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115-627: Spark plugs may also be used for other purposes; in Saab Direct Ignition when they are not firing, spark plugs are used to measure ionization in the cylinders – this ionic current measurement is used to replace the ordinary cam phase sensor, knock sensor and misfire measurement function. Spark plugs may also be used in other applications such as furnaces wherein a combustible fuel/air mixture must be ignited. In this case, they are sometimes referred to as flame igniters . In 1860 Étienne Lenoir used an electric spark plug in his gas engine ,

230-490: A capacitance discharge to eliminate oxides before direct current heating, was patented by G. F. Taylor in 1932. This originated sintering methods employing pulsed or alternating current , eventually superimposed to a direct current. Those techniques have been developed over many decades and summarized in more than 640 patents. Of these technologies the most well known is resistance sintering (also called hot pressing ) and spark plasma sintering , while electro sinter forging

345-518: A magneto -based ignition system by Robert Bosch's engineer Gottlob Honold in 1902 made possible the development of the spark-ignition engine . Subsequent manufacturing improvements can be credited to Albert Champion , to the Lodge brothers , sons of Sir Oliver Lodge , who developed and manufactured their father's idea and also to Kenelm Lee Guinness , of the Guinness brewing family , who developed

460-478: A combination of copper , nickel - iron , chromium , or noble metals . In the late 1970s, the development of engines reached a stage where the heat range of conventional spark plugs with solid nickel alloy centre electrodes was unable to cope with their demands. A plug that was cold enough to cope with the demands of high speed driving would not be able to burn off the carbon deposits caused by stop–start urban conditions, and would foul in these conditions, making

575-602: A form of hot pressing, to enable lower temperatures and taking less time than typical sintering. For a number of years, it was speculated that the existence of sparks or plasma between particles could aid sintering; however, Hulbert and coworkers systematically proved that the electric parameters used during spark plasma sintering make it (highly) unlikely. In light of this, the name "spark plasma sintering" has been rendered obsolete. Terms such as field assisted sintering technique (FAST), electric field assisted sintering (EFAS), and direct current sintering (DCS) have been implemented by

690-506: A glass of water adhere to each other, which is driven by the temperature difference between the water and the ice. Examples of pressure-driven sintering are the compacting of snowfall to a glacier, or the formation of a hard snowball by pressing loose snow together. The material produced by sintering is called sinter . The word sinter comes from the Middle High German sinter , a cognate of English cinder . Sintering

805-606: A great range of material properties. Changes in density, alloying , and heat treatments can alter the physical characteristics of various products. For instance, the Young's modulus E n of sintered iron powders remains somewhat insensitive to sintering time, alloying, or particle size in the original powder for lower sintering temperatures, but depends upon the density of the final product: E n / E = ( D / d ) 3.4 {\displaystyle E_{n}/E=(D/d)^{3.4}} where D

920-454: A heat range system in which the numbers become bigger as the plugs get hotter. As a result, heat range numbers need to be translated between the different manufacturers and cannot be casually interchanged as equals. The spark plug's firing end will be affected by the internal environment of the combustion chamber. As the spark plug can be removed for inspection, the effects of combustion on the plug can be examined. An examination, or "reading" of

1035-408: A high relative density and a small grain size. Therefore, being able to control these properties during processing is of high technical importance. Since densification of powders requires high temperatures, grain growth naturally occurs during sintering. Reduction of this process is key for many engineering ceramics. Under certain conditions of chemistry and orientation, some grains may grow rapidly at

1150-419: A longer period. Special "anti-fouling" adapters are sold which fit between the plug and the head to reduce the protrusion of the plug for just this reason, on older engines with severe oil burning problems; this will cause the ignition of the fuel-air mixture to be less effective, but in such cases, this is of lesser significance. The operating temperature of a spark plug is the actual physical temperature at

1265-409: A lower affinity for water and a lower plasticity index than clay , requiring organic additives in the stages before sintering. Sintering begins when sufficient temperatures have been reached to mobilize the active elements in the ceramic material, which can start below their melting point (typically at 50–80% of their melting point ), e.g. as premelting . When sufficient sintering has taken place,

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1380-455: A marine spark plug's shell is double-dipped, zinc-chromate coated metal. The central electrode is connected to the terminal through an internal wire and commonly a ceramic series resistance to reduce emission of RF noise from the sparking. Non-resistor spark plugs, commonly sold without an "R" in the plug type part number, lack this element to reduce electro-magnetic interference with radios and other sensitive equipment. The tip can be made of

1495-432: A modified sintering method which combined electric current with pressure . The benefits of this method were proved for the sintering of refractory metals as well as conductive carbide or nitride powders. The starting boron – carbon or silicon –carbon powders were placed in an electrically insulating tube and compressed by two rods which also served as electrodes for the current. The estimated sintering temperature

1610-530: A narrow range, for purposes of limiting emissions. Racing engines, however, still benefit from picking a proper plug heat range. Very old racing engines will sometimes have two sets of plugs, one just for starting and another to be installed for driving once the engine is warmed up. Spark plug manufacturers use different numbers to denote heat range of their spark plugs. Some manufacturers, such as Denso and NGK, have numbers that become higher as they get colder. By contrast, Champion, Bosch, BRISK, Beru, and ACDelco use

