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, Matthew Beecham finds that manufacturers are still pushing back the technical boundaries. 

Ignitability and durability are the two main factors pushing spark plug innovations, according to Sean Lyon, senior product manager, Autolite, adding:“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.”

Tim Howes, technical services manager, NGK Spark Plugs (UK) Ltd agrees that the demand for plugs with greater ignition performance, longer service life and reduced general dimensions continues apace. “Ever leaner air/fuel mixtures and higher applied voltages create significant challenges for plug design. As with the modern high speed diesel engine, the spark ignition engine has seen the space occupied by the valves increase significantly, thus reducing the space available for the spark plug. “

Direct injection or GDI (Gasoline Direct Injection) is becoming the fuel delivery system of choice for automakers. With the first commercial introduction in 1996 by Mitsubishi, nearly all automakers currently offer at least one advanced powerplant equipped with these systems - with more platforms scheduled.

However, Louis Camilli, founder and president of Enerpulse Inc believes that there are operating nuances with GDI that continue to prevent wholesale adoption of the process. He told us:  “One is that, in some engines, devastating knock occurs during lean operation with no warning.  A second is that not all combustion chamber designs are suitable for stratified charge lean operation using GDI. These are engineering issues that will be resolved over time and may be mitigated using the Pulstar high-power discharge ignition. To date the only change to the design of spark plugs has been the migration to a cooler heat range with added thickness to the insulator projecting into the cylinder for added mechanical strength.”

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,” said Jeff Boehler, chief engineer, fellow, Autolite.  “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?”