Ceramic glow plugs
As opposed to a metal rod glow plug, the heating coil of a ceramic glow plug has an especially high melting point. It is also sheathed in silicon nitrite, an extremely rugged ceramic material. The combination of the heating coil and ceramic sheath enable higher temperatures and extremely short preheating times due to excellent thermal conductivity. Also, ceramic glow plugs have a more compact design. This is important, because there is very little free space in today’s engines.
In an SRC (Self Regulating Ceramic) glow plug the heating element is made of ceramic with a sintered metal heating coil. An HTC (High Temperature Ceramic) or NHTC (New High Temperature Ceramic) glow plug has a heating element and a heater made of ceramic.
The NHTC ceramic glow plug was specially developed by NGK to enable automobile manufacturers to comply with the Euro 4 and Euro 5 emissions standards. One of the goals of these standards is to reduce the compression ratio in diesel engines. NHTC glow plugs reach a temperature of 1,000 °C in less than two seconds and can after-glow for more than ten minutes at temperatures of up to 1,350 °C. Optimal combustion is assured even with low compression ratios. In addition, the NHTC glow plug can glow intermediately to prevent cooling of the particle filter in deceleration phases.
Ceramic glow plugs: the technical optimum
For more than 20 years automobile manufacturers have been using NGK glow plugs as standard equipment. But can these glow plugs be replaced with comparatively less expensive metal glow plugs?
The answer: many things “can” be done, of course. The question is, what risk is involved. In cars that have NGK ceramic glow plugs installed at the factory, only NGK ceramic glow plugs should be used when it comes time to replace the glow plugs.
The reason: These glow plugs were developed in-house for the respective engines. Ceramic glow plugs from NGK guarantee a long service life and ensure a reliable and fast ignition, even at the lowest outside temperatures. At the same time, they reduce harmful emissions. Although they at first appear to be somewhat more expensive than metal glow plugs, one should consider the following: Metal glow plugs can make it difficult to start a car at extremely cold sub-zero temperatures.
When changing to metal glow plugs, all of the glow plugs have to be replaced, including those that are intact.