Basically Convectional Ignition systems are of 2 types:
(a) Battery or Coil Ignition System, and
(b) Magneto Ignition System
Both these conventional, ignition systems work on mutual electromagnetic induction principle.
Battery or Coil Ignition System:
-used in 4-wheelers, but now-a-days it is more commonly used in 2-wheelers also (i.e. Button start, 2-wheelers like Pulsar, Kinetic Honda; Honda-Activa, Scooty, Fiero, etc.)
- The ignition system is divided into 2-circuits:
(i) Primary Circuit:
-consists of 6 or 12 V battery, ammeter, ignition switch, primary winding
-it has 200-300 turns of 20 SWG (Sharps Wire Gauge) gauge wire, contact breaker, capacitor.
(ii) Secondary Circuit:
-consists of secondary winding or coil which have 21000 turns of 40 (S WG) gauge wire.
-bottom end of which is connected to bottom end of primary and top end of secondary winding or coil is connected to centre of distributor rotor.
-distributor rotors rotate and make contacts with contact points and are connected to spark plugs which are fitted in cylinder heads.
C=condenser, P=primary coil, S=secondary coil, R1=ballast resistance, SW1=ignition switch, SW2=contact breaker
Fig. 22. Circuit diagram for a conventional spark ignition system
Working:
-When the ignition switch is closed and engine in cranked, as soon as the contact breaker closes, a low voltage current will flow through the primary winding. It is also to be noted that the contact beaker cam opens and closes the circuit 4-times (for 4 cylinders) in one
revolution. When the contact breaker opens the contact, the magnetic field begins to collapse. Because of this collapsing magnetic field, current will be induced in the secondary winding. And because of more turns (@ 21000 turns of secondary, voltage goes unto 28000-30000 volts. This high voltage current is brought to centre of the distributor rotor. Distributor rotor rotates and supplies this high voltage current to proper stark plug depending upon the engine firing order. When the high voltage current jumps the spark plug gap, it produces the spark and the charge is ignited-combustion starts-products of combustion expand and produce power.
-The Function of the capacitor is to reduce arcing at the contact breaker (CB) points. Also when the CB opens the magnetic field in the primary winding begins to collapse. When the magnetic field is collapsing capacitor gets fully charged and then its tarts discharging and helps in building up of voltage in secondary winding.
-Contact breaker cam and distributor rotor are mounted on the same shaft.
-In 2-stroke cycle engines these are motored at the same engine speed. And in 4-stroke cycle engines they are motored at half the engine speed.
- A good spark is available at low speed also.
- Occupies more space.
- Recharging is a must in case battery gets discharged.
Magneto Ignition System:
- magneto will produce and supply the required current to the primary winding or coil
- rotating magneto with fixed coil or rotating coil with fixed magneto for producing and supplying current to primary, remaining arrangement is same as that of a battery ignition system
-no battery required
- during starting the quality of spark is poor due to slow speed
-very much compact
Fig. 23. High tension magneto ignition system
Disadvantage of conventional ignition systems
Following are the drawbacks of conventional ignition systems:
(a)Because of arcing, pitting of contact breaker point
(b)Poor starting: After few thousands of kilometres of running, the timing becomes inaccurate, which results into poor starting (Starting trouble).
(c)At very high engine speed, performance is poor because of inertia effects of the moving parts in the system.
(d)Sometimes it is not possible to produce spark properly in fouled spark plugs.
Due to above problem electronic ignition system is used.
(a) Battery or Coil Ignition System, and
(b) Magneto Ignition System
Both these conventional, ignition systems work on mutual electromagnetic induction principle.
Battery or Coil Ignition System:
-used in 4-wheelers, but now-a-days it is more commonly used in 2-wheelers also (i.e. Button start, 2-wheelers like Pulsar, Kinetic Honda; Honda-Activa, Scooty, Fiero, etc.)
- The ignition system is divided into 2-circuits:
(i) Primary Circuit:
-consists of 6 or 12 V battery, ammeter, ignition switch, primary winding
-it has 200-300 turns of 20 SWG (Sharps Wire Gauge) gauge wire, contact breaker, capacitor.
(ii) Secondary Circuit:
-consists of secondary winding or coil which have 21000 turns of 40 (S WG) gauge wire.
-bottom end of which is connected to bottom end of primary and top end of secondary winding or coil is connected to centre of distributor rotor.
-distributor rotors rotate and make contacts with contact points and are connected to spark plugs which are fitted in cylinder heads.
C=condenser, P=primary coil, S=secondary coil, R1=ballast resistance, SW1=ignition switch, SW2=contact breaker
Fig. 22. Circuit diagram for a conventional spark ignition system
Working:
-When the ignition switch is closed and engine in cranked, as soon as the contact breaker closes, a low voltage current will flow through the primary winding. It is also to be noted that the contact beaker cam opens and closes the circuit 4-times (for 4 cylinders) in one
revolution. When the contact breaker opens the contact, the magnetic field begins to collapse. Because of this collapsing magnetic field, current will be induced in the secondary winding. And because of more turns (@ 21000 turns of secondary, voltage goes unto 28000-30000 volts. This high voltage current is brought to centre of the distributor rotor. Distributor rotor rotates and supplies this high voltage current to proper stark plug depending upon the engine firing order. When the high voltage current jumps the spark plug gap, it produces the spark and the charge is ignited-combustion starts-products of combustion expand and produce power.
-The Function of the capacitor is to reduce arcing at the contact breaker (CB) points. Also when the CB opens the magnetic field in the primary winding begins to collapse. When the magnetic field is collapsing capacitor gets fully charged and then its tarts discharging and helps in building up of voltage in secondary winding.
-Contact breaker cam and distributor rotor are mounted on the same shaft.
-In 2-stroke cycle engines these are motored at the same engine speed. And in 4-stroke cycle engines they are motored at half the engine speed.
- A good spark is available at low speed also.
- Occupies more space.
- Recharging is a must in case battery gets discharged.
Magneto Ignition System:
- magneto will produce and supply the required current to the primary winding or coil
- rotating magneto with fixed coil or rotating coil with fixed magneto for producing and supplying current to primary, remaining arrangement is same as that of a battery ignition system
-no battery required
- during starting the quality of spark is poor due to slow speed
-very much compact
Fig. 23. High tension magneto ignition system
Disadvantage of conventional ignition systems
Following are the drawbacks of conventional ignition systems:
(a)Because of arcing, pitting of contact breaker point
(b)Poor starting: After few thousands of kilometres of running, the timing becomes inaccurate, which results into poor starting (Starting trouble).
(c)At very high engine speed, performance is poor because of inertia effects of the moving parts in the system.
(d)Sometimes it is not possible to produce spark properly in fouled spark plugs.
Due to above problem electronic ignition system is used.
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