2025/2026 Hybrid Powerunit speculation

[Tommy Cookers]

for 11 years nobody's been 'chasing the 15000 rpm cap' because the fuel rate is capped at 10500 rpm ....
I doubt this been changed for 2026

[bananapeel23]

for 11 years nobody's been 'chasing the 15000 rpm cap' because the fuel rate is capped at 10500 rpm ....
I doubt this been changed for 2026

Exactly, thats why I said to open up the energy flow (which is just fuel flow expressed in a way that accounts for the energy density of the fuel) and increase max fuel.

Increase the energy flow enough to make hitting the 15000 RPM cap practically viable, but difficult. I don't know how the maths work, but the current RPM levels were predicted based on fuel flow. If someone could calculate how much fuel flow would be required to have the optimal power band reach all the way to 15000 RPM if you have an ICE that is slightly more efficient than current ICE:s. I'm guessing 120kg/h or so?

[wuzak]

for 11 years nobody's been 'chasing the 15000 rpm cap' because the fuel rate is capped at 10500 rpm ....
I doubt this been changed for 2026

Yes, the fuel flow is constant above 10,500rpm.

[wuzak]

for 11 years nobody's been 'chasing the 15000 rpm cap' because the fuel rate is capped at 10500 rpm ....
I doubt this been changed for 2026

Exactly, thats why I said to open up the energy flow (which is just fuel flow expressed in a way that accounts for the energy density of the fuel) and increase max fuel.

Increase the energy flow enough to make hitting the 15000 RPM cap practically viable, but difficult. I don't know how the maths work, but the current RPM levels were predicted based on fuel flow. If someone could calculate how much fuel flow would be required to have the optimal power band reach all the way to 15000 RPM if you have an ICE that is slightly more efficient than current ICE:s. I'm guessing 120kg/h or so?

It's not the actual fuel flow that is the issue, but the point at which the maximum fuel flow is reached.

Currently it is 10,500rpm, but that could be moved to 12,500rpm, or more, if desired.

The other issue is the number of gears.

Currently they have 8 speed gearboxes, for 2026 it may be down to 6, which means bigger spacing between gears and more need to rev the engine out.

[Hoffman900]

The teams have been chasing higher rpm despite the fuel flow rate being constant from 10,500rpm and up.

They do this by:

1)Reducing FMEP (friction)
2) The new faster combustion processes that allow stable combustion at ever increasing lambda values. That is the whole thinking behind Honda’s HCCI / TJI hybrid and Ferrari’s “Super fast” combustion.
3) reduce pumping losses

In Honda’s (translated) words:

As a result, the main combustion speed becomes much faster than conventional combustion, making it possible to reduce time loss and unburned loss while increasing the dilution rate, significantly increasing ICE thermal efficiency

The key here is increasing dilution rate, which is a byproduct of increasing rpm with a fixed fuel flow.

I need to dig it up somewhere (might be in a Race Engine Technology issue) but they are trying (slowly) to increase rpm’s because you always want that and they have found quite a bit relative to where they started in 2016.

The fuel flow vs a not-attainable RPM limit was about pushing teams to try to find ways to extract more energy out of the system with increasing dilution. Basically it’s the carrot on the end of the rope.

[gruntguru]

for 11 years nobody's been 'chasing the 15000 rpm cap' because the fuel rate is capped at 10500 rpm ....
I doubt this been changed for 2026

Exactly, thats why I said to open up the energy flow (which is just fuel flow expressed in a way that accounts for the energy density of the fuel) and increase max fuel.

Increase the energy flow enough to make hitting the 15000 RPM cap practically viable, but difficult. I don't know how the maths work, but the current RPM levels were predicted based on fuel flow. If someone could calculate how much fuel flow would be required to have the optimal power band reach all the way to 15000 RPM if you have an ICE that is slightly more efficient than current ICE:s. I'm guessing 120kg/h or so?

