There are three things a gasoline engine needs: air, fuel and spark. The spark plug ignites the air/fuel mixture, producing the combustion that powers the engine. Despite the fact that spark plugs have featured in vehicles for more than a century, manufacturers are still pushing back the technical boundaries. In this interview, Matthew Beecham talked with Sean Lyon, senior product manager, Autolite and Jeff Boehler, chief engineer, fellow, Autolite about the spark and glow plug market.
just-auto: Could we start by asking if you could summarize the factors that influence the design of a glow plug?
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Autolite: Glow plug design has evolved along with improvements in the diesel engine. Instant start like a spark ignition engine is desirable, but not possible because it takes time for the glow plug to heat. Years ago, batteries were 6-volt, so the glow plug was turned on and it took one minute or more for the glow plug to heat. When 12-volt batteries became popular, the same plug would heat much faster, but a controller was required to mimic the heat up time and turn the power off before meltdown.
Today the glow plug itself limits its own temperature by incorporating a second coil of wire whose resistance increases rapidly with temperature. This provides fast warm-up without melt down, eliminating the controller. The size and length of the heated portion is determined by the amount of heat (watts) and surface temperature needed by the engine. Thread size, diameters, lengths, terminal style, etc. are all defined by the desires of the engine developer.
We’ve seen rapid start glow plugs emerge on the market. How do you see that technology evolving?
The desire for instant starting, like a spark ignition engine, is always present. The most recent major design improvement is the incorporation of a second coil of wire to limit the maximum temperature. This self-compensating glow plug eliminates the need for a controller, which is a welcome improvement in system reliability. In the near future, there will be small improvements to extend the life and reduce the cost of the glow plug. In the far future, changes in glow plug design will follow ingenious ideas of the diesel engine developers.
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By GlobalDataIn terms of technical specification of glow plugs, what else do you see happening? i.e. longer and thinner plugs?
The newer plugs will be similar to that of the Duramax: long bodies with a 3.5mm diameter heating element. That is the norm in Europe, and they seem to be five or six years ahead of us in diesel engine design.
What are the factors pushing innovations in spark plugs?
Ignitability and durability. In terms of the key factors pushing spark plug innovation right now however, relates to an issue we are all concerned about these days: the high cost of fuel. Fuel cost and government regulations on vehicle emissions and fuel economy are driving engine technology toward smaller-displacement engines with higher power density. This is being achieved with direct injection, charge air boosting, and more dilute air-to-fuel ratios. These engine design changes result in the need for smaller-diameter and longer spark plugs that offer improved ignitability through finewire electrode tip designs. In terms of Autolite’s innovations, our engineering team has spent the last three years developing a 12-millimeter plug that will maintain the quality and performance that Autolite products are known for, while delivering the value that our customers demand.
We’ve heard a lot about precious metal spark plugs becoming increasingly popular in the US, though technically speaking, what are you seeing in terms of copper core technologies?
The trend for modern engine design is increasing demand for spark plugs with precious metal-enhanced electrodes, so the most significant trend with copper-core spark plugs is a notable decrease in demand. The resulting changes in copper-core spark plugs are less revolutionary and more evolutionary. Areas of improvement include new electrode material alloys that result in small improvements in durability without a significant impact on cost.
What other trends are you seeing in the evolution of spark plugs?
With 75 years of experience and as the official spark plug of NASCAR, we’ve learned a great deal about spark plugs and the evolution of the industry at large. One trend we’re seeing is higher-efficiency engines with increased power density, which is also driving the need for improvements in spark plug insulator material. The higher operating temperatures and smaller-diameter 12-mm spark plugs typical of these new engines result in higher stress on the spark plug insulator.
Even though spark plug technology is improving, can it really catch-up with engine life? i.e. is a ‘life of engine’ spark plug a possibility?
The parts of a spark plug that wear out are the electrodes and related spark gap. Material and manufacturing technologies could provide spark plugs that may last a very long time, but the cost of these plugs may not always be a wise investment. Today you will see many cars on the road with a couple hundred thousand miles on them. While still running, these engines are probably no longer able to perform at top efficiency. As these high-mileage engines and related systems age and degrade, the spark plug may be degraded in other ways than gap wear, such as fouling from excess oil consumption or mechanical damage due to excessive detonation. So the real question to be answered first is: What is the life of an engine?
With longer life spark plugs, what is the impact on the aftermarket?
Longer-life spark plugs are leading to longer plug change intervals. While this reduces the number of plugs purchased in the aftermarket during a year’s time, retails for these longer-life plugs are higher. In addition, one of the bigger issues technicians face with long-life plugs is removal. While the plug may last 100,000 miles and beyond, dissimilar corrosion of the steel spark plug shell and aluminum cylinder heads can cause removal issues.
Looking at the distribution channels in North America, what are the big changes you are seeing at the moment? Is there anything in particular in the change or structure that is driving that? How do you see these channels developing?
We are seeing the auto parts retailers and repair shops getting a larger share of the spark plug market and taking it mostly from the discount/department stores. The trends that continue to drive this shift are engine, complexity (OEM’s making it more difficult to change your spark plugs) and consumers desire for more interaction with a counterperson (which discount retailers do not offer) for their questions.
What’s happening to brand names in the market place? Is the power of brands increasing or diminishing with the changes? Anything in particular in the change or structure that is driving that?
Autolite prides itself on being a brand with engine electrical technology that strives to outperform original equipment at every turn. In our opinion, because spark plugs are such an integral part in a vehicle’s engine, brand is important. In fact, private label spark plugs have been introduced several times in the aftermarket and failed quickly because they were not known brands. When it comes to spark plugs, consumers understand the importance of buying a quality plug with a recognized brand name.
