How does a car ignition work

How does the ignition work?

In internal combustion engines, chemical energy is principally converted into mechanical work. To do this, a mixture of fuel, gasoline or diesel, is first made with air. This takes place in the engine, more precisely in the carburetor or the injection into the cylinder.

How does the ignition work in a diesel engine?

Diesel engines are so-called compression-ignition engines. The pressure and temperature are so high that the mixture of fuel and air can self-ignite. Before the engine starts, these conditions are not yet met, which is why starting and environmentally friendly operation of the engine with few pollutants is not possible. For this purpose there are glow plugs in the diesel engine, which in a very short time produce the temperature required to ignite the mixture. The glow plugs also work after the engine has been started and while driving to allow the diesel engine to emit fewer pollutants and to run efficiently.

The compression is of great importance for the diesel engine, since the fuel-air mixture in the cylinder has to ignite itself. In the opposite, the petrol or Otto engines, there is a compression ratio of 14: 1 and ignition is achieved via its own ignition system. However, this compression is not sufficient in a diesel engine. The compression ratio is therefore increased to 19 to 23: 1. With this compression and the high pressure, the fuel mixture can self-ignite in a warm engine. However, if the engine and the mixture itself are not yet warmed up, self-ignition is more difficult. In addition, the required compression pressure cannot be achieved with the cold engine. In addition, the piston and cylinder wall may not be flush, i.e. not tight. For this reason, a so-called glow plug system is used in diesel engines with an antechamber. A glow plug or glow plug in each cylinder heats up to over 1000 degrees so that the engine can start. The glow plugs help the engine to keep emitting fewer pollutants as the engine continues to run. The process is often used in diesel engines with direct injection, which only need to preheat at very low outside temperatures.

What are glow plugs?

Glow plugs are made of metal and, in newer engine versions, also made of ceramic. The glow plug can also be screwed into its place of use, the combustion chamber, from the outside. Glow plugs made of metal have a heating coil and a control coil, as well as an insulation that is pressed from an insulating material in powder form. In the heating coil in the front part of the candle, a temperature of over 1000 degrees is generated using electricity of up to 40 amps. The electrical resistance must remain in the heating coil regardless of the temperature. For this purpose, material made from steel alloys is used. The control coil in the back of the candle ensures that the heating coil does not overheat, as its own resistance increases the higher the temperature rises. This prevents the entire glow plug from overheating.
Glow plugs used to take up to a full minute to pre-glow. These days, pre-glowing is faster. For example, glow plugs with on-board voltage only need three seconds to reach 850 degrees. Other technologies, such as so-called pulse width modulation, require the same time for more than 1000 degrees.

However, metal glow plugs have the disadvantage that they age quickly. Over time, they lose the power to start the engine at the intended temperature. Glow plugs made of ceramic material, on the other hand, do not experience this aging process and get hot much faster. In addition, they can heat up to 1300 degrees.

How do you recognize defective glow plugs?

To preheat a cold diesel engine, a lot of current is drawn from the battery. The battery should therefore function properly, especially in the colder months of the year, when longer preheating is necessary and the battery is not as strong as at warmer temperatures. With gasoline-powered engines (Otto engines), such a high power is not necessary for starting. Sometimes it may be necessary to preheat the engine several times if it does not start at very low temperatures. If that doesn't help either, a malfunctioning glow system could be the reason. It can also be due to a fuse, the glow plug relay, the control unit or the cables. Glow plugs can easily be checked for proper functioning. An ohmmeter is used to test the resistance of the glow plugs between ground and plugs. If no resistance can be found, the individual glow plug is very likely no longer functional. It is also important that the differences between the individual candles are not too blatant. However, only completely defective glow plugs can be recorded with the ohmmeter; what performance they still perform is not measured.

How does the ignition work in a petrol engine?

Since the gasoline engine only uses fuel-air mixtures with a compression ratio of around 14: 1 that do not self-ignite, ignition via a spark plug is required. The spark plug is supplied with a voltage of up to 36,000 volts so that this voltage jumps from the center electrode to the ground electrode and the ignition spark ignites the compressed mixture in the cylinder. The ignition distributor with its ignition cables provides the power supply for the individual cylinders. The ignition coil, or the ignition module, produce the corresponding pulse with high voltage.

What are spark plugs?

Spark plugs are inserted into the cylinder's combustion chamber from outside the cylinder. The spark plugs usually have the following components: A ground electrode, which is connected to the ground via a thread, a center electrode, which usually has a copper core, as well as a sealing ring, the insulator and leakage current barriers. There is also a connection contact on the spark plug. The spark plug has to ignite the fuel-air mixture in the combustion chamber of the cylinder under different conditions in the engine compartment. A so-called “rich mixture” is required for a cold engine, in which more fuel is injected. If the car is often only moved for a short time, mixture residues are also deposited more heavily on the spark plug. For this reason, it is important that the spark plug is heated to 400 degrees as quickly as possible so that such deposits can be removed by the combustion. At more than 900 degrees, so-called glow ignitions can occur, which should also be avoided. The demands on the spark plug are high, with a long service life of up to 100,000 kilometers being aimed for. Therefore, the industry often uses or develops new materials and changes the design of the electrodes.

A common standard spark plug has a ground electrode, the so-called front or roof electrode. Spark plugs that have more than one ground electrode, i.e. with two, three or even four electrodes, have the significant advantage that the spark paves the best way. This can mean that, for example, deposits on one electrode prevent the spark from being picked up, but another ground electrode is available to pick it up. In this way, the ignition is also secured in the long term. The standard material was mostly an alloy of iron, nickel and chromium. There are now alloys with iridium, silver and platinum that improve the performance of spark plugs.

