pressing, the glass sealant occupies a larger volume than after this operation, and the contact rod cannot fully enter the insulator channel. It protrudes above the insulator by about a third of the length. The workpiece is heated to a temperature of 700-900 "C and with a force of several tens of kilograms, the contact rod is inserted into the glass sealant softened under the influence of temperature. At the same time, it flows into the gaps between the insulator channel, the head of the central electrode and the contact head. After cooling, the glass sealant hardens and securely fixes both parts in the insulator channel Between the ends of the electrode and the contact head, a sealing plug is formed with a height of 1.5 to 7.0 mm, completely blocking the insulator channel from gas breakthrough
If it is necessary to build in the circuit of the central electrode, electrical resistance is used to suppress electromagnetic interference resistive glass sealant. After cooling, the sealing plug acquires the electrical resistance of the required value.
The core is installed in the candle body so that it comes into contact with its conical surface with the corresponding surface inside the body. A sealing-heat-removing washer (copper or steel) is installed between these surfaces.
The fixing of the core is carried out by rolling the shoulder of the housing onto the belt of the insulator. The sealing of the connection insulator - body is carried out by the method of upsetting the body in a heated state (thermosetting).
Side electrode-masses" of rectangular section are welded to the end of the body and bent towards the central one. On the plinth of the housing with an emphasis on a flat supporting surface is installed sealing ring, designed to seal the connection between the spark plug and the engine.
On the threaded part of the contact rod is installed contact nut, if required by the design of the high-voltage wire lug. In some candles, the contact rod does not have a threaded head, it is immediately stamped in the form of a contact nut.
INSULATOR
To ensure uninterrupted sparking, the insulator must have the necessary dielectric strength even at high operating temperatures. The voltage applied to the insulator during engine operation is equal to the breakdown voltage of the spark gap. This voltage increases with increasing pressure and gap size and decreases with increasing temperature. On engines with a classic ignition system, spark plugs with a spark gap of 0.5-0.7 mm are used. The maximum breakdown voltage under these conditions does not exceed 12-15 kV (peak value). On engines with electronic ignition systems, the installation spark gap is 0.8-1.0 mm. During operation, it can increase to 1.3-1.5 mm (for both systems). In this case, the breakdown voltage can reach 20-25 kV.
The design of the insulator is relatively simple - it is a cylinder with an axial hole for installing the central electrode.
in the middle part of the insulator there is a thickening, the so-called "belt" for connection with the housing. Below the girdle is a thinner cylindrical part - -dulce-, turning into a thermal cone. At the transition point from the neck to the thermal cone, there is a conical surface intended for installation between the insulator and the body of the heat-removing sealing washer. Above the girdle is the head, and at the point of transition from the girdle to the head there is a shoulder for rolling the body shoulder when assembling the candle.
Permissible, taking into account the safety factor, the wall thickness is determined by the dielectric strength of the insulator material. According to domestic standards, the insulator must withstand a test voltage of 18 to 22 kV (effective value), which is 1.4 times greater than the amplitude. For most automotive candles, this value is about 25 mm. A further increase is ineffective and leads to a decrease in the mechanical strength of the insulator. To exclude the possibility of electrical breakdown on the surface of the insulator, its head is provided with annular grooves (current barriers) and coated with a special glaze to protect it from possible contamination.
The function of protection against surface overlap on the side of the combustion chamber is performed by a thermal cone. This most important part of the insulator, with relatively small dimensions, withstands the above voltage without overlapping on the surface.
Initially, ordinary porcelain was used as an insulator material. but such an insulator poorly resisted thermal effects and had low mechanical strength.
With an increase in engine power, more reliable insulators were required. than porcelain. Mica insulators have been used for a long time. However, when using lead-added fuels, the mica was destroyed. Insulators again began to be made of ceramic, but not from porcelain, but from especially durable technical ceramics.
The most common and cost-effective for the production of insulators is the isostatic pressing technology, when granules of the required composition and physical properties are made from pre-prepared components. Preforms of insulators are pressed from granules at high pressure, ground to the required dimensions, taking into account shrinkage during firing, and then fired once.
Modern insulators are made from high alumina structural ceramics based on alumina. Such ceramics, containing about 95% alumina, are able to withstand temperatures up to 1600 °C and have high electrical and mechanical strength.
The most important advantage of alumina ceramic is that it has a high thermal conductivity. This significantly improves the thermal characteristic of the candle, since the main heat flow passes through the insulator, entering the candle through the thermal cone and the central electrode (Fig. 10).
FRAME
The metal housing is designed to install a spark plug in the engine and ensures tightness of the connection with the insulator. Welded to its end side electrode, and in designs with an annular spark gap, the body directly performs the function ground electrode.
The body is made by stamping or turning from structural low-carbon steels.
inside the housing there is an annular protrusion with a conical surface. on which the insulator rests. An annular groove is made on the cylindrical part of the body, the so-called thermosetting groove. In the process of assembling the candle, the upper shoulder of the body is rolled onto the insulator belt. Then it is heated and deposited on a press, while the thermosetting groove is subjected to plastic deformation, and the body tightly covers the insulator. As a result of thermal precipitation, the body is in a stressed state, which ensures the tightness of the candle for the entire service life.
