Ignition system: how does it work?

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One of the main systems providing stable work of engine is called the ignition system. Its components provide formation of electric spark, which ignites the air-fuel mixture in cylinders of combustion engine. It is also a part of engine electrical system. Most drivers have general idea of ignition system. And those, who are interested, we suggest to read our article.

1. Operational principle of ignition system
2. Components of ignition system
3. Failures of ignition system
Ignition system: how does it work?

1. Operational principle of ignition system

The operational principle of ignition system is based on gathering and transformation by ignition coil of low 12V potential of vehicle electric power system into higher one (to 30000V), and then transfer this electric potential to necessary spark plug.

Formation of spark on a plug in specific period of time is also a part of system’s operational process.

If the whole working process of ignition is divided into stages, then it’ll consist of:
1. Electric power storage stage;
2. Power conversion;
3. Distribution of electric power between spark plugs;
4. Formation of spark;
5. Ignition of the air-fuel mixture.

In contact ignition system (now it is rarely used on some classic cars), the ignition distributor controls and distributes electric power among cylinders. Later, with its development, transistorized coil ignition appeared. It differs from previous one by presence of transistor commutator in ignition coil primary circuit.

The alternative to contact is breakerless ignition system. In this type of system transistor commutator, which maintains connection with breakerless pulse sensor, is used for “controlling” power storage. The transistor commutator serves as breaker, and distribution of high voltage is performed by mechanical distributor.

Aside contact and breakerless ignition systems, there is also electronic ignition, which is used on modern vehicles and uses an electronic control unit. It controls electric power storage and distribution. In early constructions, it controlled also a fuel injection system simultaneously with ignition system (the so-called “united system”). Nowadays the ignition control is a part of vehicle power unit control.

Ignition system: how does it work?

2. Components of ignition system

As you might have noticed, all types of ignition systems are very similar to each other, and differ only by control impulse formation. That’s why main components of each of them are the same. These are: - feed source (at the moment of engine starting this is battery, while engine is operational – alternator);
- ignition starter switch (ignition lock) is a contact device with mechanical or electric application of voltage to ignition system. Usually it fulfills 2 functions: supplies with power vehicle power network and ignition system, and also supplies starter electromagnetic switch;
- storage unit stores power and transforms into necessary amount for occurrence of electrical discharge between plug electrodes.

All storage units are relatively divided into inductive and capacitive. Inductive storage unit is the simplest one: it is an ignition coil, which is a single winding transformer: its primary winding is connected to “+”, and circuit interrupting device – to “-“. During operation of mechanism (f.e., ignition wipers) self-induction electric potential occurs in primary winding, and in secondary – high potential, which is sufficient for disruption of plug air gap.Capacitive storage is a rated capacity, which charges from high voltage, and then transfers its energy to spark plug;

- spark plug is a device with 2 electrodes placed on a distance of 0.15-0.25 mm. It is also called a porcelain insulator, placed on metal thread. In the middle of the insulator is a conductor, which is the first electrode, while the second electrode is thread;

- ignition distribution system is used for transferring power between capacitive storage and plugs in specific moment. The system consists of: ignition distributor (autotrembler, which is usually installed in cam box) is a device, which distributes high voltage through conducting wires to plugs. There are 2 types of ignition distribution: mechanical and static.

Mechanical option is a shaft driven by engine and voltage through wires distributed by rotor.Static ignition distribution has no rotating parts. In this case ignition coil connects with plug directly and is controlled by related unit. For example, if engine has 4 cylinders, then it’ll have the same number of coils. There are no high-voltage wires here.

Ignition system: how does it work?

- commutator is an electronic device of pulse generating controlled by coil. It connects to coil’s supply circuit and, after the signal from control unit, disrupts the supply. As a result, self-induction voltage occurs;

- ignition system control unit is a microprocessor unit, which, depending on data from crankshaft position sensor, temperature sensor, camshaft position sensor and lambda sensors, determines the moment of impulse coming to ignition coil;

- high-voltage wire is a solid wire with high level of isolation;

- inner conductor is used for microwave range static elimination and may have a spiral form.

3. Failures of ignition system

As was mentioned above, on modern car can be installed different types of ignition: contact, breakerless and electronic. During exploitation of any of them problems appear (failures). Of course, due to different constructional peculiarities, these failures can be different, but there are also common failures: of kinetic coil, spark plugs, disruption of high and low voltage circuits connection (this can be caused by break of wire, contact oxidation etc.)

In case if electronic system installed in car, there are also such failures as: failure of electronic control unit and input sensors. In breakerless ignition system such problem may occur with transistor commutator, transducer sensor cover etc.

Main reasons that cause ignition system failures are following:
- mishandling (use of low quality fuel, no maintenance service or unskilled one);
- use of non-original constructional components of low quality (ignition coil, plugs, high-voltage wires etc.);
- undermining by environment (weather elements, mechanic damage).

The most widespread failures of ignition system are defects of spark plugs. Nowadays, when this component is available for user, this problem can be easily solved: buy a new detail and failure is fixed.

Positive aspect is the fact that most of possible failures of the system described above are things of the past as the contact ignition system and its low quality components. It is possible to identify failures by external characteristics. Though, you should remember that symptoms of ignition system failures are similar to ones of other systems, first of all, of injection system and fuel supply system. So, the best option is to perform a comprehensive diagnosis.

Ignition system: how does it work?

External characteristics of ignition system failure are:
- unstable idle work of engine, difficult start of power unit;
- increase of fuel consumption level and engine power reduction.

Nowadays the most widespread are breakerless and electronic ignition systems. That’s why let’s observe symptoms of their failures. Starting with breakerless ignition system:

If engine doesn’t start or starts with difficulties, then:
- this might be failure of high-voltage wires;
- failures of coil or plugs.

If in idle mode the work of engine is unstable, then:
- cover of distribution sensor might be damaged;
- failure of transistor commutator or distribution sensor, or spark plugs.

Symptoms of electronic ignition system failures:
- if engine doesn’t start or starts with difficulties, then the problem might be as in breakerless system (failure of high-voltage wires, problems with plugs or coil);
- if idle work of engine is unstable, then the failure might be in input sensors (Hall sensor, crankshaft rotation sensor) or in ECU
- if there is an increased fuel consumption, then the problem might be in spark plugs or one/few sensors;
- engine power reduce is usually caused by failures of ECU.

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