1725-402: A new type of "surface discharge" plug was developed, presenting an almost flat face to the combustion chamber. A stubby centre electrode projects only very slightly, and the entire earthed body of the plug acts as the side electrode. The electrodes thus sit just beyond the reach of the passing apex seal, while the spark is accessible to the fuel/air mixture. The arc gap remains constant throughout

1840-444: A particle size around the penetration depth of microwaves in the particular material. The sintering process and side-reactions run several times faster during microwave sintering at the same temperature, which results in different properties for the sintered product. This technique is acknowledged to be quite effective in maintaining fine grains/nano sized grains in sintered bioceramics . Magnesium phosphates and calcium phosphates are

1955-415: A pointed electrode but a pointed electrode would erode after only a few seconds. Instead, the electrons emit from the sharp edges of the end of the electrode; as these edges erode, the spark becomes weaker and less reliable. At one time it was common to remove the spark plugs, clean deposits off the ends either manually or with specialized sandblasting equipment and file the end of the electrode to restore

2070-408: A poor seal or incorrect reach would result because of the threads not properly seating in the heads. The length of the threaded portion of the plug should be closely matched to the thickness of the head. If a plug extends too far into the combustion chamber, it may be struck by the piston, damaging the engine internally. Less dramatically, if the threads of the plug extend into the combustion chamber,

2185-453: A recessed central electrode surrounded by the spark plug thread, which effectively becomes the ground electrode (see "surface-discharge spark plug", below). Also there is the use of a V-shaped notch in the tip of the ground electrode. Multiple ground electrodes generally provide longer life, as when the spark gap widens due to electric discharge wear, the spark moves to another closer ground electrode. The disadvantage of multiple ground electrodes

2300-515: A relative density higher than 75% of theoretical sample density. This will remove supercritical pores from the body. The sample will then be cooled down and held at the second sintering temperature until densification is completed. Grains of cubic zirconia and cubic strontium titanate were significantly refined by TSS compared to CRH. However, the grain size changes in other ceramic materials, like tetragonal zirconia and hexagonal alumina, were not statistically significant. In microwave sintering, heat

2415-436: A removable nut or knurl, which enables its users to attach them to two different kinds of spark plug boots. Some spark plugs have a bare thread, which is a common type for motorcycles and ATVs. Finally, in very recent years, a cup-style terminal has been introduced, which allows for a longer ceramic insulator in the same confined space. The main part of the insulator is typically made from sintered alumina (Al 2 O 3 ),

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2530-399: A simple single piece construction at low cost but high mechanical reliability. The dimensions of the insulator and the metal conductor core determine the heat range of the plug. Short insulators are usually "cooler" plugs, while "hotter" plugs are made with a lengthened path to the metal body, though this also depends on the thermally conductive metal core. Because the spark plug also seals

2645-424: A sinterisation cycle of a particular ceramic's formulation (i.e., tails and frits) can be easily obtained by observing the expansion-temperature curves during optical dilatometer thermal analysis. In fact, sinterisation is associated with a remarkable shrinkage of the material because glass phases flow once their transition temperature is reached, and start consolidating the powdery structure and considerably reducing

2760-408: A spark gap which can be adjusted by the technician installing the spark plug, by bending the ground electrode slightly. The same plug may be specified for several different engines, requiring a different gap for each. Spark plugs in automobiles generally have a gap between 0.6 and 1.8 mm (0.024 and 0.071 in). The gap may require adjustment from the out-of-the-box gap. A spark plug gap gauge

2875-453: A spark plug is affected by the construction of the spark plug: the types of materials used, the length of insulator and the surface area of the plug exposed within the combustion chamber. For normal use, the selection of a spark plug heat range is a balance between keeping the tip hot enough at idle to prevent fouling and cold enough at maximal power to prevent pre-ignition or engine knocking . By examining "hotter" and "cooler" spark plugs of

2990-451: A spark to effectively ignite the fuel-air mixture, but the plug will almost always fire on each cycle. A gap that is too wide might prevent a spark from firing at all or may misfire at high speeds, but will usually have a spark that is strong for a clean burn. A spark which intermittently fails to ignite the fuel-air mixture may not be noticeable directly, but will show up as a reduction in the engine's power and fuel efficiency . Gap adjustment

3105-451: A very hard ceramic material with high dielectric strength , printed with the manufacturer's name and identifying marks, then glazed to improve resistance to surface spark tracking. Its major functions are to provide mechanical support and electrical insulation for the central electrode, while also providing an extended spark path for flashover protection. This extended portion, particularly in engines with deeply recessed plugs, helps extend

3220-448: A wicking structure in certain types of heat pipe construction, where the porosity allows a liquid agent to move through the porous material via capillary action . For materials that have high melting points such as molybdenum , tungsten , rhenium , tantalum , osmium and carbon , sintering is one of the few viable manufacturing processes. In these cases, very low porosity is desirable and can often be achieved. Sintered metal powder

