CTAO.info - Car Technical Assistance Online

The spark plug is simple as theory: it pushes the electricity to form an electrical arc through the air. A very high voltage is necessary to create a good sparkle, between 40 and 100 thousands volts. An isolated path is needed so that this tension can reach the electrode, where it can cross the space and enter into the engine block, to which comes to ground.

The spark plug must also resist to high temperatures and the pressure inside the cylinder and it must be protected so that the admixtures in the fuel can’t form deposits. During the functioning of the engine, the main parts of the spark plug, especially the insulator and the central electrode get hot. The thermal loads of the spark plug are caused by the temperature difference between the existing temperature that enters the combustion chamber and the exposed part of the environment, close to the temperature variations of the re circulating gas, between

50 – 120 C degrees through inlet and 2000-2800 C during fuel combustion. During functioning , the thermic flux is transmitted through the radiation of the fluid, through the combustion head pipe and through radiation and convection of the environment.

The optimal functioning of the spark plug takes place when the inferior part of the insulator has a temperature between 500-600 C and the so called auto-cleaning of the spark plug takes place (ideal combustion of deposits).

At temperatures of over 800-900 C of the insulator and of the central electrode’s insulator late ignitions of the motor fluid take place. In this case the engine loses power and goes on clattering (vibrations). In some cases the ignition (combustion) of the mixture can take place during aspiration (suction), emerging shots (misfires) in the carburetor and even fire danger.

The appropriate choice is then of great importance. This presumes the acknowledgement of the spark plug operating temperature, which reflects the capacity of the spark plug to transmit heat from the combustion chamber to the outside environment. Each motor vehicle producer recommends the use of one spark plug model until a certain number of miles is reached (by their recommendation, usually 300.000 km). If you wish to know which type of spark plug is recommended for your car, leave a response with your car details and CTAO.info will be answering shortly with the recommended model for your car.

From the use of central electrodes with cupriferous core and nickel-chrome cooling tank you can obtain a series of advantages, this spark plug covers a wider range of operating temperatures (at least 2 operating temperatures than a normal one).

These spark plugs, also know as thermoelastic plugs ensure faster ignition (it reaches the operating temperature faster) and in the functioning of the engine in load or additional load it will not overheat (the cooper core ensures a proper transfer of heat).

While functioning the spark plug must resist to electrical loads, mechanical and chemical. The electrical loads appears because of the high voltage 4-8 KV in normal regime and 11-15 KV at the start of a cold engine.

Mechanical loads are caused by the variations of the gas pressure in the cylinders, as to the variations and snatching during running of the engine. The spark plugs must be constructed so that they ensure tightness towards functioning pressure.

The chemical loads refer especially to the building materials of the electrodes, they can be easily damaged if built from improper materials.

All spark plugs have an operating temperature (temperature of self-cleaning), so that the spark plugs are not adequate, respectively if they operate at a lower temperature than the one indicated the calamine deposits will emerge untimely of if they operate at a higher temperature, the electrodes will deteriorate.

Another cause that leads to their malfunctioning or suspension is the excessive oil consumption, this fact being easily to observe due to the necessity of excessive supplementation of the engine oil and a white colored smoke at exhaust.

The rich mixture (air – fuel) leads to incomplete combustion of the mixture and to calamine deposits (blackening of the spark plug). The rich mixture can have multiple causes, which of we remind: unclean air filter (dust precipitation), malfunction of the carburetor, etc.

A more serious cause is the deterioration, perforation or unsealing of the cylinder head gasket between the cylinders. This can be determined by the measurement of the compression of two consecutive cylinders that have equal compression between each other but smaller than the rest.

A malfunction of the ignition system leads to a fast deterioration of the spark plugs. Because the number of elements forming the ignition system is high, it will be explained in detail in another article.