IGNITION SYSTEM OF SI ENGINE

DEFINATION,REQUIREMENT,TYPES,ADVANTAGE,DISADVANTAGE

1. A.Y.DADABHAI TECHNICAL INSTITUTE (POLYTECHNIC) KOSAMBA. CERTIFICATE This is to certify that Mr. MUBASSIR I. GHONIYA has satisfactorily completed his PPT work on IGNITION SYSTEM OF SI ENGINE in T.E-II course in mechanical engineering department as per the GTU regulation. Date :- Guide External faculty H.O.D Sign Sign Sign

2. A.Y.DADABHAI TECHNICAL INSTITUTE, KOSAMBA Subject:- IGNITION SYSTEM OF SI ENGINE SUBMITTED BY GHONIYA MUBASSIR AHMED IMTIYAZ AHMED Enrolment No:- 136010319024 Guide BY:- Y.A.S

3. DEFINATION OF IGNITION SYSTEM The system in an internal-combustion engine that produces the spark to ignite the produces the spark to ignite the mixture of fuel and air: includes the battery , spark plugs, and associated switches and wiring. It known as the ignition system

4. INFORMATION ABOUT IGNITION SYSTEM IN SI ENGINE The term spark-ignition engine refers to internal combustion engines generally, petrol engines. Where the combustion process of the air-fuel mixture is ignited by a spark from a spark plug. Spark-ignition engines are commonly refer to as “gasoline engines” in America ,and “petrol engines” in Britain and the rest of the world . The working cycle of spark ignition engines may be either two stock or four stroke A four stroke spark ignition engines is an Otto cycle

5. It consist following four stroke. Suction stroke Compression stroke Power stroke Exhaust stroke The combustion in spark ignition engine is initiated by an electrical discharge across the electrodes of a spark plug, which usually occurs fro 100 to 300 before TDC depending upon the chamber geometry and operating conditions. The ignition system provides a spark of sufficient intensity to ignite the air fuel mixture at the predetermined position in the engine cycle under all speeds and load condition.

6. IGNITION SYTEM REQUIREMENT It should provide a good spark between the electrodes of the plugs at the correct timing The duration of the spark must be long enough with sufficient energy to ensure that ignition of the mixture has a high chance of occurring The system must distribute this high voltage to each of the spark plug at exact time in every cycle , i.e., i t must have in it a distributing device It should function efficiently over the entire range of engine speed It should be light, effective and reliable in service

7. The development of high speed, high compression internal combustion engine requires reliable high-speed ignition speed ignition system. This is met by a high-tension ignition system that uses a spark plugs as the source of ignition. The electrical energy to the spark plug is supplied by one of the following systems and is termed accordingly.

8. TYPES OF IGNITION SYSTEM COIL IGNITION SYSTEM MAGNETO IGNITION SYSTEM ELECTRONIC IGNITION SYSTEM

9. 1.COIL IGNITION SYSTEM

10. The primary circuit consists of the battery, ammeter, ignition switch, primary coil winding, capacitor, and breaker points. The functions of these components are: BATTERY PROVIDES THE POWER TO RUN THE SYSTEM IGNITION SYSTEM ALLOWS THE DRIVER TO RUN TURN THE SYSTEM ON AND OFF. PRIMARY COIL PRODUCES THE MAGNETIC FIELD TO CREATE THE HIGH VOLTAGE IN THE SECONDARY COIL. BREAKER POINT A MECHANICAL SWICH THAT ACTS AS THE TRIGGERING MECHANISM. CAPACITOR PROTECS THE POINT FROM BURNING OUT

11. The secondary circuit converts magnetic induction into high voltage electricity to jump across the sparkplug gap, firming the mixture at the right time. The function of the

12. Secondary Coil Coil wire : the part of the coil that creates the high voltage Electricity A hire insulated wire to take high voltage to the distributor cap Distributor cap : a plastic cap which goes on top of the distributor, to hold the high tension wires in the right order Rotor : spins around on the top of the distributor shaft, and distributes the spark to the right spark plug Spark plug Leads : another highly insulated wire that takes the high voltage from the cap to the plugs Spark plugs : take the electricity from the wires, and give it an air gap in the combustion chamber to jump across,

13. The ignition switch provided, connects and disconnects the ignition system from the battery. hence the engine can be started or stopped a will. When the ignition system is “ON "the contact breaker points are closed. This allows the current to flow from the battery trough primary winding of the ignition coil and back to battery through earthlings . The magnetic field across the primary winding is developed. This will induce back e.m.f. this will oppose the battery current. With the result, the current in the primary will slowly developed. This will delay the building up of magnetic field. A voltage is induced in the secondary windings. But the e.m.f.is too low to produce a spark at the spark plug.