It's not the actual fuel flow that is the issue, but the point at which the maximum fuel flow is reached.

Currently it is 10,500rpm, but that could be moved to 12,500rpm, or more, if desired.

The other issue is the number of gears.

Currently they have 8 speed gearboxes, for 2026 it may be down to 6, which means bigger spacing between gears and more need to rev the engine out.

I assume @bananapeel23 is suggesting a small increase in fuel flow limit between 10,500 and 15,000 i.e. a two taper limit rather than one taper plus flat-top. Perhaps just enough to offset the increasing friction - allowing constant power from 10,500 to 15,000 although at the cost of greater fuel use at the higher revs.

I see some benefit in going one step further and setting limits that might allow a small power increase at the higher revs - encouraging teams to rev higher and juggle overall fuel use against brief short term power gains.

[FW17]

It will be good if they go back to the previous suspension and 2016 tyres from weight saving point of view.

In terms of front to rear balance sooner or later they would be wise to put the MGUK in the front, May be 2028

[Tommy Cookers]

So many things !! ....
(Thing 1)

In Honda’s (translated) words:

As a result, the main combustion speed becomes much faster than conventional combustion, making it possible to reduce time loss and unburned loss while increasing the dilution rate, significantly increasing ICE thermal efficiency

The key here is increasing dilution rate, which is a byproduct of increasing rpm with a fixed fuel flow.

Honda's words are a vindication ...
I have written for years of this (heat dilution disproportionately reducing energy dumped to coolant etc) ... but ....
we don't know what dilution (how lean) F1 runs (because we don't know the boost/(Miller) valve timing combo used) ....
it doesn't seem hugely lean


the 2026 ICE rules are written around further-increased leaning (ie more heat dilution) because ....

(Thing 2) fuel energy capacity is greatly reduced but ICE capacity is unchanged and ...

(Thing 3) the deletion of the MGU-H is in part ... because ....
more dilution needs relatively 'more' compressor work - reducing (turbocharger) turbine work available to recover ...

(Thing 4) - the reduced fuel energy means this 2026 dilution needs less boost than is used with the present engines

(Thing 5) the managed combustion amounting to an extension of the fuel's explosive range allowing increased leaning ....

what's not to like ?

[bananapeel23]

Exactly, thats why I said to open up the energy flow (which is just fuel flow expressed in a way that accounts for the energy density of the fuel) and increase max fuel.

Increase the energy flow enough to make hitting the 15000 RPM cap practically viable, but difficult. I don't know how the maths work, but the current RPM levels were predicted based on fuel flow. If someone could calculate how much fuel flow would be required to have the optimal power band reach all the way to 15000 RPM if you have an ICE that is slightly more efficient than current ICE:s. I'm guessing 120kg/h or so?

It's not the actual fuel flow that is the issue, but the point at which the maximum fuel flow is reached.

Currently it is 10,500rpm, but that could be moved to 12,500rpm, or more, if desired.

The other issue is the number of gears.

Currently they have 8 speed gearboxes, for 2026 it may be down to 6, which means bigger spacing between gears and more need to rev the engine out.

I assume @bananapeel23 is suggesting a small increase in fuel flow limit between 10,500 and 15,000 i.e. a two taper limit rather than one taper plus flat-top. Perhaps just enough to offset the increasing friction - allowing constant power from 10,500 to 15,000 although at the cost of greater fuel use at the higher revs.

I see some benefit in going one step further and setting limits that might allow a small power increase at the higher revs - encouraging teams to rev higher and juggle overall fuel use against brief short term power gains.

