How F1's ingenious ignition revolution brought an instant power boost

In late 2015 stories emerged of an engineer from Mercedes High Performance Powertrains leaving the organisation to join Ferrari and taking knowledge with him that would benefit the Scuderia. At the time much was made of secret spark plug technology that Mercedes had exploited. It was said this had not only been the largest contributor to the phenomenal performance of the Mercedes engine in 2014 and 2015, now it had also been leaked to Ferrari.

Perhaps the first thing to say to put the record straight is that it is highly unlikely this was the case. Of course, when engineers transfer from one competitor to another – be they chassis or engine specialists – an amount of intellectual property is transferred with them, but this knowledge is only that which is in their heads. The consequences of industrial espionage are so severe that no one would risk an accusation these days.

Of more interest is how and why a spark plug could make a significant difference to the performance of an engine when racing engines have always relied on highly specialised plugs for many years. The answer lies in the fact that the ignition of a current F1 engine is extremely different to either that of a conventional road car engine or indeed any race engine prior to the 1.6-litre turbo-hybrid V6 introduced in 2014.

The reason lies in a simple sentence in the regulations that upended many years of race engine design philosophy when this hybrid engine was introduced. That sentence was Article 5.1.4 of the 2014 technical regulations, which stated fuel mass flow must not exceed 100kg/hr.

The introduction of turbo-hybrid technology changed the face of F1 engine development

Photo by: Sutton Images

Up until this point race engine design was very much based on getting as much air into an engine in a given time as was possible and then adding the requisite amount of fuel to produce a good burn in the cylinder. Getting air into the engine relied on good gas flowing of the inlet, high engine speeds or, in the extreme, pressure charging. The fuel injected would be close to that required for complete combustion at what is known as the stoichiometric ratio. This is simply the ratio of fuel and air that gives the most complete combustion and is determined by the chemistry of the fuel.

The stoichiometric ratio for gasoline is around 14.7:1, that is for every gram of fuel burnt, 14.7 grams of air is needed. For E10 (introduced this season) the ratio is around 14.1:1. When an engine is running with a stoichiometric ratio it is also said to be running at λ1 (Lambda 1). Maximum power is generally produced with a slightly rich mixture – that is one that has excess fuel in it. While this may give good power it is not very efficient.

The pre-chamber is different. This is a device that improves the combustion and is therefore fundamental to both power and efficiency

With the fuel limitations imposed in 2014, it was soon obvious that the best way to run the engines was in fact on the lean side (deficit of fuel). The excess air added to the energy in the exhaust. This was then recovered by the MGU-H (the motor/generator attached to the turbocharger). The trouble with a lean mixture is that it is hard to ignite initially but at the same time it is prone to igniting earlier in the compression stroke than is desired – creating what is known as ‘detonation’ or ‘knock’, which damages the engine.

Gas engines had solved this problem many years earlier by forming a small chamber around the spark plug into which a relatively rich mixture was introduced. This was easily ignited by the spark plug and the resulting rapidly expanding flame was ejected out of small holes in the chamber, much like a flame thrower fires a jet of flame. This was known as pre-chamber ignition and later, when further developed by the Mahle company, turbulent jet ignition. 

Logically, a small injector would be used to introduce a tiny quantity of fuel into the pre-chamber and then a larger injector would inject the majority of the fuel into the cylinder where it would be ignited by the plasma jets shooting out of the pre-chamber. This arrangement is known as an active pre-chamber.

Mercedes led the way with its turbo-hybrid V6

Photo by: Erik Junius

Unfortunately, F1 regulations only allowed one injector per cylinder and so that injector, which was positioned in the cylinder head, had to be arranged so that it sprayed a small amount of fuel into the pre-chamber via one or more of the holes. This entailed very precise positioning of the spark plug with its attached pre-chamber, but once the geometry had been developed it led to a very effective system.

It is widely acknowledged that Mercedes was the first to run this in an F1 engine, but Ferrari was not far behind, introducing its own system for the 2015 Canadian GP where rivals noted a distinct upturn in the performance of the works Ferrari engine.

It is rare in engine development for a single upgrade to make a significant difference in power. I can remember the days when exotic fuels were allowed – we were literally able to pour in a significant increase in power – and in the early turbo days the power was directly proportional to the amount of boost you could run without the engine destroying itself.

The pre-chamber is different. This is a device that improves the combustion and is therefore fundamental to both power and efficiency. When first introduced it probably instantly added over 20bhp, and during the early phase of development this is likely to have increased substantially. 

This technology has already found its way into road cars with the system used in the Nettuno engine in the Maserati MC20. This claims to improve fuel economy by 3% for the relatively minor cost of €150 per engine. Other manufacturers are working on similar systems – yet another example of F1 engineering rolling down into production cars for the benefit of all.

Maserati's Nettuno engine features pre-chamber technology

Photo by: Maserati Media Center