14. The breaker point is opened by the distributor arm when we want a spark in the engine. This opens the primary circuit. The magnetic field in the primary field collapses. The resulting induced current will flows in the same directiopn as the battery current. It charge the condenser. When the voltage of the battery across the condenser plates, the flows of the current is reversed. The magnetic field in the coil of the primary winding reverses due to the quick reversal of the current in the primary winding. This will cause a very high voltage to be induced in the secondary winding. This depends upon the number of turns of the secondary to primary wind. This induced voltage is of the order of 10 KV to 20 KV.

15. When the contact breaker in the primary circuits is opened, the distributor rotor connects with a contact to the spark plug. This high induced voltage jumps across the air gap of the spark plug. This will produce the spark for ignition system battery of 6V to V used. The voltage induced is 6 V to 24 V used. The voltage induced is 6kV to 10kV.

16. ADVANTAGES OF THE COIL IGNITION SYSTEM At the time of starting and idling at low speed good sparkling is available. Initial expenditure is less . Hence, this system is used in cars and commercial vehicles. Maintenance cost is less. Distributor drive is simple and non-complicated. By adjusting spark-timing complete ignition system is not adversely affected.

17. DISADVANTAGE OF COIL IGNITION SYTEM If the battery is discharged, then it is not possible to start the engine. Battery is to be checked regularly. It occupies more space. Its wiring is complicated. The intensity of spark decreases with increase in speed.

18. 2. Magneto ignition system The high powered, high speed spark ignition engines like aircraft, sports and racing cars use magneto ignition system. The basic components of a magneto ignition system consist of a magneto, breaker points, capacitor, ignition switch, distributor, spark plug leads, and spark plugs. Magneto can either be rotating armature type or rotating magneto type. In the former, the armature consisting of the primary and secondary windings all rotate between the poles of a stationary magneto, revolves and the winding are kept stationary.

19. Electric circuits Uses a changing magnetic field to generate current in primary and secondary circuits

20. Magnetic flux • As magnet approaches, induces magnetic flux in armature • Breaker points close and current dissipates through primary circuit

21. Spark fires • After magnet rotate past armature flux reverses direction, and the breaker points open • Change in magnetic flux produces 170 volts in primary circuit • Induces 10,000 volts in secondary circuit, firing spark plug

22. Breaker points • Crankshaft rotation causes mechanical actuation of breaker

23. ADVANTAGES OF MAGNETIC IGNITION SYSTEM Since there is no battery or connecting table, the system is more reliable. For medium and very high speed engines, the system is more suitable. The space require is less, by using cobalt steel and nickel aluminium magnet metals energy. This system in fairly reliable with resent development.

24. DISADVANTAGES OF MAGNETO IGNITION SYSTEM At low speed and during cranking the voltage is very low. Suitable modifications are necessary in the circuit to overcome this. Adjustment of the spark timing has determined effect upon the spark voltage or energy. The burning of the electrodes will result with powerful sparks at high engine speeds. More costly. Starting is troublesome.

25. 3. Electronic ignition system The disadvantage of the mechanical system is that it requires regular adjustment to compensate for wear, and the opening of the contact breakers, which is responsible for spark timing, is subject to mechanical variations. In addition, the spark voltage is also dependent on contact effectiveness, and poor sparking may lower the engine efficiency . Electronic ignition system has solved these problems

26. .

27. In this system, the contact breaker points are replaced by an angular sensor of some kind - either optical, where a vane rotor breaks a light beam, or more commonly using a hall effect sensor, which responds to a rotating magnet mounted on a suitable shaft. The sensor output processed by a suitable circuitry is then used to trigger a switching device such as a thyristor, which switches a large flow of current through the coil. The rest of the system remains the same as the mechanical system. The lack of moving parts compared with mechanical system leads to greater reliability and longer service intervals. In some order cars, it was usually possible to retrofit an electronic ignition system in place of the mechanical one.

28. The spark plug ignites the air-fuel mixture inside the cylinder. This occurs when high voltage, triggered at precisely the right instant, bridges the gap between the center and the ground electrodes. It also provides a secondary purpose of helping to channel some heat away from the cylinder. Spark plugs

29. Firing order Firing order indicates the sequence or order in which the firing impulses occur in a multi-cylinder spark ignition engine. It is chosen to give a uniform torque, and hence a uniform distribution of firing per revolution of the engine . This is naturally dictated by the engine design , the cylinder arrangement and the crankshaft design. The firing order be such that there must always be a proper balance so as to minimize the engine Vibration.