3335-449: Is a capacitor discharge ignition developed by Saab Automobile , then known as Saab-Scania, and Mecel AB during the 1980s. It was first shown in 1985 and put into series production in the Saab 9000 in 1988. One of the first instances of using the system was for a Formula Three racing engine (on B202 basis) developed with the help of engine builder John Nicholson , first shown in

3450-434: Is a determining factor for properties such as strength and electrical conductivity. To yield the desired bond area, temperature and initial grain size are precisely controlled over the sintering process. At steady state, the particle radius and the vapor pressure are proportional to (p 0 ) and to (p 0 ) , respectively. The source of power for solid-state processes is the change in free or chemical potential energy between

3565-402: Is a disc with a sloping edge, or with round wires of precise diameters, and is used to measure the gap. Use of a feeler gauge with flat blades instead of round wires, as is used on distributor points or valve lash, will give erroneous results, due to the shape of spark plug electrodes. The simplest gauges are a collection of keys of various thicknesses which match the desired gaps and the gap

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3680-422: Is accomplished by marking the location of the gap on the outside of the plug, installing it, and noting the direction in which the mark faces. Then the plug is removed and washers are added to change the orientation of the tightened plug. This must be done individually for each plug, as the orientation of the gap with respect to the threads of the shell is random . Some plugs are made with a non-random orientation of

3795-610: Is adjusted until the key fits snugly. With current engine technology, universally incorporating solid state ignition systems and computerized fuel injection , the gaps used are larger on average than in the era of carburetors and breaker point distributors, to the extent that spark plug gauges from that era cannot always measure the required gaps of current cars. Vehicles using compressed natural gas generally require narrower gaps than vehicles using gasoline. The gap adjustment (also called "spark plug gapping") can be crucial to proper engine operation. A narrow gap may give too small and weak

3910-456: Is affected by the change in pressure and differences in free energy across the curved surface. If the size of the particle is small (and its curvature is high), these effects become very large in magnitude. The change in energy is much higher when the radius of curvature is less than a few micrometers, which is one of the main reasons why much ceramic technology is based on the use of fine-particle materials. The ratio of bond area to particle size

4025-425: Is an electric current assisted sintering (ECAS) technology originated from capacitor discharge sintering . It is used for the production of diamond metal matrix composites and is under evaluation for the production of hard metals, nitinol and other metals and intermetallics. It is characterized by a very low sintering time, allowing machines to sinter at the same speed as a compaction press. Pressureless sintering

4140-431: Is called hot isostatic pressing . To allow efficient stacking of product in the furnace during sintering and to prevent parts sticking together, many manufacturers separate ware using ceramic powder separator sheets. These sheets are available in various materials such as alumina, zirconia and magnesia. They are additionally categorized by fine, medium and coarse particle sizes. By matching the material and particle size to

4255-406: Is commonly used. Materials for which liquid phase sintering is common are Si 3 N 4 , WC , SiC , and more. Liquid phase sintering is the process of adding an additive to the powder which will melt before the matrix phase. The process of liquid phase sintering has three stages: For liquid phase sintering to be practical the major phase should be at least slightly soluble in the liquid phase and

4370-482: Is generally considered successful when the process reduces porosity and enhances properties such as strength, electrical conductivity , translucency and thermal conductivity . In some special cases, sintering is carefully applied to enhance the strength of a material while preserving porosity (e.g. in filters or catalysts, where gas adsorption is a priority). During the sintering process, atomic diffusion drives powder surface elimination in different stages, starting at

4485-446: Is irrelevant in series with the plug resistor or wires). The smaller electrode also absorbs less heat from the spark and initial flame energy. Polonium spark plugs were marketed by Firestone from 1940 to 1953. While the amount of radiation from the plugs was minuscule and not a threat to the consumer, the benefits of such plugs quickly diminished after approximately a month because of polonium's short half-life, and because buildup on

4600-416: Is not recommended for iridium and platinum spark plugs, because there is a risk of damaging a metal disk welded to the electrode. Over the years variations on the basic spark plug design have attempted to provide either better ignition, longer life, or both. Such variations include the use of two, three, or four equally spaced ground electrodes surrounding the central electrode. Other variations include using

4715-420: Is said to be "cold" if it can conduct more heat out of the spark plug tip and lower the tip's temperature. Whether a spark plug is "hot" or "cold" is known as the heat range of the spark plug. The heat range of a spark plug is typically specified as a number, with some manufacturers using ascending numbers for hotter plugs, and others doing the opposite – using ascending numbers for colder plugs. The heat range of

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4830-429: Is sometimes generated internally within the material, rather than via surface radiative heat transfer from an external heat source. Some materials fail to couple and others exhibit run-away behavior, so it is restricted in usefulness. A benefit of microwave sintering is faster heating for small loads, meaning less time is needed to reach the sintering temperature, less heating energy is required and there are improvements in

4945-429: Is still considered part of powder metallurgy) is liquid-state sintering in which at least one but not all elements are in a liquid state. Liquid-state sintering is required for making cemented carbide and tungsten carbide . Sintered bronze in particular is frequently used as a material for bearings , since its porosity allows lubricants to flow through it or remain captured within it. Sintered copper may be used as

