Saturday, 14 January 2012

Lecture : A Formula One Piston

NSB was chuffed to have the chance to attend a talk by Jody Hayes (Materials Engineer at Mercedes-AMG High Performance Powertrains) entitled “A Formula One Piston - The Engineering Challenge” today.
The talk was an East Midlands Materials Society Event held at Nottingham University.
As is often the case with these things, the talk opened your eyes to the things that you didn’t know you didn’t know, and is what this blog post is, loosely, written around.

A F1 piston has a hard life
One of the points Jody made early in the talk was to illustrate the kinds of forces that a Formula 1 engine has to face, and he did this with some startling statistics showing what an engine running at its maximum speed of 18000rpm will go through in just one second
  • 300 rotations
  • Values opening and closing 150 times
  • 360 litres of fuel/air mixture is consumed
  • 3 litres of coolant is pumped around the engine
  • 1 litre of oil is pumped around the engine

Moving on to focus on the piston, Jody describes the particular challenges that it has to face:
  • 10,000g force
  • >100bar pressure
  • 3,000km life
  • 12hr service time
  • 350C temp (top surface)
  • 200C temp (bottom surface)
  • Fatigue (repeated cycling of loads can cause a fatigue failure)
  • Creep (applying load at a high temperature can result in the material slowly deforming, called “creep”)
  • Thermal Expanison (the piston must expand when hot at the same rate as the rest of the engine)
  • Thermal Conductivity (the ability to conduct heat away from the top surface helps improve performance)
  • Wear (the piston should have little friction against the cylinder bore and should not be vulnerable to wear by the piston rings
  • Mass (the lower the mass the lower the loads)

Piston Materials
Jody pointed out that the MotorSport industry tended to source materials from the Aerospace and Defence industries, because these are sectors where materials are put to the limit and also because they are able to afford the development of new materials (for example, it can cost £15million to develop a new alloy).
One factor that limits what materials can be used are the FIA rules, which have been written to effectively outlaw certain materials such as Metal Matrix Composites. This is often done in an attempt to reduce costs.
The materials allowed for pistons are described (in rule 5.17.1) as “an aluminium alloy which is either Al‐Si ; Al‐Cu ; Al‐Mg or Al‐Zn based.” (although other rules do allow the addition of small amounts of other elements to the alloy. The rules essentially allow the following :

2000 series : Aluminium alloyed with Copper
4000 series : Aluminium alloyed with Silicon
5000 series : Aluminium alloyed with Magnesium
7000 series : Aluminium alloyed with Zinc

Jody showed a chart that plotted the hardness (which relates to strength) of some alloys from these series against temperature. It could clearly be seen that 2618 showed the best balance of hardness at room temperature and, critically, hardness at 200-350C
High strength also suggests good resistance to fatigue failure and, as Jody pointed out “Fatigue is what kills the engine”
So where has this wonder alloy 2618 come from?
Gobsmackingly, it was originally developed in the 1930s by Aero-engine manufacturer Rolls Royce. At the time it was called RR58 and was used for the engines of Schneider Trophy planes and for the famous Merlin aeroengine. Later applications included turbine blades in early jet engines and as the main structural material in Concorde.

Merlins being manufactured

Concorde, such a pretty plane (sigh)

The composition of 2618 is Al(93.7%), Cu(2.3%), Mg(1.6%), Fe(1.1%), Ni(1.0%), Si(0.18%), Ti(0.07%).

See here for information on what all those alloying elements do
See here for some data on the 2618 alloy
See here for the early history of 2618

If you would like to find out more about the hardening mechanisms 2618, you can see here and here.

2618 is not perfect, however, and suffers from poor wear resistance. This tends to manifest itself as wear between the piston and the piston rings, although careful design or coatings can reduce the problem.

So what happens when it all goes pear shaped?
When a piston fails, often all that is left is a handful of metallic gravel, along the lines of this image.

The first step in investigation a failure is getting all the pieces as the key ot determining the cause of the failure may lie in one of that smallest fragments.

The next step is to photograph and document everything.

And only then can the components be analysed by microscopy, sectioned or assessed in other ways.

Mercedes-AMG High Performance Powertrains
Jody concluded by providing some background on Mercedes-AMG. Based in Brixworth, Northamptonshire, the firm employs some 400 people and exists for the single aim of manufacturing and supporting engines (and KERS) for Formula 1 (click here for a short company history).

Currently supplying three teams, Mercedes-AMG manufacture 48 engines per year for the teams (6 per driver) as well as a number of additional engines for testing and development.

Engineering departments cover all the disciplines one would expect of an organisation at the cutting edge, including design, manufacturing, reliability, systems integration and electronics.

If you are interested in a career with this undeniably glamorous and high-tech company, you may be interested to know that Mercedes-AMG High Performance Powertrains has programmes for Graduates, Apprenticeships and Undergraduate placements. You can find out more here:

So there you go. A very interesting talk, which has left NSB having trouble getting over the fact that 2618 is such an old alloy. . . .

Of course, no article about Formula One is complete without a short clip of cars from the early 90s with sparking undertrays, so let us bid you goodbye with this :

Image Sources : Merlin, Concorde, Mercedes.

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