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Weekend Debate: Oil burning in F1 engines - a fan's view and an engineer's view

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Weekend Debate: Oil burning in F1 engines - a fan's view and an engineer's view
Sep 23, 2017, 9:45 AM

One of the most talked about intrigues in F1 this season has been what the engine makers are up to when they burn oil to gain performance.

One of the most talked about intrigues in F1 this season has been what the engine makers are up to when they burn oil to gain performance. For most fans who like cars and F1, oil is for lubrication, not combustion. So what is going on?

This month the FIA reduced the amount of oil that can be used, to try to close off the practice, but what exactly is going on inside these engines?

One of our JA on F1 readers, Tachi, posted his explanation in the comments section, of how oil burning in F1 engines works. And in the interests of bringing the fans closer to the sport and providing insight, we sent it to an F1 engineer for a response.

Tachi wrote: "Races are ~300km, so they can burn ~3 litres of oil. They will also burn 145 litres of fuel. So burning oil is like have 2% more fuel. Distributed over a race, that is not much. Where it makes a BIG difference, is over 1 lap...

Remember that the cars have a mandatory fuel FLOW limit of 100 kg / hour. This effectively limits the output of the engine. Power gains can only be made with efficiency gains. Consider a track where a typical lap 1.5 minutes (1/40th or 0.025 hour). The fuel flow restriction limits them to 0.025*100kg = 2.5kg of fuel, or ~3.4 litres of fuel.

If the typical track is 5km long, and a driver does 18 laps over the duration of qualifying, that is 18*5 = 90km, so they can legally burn 0.9 litres of oil. Let's just say they use half of that on each Q3 hot lap. Instead of 3.4 litres of fuel, they now have 3.8 litres of fuel for each hot lap = 11% more fuel for each special lap thanks to oil burn. Yes, that means ~11% more power.

Now you know why they can go so much faster in Q3, or selected special laps in a race (pit in, pit out, restart, etc). The strategy is where to spend the "oil fuel". Clever, sneaky, cheating--call it what you will.

That's what the oil burning is all about."

Regular readers know that we have a network of F1 engineers, who are happy to help out (on condition of anonymity) with analysis on JA on F1 to help fans to understand the sport better.

So we put Tachi's comments to one and this was his response.

Renault F1 team

F1 engineer writes: So your reader Tachi almost has the race description right except the engines do use oil as a lubricant so he can't count all of the oil as additional power - far from it in fact.

But a small percentage could be considered as having done its job as lubrication and still find its way to the combustion chamber.

Now it isn't fuel, so it isn't burning at the same 'power' rate. However I am sure that in recent years oil development has had a consideration for also making it burn well when and if it does find itself in the combustion chamber at a convenient time in the 'bang' cycle.

For qualifying: it is true that within the rules you can replenish oil after qualifying in parc ferme.

So potentially if you can have a different, much faster flow of oil into that combustion chamber in qualifying than you would naturally need or get in the race, then you would benefit at a higher rate in qualifying.

Tachi has made a reasonable point in that respect. However his numbers are not correct and you cant burn at 100kg/hour on a lap because it also has a rev condition in the rules. Plus you do have to lift off at sone point around the lap!

On top of this you can't change oil specification from qualifying to race, so it still isn't the same as having an extra tank of equally powerful stuff as fuel that you can open the tap on in qualifying. In other words, the oil is still limited to needing to be suitably lubricating for the race.

So like these things normally are in F1, it will be a little help and everybody will aim to use the maximum they can, but it isn't a silver bullet. It is certainly not 11 per cent power as your man has calculated).

The qualifying modes that they often talk about are simply the qualifying usage of their higher performing strategy modes: The engines are tested as being good for a certain mileage - but this is actually broken down into something that we will call "damage cycles"; like fatigue damage cycles in metals and it helps give you a number which is relevant across different conditions and track rpm/torque usage histograms (noting that every track is different).

For each engine your total allowable 'damage' is then kept as a running account. You will then brake it down into x laps available at strategy mode 1 which is most 'damaging' then y laps in mode 2, z laps in mode 3 and so on.

When you have a fast car you don't need to use the highest modes until Q3 and ultimately if you really want to make sure you aren't going to break down within the life of that engine you try to use them sparingly and keep the damage down or at least some in your pocket for a tricky day or a close fight in a race. [JA note: this is what we argued in the Italian GP strategy report that Mercedes did with its works and customer cars at Monza to make life difficult for the two Ferrari cars, which were starting behind Ocon and Stroll on the grid]

As Mercedes generally have a very fast car, they can maximise that approach. So when they are sure they can get to Q3 without using the higher modes then they don't. Then when they do 'turn it up' it will give them a bigger step than those mid-field teams that have been using the higher end of the range in Q2.

Mercedes are particularly good at this 'damage' cycle system and they analyse the harmonics in the engine through its life to understand things like levels of piston slap, blow-by and wear characteristics and so on. Ferrari has also made good gains here.

So the 'damage' cycles left on the engine can be really well re-evaluated through the life of the engine. They can consider whether to turn it up for longer than planned at race 2 of its cycle, for example.

Renault have been playing catch up in this respect and the steps between modes are still not as big or elaborate. So Red Bull for example won't have a few laps at that big step that Mercedes do. [JA note: Verstappen and Ricciardo confirmed this in the Singapore post qualifying FIA press conference.]

Conclusion

So there you have it, a good insight into damage cycles and oil burning, hopefully explaining what is going on. Thanks to Tachi and our F1 engineer friend for the ideas.

As a final thought, the above leads to several conclusions, but one of them is that if I were Mercedes supplying customers and my own team I would probably have a slightly more conservative set of strategies for the customer teams and would be more likely to push the overall total damage permitted on an engine in my own team's engine either in total amount or by more extremes at the 'peak damage' cycles.

What do you think? Leave your comments in the section below?

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Series Formula 1
Tags innovation