August 06 2023

Illustrate basic structure and operation of an ignition system.

Function

The function of ignition system is to create an electrical spark in cylinder at most opportune moment to ignite air/fuel mixture in cylinder.

The ignition system performs three main functions:

① It must be possible to create an electric spark with sufficient energy, having enough heat to ignite mixture in combustion chamber;

② The spark can be maintained long enough to burn fuel in combustion chamber;

③ An ignition spark must be provided for each cylinder to ensure that combustion process can start at proper timing of compression stroke.

Ignition distribution system

Distributor performs following functions:

■ Distribute high voltage secondary coils to spark plugs of each cylinder in correct order.

■ Turn off primary current of ignition coil in time.

■ Ignition timing is adjusted according to engine operating conditions (load, speed, etc.).

The main structure of ignition distribution system is shown in figure below ▼

Maintenance advice. The distributor is driven by camshaft so speed is only 1/2 of engine speed.

Chain and analysis of ignition distribution system (1) ▼

Analysis:

As shown in diagram above, a current flows when motor is started.

Primary circuit: battery → ignition switch → ignition coil positive → ignition coil negative → distributor breaker contact → ground. The distributor cam rotates, contacts open, and field strength of primary circuit decreases.

Secondary circuit: A high voltage is induced in secondary of coil and exits from center terminal of coil → distributor cap → distributor cap → spark plug wire terminal on distributor cap → spark plug wire → spark plug → ground.

Chain and analysis of ignition distribution system (2) ▼

Analysis:

As shown in picture above, if engine was off but distributor breaker contacts are closed, ignition coil will be energized. At this time, adding a rectifier resistor can protect the ignition coil and prevent overheating.

Battery → Ignition switch → Ballast resistance → Ignition coil positive terminal → Ignition coil negative terminal → Distributor breaker contact → Ground.

Electric ignition system

1 - ignition switch, 2 - battery, 4 - spark plug,

3—ignition coil with igniter; 5—Engine ECU;

6—camshaft position sensor, 7—crankshaft position sensor

Illustration

As shown above, ignition system consists of a power source (battery), a sensor, an ECU, an igniter, an ignition coil, a spark plug, etc. The ignition system generates high voltage sparks and ignites compression mixture in cylinder at best timing gas. Based on signals received from various sensors, engine ECU (electronic control unit) controls to achieve best ignition timing.

Volkswagen Jetta/Santana ignition system (old models)

1 - ignition wire; 2 - ignition coil (identification with ignition wire: A - cylinder 1, B - cylinder 2, C - cylinder 3, D - cylinder 4); 3, 9 - bolts (10 Nm); 4, 6, 11—connector connector; 5—spark plug; 7—bolt (20 Nm); 8—knock sensor; 10—Hall sensor (G40); 12—O-ring

Illustration

As shown in figure above, each ignition coil has two high voltage output terminals, which can directly drive two spark plugs to ignite simultaneously. Two spark plugs connected to an ignition coil are mounted on two cylinders in same crank direction. When one of cylinders is in normal ignition position, other cylinder is in final stage of exhaust stroke. At this time, pressure in cylinder is low, and density of gas on spark plug is small, and only a few thousand volts of voltage is needed to breakdown discharge. Therefore, although two spark plugs fire at same time, most of ignition energy is released into main ignition cylinder, and only a small amount of energy is lost at second spark plug, and this part of energy can be compensated by loss from non-distribution.

Independent ignition system (ignition coil)

Independent ignition system: as shown in figure above, each ignition coil is installed directly on spark plug, that is, one cylinder has an independent ignition coil. Now there are many cars that use independent ignition systems, and Volkswagen vehicles mostly use this ignition system.