No. I'm suggesting that they simply raise the fuel flow limits and race fuel by however much is required to make hitting 15000 RPM viable with further development of the super efficient combustion technology being used now. Meaning if you get slightly more complete combustion, the part of your power curve where you would want to upshift with a 6 or 7-speed gearbox would be at 15000.

if current cars reach peak efficiency at 10500-11000 RPM. Increase the fuel flow enough that the 1.6L V6 turbo would reach peak power at something like 13200 RPM, making 15000 RPM not the most efficient rev range, but efficient enough to where the power curve still makes you want to rev all the way to 15000 RPM before you upshift. Obviously that would require the fuel flow limit to increase gradually from 100kg/h at 10500RPM to 120kg/h (or whatever number is appropriate) at 13200 RPM or 13500 or something in that ballpark.

Basically I'm advocating for more fuel so we can have more power and more noise. I'm basically saying that they should deprioritize fuel burn when they have biopfuels and simply let them go crazy. I guess they could cap boost or something if they want to keep the power somewhat in check, because I imagine 120kg/h fuel flow would make the cars a bit too powerful, since they would be putting out something ridiculous like 1600HP if they were deploying ERS and going full power.

Basically I want a set of regulations that just goes crazy with power and noise, but still has a really strong focus on combustion efficiency, while adding incentives for developing road relevant, lightweight batteries. Like I'm certain they could cut the battery weight in half or even more while retaining the same capacity and degradation if they removed the weight floor, even if they required the battery costs to be somewhat under control.

[Hoffman900]

Honda's words are a vindication ...
I have written for years of this (heat dilution disproportionately reducing energy dumped to coolant etc) ... but ....
we don't really know how much dilution (how lean) F1 is running (because we don't know what boost is used) ....
it doesn't seem hugely lean

From Pat Symond’s presentation:
* Thermal Efficiency of 52%
* BSFC 167gms/kw-hr (0.27lbs/hp-hr), occurs at peak power
* 800bhp from 1.6L (then another ~200hp or so from the hybrid unit)
* Lambda 1.3-1.4.
* Rules limited 18:1 geometric compression ratio. All are at max
* Spark assisted HCCI, which Honda pretty much showed (earlier in the thread)
* They are Miller Cycle engines, with IVC before BDC
* Separate oil circuit for piston oil jets that runs cooler than the other circuits
* Miller Cycle requires very aggressive intake valve opening / closing designs and a lot of boost
* Valve angles low (5-7*), obviously done for squish geometry
* "Omega" piston bowls. Illustration in video helps visualize that
* Modeling from the FIA shows around 5.5bar boost (~80psi or so) and 50% mass fraction burn by 8* ATDC. Lose 1-2% of MFB in the prechamber. Quick combustion from 2-80% MFB and a slowing combustion beyond that. This final 20% with slowing combustion speed is where knock can occur.

Honda’s tech review on 2021:
https://www-jsae-or-jp.translate.goog/e ... r_pto=wapp

Including a compressor map:


Compare that to the fuel flow limited DI / spark plug Audi DTM engine which runs at Lambda 1.15-1.38.
https://www.highpowermedia.com/Product/ ... -issue-136

[dren]

I somehow missed Honda's tech review. Thanks for posting the link! I can't believe they 'accidentally' stumbled upon the self ignition.

[Hoffman900]

I somehow missed Honda's tech review. Thanks for posting the link! I can't believe they 'accidentally' stumbled upon the self ignition.

Someone I know refers to it as “stumble discovery”.

A lot of new ideas are found that way. Just an accident while trying to test / work on something else.

[Hoffman900]

More sources:

All co-authored with Ferrari and open source to download:

Model-Based Pre-Ignition Diagnostics in a Race Car Application

https://www.mdpi.com/1996-1073/12/12/2277

Abstract

Since 2014, Formula 1 engines have been turbocharged spark-ignited engines. In this scenario, the maximum engine power available in full-load conditions can be achieved only by optimizing combustion phasing within the cycle, i.e., by advancing the center of combustion until the limit established by the occurrence of abnormal combustion. High in-cylinder pressure peaks and the possible occurrence of knocking combustion significantly increase the heat transfer to the walls and might generate hot spots inside the combustion chamber. This work presents a methodology suitable to properly diagnose and control the occurrence of pre-ignition events that emanate from hot spots. The methodology is based on a control-oriented model of the ignition delay, which is compared to the actual ignition delay calculated from the real-time processing of the in-cylinder pressure trace. When the measured ignition delay becomes significantly smaller than that modeled, it means that ignition has been activated by a hot spot instead of the spark plug. In this case, the presented approach, implemented in the electronic control unit (ECU) that manages the whole hybrid power unit, detects a pre-ignition event and corrects the injection pattern to avoid the occurrence of further abnormal combustion.

