Ignition system technology has taken a number of twists and turns over the past fifty years. Matthew Beecham reports on some technical trends in the OE and aftermarket.
“In the past, the sole purpose of an ignition system was to ignite a combustible mixture in the combustion chamber,” said Peter Weyand, engineering manager ignition, Europe, Delphi, “A simple task that just had to take into account boundary conditions for packaging, size, weight and, of course, cost. Today, the most important factor that drives the design of an ignition system is the combustion system. Some of the advanced combustion methods like homogeneous or stratified direct injection, or highly dilute (lean and/or high EGR) combustion have requirements that cannot be addressed any more with comparably simple ignition systems.
“Smart ignition systems have thus been developed. The first step to a smart ignition was an improved self-diagnostics and feedback of ignition current and voltage waveforms to the ECU. These offer information regarding the combustion event. Especially for combustion methods that have a less predictable cycle to cycle behaviour, like GDI [gasoline direct injection], this immediate insight helps the ECU control strategy.
“The most advanced systems are using this combustion information to adjust the actual ignition algorithm “on the fly”. These systems are usually MultiCharge Ignition systems or their derivatives that fire several times to increase the probability to even ignite mixtures under severe air/fuel ratio conditions. Ion sensing capable ignition systems or quasi alternating current systems are addressing certain problems that are not or barely resolvable with a standard single spark system.”
In terms of ignition system design and technical specifications, there are some regional differences too. The differences result directly from the combustion methods used, says Weyand. “The US and the varying fuel quality will not allow stratified DI in the near future. Also, fuel cost and vehicle size does not help the downsizing, at least not to the extent as we are experiencing this in Europe. This of course, has direct influence on the specifications since lower mean effective pressure and MPFI engines do not require the high European voltage and energy demands. Of course, all OEMs are working on downsizing, and it is clear that engine manufacturers building “world engines” have common specifications already, regardless of the sales market.”
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Another trend is toward increasing energy requirements. For example, the trend toward direct injection gasoline applications is driving the need for higher levels of ignition energy. As a result, those levels of ignition energy can only be delivered by coil and plug type applications. Indeed, with the constant demands for increasingly fuel efficient engines it naturally means that we are looking to ignite ever weaker fuel/air mixtures this has resulted in increasing ignition energy requirements. GDI does not in itself necessitate higher energy levels, but since direct injection is being used as a tool to improve fuel economy and meet increasingly stringent emission regulations then of necessity we are seeing a trend of increased ignition energy going hand in hand with the development of GDI.
In terms of ignition coil performance itself, carmakers continue to demand reliable, smaller units. Multi-valve engines in particular place even greater size limitations on coil design. The European trend towards down-sizing gasoline engines is prompting the need for smaller, narrower and longer spark plugs. Spark plugs must last longer, too. Ignition coils are also becoming smaller and lighter despite the requirement for increased energy content. This has led to more use of so-called plug top ignition coils which typically have higher energy content compared to pencil coils.
In terms of technical trends in the ignition system aftermarket, Claver Joseph, IAM vehicle electronics product manager, Delphi, sees the ignition system as a key component in today’s engine management system. She told just-auto: “As the transition from traditional mechanical technology is replaced by electronic systems, there is a natural growth and demand for these products. This inevitably means that the market place has now become competitive. Some aftermarket suppliers provide lower quality products that can lead to ongoing problems and unreliable repairs. Delphi is recognised for delivering high quality OE products to its OEM’s and aftermarket customers.”
Shin Nishioka, spark plug engineer, Denso Europe BV, business unit aftermarket, added that there are a number of other trends and influences on ignition systems in the aftermarket at present, including the introduction of fine-wire, non-precious metal spark plugs, rise in demand for super ignition spark plugs and precious metal spark plugs. He told just-auto that the number of vehicles manufactured with, or converted to, LPG operation has increased in Europe in recent years; a system that creates particular demands on the ignition system.
“As a result of these combustion characteristics, not only does the spark plug have to deal with the higher temperature inside LPG engines, but spark plug corrosion also occurs more quickly. The spark plugs used in LPG vehicles must therefore be specifically suitable for LPG engines. Fit a conventional spark plug in a vehicle that runs on LPG, and a variety of problems may arise. The spark plug may not spark, causing misfiring.
“Voltage will also be generated in the ignition coil and if this is too high, irreparable damage will be caused to the ignition coil. Faults may also arise in the LPG controller. The solution is to change from standard spark plugs to fine-wire, precious metal spark plugs with a different heat range.
“Denso’s advanced iridium tough spark plugs provide the optimal solution for gas operated engines, making conversion and servicing not only easier, but also more reliable.”