Environmental news
Motorsport Development UK
Motorsport industry
Motorsport technology
Sporting regulations and results

Author: Ian Bamsey

Source: Race Engine Technology

Publication Date: 10^th June 2008

Elsewhere in this issue John Stowe investigates electronic engine control technology. Fundamental to that technology is the characteristics of the spark plugs and fuel injectors that come under its command. While by definition spark plugs are as old as the spark-ignition engine, electronically controlled injectors came with the development of electronic engine control units in the seventies and did not arrive in racing until the eighties.

ERA (later to become Zytek) and Bosch were the pioneers, the former with Toleman/Hart in Formula One, the latter with Porsche in Formula One and Group C. In fact Bosch won the 1983 World Championship with BMW but that electronic control system governed the operation of a high-pressure mechanical injection pump. It was the Motronic system fitted to the Porsche 956 Le Mans car in 1983 then the McLaren-Porsche Formula One car that was the pioneer of solenoid-operated injectors in racing, together with the conceptually very similar ERA system, which used Bosch injectors.

In those early days the four-cylinder Hart turbo engine was seen on occasion with as many as four injectors per cylinder and twin plugs. But at this time boost level was forging ahead of fuel development; following the introduction of what came to be known as rocket fuel one plug became adequate, together with a pair of injectors per cylinder. Today outside of Top Fuel/Funny Car racing a single plug is invariably adequate for the needs of the racing engine and often, with fuel pressure sometimes far higher than in pioneering days of electronics, a single injector gets the job done.

The spark plug has benefited since the seventies from the development of capacitor discharge (CD) ignition systems, which use a thyristor condenser, or ‘capacitor’ to store electrical energy as it builds up. The term thyristor indicates a switching device and the current it supplies to the coil is at much higher voltage than earlier systems could muster. Since the CD system spark kicks off from higher voltage a higher secondary voltage can be supplied to the plug. The development of the CD system brought a higher energy, shorter duration spark.

The next development was the distributorless system, often using an individual coil for each plug. At first this approach, which permitted individual cylinder ignition control caused a loss of spark energy but on-going development overcame that drawback. Similarly the early electronic injection systems worked at less than 10 bar fuel pressure but, with development, three-figure pressure was obtained using fundamentally the same injector technology.

By the end of the last century operating fuel pressure of 40 bar was possible, then Bosch developed a system that used 90-volt triggering to operate at 120 bar, vastly improving atomisation through reduced droplet size. Subsequent to that the development of peizoelectric injectors promised significantly higher operating pressures. In fact before the rules put a cap of 100 bar, Formula One indirect injection systems were marching towards 500 bar in the quest for ever better fuel preparation.

The Spark Plug

On the face of it there isn’t a lot of scope for development of a device that jumps a spark between two electrodes, a central one fed a pulse of very high voltage and highly insulated and a side one earthed to the cylinder head via the metal body. Nevertheless, there has been on-going improvement in conducting and insulating materials since the dawn of the spark ignition engine and also in detail design. One of the pioneers of the spark plug, Bosch reckons to have produced around 20,000 variations over the last 100 years. The platinum centre electrode and the quadrupling of side electrodes were innovations that it pioneered in racing.

Whereas 14 mm remains the industry standard, in the quest for maximum valve area today’s Formula One engines use a plug that is just 8 mm in diameter. As we noted in the last issue, for such a plug Federal Mogul company Champion employs stainless steel and an advanced ceramic material. That material offers higher mechanical strength than that used traditionally for spark plugs together with a higher dielectric strength (which means a higher resistance to the flow of electrical energy through it). In the face of high cylinder pressures Champion uses a ‘hot lock’ manufacturing technique whereby the shell is locked over the insulator under temperature.

A very recent development is the ‘Pulstar Pulse Plug’ from Enerpulse Inc of Albuquerque, New Mexico. In effect this incorporates a capacitor into the centre electrode, above the tip. According to the company, the normal heating of the plug assembly during ionisation (the process whereby the dielectric strength of the gas between the electrodes is overcome, to allow electrons to bridge it, which lasts about 5 millionths of a second) is avoided. The energy normally wasted in unnecessary heating is stored by the capacitor, which it calls a ‘Pulse Circuit’. Once ionisation is complete the capacitor discharges what is claimed to be ten times more energy for just 2 billionths of a second whereas by contrast it reckons that the normal spark event occupies 30 millionths.

The Pulstar follows on from the trend to incorporate an additional capacitor into the secondary ignition circuit as a means of boosting spark power. Such an approach is used by SmartFire (RET issue 012), which also employs the secondary capacitor as the source of a low tension current that follows the main spark discharge across the gap as a means of ‘reading’ in-cylinder conditions. SmartFire was developed by Woodward and is nowadays marketed through Superflow and works with any regular spark plug. However, Woodward and Autolite have co-developed a projected surface gap plug with a specific design of tip that optimises the operation of the combustion sensing process, a process that has been exploited on track in series including Formula One and NASCAR Cup.

We discussed contemporary spark plug technology with Ed Van Dyne of Woodward. We asked him: What recent development of insulation material has there been and what do you foresee in the future?

“The insulation material is still the same good old alumina. What’s new is injection molding it for better consistency of the density of the alumina and more even shrinkage, allowing part thickness to get smaller and therefore plug diameters to get smaller.”

What recent development of electrode material has there been and what do you foresee in the future?

