The power in a gasoline engine is derived from the burning of gas in the engine cylinder. In order to explode this gas, an electric spark is made to jump across the electrode of spark plug, inside the cylinder. To provide this spark an ignition system is essential. The object of ignition system is to provide a hot and timed spark at the end of compression stroke to ignite the compressed air fuel mixture in proper sequence of firing order. To fulfil this requirement, generally two types of ignition systems are used in automobile engines.
(a) Magneto Ignition System. A magneto is a device, which produces a low tension current and then converts it into a high tension current.
(b) Battery or Coil Ignition System. In this system the series of components are used to convert the low tension current into high tension current in order to ignite the combustible mixture inside the cylinders. It consist of a soft iron core with a primary and secondary winding of copper wire, the whole being housed in a metal cylinder which can be secured in any convenient position in the vicinity of the engine. Interruption of the primary circuit by means of a mechanically operated switch (contact breaker) and the consequent collapse of the magnetic field around the secondary winding induce a high voltage in the secondary windings. An ignition coil has three terminals, one for the LT lead from the battery, one for a LT lead from coil to contact breaker points and the third one for a high tension lead to the distributor.
NAME OF THE COMPONENTS
This system consists of following components.
(a) Battery or Accumulator. This is an apparatus designed for the storage of electricity in chemical form. The electricity generated by a dynamo is converted into chemical energy and stored in the battery.
(b) Ammeter. Ammeter is mounted on instrument panel and it is connected in series with the primary circuit. When ignition s/w is switched ‘ON”, the current flows from battery to the ignition coil and the ammeter shows the direction of flow of current which indicates whether dynamo/alternator is charging or not.
(c) Ignition Coil. The purpose of ignition coil is to change the low voltage of 06 or 12 volts into high voltage of 20,000 to 30,000 volts. It consists of a soft iron core with primary winding and secondary winding of copper wire, housed in a metal cylinder which can be mounted in any convenient place in the engine.
(d) Condenser. Condenser is a device used for storing of electric charge for a short time. As the condenser is connected parallel to the CB points it helps in quicker collapse of magnetic flux and prevents arcing of the contact points thus increasing their life.
LAY OUT OF IGNITION SYSTEM
COIL IGNITION SYSTEM
This system operated by electrical current supplied by battery. Mainly it consists primary winding and secondary winding inside the coil.
The function of distributor is to make and break the primary circuit and distribute high tension current to various plugs according to firing order. It consists of housing, driving shaft with breaker point, cam breaker plate with contact points, condenser, rotor, advance and retard mechanism and cap. The shaft is driven by the engine camshaft directly or indirectly through the oil pump drive shaft. The drive shaft is rotated at the half of the engine speed in case of 4 stroke engine. When the shaft moves it opens and closes the breaker points.
OPERATION OF DISTRIBUTOR
When the switch is turned ‘ON’ with CB points in closed position. Low voltage current flows from the battery through ammeter, Switch, to the primary winding of coil and earthed through CB points. These current sets up a magnetic field around the primary winding and intensified by soft iron core. As the CB points are made to open by the rotation of the distributor shaft, the primary circuit is broken (interrupted) and the magnetic field around the primary winding collapses. This sudden collapsing induces a very high voltage in the secondary winding and flows from the high tension terminal of coil to the central terminal of the distributor cap, from where it flows to the various spark plugs through carbon brush, rotor arm, segments and HT leads according to the firing order of cylinders.
SPARK PLUG AND CHAMPION SPARK PLUG CLEANER AND TESTER
Spark Plug is a device to produce electric spark to ignite the compressed air fuel mixture inside the cylinder. It is screwed in the top of the cylinder so that its electrodes are projected in the combustion chamber. The upper end of the centre electrode is connected to the spark plug terminal where HT cable from the ignition coil is connected.
This machine is used for cleaning dirty spark plugs by sand blasting using by compressed air. Provision is also made in this machine to blow the spark plug after cleaning to free the sand adhering the plug. A booster coil to provide stream of sparks and a pressure gauge is provided in this machine. Various rubber washers are provided to suit the different sizes of plugs. The procedure of cleaning and testing is described in practical.
PROCEDURE OF CLEANING AND TESTING OF SPARK PLUG IN CHAMPION SPARK PLUG CLEANER AND TESTER
(i) Clean all spark plugs in spirit or petrol.
(ii) Dry thoroughly in air blast.
(iii)Place plug in correct size rubber washer of the champion plug cleaner and tester.
(iv)Turn ‘ON’ the abrasive blast and rotate the plug slowly for approximately 10 seconds.
(v)Turn ‘ON’ the air blast to dislodge abrasive particles from plug before removing from tester.
(vi)Visually check for excessive burning, erosion of electrodes porcelain cracks, and any other defects. Discard unserviceable plugs.
(vii)Screw the plug to be tested into the tester and connect lead. Turn ‘ON’ air until gauge reads a maximum of 100 lbs Sq unit.
REMOVAL, VIEWING AND GAP SETTING AND REFITTING OF SPARK PLUG
(a) Removing the Spark Plug.
(i) Disconnect the battery.
(ii) Remove all the HT leads from the plugs and mark No.1 Spark Plug HT lead.
(iii) Unscrew each spark plug one or two turns by using a spark plug spanner.
(iv) Blow out all carbon and dirt from each spark plug with compressed air, otherwise dirt will fall inside the cylinder.
(v) Unscrew and remove the plug carefully.
(b) Viewing and Gap Setting.
(i) Examine each plug for excessive burning and erosion of electrodes, blistering of porcelain at the firing tip black deposits and oil fouling.
(ii) Note that these are the indicators of an improper mechanical condition of the engine.
(iii) Adjust the plug gap to 0.76 mm by bending the earth electrode.
(iv) Press the button and observe the spark through the aperture. The spark should be regular, light blue to white in colour and jumping between electrodes only. Discard any plug which does not attain these standards.
(v) Remove and reset the gap to 0.76 mm.
(i) Install each plug carefully into its mounting threads.
(ii) Tighten the plugs with plugs spanner.
(iii) Reconnect the high-tension leads properly as per firing order.
(d) Testing of Spark Plug when Engine is Running . To find out if the plugs are working properly with the engine running at idling speed, take a screw driver and short circuit the high tension current. If the engine speed drops the spark plug is working properly. If the speed doesn’t drops the plugs are not working and it must be replaced immediately.