5060-405: Is that a shielding effect can occur in the engine combustion chamber inhibiting the flame face as the fuel air mixture burns. This can result in a less efficient burn and increased fuel consumption. They also are difficult or nearly impossible to adjust to another uniform gap size. A piston engine has a part of the combustion chamber that is always out of reach of the piston; and this zone is where

5175-437: Is the density, E is Young's modulus and d is the maximum density of iron. Sintering is static when a metal powder under certain external conditions may exhibit coalescence, and yet reverts to its normal behavior when such conditions are removed. In most cases, the density of a collection of grains increases as material flows into voids, causing a decrease in overall volume. Mass movements that occur during sintering consist of

5290-410: Is the latest advancement in this field. In spark plasma sintering (SPS), external pressure and an electric field are applied simultaneously to enhance the densification of the metallic/ceramic powder compacts. However, after commercialization it was determined there is no plasma, so the proper name is spark sintering as coined by Lenel. The electric field driven densification supplements sintering with

5405-677: Is the sintering of a powder compact (sometimes at very high temperatures, depending on the powder) without applied pressure. This avoids density variations in the final component, which occurs with more traditional hot pressing methods. The powder compact (if a ceramic) can be created by slip casting , injection moulding , and cold isostatic pressing . After presintering, the final green compact can be machined to its final shape before being sintered. Three different heating schedules can be performed with pressureless sintering: constant-rate of heating (CRH), rate-controlled sintering (RCS), and two-step sintering (TSS). The microstructure and grain size of

5520-548: Is used to make frangible shotgun shells called breaching rounds , as used by military and SWAT teams to quickly force entry into a locked room. These shotgun shells are designed to destroy door deadbolts, locks and hinges without risking lives by ricocheting or by flying on at lethal speed through the door. They work by destroying the object they hit and then dispersing into a relatively harmless powder. Sintered bronze and stainless steel are used as filter materials in applications requiring high temperature resistance while retaining

5635-487: Is welded or hot forged to the side of the metal shell. The side electrode also runs very hot, especially on projected nose plugs. Some designs have provided a copper core to this electrode, so as to increase heat conduction. Multiple side electrodes may also be used, so that they don't overlap the central electrode. The ground electrode can also have small pads of platinum or even iridium added to them in order to increase service life. Spark plugs are typically designed to have

5750-464: The Trionic engine management system. Sintered Sintering or frittage is the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquefaction . Sintering happens as part of a manufacturing process used with metals , ceramics , plastics , and other materials. The atoms/molecules in the sintered material diffuse across

5865-573: The jacket , as many people call it) of the spark plug withstands the torque of tightening the plug, serves to remove heat from the insulator and pass it on to the cylinder head, and acts as the ground for the sparks passing through the central electrode to the side electrode. Spark plug threads are cold rolled to prevent thermal cycle fatigue. It's important to install spark plugs with the correct "reach," or thread length. Spark plugs can vary in reach from 0.095 to 2.649 cm (0.0375 to 1.043 in), such for automotive and small engine applications. Also,

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5980-592: The 1930s, lead deposits on the mica became a problem and reduced the interval between needing to clean the spark plug. Sintered alumina was developed by Siemens in Germany to counteract this. Sintered alumina is a superior material to mica or porcelain because it is a relatively good thermal conductor for a ceramic, it maintains good mechanical strength and (thermal) shock resistance at higher temperatures, and this ability to run hot allows it to be run at "self cleaning" temperatures without rapid degradation. It also allows

6095-464: The KLG brand. Helen Blair Bartlett played a vital role in making the insulator in 1930. The function of a spark plug is to produce a spark at the required time to ignite the combustible mixture. The plug is connected to the high voltage generated by an ignition coil or magneto . As current flows from the coil, a voltage develops between the central and side electrodes. Initially no current can flow because

6210-504: The United States, common thread (nut) sizes are 10mm (16mm), 12mm (14mm, 16mm or 17.5mm), 14mm (16mm, 20.63mm) and 18mm (20.63mm). The top of the spark plug contains a terminal to connect to the ignition system . Over of the years variations in the terminal configuration have been introduced by manufacturers. The exact terminal construction varies depending on the use of the spark plug. Most passenger car spark plug wires snap onto

6325-431: The ability to regenerate the filter element. For example, sintered stainless steel elements are employed for filtering steam in food and pharmaceutical applications, and sintered bronze in aircraft hydraulic systems. Sintering of powders containing precious metals such as silver and gold is used to make small jewelry items. Evaporative self-assembly of colloidal silver nanocubes into supercrystals has been shown to allow

6440-409: The additive should melt before any major sintering of the solid particulate network occurs, otherwise rearrangement of grains will not occur. Liquid phase sintering was successfully applied to improve grain growth of thin semiconductor layers from nanoparticle precursor films. These techniques employ electric currents to drive or enhance sintering. English engineer A. G. Bloxam registered in 1906

6555-441: The better the ignition of the air-fuel mixture will be, although experts believe the process is more complex and dependent on combustion chamber shape. On the other hand, if an engine is "burning oil", the excess oil leaking into the combustion chamber tends to foul the plug tip and inhibit the spark; in such cases, a plug with less protrusion than the engine would normally call for often collects less fouling and performs better, for

