NGK glow plugs under the spotlight
The heart of a diesel engine
The glow plug, like the spark plug, plays a vital role in the starting of an engine. In this case, the diesel engine. But unlike the spark plug, which ignites the fuel, the glow plug’s key function is to boost the temperature necessary for the self-combustion of the diesel fuel. And, like spark plugs, millions of vehicles around the globe depend on the reliability and robustness of NGK glow plugs. Over decades the brand has worked tirelessly in its endeavour to manufacture a product that not only saves on fuel but contributes to making the vehicle it is fitted in more environmentally friendly.
Durability is key to efficient ignition in a combustion engine. The diesel powertrain of a naturally aspirated engine works by drawing ambient air into the cylinder through the piston, where it is highly compressed. This compression raises the temperature of the air to more than 500 degrees centigrade. When diesel fuel is now added to the chamber, it causes the fuel to ignite. But if the engine is cold, it will struggle to hit the correct temperature for ignition, and it is here that the glow plug plays a big part.
As its name suggests, the unit glows hot to preheat the combustion chamber and through this action combustion is guaranteed time after time. But modern glow plugs do more than just preheat, they also continue operating once the vehicle is travelling, to help ensure that the engine maintains a steady temperature. In this way, the engine is smoother, its emissions of hydrocarbons and carbon monoxide are significantly reduced, and fuel is saved. In today’s modern diesel engines glow plugs play an even bigger role as they are crucial to supporting the regeneration of diesel particle filters (DPF) in vehicles, by quickly helping them reach the required temperature to burn off accumulated soot. Additionally, their services are essential in vehicles that operate with stop and start engines where temperatures often fluctuate.
More than a sibling
Like the spark plug, its sibling in petrol passenger cars, the glow plug is fitted into the vehicle’s cylinder head and heat is generated electrically. The exception is its use in some heavy-duty applications, where glow plugs are fitted in the intake manifold and operate by igniting the diesel directly in this manifold rather than relying on electrically generated heat.
Broadly speaking there are two types of glow plug: metal glow plugs and ceramic glow plugs. The two technologies operate in a similar way and have the advantage of being able to heat to high temperatures, making them well suited to a wide variety of vehicles. As a core competence of Niterra, it is common to think of ceramic as an insulator, but here in the glow plug it includes materials based on metallic oxides, which allow the plug to conduct a current as effectively as its metal relative. Ceramic glow plugs were developed by NGK to comply with ever-stricter emissions regulations. Their high tolerance to heat and their suitability for extremely cold conditions means ceramic glow plugs can sustain a so-called ‘after glow’ for more than ten minutes after activation, at temperatures of up to 1,350°C. This reduces engine smoking and consequently the release of harmful hydrocarbon and carbon-monoxide emissions, and contributes to a smoother engine turnover.
Modern metal glow plugs are made of heat-resistant metal and their heating coils are protected by a layer of magnesium oxide, which not only affords excellent thermal conductivity, but also protects the coil from vibration and shock which could damage it. Essentially there are three main types of metal glow plugs: standard glow plugs, self-regulating glow plugs, and AQGS (advanced quick glow system) glow plugs.
NGK glow plugs are a first choice for both OE and Aftermarket customers seeking excellent durability and an ability to start repeatedly from low ambient temperatures. Not only that, but they ensure stable idling during an engine’s warming up phase, and their robust construction means that they afford a high resistance to corrosion while offering unparalleled heat transfer properties. Added to this, their unique shell design provides perfect gas sealing properties, good protection of the inner heating coils and high resistance to deformation and a high shear torque. No wonder then that the brand’s advanced quick glow system (AQGS), a particularly fast heating metal glow plug, is designed to be fitted in models from a wide range of well-known vehicle manufacturers.
The nature of maintenance
As with spark plugs, it is always important to check the instructions to see how best to exchange glow plugs.
In order to get the maximum lifespan out of the components, special attention must be paid to removing and replacing glow plugs. Added to this, there are a few problems that can impede the proper function of glow plugs. Chief among these is the diesel engine’s tendency to allow a buildup of soot in the glow plug’s tube. Once the old plug has been removed it is essential to clean this tube with a reamer to remove any deposits before fitting a new plug. Failure to do this can lead to the new glow plug being damaged during installation, or an inability of the glow plug to attain an optimal operating temperature. Other issues concern the incorrect torque application used when fitting the plugs and their loosening during operation, both of which can be remedied by tightening to the correct torque. In more extreme cases, the glow plugs can be damaged by a thermoshock. That can happen if a defective fuel injection valve does not close completely, or when oil or water enter the combustion chamber.
This feature is intended to provide some technical background into one of NGK brand’s main products and a key component in diesel vehicles. This article is the second in a series of features that seek to draw attention to the technical background of Niterra’s state-of-the-art automotive products. The next subject under the spotlight will be ignition coils, leads & caps. The first article of this series about spark plugs can be found here.
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