Ignition systems

The ignition system is one of the most important systems on the internal combustion engine. The purpose of the system is to ignite the fuel-air mixture in the combustion chamber. There are several components in the system which are used to create spark and regulate timing. Diesel systems do not have an electronic ignition system as pressure is used to ignite the fuel, however glow plugs are used to preheat the combustion chamber. Virtually all petrol engines have spark ignition.

What two substances are mixed together to form electrolyte a battery?

An automotive battery has lead plates and an electrolyte solution which is made up of Sulfuric acid and distilled water. This cause a chemical reaction and releases electrons and produce electricity.

What three elements are required to make a petrol engine run effectively?

For a petrol engine to run effectively and efficiently it requires: Spark, Air, and Fuel. This include the quality and delivery of these elements. The spark needs to be powerful to overcome the compression in the cylinder and ignite the fuel. it also has to be delivered at precisely the right moment. The flow of air into the engine has to be consistent and the amount of air has to sufficient otherwise the engine will not run. Fuel must also be delivered consistently and in the right amounts. to little and the engine will not run or will run poorly, too much fuel and the engine will flood.

Explain the operation of a 'kettering ignition system', including all components from the battery to the spark plug

The Kettering ignition system is a mechanical ignition timing system used on outboard motors and early cars. Electricity from the battery travels to the coil and charges it up there are capacitors on the line which stop voltage spikes , the release of spark is controlled by a cam on the crankshaft which opens a contact breaker and creates a spark. the spark is distributed to the spark plugs by a distributor or on multi coil engines through a C coil on cylinder head. disadvantages of the Kettering system is the potential for wear on the contact breakers and cam lobe, which in turn affects sparking.

Give an explanation of dwell angle in a distributor

Dwell angle is a measurement of the amount of time that a coil has to charge before it releases another spark. An average dwell angle on a 4 cylinder engine is 52 degrees. Which means that the coil has 52degrees to recharge and fire a spark on the distributor. if the dwell angle is too small the spark may not be fully charged and if it is too large the engine may misfire. Dwell angle can be adjusted on a distributor engine with a mechanical adjustment ( a screw, or movement). Dwell angle is adjusted on electronic ignition systems through a computer.

 

Explain why the 'Heat range' of a spark plug is so important.

A spark plug operates in a specific heat range to maximise efficiency some plugs have more thermal efficiency than others. If a spark plug is not hot enough when it is idling then the spark plug can be fouled up quite easily. If a spark plug is not 'cold' enough when the engine is at high RPM then the tip of the spark plug make cause detonation or knocking  because of high temperature. The spark plug needs to operate in the heat range that is required by the engine.

What is a capacitor discharge system and how does it operate? 

Capacitor discharge is a type of electronic ignition. It is used widely in outboard motors. It operates on similar principles to other electronic ignition systems. The voltage in the system is increased to about 400-600 V by a transformer in the capacitor module. This system has a large capacitor which stores a high amount of voltage and then fires this voltage to a coil when it is triggered. When the release is triggered a rectifier allows current to flow to the coil and voltage is increased further from the 400-600V of the capacitor discharge to about 40kV at the spark plug. This system is quite simple and reliable with no parts that can wear and affect the ignition. it also has a very fast recharge time for the capacitor reducing the dwell angle. however the limited spark duration can be too short to provide reliable ignition in some engines.

The capacitor module contains the transformer and capacitor.