6670-480: The boundaries of the particles, fusing the particles together and creating a solid piece. Since the sintering temperature does not have to reach the melting point of the material, sintering is often chosen as the shaping process for materials with extremely high melting points, such as tungsten and molybdenum . The study of sintering in metallurgical powder-related processes is known as powder metallurgy . An example of sintering can be observed when ice cubes in

6785-427: The ceramic body will no longer break down in water; additional sintering can reduce the porosity of the ceramic, increase the bond area between ceramic particles, and increase the material strength. Industrial procedures to create ceramic objects via sintering of powders generally include: All the characteristic temperatures associated with phase transformation, glass transitions, and melting points, occurring during

6900-413: The ceramics may vary depending on the material and method used. Constant-rate of heating (CRH), also known as temperature-controlled sintering, consists of heating the green compact at a constant rate up to the sintering temperature. Experiments with zirconia have been performed to optimize the sintering temperature and sintering rate for CRH method. Results showed that the grain sizes were identical when

7015-402: The characteristic markings on the firing end of the spark plug can indicate conditions within the running engine. Engine and spark plug manufacturers will publish information about the characteristic markings in spark plug reading charts. A light brownish discoloration of the tip of the block indicates proper operation; other conditions may indicate malfunction. For example, a sandblasted look to

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7130-431: The combustion chamber escapes through the exhaust gases, the side walls of the cylinder and the spark plug itself. The heat range of a spark plug has only a minute effect on combustion chamber and overall engine temperature. A cold plug will not materially cool down an engine's running temperature. (A too hot plug may, however, indirectly lead to a runaway pre-ignition condition that can increase engine temperature.) Rather,

7245-469: The combustion chamber of the engine when installed, seals are required to ensure there is no leakage from the combustion chamber. The internal seals of modern plugs are made of compressed glass/metal powder, but old style seals were typically made by the use of a multi-layer braze . The external seal is usually a crush washer , but some manufacturers use the cheaper method of a taper interface and simple compression to attempt sealing. The metal case/shell (or

7360-429: The conductors would block the radiation that improved engine performance. The premise behind the polonium spark plug, as well as Alfred Matthew Hubbard 's prototype radium plug that preceded it, was that the radiation would improve ionization of the fuel in the cylinder and thus allow the plug to fire more quickly and efficiently. The side electrode (also known as the "ground strap") is made from high nickel steel and

7475-472: The conventional spark plug is located. A Wankel engine has a permanently varying combustion area; and the spark plug is inevitably swept by the rotor's apex seals. If a spark plug were to protrude into the Wankel's combustion chamber it would be hit by the passing apex seal, but if the plug were recessed to avoid this, mixture access to the spark would be reduced, leading to misfire or incomplete combustion. So

7590-449: The cylinder head with a single-use hollow or folded metal washer which is crushed slightly between the flat surface of the head and that of the plug, just above the threads. Some spark plugs have a tapered seat that uses no washer. The torque for installing these plugs is supposed to be lower than a washer-sealed plug. Spark plugs with tapered seats should never be installed in vehicles with heads requiring washers, and vice versa. Otherwise,

7705-418: The discharge process, resulting in a hotter and longer-duration spark. As the current of electrons surges across the gap, it raises the temperature of the spark channel to 60,000  K . The intense heat in the spark channel causes the ionized gas to expand very quickly, like a small explosion. This is the "click" heard when observing a spark, similar to lightning and thunder . The heat and pressure force

7820-489: The electrical field strength is greatest; this is from wherever the radius of curvature of the surface is smallest, from a sharp point or edge rather than a flat surface (see corona discharge ). Using the colder, blunter side electrode as negative requires up to 45 percent higher voltage, so few ignition systems aside from wasted spark are designed this way. Waste spark systems place a greater strain upon spark plugs since they alternately fire electrons in both directions (from

7935-459: The electrical insulation and prevent electrical energy from leaking along the insulator surface from the terminal to the metal case. The disrupted and longer path makes the electricity encounter more resistance along the surface of the spark plug even in the presence of dirt and moisture. Some spark plugs are manufactured without ribs; improvements in the dielectric strength of the insulator make them less important. On modern (post 1930s) spark plugs,

8050-430: The engine misfire. Similarly, a plug that was hot enough to run smoothly in town could melt when called upon to cope with extended high speed running on motorways. The answer to this problem, devised by the spark plug manufacturers, was to use a different material and design for the centre electrode that would be able to carry the heat of combustion away from the tip more effectively than a solid nickel alloy could. Copper

8165-404: The entire service life of a surface-gap spark plug, and the spark path will continually vary (instead of darting from the centre to the side electrode as in a conventional plug). A further advantage of the surface-gap design is that the side electrode cannot break off and potentially cause engine damage, though this also doesn't often happen with conventional spark plugs. Most spark plugs seal to

8280-455: The examples which have been processed through the microwave sintering technique. Sintering in practice is the control of both densification and grain growth . Densification is the act of reducing porosity in a sample, thereby making it denser. Grain growth is the process of grain boundary motion and Ostwald ripening to increase the average grain size. Many properties ( mechanical strength , electrical breakdown strength, etc.) benefit from both

