Diesel engines do not use a spark plug to ignite the air/fuel mixture instead they rely on the heat generated by greatly compressing the air within the cylinder and then injecting diesel fuel at the appropriate time which burns spontaneously. When the engine is cold it is considerably more difficult to get the air/fuel mixture to burn and to achieve stable combustion therefore a method of adding heat energy to the mixture is usually required.
A glow plug is essentially an electrical heating element installed within the combustion space. By elevating the temperature of the air within the combustion chamber the glow plug promotes easier cold starting, improved driving performance from cold and a significant reduction of unwanted emissions. Unlike a spark plug a glow plug usually works for a short period of time upon starting the engine however more stringent emission regulations often require significantly longer periods of operation.
Diesel engines have evolved considerably over recent years and so has glow plug design. This means that we now stock around 150 different part numbers with several major design differences. Although performance criteria differ greatly they are all manufactured to the same demanding standards.
NGK glow plugs can be broadly classified in two groups, metal sheathed and ceramic types. For more information on each type click on the relevant links.