216190 130120119094 111_114
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The document discusses ignition systems used in internal combustion engines, detailing their operation, requirements, and various types such as battery ignition, magneto ignition, and electronic ignition systems. It explains the importance of spark timing, the role of the starter motor, and the functioning of spark plugs in igniting the air-fuel mixture. Additionally, it contrasts older ignition methods like glow plug and contact ignition with modern high-tension systems required for high-speed and high-compression engines.
216190 130120119094 111_114
- 1. Gandhinagar Institute of Technology Subject : Internal Combustion Engine (2161902) Topic : Ignition Systems Mechanical : 6th : B : 2 Prepared By : Bhautik Malviya (130120119094) Pavan Narkhede (130120119111) Darshit Panchal (130120119114) Guided By : Prof. Nirav Joshi
- 2. Introduction The combustion in a spark ignition engine is initiated by an electrical discharge across the electrodes of a spark plug, which usually occurs from 10° to 30° 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 conditions.
- 3. Introduction – contd. In a four stroke, four cylinder engine operating at 3000 rpm, individual cylinders require a spark at every second revolution, and this necessitates the frequency of firing to be (3000/2) X 4 = 6000 sparks per minute or 100 sparks per second. This shows that there is extremely short interval of time between firing impulses.
- 4. Introduction – contd. The internal combustion engines are not capable of starting by themselves. Engines fitted in trucks, tractors and other industrial applications are usually cranked by a small starting engine or by compressed air. Automotive engines are usually cranked by a small electric motor, which is better known as a starter motor, or simply a starter. The starter motor for SI & CI engine operates on the same principle as a direct current electric motor.
- 5. Ignition system - Requirements 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 the ignition of the mixture has a high chance of occurring The system must distribute this high voltage to each of the spark plug at the exact time in every cycle , i.e., it 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
- 6. Glow plug ignition One of the early ignition system employed was the glow plug ignition used in some kind of simple engines like model aircraft. A glow plug is coil of nichrome wire that will glow red hot when an electric current is passed through it. This ignites the air-fuel mixture upon contact. The coil is electrically activated from engine starting, and once it runs, it will retain sufficient residual heat on each stroke due to heat generated on the previous stroke. Glow plugs are also used to aid starting of diesel engine.
- 7. Contact ignition The other method used was the contact ignition. It consisted of copper or brass rod that protruded into the cylinder, and was heated using the external source. Heat conduction kept the end of the hot rod, and ignition takes place when the combustible mixture comes into its contact. Naturally that was very inefficient as the fuel would not be ignited in a controlled manner. This type of arrangement was quickly superseded by spark ignition.
- 8. Modern ignition systems The development of high speed, high compression internal combustion engine requires a reliable high speed ignition system. This is met by a high high-tension ignition system that uses a spark plug as the source of ignition. The electrical energy to the spark plug is supplied by one of the following systems and is termed accordingly. 1. Battery ignition system 2. Magneto ignition system 3. Electronic ignition system
- 10. Battery ignition systems 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 switch : allows the driver to turn the system on & off Primary coil : produces the magnetic field to create the high voltage in the secondary coil Breaker points : a mechanical switch that acts as the triggering mechanism Capacitor : protects the point from burning out
- 11. Battery ignition systems The secondary circuit converts magnetic induction into high voltage electricity to jump across the spark plug gap, firing the mixture at the right time. The functions of the component are: Secondary coil : the part of the coil that creates the high voltage electricity Coil wire : a highly insulated wire to take the high voltage to the distributor cap Distributor cap : a plastic cap which goes on top of the distributor, to hold the high tension wire 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 : takes the electricity from the wires, and give it an air gap in the combustion chamber to jump across, to light the mixture.
- 12. Magneto ignition systems The high powered, high speed spark ignition engines like aircraft, sports and racing cars use magneto ignition system. The basic component of magneto ignition system consists 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, while in the second type, the magneto revolves and the windings are kept stationary.
- 14. Electronic ignition systems 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. Electric ignition system has solved this problems.
- 16. Spark plugs The spark plug ignites the air-fuel mixture inside the cylinder . This occurs when the 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.
- 17. A cold plug has the advantage of quicker heat transfer. It has a shorter insulator, and thereby allowing heat to travel a shorter distance. A hot plug has a longer insulator, and therefore, heat travel path from firing tip to electrode is longer. This enables it to operate at higher temperature to compensate for the cooler running engine.
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