8395-410: The expense of their neighbours during sintering. This phenomenon, known as abnormal grain growth (AGG), results in a bimodal grain size distribution that has consequences for the mechanical, dielectric and thermal performance of the sintered material. For densification to occur at a quick pace it is essential to have (1) an amount of liquid phase that is large in size, (2) a near complete solubility of

8510-415: The firing process used in the manufacture of pottery and other ceramic objects. Sintering and vitrification (which requires higher temperatures) are the two main mechanisms behind the strength and stability of ceramics. Sintered ceramic objects are made from substances such as glass , alumina , zirconia , silica , magnesia , lime , beryllium oxide , and ferric oxide . Some ceramic raw materials have

8625-405: The first patent on sintering powders using direct current in vacuum . The primary purpose of his inventions was the industrial scale production of filaments for incandescent lamps by compacting tungsten or molybdenum particles. The applied current was particularly effective in reducing surface oxides that increased the emissivity of the filaments. In 1913, Weintraub and Rush patented

8740-415: The first internal combustion piston engine. Lenoir is generally credited with the invention of the spark plug. Early patents for spark plugs included those by Nikola Tesla (in U.S. patent 609,250 for an ignition timing system, 1898), Frederick Richard Simms (GB 24859/1898, 1898) and Robert Bosch (GB 26907/1898). Only the invention of the first commercially viable high-voltage spark plug as part of

8855-447: The first ion sensing ignition system on a production car. The system puts a low voltage over the spark plugs when they are not fired to measure ionization in the cylinders. The ionic current measurement is used to replace the ordinary knock sensor and misfire measurement function. The spark plugs are directly coupled to the "DIC" (or "IDM") which houses the ignition coils and electronics that measure cylinder ionization for use by

8970-427: The formation of necks between powders to final elimination of small pores at the end of the process. The driving force for densification is the change in free energy from the decrease in surface area and lowering of the surface free energy by the replacement of solid-vapor interfaces. It forms new but lower-energy solid-solid interfaces with a net decrease in total free energy. On a microscopic scale, material transfer

9085-490: The fuel and air in the gap is an insulator, but as the voltage rises further it begins to change the structure of the gases between the electrodes. Once the voltage exceeds the dielectric strength of the gases, the gases become ionized . The ionized gas becomes a conductor and allows current to flow across the gap. Spark plugs usually require voltage of 12,000–25,000 volts or more to "fire" properly, although it can go up to 45,000 volts. They supply higher current during

9200-525: The gap and are usually marked as such by a suffix to the model number; typically these are specified by manufacturers of very small engines where the spark plug tip and electrodes form a significantly large part of the shape of the combustion chamber. The Honda Insight has indexed spark plugs from factory, with four different part numbers available corresponding to the different degrees of indexing to achieve most efficient combustion and maximal fuel efficiency. Saab Direct Ignition Saab Direct Ignition

9315-410: The gases to react with each other, and at the end of the spark event there should be a small ball of fire in the spark gap as the gases burn on their own. The size of this fireball, or kernel, depends on the exact composition of the mixture between the electrodes and the level of combustion chamber turbulence at the time of the spark. A small kernel will make the engine run as though the ignition timing

9430-407: The ground electrode to the central electrode, not just from the central electrode to the ground electrode). As a result, vehicles with such a system should have precious metals on both electrodes, not just on the central electrode, in order to increase service replacement intervals since they wear down the metal more quickly in both directions, not just one. It would be easiest to pull electrons from

9545-403: The latter portions of the process, boundary and lattice diffusion from the boundary become important. Control of temperature is very important to the sintering process, since grain-boundary diffusion and volume diffusion rely heavily upon temperature, particle size, particle distribution, material composition, and often other properties of the sintering environment itself. Sintering is part of

9660-415: The leftover powder is still pure, so it can be recycled. Particular disadvantages of the powder technology include: Plastic materials are formed by sintering for applications that require materials of specific porosity. Sintered plastic porous components are used in filtration and to control fluid and gas flows. Sintered plastics are used in applications requiring caustic fluid separation processes such as

9775-425: The level of torque currently being produced by the engine will strongly influence spark plug operating temperature because the maximal temperature and pressure occur when the engine is operating near peak torque output (torque and rotational speed directly determine the power output). The temperature of the insulator responds to the thermal conditions it is exposed to in the combustion chamber, but not vice versa. If

9890-465: The liquid concentration must also create the required capillary pressure within range, else the process ceases. The vitrification rate is dependent upon the pore size, the viscosity and amount of liquid phase present leading to the viscosity of the overall composition, and the surface tension. Temperature dependence for densification controls the process because at higher temperatures viscosity decreases and increases liquid content. Therefore, when changes to

10005-519: The main effect of a "hot" or "cold" plug is to affect the temperature of the tip of the spark plug. It was common before the modern era of computerized fuel injection to specify at least a couple of different heat ranges for plugs for an automobile engine; a hotter plug for cars that were mostly driven slowly around the city, and a colder plug for sustained high-speed highway use. This practice has, however, largely become obsolete now that cars' fuel/air mixtures and cylinder temperatures are maintained within

