The remarkable hidden work of an F1 cars’ most abused component

Among the many innovations brought to the sport during the last season was an element of ‘show and tell’. Formula 1 engineers are, by nature, extremely secretive. Many would say overly secretive.

However, there are many fans who take a keen interest in the technical aspects of the cars and follow their development avidly. The show and tell requires each team to disclose to the FIA the changes it’s made to its cars. The FIA then collates and publishes this while the team has to put its cars, and a reluctant engineer, on display to journalists before the cars run on Friday.

Of course most of the development that takes place during the season is concerned with aerodynamics and the changes made are generally quite visible once pointed out. Components under the skin are far more difficult to see although each team employs photographers to try and capture details on their rivals’ cars. Some details, of course, will remain forever hidden and today we’re going to look at one of these – the piston.

The piston must be the most abused component on a racing car. Hidden deep in the engine, it experiences some amazingly harsh conditions. Although current engines are allowed to rev to 15,000 rpm, they rarely exceed 13,000 owing to the fuel-flow limitations. Even at this speed the piston has to travel up the bore and back down again over 200 times a second.

Before reading on, just think about that number. If one were able to see the piston it would be a blur. On each revolution of the engine it’s travelling down the cylinder, accelerating from zero to around 60 mph and back to zero in just over 2 milliseconds before reversing and travelling back up the cylinder. The rapid reversal, during which the piston experiences over 600G of acceleration, puts enormous inertial loads on it. These are such that the 300-gram piston can have an apparent weight of nearly 2 tonnes.

Given the rigorous conditions F1 pistons are subjected to, it's perhaps surprising that this doesn't happen more frequently

Photo by: Motorsport Images

On top of all this the piston has to withstand the enormous pressures and temperatures of combustion. For a given architecture of engine, the torque it can produce is a function of the pressure exerted on the piston. Racing engine design therefore tries to maximise this with very high compression ratios, high turbo boost and aggressive combustion.

All of this leads to peak cylinder pressures which can reach or even exceed 200bar (nearly 3,000psi) in normal use. While the control systems on the engine will try and avoid knock it can happen occasionally, sending the cylinder pressures much higher. Even at 200bar the load on the piston is around 10,000kg, equivalent to the weight of 12 F1 cars.

The peak stresses in a piston, which occur in the centre of the crown and around the ring grooves, could be controlled such that they were below the fatigue limit, therefore giving the piston much longer life

If this load wasn’t enough, the piston also experiences very high temperatures. Earlier this year, we explored the amazing pre-chamber combustion system employed on current F1 engines. While these are great for efficiency, allowing a very lean mixture to burn, they impose further stress on the piston as the plasma jets emitted from the pre-chamber impinge on the piston with even higher temperatures than the bulk combustion temperature, which itself will be over 2,500 degrees centigrade.

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Of course no conventional metallic material could withstand these temperatures and so the piston needs cooling. While an amount of heat is conducted away through the piston rings to the cylinder wall, the majority of the cooling is done by squirting oil from dedicated jets onto the underside of the piston. The location and aiming of these jets is vital to minimising the chances of piston failure, but even this is enormously complex as the jets try to hit the correct part of the piston through the maelstrom that exists in the crankcase.

Petrol-engined road car pistons are made from a relatively conventional high-silicon aluminium and, other than for very high-performance cars, will be cast. For a racing engine pistons are forged, generally from high-quality aluminium alloys. For many years the material of choice was 2618 aluminium which had first been developed by Rolls Royce for aero engines in WW2.

Over the years materials developed rapidly. Aluminium beryllium was the ultimate although it was outlawed in 2000 owing to the health hazards of machining it. High lithium-content alloys are banned on cost grounds, so relatively common materials such as 2219 aluminium are used these days.

Engineers are put up to talk media through the changes to their cars at each event - but some of the more remarkable goings on are hidden from view

Photo by: FIA Pool

However, the introduction of the hybrid turbo engines to F1 in 2014 highlighted the frailty of even these high-performance materials. Damage to the piston crown from detonation and ring groove wear became limiting factors.

This led to more complicated arrangements: multiple inserts and coatings were needed to make the base material survive the rigours associated with the arduous conditions (and extended life expected of the new generation of engines). One of these coatings was Diamond-Like Carbon, DLC, an exotic material when introduced in Formula 1 but now found in many road engines as part of the quest for low friction and improved fuel consumption.

Ultimately it became logical to switch to steel although the minimum regulated piston weight of 300 grams became something of a challenge. The change of material helped in many ways. The peak stresses in a piston, which occur in the centre of the crown and around the ring grooves, could be controlled such that they were below the fatigue limit, therefore giving the piston much longer life. The improved integrity of the ring grooves is also important in controlling oil consumption, something which these days is regulated to eliminate some of the tricks that were being
 played a few years ago.

So while bodywork may be the visible change that gets the journalists and the fans talking,
 there’s every bit as much leading-edge development going on under the skin. Unfortunately, it’s much harder to find out about.

Piston technology is an unseen yet remarkable element of improvement in modern F1 cars

Photo by: Alfa Romeo