Rice. 10. Heat fluxes in the candle insulator
ELECTRODES
As mentioned above, in order to improve the ignition efficiency, the electrodes of the spark plug should be as thin and long as possible, and the spark gap should have the maximum allowable value. On the other hand, to ensure durability, the electrodes must be sufficiently massive.
Therefore, depending on the requirements for power, fuel efficiency and toxicity of engines, on the one hand, and the requirements for the durability of the spark plug, on the other hand, a separate design of electrodes was developed for each type of engine.
Appearance bimetallic electrodes made it possible to solve this problem to a certain extent, since such an electrode has sufficient thermal conductivity. Unlike the usual "monometallic" when working on the engine, it has a lower temperature and, accordingly, a longer resource. In cases where it is necessary to increase the resource, two "mass" electrodes are used (Fig. 11). On candles of foreign production, three or even four electrodes are used for this purpose. The domestic industry produces candles with such a number of electrodes only for aircraft and industrial gas engines It should be noted that with an increase in the number of electrodes, the resistance to carbon deposits decreases and cleaning from carbon deposits becomes more difficult.
The following requirements are imposed on the electrode material: high corrosion and erosion resistance: heat resistance and scale resistance: high thermal conductivity; plasticity sufficient for stamping. The cost of the material should not be high. The most widespread in the domestic industry for the manufacture of central electrodes of spark plugs are heat-resistant alloys: iron-chromium-titanium, nickel-chromium-iron and nickel-chromium with various alloying additives
Side electrode "mass" should have high heat resistance and corrosion resistance. It must have good weldability with ordinary structural steel, from which the body is made, therefore, a nickel-manganese alloy is used (for example, NMts-5). The side electrode must have good ductility in order to be able to control the spark gap.
In order to reduce the quenching effect of the electrodes, when refining the candles, grooves are made on the electrodes, and through holes are made in the ground electrode. Sometimes the side electrode is divided into two parts, turning a single-electrode candle into a two-electrode one.
BUILT-IN RESISTOR
A spark discharge is a source of electromagnetic interference, including radio reception. To suppress them, a resistor is installed between the central electrode and the contact head, which at a temperature of 25 ± 10 "C has an electrical resistance of 4 to 13k0m. "C and high voltage pulses.
ADDITIONAL INSULATOR
Even small losses of ignition energy lead to a weakening of the spark with all the unpleasant consequences: start-up deterioration, unstable idling, loss of engine power, excessive fuel consumption, increased exhaust gas toxicity, etc. If the surface of the insulator is covered with soot, dirt or just moisture, there is a leakage of current "to ground". It is detected in the dark in the form of a corona discharge on the surface of the insulator. Leakage through the contaminated surface of the thermal cone of the insulator in the combustion chamber of the engine can lead to a failure in sparking. The most radical way to increase the electrical strength of the insulation is to install an additional insulator in the form of a ceramic bushing between the body and the contact head of the candle. Thus, the candle acquires double protection against current leakage "to ground".
This technical development is protected by a patent and implemented in our country by Avtokoninvest CJSC (Moscow).
PRECHAMBER CANDLES
Rice. 12. Pre-chamber spark plug
There are various versions of the candle device, in which the working chamber is made in the form of a prechamber. They are used to improve the combustion of the working mixture. Pre-chamber spark plugs are similar to spark plugs for forced sports engines, where the electrodes for protection against overheating are installed deep inside the working chamber of the body. The difference is. that hole. connecting the working chamber (pre-chamber) with the engine cylinder, make a special shape. When compressed, the fresh mixture enters the prechamber, a spark discharge occurs in the region of the vortex flow, and the formation of the primary ignition site becomes more intense. This ensures rapid propagation of the flame in the prechamber. The pressure rises rapidly and throws out a flame that penetrates the engine combustion chamber and intensifies the ignition of even a very lean working mixture.
When burning gases flow from the prechamber into the engine cylinder, due to the turbulence of the combustible mixture, the combustion process is accelerated and becomes more efficient. This. in turn, can lead to an improvement in indicators characterizing fuel efficiency and exhaust gas toxicity.
The disadvantages of pre-chamber candles are that the damping effect of the electrodes is great, and the resistance to carbon deposits is low. Ventilation of the prechamber is difficult and the combustible mixture in it contains an increased amount of residual gases. When burning gases flow from the prechamber into the cylinder, additional heat losses occur. One of the variants of the pre-chamber candle is shown in Fig. 12.
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.
Good day! I welcome you to the pages of this blog. Far from the last place, in this most complex mechanism, like a car, is occupied by spark plugs. Even more, it is one of the most important elements of the engine. And the quality of the engine will depend on how clearly they work, how well they are looked after.
All about spark plugs: the principle of operation, features of operation and care.
So. A spark plug is a device that ignites a mixture of fuel and air, in a gasoline type. Ignition is carried out by an electric charge arising between the electrodes and a voltage of several thousand volts.