The ignition coil or an ignition distributor supply the spark plug with high voltage. The ignition cables are specially equipped for this task of transmitting the voltage. Because of the up to 36,000 volts, they must have a much stronger insulation than normal cables, but without losing voltage on the way to the spark plugs. The control of the motor regulates the voltage transmission with pulses. This can affect radio reception or other electrical devices such as the engine control itself. The suppression of the possible interference is usually already done by the ignition cable.

You need a resistor so that the cables do not cause interference. With regard to the high voltage for the ignition, the resistance is so low that the ignition does not experience any reduced power. In the case of gasoline-powered engines (Otto engines), ignition cables made of copper are usually used because they have little resistance. However, these cables do not by themselves contribute to interference suppression. For this reason the resistance is in the connector of the cable. Ignition cables made of copper are used in the event that the path to the spark plugs is of different lengths. This type of cable has a copper core that is tinned to prevent corrosion. The cables are sheathed with silicone rubber, which has a temperature resistance of 200 degrees. In addition, the ignition cables must also be protected from oil and gasoline.

Ignition cables with resistance, in turn, have inherently anti-interference properties, as they are made of electromagnetic carbon and silicone. They are mostly used in vehicles where the ignition cables must be of the same length. This is because as the length of the cable increases, so does the resistance in the cable. An additional resistor for interference suppression, as is the case with copper cables, is not required.

What are ignition cables with reactance?

These ignition cables are characterized by the fact that an induction voltage is produced in them. A stainless steel mesh surrounds a magnetic and conductive silicone layer. This creates a pulsating magnetic field. The induction voltage in the ignition cable is canceled by storing and releasing energy from the ignition coil. The resistance in these ignition leads also depends on the current speed of the engine.

How do you examine ignition cable defects?

Because of the high voltage used in the systems, work on the ignition cables should not be carried out with the engine or ignition switched on, as this can be life-threatening. At certain time intervals, the ignition cables should be examined for defects that may occur in the sheath. Damaged sheathing can trigger short circuits to ground. And of course, it is essential that the cables are properly laid, otherwise the insulation could be damaged by hot parts in the engine compartment, such as the exhaust manifold. The situation for the ignition cables in the cooling fan is just as bad. It is well known that martens also tamper with the ignition cables because they like to bite into the insulating material.

The gasoline-air mixture must be ignited, which requires a high voltage. The battery in the vehicle only provides 12 volts, which is why the voltage has to be converted via the ignition coil.

How does an ignition module work?

Ignition coils have two windings, the so-called primary and secondary windings. If current is passed through the primary winding, a magnetic field is created. This has an impact on the secondary winding, namely that energy is stored in it. If the current of the primary winding is switched off, a high voltage is created in the second coil that is high enough to trigger the spark for ignition. This shutdown of the current in the primary coil was once done by mechanical breakers. Nowadays, electronic ignition modules take care of this task, as they are not so maintenance-intensive and do not have to be readjusted regularly.

A transistor in the ignition module controls the mechanical interruption completely without contact, which means that there is no longer any wear. Moisture also no longer interferes with the process, as was the case with the mechanical breaker contacts. New generation ignition modules are more reliable and usually also include overload protection for the ignition coil.

In order for the ignition module to be able to precisely control the ignition point, it needs sensor information. There are two alternatives: An inductive sensor detects the position of the camshaft with the help of a magnet and a coil. When the camshaft rotates, a voltage is created the moment the magnet passes the coil, which triggers a pulse. A so-called Hall sensor is the other alternative for detecting the control signal: a square-wave signal is generated with the aid of a slotted disc located between the magnet and the sensor. This means that the ignition module can be controlled much more precisely than with the inductive alternative.

There is a voltage network of around 12-14 volts in cars. However, this is not sufficient to trigger the spark via the spark plug. This takes at least 6,000 volts. The ignition coil increases the voltage to 36,000 volts with the aid of induction.

What are ignition coils?

In ignition coils, a voltage is also generated inductively in the second winding, the secondary winding, when current flows through the primary winding. This voltage is stored in the ignition coil via a magnetic field. The magnetic field generated in this way collapses again when there is no longer any voltage in the primary winding. The high voltage that exists in the secondary winding is now distributed and an ignition spark is created in the spark plug. The primary winding usually has a resistance that is less than 0.8 ohms. In comparison, the secondary winding has a resistance that is 10,000 times higher, i.e. around 8,000 ohms.

What are the differences in ignition distribution systems?

The distribution of the energy from the ignition coil was previously done by a rotating distributor finger. The voltage is conducted from the distributor ignition coil to the distributor via an ignition cable. The distributor finger referred to then distributes the voltage to the individual ignition cables of the various cylinders. With this type of distribution, moisture penetration often led to difficulties with starting and ignition failures. In order to make over-revving the engine impossible, an interrupter contact, which was operated by centrifugal force, used to be built into the distributor finger. The slow function and the high susceptibility to wear were the main disadvantages of these mechanically based ignition systems.

As transistor ignitions became available, at least the wear on the breaker contact could be reduced. With the start of the ignition modules, this vulnerable component was completely dispensed with. The interruptions in the flow of current in the ignition coil are produced by a transistor in ignition modules. Today, fully electronic ignition controls make the mechanics in the ignition distribution superfluous. Plug-in ignition sinks are used, for example, so that each spark plug has its own ignition sink. The coils are located directly on the candle and thus prevent losses. An even more recent development are the block ignition coils, which can use several ignition coils to distribute the ignition voltage to several candles.