Will the new engines run at the regulated fuel limit at most times?

This topic contains 11 replies, has 5 voices, and was last updated by  Stjuuv 3 years, 8 months ago.

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    The new rules limit the maximum fuel flow at 100 kg/h, but at revs under 10,500, the allowed fuel flow is even lower:

    5.1.4 Fuel mass flow must not exceed 100kg/h.
    5.1.5 Below 10500rpm the fuel mass flow must not exceed Q (kg/h) = 0.009 N(rpm)+ 5.5.

    Since the turbo pressure is not limited, and there has been talk of up to 3,5 bar pressures reasonably available to the engine, will the engines (if not limited electronically) be able to handle the maximum fuel flow at very low revs, and will the turbo pressure be reduced even below 10k rpm?

    And will that mean that the engines will be at maximum possible power even way below the 15k rpm limit, making the higher revs pretty much useless, unless in the 8th gear?

    I tried looking at it like this:

    For the sake of simplicity, I will use the ideal burning mixture λ=1 of petrol at 14,7:1 (since the fuel used shouldn’t differ much from petrol). Burning the maximum amount of 100 kg/h of fuel would require 1470 kg/h of air. Without turbocharging (and other effects in the intake manifold that increase cylinder pressure), the 1,6L engine can cycle 200L of air per second at 15k rpm, which translates to 720,000 L/h, which at a density of 1,225 g/L makes 882 kg/h of air. That means that you could overcharge the engine to 1,67 bar at 15k rpm, until you have enough air to burn the fuel, and would start getting a lean mixture.

    I am not that familiar with engines and turbocharging, but I think that even naturally aspirated engines need a bit richer mixture than 14,7:1 to get maximum power, and perhaps it’s even more so for the turbocharged engines, so in that case it would mean that the boost at 15k rpm could even be lower than 1,5 bar (0,5 bar overpressure).

    At 10,500 rpm, the λ=1 limit would be at about 2,4 bar, so even then we don’t get to the limit the engines could realistically take, and even at 10,500 rpm, the engine could use all the available fuel, and most likely be at or close to the maximum power.

    Would this mean that since the engines are at maximum designed power very early, the only real difference between engines and teams could be the thermal efficiency of the engine (said to be around 40% for Mercedes, for example)?

    Also, since this means that the regulations (and the thermal efficiency) will very much be the limiting factor in engine power, would this mean that we can’t expect much development in terms of engine performance (aside from reliability), since increasing the thermal efficiency will likely hit a wall sooner rather than later?

    Using the combustion energy of petrol (which, again, should be a good enough assumption), we can get the maximum possible power under a fixed thermal efficiency at, for example, 40%. With the combustion energy being at about 42,4 MJ/kg and the fuel flow at 100 kg/h, we get the thermal energy in the engine as 4240 MJ/h or 1,178 MJ/s, which translates to a thermal power of 1178 kW. Taking into account the hypothetical thermal efficiency of 40% (way better than modern diesel cars btw), we get a mechanical power output of 470 kW for the new engines.

    Since increasing thermal efficiency is not something that is easily done, and the potential gains from increasing the thermal efficiency by 1% being a bit lower than 12 kW, can we expect the engine development race to be pretty much dead, after the initial unreliabilities are solved?

    Would appreciate any feedback and/or error sightings in my logic.



    Another issue that will arise, is that if we assume that the power curve will pretty much plateau after 10,500 rpm, it means that each upshift could change the gear ratio by a bit more than 1,4 times (from 15,000 rpm down to 10,500 rpm), and you would still immediately be at about the same power after the upshift. Assuming that the maximum top speed you will need all season long is about 360 km/h in 8th gear, you can cover the entire range of speeds with the car being between 10,500 and 15,000 rpm at all times (with speeds of 360/257/184/131/94/67/48/34 km/h for gears 8 through 1 being at the limiter). In this scenario, the lower gears will probably shift too often for the acceleration capabilities, but wouldn’t this be the optimal solution? There is even room for making the first gears longer, and limiting the maximum rpm for higher gears to save the engine, and you could still be above 10,500 rpm, and at maximum fuel and close to maximum power at all times.

    Does this make sense? And will the engines use maximum allowed revs at all this year?



    Another observation from today – since according to Toto Wolff, at least Mercedes were limiting their revs to 9000-10000 rpm today (https://twitter.com/ianparkesf1/status/428172858112876544), and considering that they must have been no slower than around 250-260 km/h on the straights (Hamiltons fastest lap averaged slightly over 180 km/h) then we can assume that at least at the moment, the transmission is set up so that they will hit the limiter in 8th gear only at around 400 km/h.

    So either they have some really long gears set up for testing, or they don’t plan to be going anywhere near 15,000 rpm in the 8th gear (or some lower gears as well). That would seem to suggest that my assumption about the engine being at maximum power output at way lower than 15,000 rpm could be correct, and we might see this in the races as well.



    Very interesting analysis. However, the theory that they can run at maximum power continuously overlooks the overall fuel limit of 100kg, if they run at a fuel flow limit of 100kg/h at all times then the fuel would only last 1 hour. For a race which lasts 1h40mins then the average fuel flow needs to be 60kg/h. There will be some saving since in reality the cars would never be at full power all of the time because of braking and turning zones in which no power is needed but I don’t know what proportion of that 1h40mins would not be consuming fuel.