10120-492: The most recent engine operating conditions and running the engine under different conditions may erase or obscure characteristic marks previously left on the spark plugs. The most valuable information is gathered by running the engine at high speed and full load, immediately cutting the ignition off and stopping without idling or low speed operation and removing the plugs for reading. Spark plug reading viewers, which are simply combined flashlight/magnifiers, are available to improve

10235-408: The neck and the surface of the particle. This energy creates a transfer of material through the fastest means possible; if transfer were to take place from the particle volume or the grain boundary between particles, particle count would decrease and pores would be destroyed. Pore elimination is fastest in samples with many pores of uniform size because the boundary diffusion distance is smallest. during

10350-429: The nibs in whiteboard markers, inhaler filters, and vents for caps and liners on packaging materials. Sintered ultra high molecular weight polyethylene materials are used as ski and snowboard base materials. The porous texture allows wax to be retained within the structure of the base material, thus providing a more durable wax coating. For materials that are difficult to sinter, a process called liquid phase sintering

10465-414: The nose of the plug. Conversely if the plug is too hot, the porcelain will be porous looking, almost like sugar. The material which seals the central electrode to the insulator will boil out. Sometimes the end of the plug will appear glazed, as the deposits have melted. An idling engine will have a different impact on the spark plugs than one running at full throttle . Spark plug readings are only valid for

10580-436: The particle undergoes grain-growth and grain-shape changes occurs. Shrinkage would result when the liquid slips between particles and increases pressure at points of contact causing the material to move away from the contact areas, forcing particle centers to draw near each other. The sintering of liquid-phase materials involves a fine-grained solid phase to create the needed capillary pressures proportional to its diameter, and

10695-464: The porosity of the material. Sintering is performed at high temperature. Additionally, a second and/or third external force (such as pressure, electric current) could be used. A commonly used second external force is pressure. Sintering performed by only heating is generally termed "pressureless sintering", which is possible with graded metal-ceramic composites, utilising a nanoparticle sintering aid and bulk molding technology. A variant used for 3D shapes

10810-428: The product properties. A failing of microwave sintering is that it generally sinters only one compact at a time, so overall productivity turns out to be poor except for situations involving one of a kind sintering, such as for artists. As microwaves can only penetrate a short distance in materials with a high conductivity and a high permeability , microwave sintering requires the sample to be delivered in powders with

10925-534: The range of 0.1 to 1 micrometres develop pressures in the range of 175 pounds per square inch (1,210 kPa) to 1,750 pounds per square inch (12,100 kPa) for silicate liquids and in the range of 975 pounds per square inch (6,720 kPa) to 9,750 pounds per square inch (67,200 kPa) for a metal such as liquid cobalt. Densification requires constant capillary pressure where just solution-precipitation material transfer would not produce densification. For further densification, additional particle movement while

11040-458: The reading of the spark plugs. "Indexing" of plugs upon installation involves installing the spark plug so that the open area of its gap, not shrouded by the ground electrode, faces the center of the combustion chamber rather than one of its walls. The theory holds that this will maximize the exposure of the fuel-air mixture to the spark, also ensuring that every combustion chamber is even in layout and therefore resulting in better ignition. Indexing

11155-407: The reduction of total porosity by repacking, followed by material transport due to evaporation and condensation from diffusion . In the final stages, metal atoms move along crystal boundaries to the walls of internal pores, redistributing mass from the internal bulk of the object and smoothing pore walls. Surface tension is the driving force for this movement. A special form of sintering (which

11270-415: The same manufacturer side by side, the principle involved can be very clearly seen; the cooler plugs have a more substantial ceramic insulator filling the gap between the center electrode and the shell, effectively allowing more heat to be carried off by the shell, while the hotter plugs have less ceramic material, so that the tip is more isolated from the body of the plug and retains heat better. Heat from

11385-723: The samples were sintered to the same density, proving that grain size is a function of specimen density rather than CRH temperature mode. In rate-controlled sintering (RCS), the densification rate in the open-porosity phase is lower than in the CRH method. By definition, the relative density, ρ rel , in the open-porosity phase is lower than 90%. Although this should prevent separation of pores from grain boundaries, it has been proven statistically that RCS did not produce smaller grain sizes than CRH for alumina, zirconia, and ceria samples. Two-step sintering (TSS) uses two different sintering temperatures. The first sintering temperature should guarantee

11500-408: The sharp edges of the threads act as point sources of heat which may cause pre-ignition ; in addition, deposits which form between the exposed threads may make it difficult to remove the plugs, even damaging the threads on aluminium heads in the process of removal. The protrusion of the tip into the chamber also affects plug performance, however; the more centrally located the spark gap is, generally

11615-525: The sharp edges, but this practice has become less frequent for three reasons: The development of noble metal high temperature electrodes (using metals such as yttrium , iridium , tungsten , palladium , or ruthenium , as well as the relatively high value platinum , silver or gold ) allows the use of a smaller center wire, which has sharper edges but will not melt or corrode away. These materials are used because of their high melting points and durability, not because of their electrical conductivity (which

