Ignition system An ignition system is a system for igniting a fuel-air mixture. Ignition systems are well known in the field of internal combustion engines such as those used in petrol (gasoline) engines used to power the majority of motor vehicles. Functions of ignition system •Provides a method of turning a spark ignition engine on & off. •Operates on various supply voltages (Battery & Alternator) •Produces high voltage arcs at the spark plug electrode. •Distributes spark to each plug in correct sequence. •Times the spark so that it occurs as the piston nears the TDC on the compression stroke. •Varies the ignition timing as engine speed, load and other conditions change. Requirements •To make a spark inside the engines cylinders which is strong enough to ignite the air/fuel mixture. In normal atmospheric conditions only about 600 Volts are needed to make a spark, however in the pressurised environment of the engines cylinders, 8000 to 30,000 volts will be required. •To ensure the spark happens at the right time for each cylinder going through the 4 Stroke Cycle i.e. just at the end of the compression stroke. The ignition system also has to change the time at which the spark occurs (the ignition timing) depending on engine operating conditions e.g. how fast the engine is turning. Factors consider for design ignition system Combustion chamber design Air-fuel ratio Engine speed range Engine load Engine combustion temperature Emission regulation Types of ignition system Mechanical ignition system Electronic ignition system Distributor-less ignition system Ignition Parts System BATTERY provides power for system. IGNITION SWITCH allows driver to turn ignition on and off. IGNITION COIL changes battery voltage to 30,000V during normal operation and has a potential to produce up to 60,000V. SWITCHING DEVICE mechanical or electronic switch that operates Ignition coil(Pick-up coil, Crank sensor, Cam sensor). SPARK PLUG uses high voltage from ignition coil to produce an arc in the combustion chamber. IGNITION SYSTEM WIRES connect components. Ignition Circuits PRIMARY CIRCUIT •Includes all the components working on low voltage (Battery, Alternator). SECONDARY CIRCUIT •Consists of wires and points between coil out-put and the spark plug ground. Ignition Coil Primary Windings are made up of several hundred turns of heavy wire wrapped around or near the secondary windings. Secondary Windings consist of several thousand turns of very fine wire, located inside or near the secondary windings. Distributor •Actuates the on/off cycle of current flow through the ignition coil primary windings. •It distributes the coils high voltage to the plugs wires. Distributor •It causes the spark to occur at each plug earlier in the compression stroke as engine speed increases, and vice versa. •Changes spark timing. •Some distributor shafts operate the oil pump. Advantages of electronic ignition system Moving parts are absent so no maintenance are required. • Contact breaker point are absent so no arcing. • Spark plug life increase by 50% & they can be use above 60000km without any problem. • More power output. • More fuel efficiency. • Better combustion in combustion chamber about 90 to95% of air-fuel mixture. Is burn compared with 70-75% with conventional • Types of Electronic Ignition System Capacitive discharge ignition system Transistorized system Piezo –electric ignition system Texaco ignition system Capacitive discharge ignition system Capacitor discharge ignition (CDI) or thyristor ignition is a type of automotive electronic ignition system which is widely used in outboard motors, motorcycles, lawn mowers, chainsaws, small engines, turbine-powered aircraft, and some cars. It was originally developed to overcome the long charging times associated with high inductance coils used in inductive discharge ignition (IDI) systems, making the ignition system more suitable for high engine speeds (for small engines, racing engines and rotary engines). The capacitive-discharge ignition uses capacitor discharge current output to fire the spark plugs. Basic principle Most ignition systems used in cars are inductive discharge ignition (IDI) systems, which are solely relying on the electric inductance at the coil to produce highvoltage electricity to the spark plugs as the magnetic field collapses when the current to the primary coil winding is disconnected (disruptive discharge). In a CDI system, a charging circuit charges a high voltage capacitor, and at the instant of ignition the system stops charging the capacitor, allowing the capacitor to discharge its output to the ignition coil before reaching the spark plug. Capacitive discharge ignition system Advantage and disadvantage •A CDI system has a short charging time, a fast voltage rise (between 3 ~ 10 kV/μs) compared to typical inductive systems (300 ~ 500 V/μs) and a short spark duration limited to about 50-80 µs. •The fast voltage rise makes CDI systems insensitive to shunt resistance, but the limited spark duration can for some applications be too short to provide reliable ignition. •The insensitivity to shunt resistance and the ability to fire multiple sparks can provide improved cold starting ability. • • • Since the CDI system only provides a short spark, it's also possible to combine this ignition system with ionization measurement. This is done by connecting a low voltage (about 80 V) to the spark plug, except when fired. The current flow over the spark plug can then be used to calculate the temperature and pressure inside the cylinder. Piezo-electric ignition system APPLICATION : Camping stoves Gas grills Lighters Potato guns •It consist small spring loaded hammer when a button is pressed , hit a quartz crystal This sudden deformation produce a high voltage & subsequence electrical discharge when ignite the gas. No external electric connection is required . Sometimes wire are used to locate the sparking location away from the crystal. •Piezo-ignition system can be operated by lever push button , only one electric spark generated when pressed the button. The development of synthetic piezo electric material produce in above 22kW by mechanical loading of a small crystal resulted in some ignition system for single cylinder engine , but due to difficulties of high mechanical loading timely control & ability to produce sufficient voltage. Transistorized system Emitter Collector Base Block diagram The electronic ignition system employed a solid state electronic device made for semi conductor transistor & thyristor are such type of device that are without opening & closing the contact . The tiny size behaves as a relay and can operates as a switch also at speed must higher than those required. Transistor is a two junction construction & thyristor is a three junction construction. Both are made for N – type and P – type semi conductor. In N-type the conductor take place through electrons and P-type in hole which are the vacuum size of the electron. They are basically made from silicon , germanium elements . After that doping with aluminum , antimony , phosphorus , indium etc. The Texaco Ignition System •The Texaco Ignition System (TTIS) is a high frequency system with a bi-directional spark current, the duration of which is a function of crankshaft rotation rather than time. The spark current characteristics differ drastically from those of conventional discharge systems and, as a result, current flow through the plug gap can be maintained under extremely turbulent conditions. •Being essentially a constant current device, it prevents excessive plug current flow during initial gap ionization, providing a good plug life; yet it has high average current to increase fuel ignition probability. •TTIS is of solid state design, and both the spark timing and spark duration are controlled by use of digital logic circuitry.