Today, special requirements are placed on candles. After all, they are subject to a variety of loads. In particular, changes in the mode of operation, from driving on highways at full throttle, to quiet trips with frequent stops in urban mode. And in the process of all this, thermal, mechanical and chemical loads affect.
Choice of spark plugs.
Requirements for modern devices:
1. Good insulating properties. modern candles should work at a temperature of 1000 degrees.
2. Reliable operation at high (up to 40,000 Volts) voltage.
3. Resistance to thermal shocks and chemical processes that occur in the combustion chamber.
4. The electrodes and the insulator must have excellent thermal conductivity.
Candles must ensure stable operation of the engine in each of the modes: both at idle and at maximum performance. Main spark plug specifications , these are glow number, operating temperature, thermal characteristic, self-cleaning, spark gap size and number of side electrodes.
Heat number.
This characteristic shows at what pressure glow ignition occurs in the cylinder, that is, upon contact with the heated sections of the candle, and not from a spark. This parameter must clearly correspond to the one recommended for your engine. You can use candles with a slightly higher glow number, and then only for a while, but in no case should you install candles with a lower value.
Spark plug operating temperature.
This indicates the temperature of the working part of the candle in this engine mode. In all its modes of operation, the temperature should be in the range of 500-900 degrees. In any scenario, whether it is idling or operating at full power, the temperature must remain within the specified limits.
Thermal characteristic.
Here we talk about the dependence of the thermal cone of insulation on the mode of operation of the engine. To increase the operating temperature, the thermal cone is increased. However, you can not heat it above 900 degrees, as there will be glow ignition.
Based on the thermal characteristics, candles can be divided into two types: cold and hot.
Cold spark plugs are used if the heating is less than the glow ignition temperature at maximum engine power. Such candles will last less if they are “cold” for a given engine, since they will not heat up to the self-cleaning temperature from carbon deposits.
Hot spark plugs are intended for those engines that need to reach the temperature of cleaning from carbon deposits at low thermal loads. If the candles are "hot" than necessary, they will cause glow ignition.
Self-cleaning candles.
This characteristic cannot be quantified. Almost all manufacturers say that their products have the highest degree of self-cleaning. However, in theory, candles should not be covered with soot at all. But in real conditions, this is almost impossible to achieve.
Number of side electrodes.
Usually, there are two electrodes on candles: one central electrode and one side electrode. But now manufacturers have begun to stamp four-electrode candles. However, this does not mean that there will be four sparks. Their purpose is to make stable sparking. This will increase the life of the candles, and improve engine performance at low speeds.
Spark gap.
The spark gap is the distance between the side and central electrodes. Each type of candle has its own specific gap, which cannot be adjusted. And if you managed to “change” this gap, then the only way to return everything to its place is to purchase new candles.
Operation and maintenance of spark plugs.
Caring for spark plugs, entirely and completely, is associated with the peculiarity of the operation of the car. Let's break down the main points:
When you install candles, tighten them only with the recommended torque. It is best to take a torque wrench, they can limit the tightening torque.
Check if the car's ignition system is working properly. Late, or vice versa, early ignition, poor contacts of spark plug wires, problems in the high voltage circuit - all this can adversely affect not only the candles, but the overall operation of the engine.
Fuel quality plays a big role. Refuel only at trusted gas stations, and only high-quality fuel. Since if there are iron impurities in gasoline, this will cause a reddish deposit on the spark plugs.
The average resource of a spark plug is from 25,000 to 35,000 kilometers. And in order for them to serve all this time, as well as to ensure high-quality operation of the engine, they should be removed and inspected from time to time.
When inspecting, pay attention to the ignition cone, carbon deposits can form there, which can tell a lot about the condition of the engine. For example: if the soot is black and oily, then too much oil in crankcase. Black and dry, means too long idling or insufficient load. White soot indicates overheating, or too early ignition timing.
Next, you will have to clean this candle from soot. There are several cleaning methods: physical and chemical. During physical cleaning, carbon deposits are removed with an emery cloth or a wire brush. In this case, no sharp objects should be used, as they can damage the ceramic insulator of the candle, which will increase the formation of soot, and the candle will fail prematurely.
During chemical cleaning, candles are kept in gasoline, dried, then kept in a solution of 20% acetic acid for half an hour. After that, they are cleaned with a brush, washed with water and dried. Acetic acid should be heated, but not more than 90 degrees. Do all this in a well-ventilated area and away from open flames, as both gasoline and acetic acid fumes are very dangerous.
After the candles are cleaned, check the gap between the electrodes. You can find the recommended clearance for your car in its owner's manual. You can check the gap with a round feeler gauge. Well, the adjustment can be done by bending the side electrode. But this should be done carefully, because if the gap is insufficient, a short circuit between the electrodes is possible, and if it is excessive, there may be no spark or a large loss of its power.
Remember, the spark plug is one of the most important parts of an engine. And its malfunction will greatly affect its performance. And in order to prevent this, all the above measures should be observed. Good luck to you!
