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Comparison of The Ignition Systems in SI Engine

The CPI system or Commence Primary Ignition 

Includes a battery, switch, resistor, coil, distributor, spark plugs, and the necessary wiring.

When ignition  is required, the breaker points are opened by the action of the distributor cam,
interrupting the primary current flow.

The resulting decay of magnetic flux in the coil induces a voltage in both the primary and secondary winding.

The major limitations of the breakeroperated inductioncoil system are the decrease in available voltage as engine speed increases due to limitations in the current switching capability of the
breaker system, and the decreasing time available to build up the primary coil stored energy.

 

The TCI or Transistor Controlled Ignition System

Use electronic triggering to maintain the required timing without wear or adjustment.
In addition to higher voltage, it provides longer spark duration (about 2 ms).
Much reduced ignition system maintenance, extended sparkplug life, improved ignition of lean and
dilute mixtures, and increased reliability and life.

The CDI or Capacitor Discharge Ignition System 

A capacitor, rather than an induction coil, isused to store the ignition energy. 

The ignition transformer steps up the primary voltage, generated at the time of spark by the discharge of the capacitor through the thyristor, to the high voltage required at the spark plug. 


The CDI or Capacitor Discharge System 


A capacitor, rather than an induction coil, is used to store the ignition energy.

The ignition transformer steps up the primary voltage, generated at the time of spark by the discharge of the capacitor through the thyristor, to the high voltage required at the spark plug.

The CDI trigger box contains the capacitor, thyristor power switch, charging device, pulse shaping unit, and control unit.

It is insensitive to electrical shunts in the high-voltage  ignition circuit that result from spark plug fouling.
 Because of the fast capacitive discharge, the spark is strong but short (0.1 to 0.3 ms).

comparison of ignition systems in si engines
Please Read :
Principles of similitude used in Engine design .
Essential features of combustion in CI engine

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