IGNITION SYSTEM
FUNCTION
The function of the ignition system is to produce a spark in the engine cylinder towards the end of the compression stroke. In a four-stroke engine, a spark should occur in each cylinder after two revolutions of the crankshaft, whereas in a two-stroke engine a spark in each cylinder is required every revolution of the crankshaft. Thus, for instance, in a 6-cylinder 4 stroke engine running at 5000 r.p.m., the number of sparks required per minute will be 15000 and these have to be timed very accurately.
REQUIREMENTS OF AN IGNITION SYSTEM
1. Spark at the plug electrodes must be regular and synchronously timed with respect to the cylinder-piston position at all speeds and loads on the engine.
2. The spark should be sufficiently strong so as to start ignition of the charge. Since lean air fuel mixtures are less conductive, they require higher ignition voltages. Thus on modem emission-controlled engines that use lean-mixtures, higher-voltage ignition system is required. Moreover , due to higher secondary voltage in these systems, it becomes necessary to increase the electrical insulation
3. The spark duration should be sufficient to establish burning of the air-fuel mixture under all conditions.
4. It should have the ability to produce spark even when a shunt is established over the spark plug electrodes, possibly due to carbon, oil or lead deposits, liquid fuel or water condensation.
5. The power consumed to produce spark should be minimum.
6. It should have service life at least equal to that of the engine.
7. The system must be easy to maintain. .
8. It must not cause radio interference
9. It should be light and compact.
10. It should be adaptable to mass production.