IGNITON
IGNITON
Is considered as the beginning of the combustion process. The ignition process must add necessary energy for starting and sustaining burning of the fuel till combustion takes place. With in the range of the mixtures normally use, which varies from air-fuel ratio 12-13 : 1 a park energy under 10 MJ is sufficient to initiate combustion.
Basic requirements
1. The system must have a source of electrical energy
2. The system must produce a peak voltage greater by safe margin than the spark plug break down voltage at all speeds.
3. The duration of the spark must be long enough with sufficient energy to ensure the ignition.
4. The system must distribute this high voltage to each of the spark plugs.
Battery ignition System
The ignition coil consists of two coils - one primary and the other secondary. The primary winding is connected to the battery through an ignition switch and the contact breaker. The secondary winding is connected to spark plugs through the distributor. A ballast resister is provided in series with the primary winding to regulate primary current. For starting purposes this resister is bypassed so that more current can flow in the primary circuit. A rotating can shaft speed operates the contact brakes and causes the breaker points to open and close.
When the ignition switch is as and the contact breaker points one closed current flows from a magnetic field. When the current flow n the primary winding stopped by opening the contact breaker points the magnetic field collapses, cuts across the secondary winding and induces a voltage, which is accompanied by a current. This magnetic field, however, also cuts the primary winding and induces a voltage in this as well as in the secondary.
In order to obtain the highest voltage in the secondary circuit a quick collapse of the magnetic field is essential. It is also necessary to prevent the axing and consequent burning of the contact points. These are activated by providing a condenser across the contact breaker. When the contact points open, the circuit instead of passing across the points in the form of an arc, flow in to the condenser and is stored by it as it becomes changed. The change in the condenser immediately discharges back into the primary circuit in a direction reverse to the flow of a battery current, thus assisting in a quicker collapse of magnetic field when the contact points open.
Due to the rapidly collapsing magnetic field, high voltage is induced in the primary circuit and still higher voltage of the order of 11 KV to 22KV in the secondary circuit. This high voltage in the secondary circuit passes through the distributor roter to one of the spark plugs leads, into the spark plug and if this voltage is higher than the breakdown voltage a spark occurs across the spark plug gap causing ignition of the combustible mixture in the combustion chamber.
References
- Automobile Engineering (Vol. 1 & 2) - K.M.Guptha
- Automotive Mechanics - Joseph Heitner
- Automobile Engineering - Harbans Singh Reyd
- Automotive Mechanics - William H. Course
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