“For long life Iridium is better than Platinum and now that it may be less expensive, given Platinum prices these days, I think it will become more common. Good old Inconel or pure Nickel are still good enough for most applications in racing where plugs get changed often.” Is there a case for the use of an in-plug capacitor?

“All plugs have some capacitance. Adding more robs peak voltage to make more high current at breakdown. This only helps on projected surface gap plugs where that high current energy is delivered to the mixture correctly. Too much capacitance will prevent the voltage from jumping the gap, causing full load misfires. So, this is risky business if the whole ignition system, including plugs are not developed together and dyno tested on the specific engine.”

Do you have any technological developments in the pipeline at Woodward?

“We are working on a SmartFire EMS that will do knock retard and misfire prevention and closed loop engine tuning for best power all in one system.”

The Electronically Controlled Injector

The basic principal of the pintle-type (moving needle) injector is that when current is applied to its solenoid coil this lifts the needle valve clear of its seat to allow pressurised fuel to pass. Originally patented by Bosch, the principle is now well-established: the trickery is in the detail design, which determines how much pressure an injector can handle, how quickly and accurately it can operate and how well it atomises the fuel as it leaves the nozzle. Typically there is just one injector per cylinder. Under which scenarios might there be a case for the use of two injectors per cylinder?

Manufacturers of Spark Plugs
Germany	Bosch +49 (0) www.bosch-motorsport.com
Japan	NGK www.ngkntk.co.jp
UK	NGK www.ngkntk.co.uk
USA	Autolite +1 www.autolite.com
	Federal Mogul (Champion) +1 www.federalmogul.com
	Pulstar +1 www.pulstarplug.com/p>
	Splitfire +49 (0) www.splitfire.com
	Woodward +1 www.woodward.com

Manufacturers of Fuel Injectors
Germany	Bosch +49 (0) www.bosch-motorsport.com
	Siemens +49 89 636-00 www.siemens.com
Italy	Magneti Marelli http://motorsport.magnetimarelli.com/
UK	ASNU 0 www.asnu.com
	Denso www.globaldenso.com
	McLaren Electronic Systems www.mclarenelectronics.com
USA	Accel DFI +1 www.accel-dfi.com
	Delphi +1 www.delphi.com
	Hilborn +1 www.hilborninjection.com
	RC Engineering 7 www.rceng.com

Ulrich Michelt of Bosch Motorsport says: “In some projects, such as motorbike systems we use two injectors per cylinder for near bank/far bank and switch from near (quick reaction) to far (better mixture of gasoline and air) with increasing rpm. Flow rate is no scenario for two injectors; we can handle that with one injector.”

Hilborn EFI Specialist Andy Starr adds: “Typically we see more than one injector used on extreme horsepower applications that use alcohol such as turbo charged or centrifugally supercharged V8 engines in drag racing. It is not uncommon to see some applications with three injectors per cylinder.”

Dr Peter van Manen, Managing Director of McLaren Electronic Systems Limited remarks: “Two injectors per cylinder has typically been used in scenarios in which either fuel efficiency and performance needs to be optimised over a wide range of engine speeds or the fuelling demands are just very high. So, it is not unusual in sportscars and motorbikes and also used to be commonplace in open wheel cars running methanol and hence very high flow rates. It has not been a common feature in Formula One for many years and is now anyway prohibited by the technical regulations.”

A major development has been the introduction of piezoelectric injectors, which exploit the fact that, upon application of an electrical current piezo crystals change their shape a small, precise and repeatable amount, returning to their original form once the current is removed. Originally developed by Siemens, the piezoelectric fuel injector has a stack of piezoelectric ceramic elements, which expand almost instantly once a voltage is applied, this action operating the needle valve with a reaction time as fast as 80 microseconds. This technology is more accurate than magnetic triggering and allows design of an injector that switches more than twice as fast, sometimes as much as five times faster further enhancing precision of control. Diesel engine needs have pushed the development of piezoelectric actuated injectors, which allow fuel to be injected as a series of short pulses for enhanced control. The next step will be the development of an injector that is not simply switched on and off by the engine control system, but has a fully controllable flow rate.

The Audi and Peugeot Le Mans turbodiesels exploit piezoelectric injectors but looking to the future, is there a likelihood of piezoelectric technology in the context of gasoline direct injection for racing engines?

Michelt says: “We have no GDI project at Bosch Motorsport at the moment; we think that piezos are still too big for gasoline racing engines. We do everything fine with our solenoid mini-injectors.”

Dr van Manen says: “Piezo is coming. Piezo is now established technology in various series applications and so is a natural contender for racing engines. There are some important hurdles to overcome still, such as the potentially higher temperatures and vibration levels in a racing engine and the challenges of achieving decent mixture preparation, and hence thermal efficiency at high revs, but these will be sorted in order to get the power and efficiency benefits of better volumetric efficiency. Currently direct injection and piezo actuation is not permitted in Formula One, so it will be other racing categories, such as sports cars, taking the lead.”

Are there any other injector technological developments in the pipeline at McLaren Electronic Systems?

Dr van Manen says: “High pressure manifold injection has proven its worth in Formula One and so other racing categories are either already following this lead or are likely to do so in the future. Current regulations in Formula One limit pressures to 100 bar but that still offers torque and power benefits over lower (and more conventionally used) fuel pressures. Design of the pumps, as well as selection of suitable injectors, is key.”

Added to the database on 10^th June 2008