Spark plugs for engines with direct petrol injection

One of the latest developments in Otto engine design are engines with direct injection. With these engines the fuel is not injected into the inlet pipe, as is the case with conventional injection systems, but directly into the combustion chamber. Combustion chamber and air inlet are designed in a way that areas with high fuel content (rich mixture) and with low fuel content (lean mixture) are formed. This operating mode is designated as stratified charging.

The spark plugs are subjected to particularly high demands by these operating conditions. In the various operating stages the conditions around the spark plug vary: There is a time when a particularly rich mixture and a time when a particularly lean mixture must be ignited. Therefore, NGK has developed spark plugs of improved ignition reliability. These feature, for instance, a very thin center electrode, made from the precious metals platinum or iridium.

In order to inflame with certainty the fuel-air mixture one must make sure that the spark plug is located in an area where the mixture is sufficiently rich.

Consequently there are many cases of spark plug design with extra projected spark gap, which means that the electrodes are reaching far into the combustion chamber. Overheating is prevented by copper cores inside the electrodes.

A particular problem for engines with direct injection is the risk of carbon deposits on the spark plug. Also in this regard, NGK has found a solution. Due to the geometrical properties NGK spark plugs have a self-cleaning effect for removing the carbon particles and supporting a stable spark. Because of these technical advantages NGK played a major role in the development of the GDI engines by Mitsubishi, Nissan, and Toyota, which are all equipped with NGK spark plugs in volume production.