    To achieve this the two extreme approaches would be to run at full power for as long as possible and then coast for the rest of the race, or to run at 60kg/h continuously. In reality the optimal solution will be somewhere in between and much of the development could be in developing a strategy and engine setup which give the best compromise over a race distance (also bearing in mind that for qualifying the fuel load isn’t such a limiting factor so there’s another compromise for optimising qualifying).

    Otherwise I would have thought that there is still a lot of scope for development on the other parts of the powertrain outside of the internal combustion engine and how that fits into the power delivery strategy.



    Yes, they certainly can’t run at maximum power at all times, but I was looking at this from the viewpoint of having maximum power potentially available to the driver at all times. At every track there will be many braking zones and corners where you cannot apply the full throttle of engine+ERS anyway, which will somewhat reduce the fuel needs, but fuel management will still be an issue.

    Looking at it again, I guess the most interesting part will be the upshifting part – with the old engines and normal aspiration, the maximum power of the engine was at all times mostly limited by the revs, and when a driver upshifted, he would always initally end up with lower power at lower revs after the upshift, until he could accelerate the revs up again. That meant that (giving some room for different power curves), it would always make sense to ride each gear out to the maximum revs, to make sure you get as much power as possible before and after the upshift. But now, that the engines could potentially have a pretty much flat power curve from 10,500-15,000 rpm, there is a much wider margin for potential gearshifts, as you won’t lose out in power by shifting too early.

    With that in mind, then I don’t think we will see any cars ending up in the limiter at the end of the straights, when the fuel load is lower – they will have no need to set the 8th gear so close to the rev limiter.

    Also, I think that this fact is behind the fact that the teams can only designate a very limited set of gear ratios for the entire year (unlike last year, where they could and would change the ratios on every track). They simply won’t need to change the ratios, unless maybe Monaco and other street circuits need a slightly different setup at lower gears.



    “However, the theory that they can run at maximum power continuously overlooks the overall fuel limit of 100kg, if they run at a fuel flow limit of 100kg/h at all times then the fuel would only last 1 hour.”

    Only if they keep the throttle fully open for a solid hour.



    @stjuuv I think your assumption that beyond a certain limit, the revs are pointless because there is no extra power generated due to the fuel flow limit. I think what you had mentioned about the revs beyond 10,500RPM being less useful is correct because of the fuel flow limitation.

    To be honest, I’m not too concerned since there is much greater power being generated from the 0-10,500RPM range compared to the outgoing V8; my understanding of the 2.4L V8s was that it produced a huge lump of power (~500hp) from 10000 – 18000RPM; so, within the same 0 – 10000RPM range, the current engine is able to provide its full power, compared to the previous V8 which could only provide ~300hp or so from 0 – 10000RPM.

    While I wish we had a 20,000RPM+ limit for the outgoing V8s, it’ll be much less of an issue with these engines. I do really like the new engine noise from the videos I’ve heard.



    The V8 engines didn’t run between 0-10,000RPM. At race speed the gearing made sure they were kept well above that at all times. Watch a few onboard laps. Even in the really slow corners they would only juuust get near 10,000RPM, and that has more to do with trying to limit wheelspin then anything else. They were practically always well above that.



    Ah, I didn’t take that into account. I had guessed that they would dip below 10k at the slowest corners (like La Source hairpin, the Montreal hairpin, etc.). I guess they’d have pretty much no power coming out of the corner, otherwise.

    I haven’t seen as many of the cool onboard laps this season (the ones that display the gear, speed, G-forces, etc.) so I’ll be sure to seek those out.

    Thanks for the clarification!



    Another thing is the turbo pressure – as far as I can see, then due to the fuel flow limits, they will be needing much more boost at lower revs than they will be needing at higher revs. Starting from 4000 rpm, the cylinder pressure should be around 2,6 bar to feed air for the maximum allowed fuel, and it will be slowly dropping to a little below 2,4 bar at 10500 rpm. After 10500 rpm, they can’t add any more fuel flow to the engine, so the required pressure will then linearly drop to below 1,7 bar at 15000 rpm, and at the same time when they need to drop the boost pressure, they will still have the same amount of exhaust gases going through the turbo, so there will be a lot of energy to be harvested by the MGU-H unit just by slowing down the turbo, which they would need to do anyway.

    Of course, every team will want to keep their engine at the 10500-15000 rpm range as much as possible (and because of the long range of maximum power, it will be easy to achieve), to provide as much power to the driver as he may need, so the lower range of revs will only be used from a standing start, but the most of the energy will come from accelerating up from 10500 rpm anyway, and that may very well mean that as long as the MGU-H unit can handle it, the teams can get most of their electrical energy from the MGU-H (since regeneration from MGU-H is not limited), and they can use a lot less than the maximum allowed regeneration of 2000 kJ per lap from the MGU-K unit, which will in turn mean less interference and better stability under braking for the drivers. That would make the MGU-K unit act more as an engine and a lot less as an energy harvester.



    From the Autosport Live commentary with Nico Rosberg:

    I know it’s a very early stage in the game, but how different does the 2014-spec car feel from the cockpit? Are the differences in handling, sound and performance obvious?

    – Nico Rosberg: “The driving is similar. The tyres are harder at the moment so that makes it a bit more difficult….and the engine is different, especially because of having the low RPM – but good torque and needing to run higher gears in the corners. Last year we did a hairpin in first gear, this year it’s maybe third.”

    This goes pretty well with my suggested gearshift points above (360/257/184/131/94/67/48/34 km/h for gears 8 through 1 being at the limiter).


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