11730-521: The sintering community. Using a direct current (DC) pulse as the electric current, spark plasma, spark impact pressure, joule heating, and an electrical field diffusion effect would be created. By modifying the graphite die design and its assembly, it is possible to perform pressureless sintering in spark plasma sintering facility. This modified die design setup is reported to synergize the advantages of both conventional pressureless sintering and spark plasma sintering techniques. Electro sinter forging

11845-502: The sintering of electrical joints at temperatures lower than 200 °C. Particular advantages of the powder technology include: The literature contains many references on sintering dissimilar materials to produce solid/solid-phase compounds or solid/melt mixtures at the processing stage. Almost any substance can be obtained in powder form, through either chemical, mechanical or physical processes, so basically any material can be obtained through sintering. When pure elements are sintered,

11960-425: The solid in the liquid, and (3) wetting of the solid by the liquid. The power behind the densification is derived from the capillary pressure of the liquid phase located between the fine solid particles. When the liquid phase wets the solid particles, each space between the particles becomes a capillary in which a substantial capillary pressure is developed. For submicrometre particle sizes, capillaries with diameters in

12075-495: The spring of 1985. The system has been revised several times over the years. The ignition system together with the ignition coils form a single transformer oil filled cassette (or two cassettes in the case of a V6 engine) which is placed directly on the spark plugs , without the need for a distributor . It was later implemented with the Saab Trionic Engine Management Systems as one of

12190-406: The terminal above the cylinder head so as to make it more readily accessible. A further feature of sintered alumina is its good heat conduction – reducing the tendency for the insulator to glow with heat and so light the mixture prematurely. By lengthening the surface between the high voltage terminal and the grounded metal case of the spark plug, the physical shape of the ribs functions to improve

12305-424: The terminal of the plug, but some wires have eyelet connectors which are fastened onto the plug under a nut. The standard solid non-removable nut SAE configuration is common for many cars and trucks. Plugs which are used for these applications often have the end of the terminal serve a double purpose as the nut on a thin threaded shaft so that they can be used for either type of connection. This type of spark plug has

12420-422: The tip of the insulator protruding into the combustion chamber is the same sintered aluminium oxide (alumina) ceramic as the upper portion, merely unglazed. It is designed to withstand 650 °C (1,200 °F) and 60 kV. Older spark plugs, particularly in aircraft, used an insulator made of stacked layers of mica , compressed by tension in the centre electrode. With the development of leaded petrol in

12535-410: The tip of the spark plug is too hot, it can cause pre-ignition or sometimes detonation/knocking , and damage may occur. If it is too cold, electrically conductive deposits may form on the insulator, causing a loss of spark energy or the actual shorting-out of the spark current. A spark plug is said to be "hot" if it is a better heat insulator, keeping more heat in the tip of the spark plug. A spark plug

12650-429: The tip of the spark plug means persistent, light detonation is occurring, often unheard. The damage that is occurring to the tip of the spark plug is also occurring on the inside of the cylinder. Heavy detonation can cause outright breakage of the spark plug insulator and internal engine parts before appearing as sandblasted erosion but is easily heard. As another example, if the plug is too cold, there will be deposits on

12765-420: The tip of the spark plug within the running engine, normally between 500 and 800 °C (932 and 1,472 °F). This is important because it determines the efficiency of plug self-cleaning and is determined by a number of factors, but primarily the actual temperature within the combustion chamber. There is no direct relationship between the actual operating temperature of the spark plug and spark voltage. However,

12880-404: The ware being sintered, surface damage and contamination can be reduced while maximizing furnace loading. Most, if not all, metals can be sintered. This applies especially to pure metals produced in vacuum which suffer no surface contamination. Sintering under atmospheric pressure requires the use of a protective gas, quite often endothermic gas . Sintering, with subsequent reworking, can produce

12995-461: Was 2000 °C. In the United States, sintering was first patented by Duval d'Adrian in 1922. His three-step process aimed at producing heat-resistant blocks from such oxide materials as zirconia , thoria or tantalia . The steps were: (i) molding the powder; (ii) annealing it at about 2500 °C to make it conducting; (iii) applying current-pressure sintering as in the method by Weintraub and Rush. Sintering that uses an arc produced via

13110-716: Was delayed, and a large one as though the timing was advanced. A spark plug is composed of a shell, insulator and the central conductor. It passes through the wall of the combustion chamber and therefore must also seal the combustion chamber against high pressures and temperatures without deteriorating over long periods of time and extended use. Spark plugs are specified by size, either thread or nut (often referred to as Euro ), sealing type (taper or crush washer), and spark gap. Common thread (nut) sizes in Europe are 10 mm (16 mm), 14 mm (21 mm; sometimes, 16 mm), and 18 mm (24 mm, sometimes, 21 mm). In

13225-531: Was the material chosen for the task and a method for manufacturing the copper-cored centre electrode was created by Floform . The central electrode is usually the one designed to eject the electrons (the cathode , i.e. negative polarity relative to the engine block) because it is normally the hottest part of the plug; it is easier to emit electrons from a hot surface, because of the same physical laws that increase emissions of vapor from hot surfaces (see thermionic emission ). In addition, electrons are emitted where

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