Time-Optimal Low-Level Control and Gearshift Strategies for the Formula 1 Hybrid Electric Powertrain

https://www.mdpi.com/1996-1073/14/1/171

Abstract

Today, Formula 1 race cars are equipped with complex hybrid electric powertrains that display significant cross-couplings between the internal combustion engine and the electrical energy recovery system. Given that a large number of these phenomena are strongly engine-speed dependent, not only the energy management but also the gearshift strategy significantly influence the achievable lap time for a given fuel and battery budget. Therefore, in this paper we propose a detailed low-level mathematical model of the Formula 1 powertrain suited for numerical optimization, and solve the time-optimal control problem in a computationally efficient way. First, we describe the powertrain dynamics by means of first principle modeling approaches and neural network techniques, with a strong focus on the low-level actuation of the internal combustion engine and its coupling with the energy recovery system. Next, we relax the integer decision variable related to the gearbox by applying outer convexification and solve the resulting optimization problem. Our results show that the energy consumption budgets not only influence the fuel mass flow and electric boosting operation, but also the gearshift strategy and the low-level engine operation, e.g., the intake manifold pressure evolution, the air-to-fuel ratio or the turbine waste-gate position.

Low-level Online Control of the Formula 1 Power Unit with Feedforward Cylinder Deactivation


https://arxiv.org/abs/2303.00372

Since 2014, the Fédération Internationale de l'Automobile has prescribed a parallel hybrid powertrain for the Formula 1 race cars. The complex low-level interactions between the thermal and the electrical part represent a non-trivial and challenging system to be controlled online. We present a novel controller architecture composed of a supervisory controller for the energy management, a feedforward cylinder deactivation controller, and a track region-dependent low-level nonlinear model predictive controller to optimize the engine actuators. Except for the nonlinear model predictive controller, the proposed controller subsystems are computationally inexpensive and are real time capable. The framework is tested and validated in a simulation environment for several realistic scenarios disturbed by driver actions or grip conditions on the track. In particular, we analyze how the control architecture deals with an unexpected gearshift trajectory during an acceleration phase. Further, we demonstrate how an increased maximum velocity trajectory impacts the online low-level controller. Our results show a suboptimality over an entire lap with respect to the benchmark solution of 49 ms and 64 ms, respectively, which we deem acceptable. Compared to the same control architecture with full knowledge of the disturbances, the suboptimality amounted to only 2 ms and 17 ms. For all case studies we show that the cylinder deactivation capability decreases the suboptimality by 7 to 8 ms.

[Hoffman900]

https://morethesis.unimore.it/theses/av ... 19-090328/ (Paper is in English)

The work aim is to compare CFD software products of two companies, SIEMENS and Convergent Science. The comparison has been carried out in different areas such as performance (comparing codes results against experimental data and against themselves), simulation time and overall software experience (user-friendliness).
The software assessed have been STAR-CD v 4.30.014, STAR-CCM+ v13.04.010 (both licensed by SIEMENS) and CONVERGE v 2.3 (licensed by Convergent Science).

The work has taken place at Ilmor Engineering Ltd. in Brixworth, Northamptonshire, UK. Different simulations have been considered for the comparison, such as:
- Steady state port flow
- Motored condition
- Mixture preparation

The object of the work has been a gasoline direct injection high performance engine. Different geometries have been assessed between the steady port flow and the other two cases. This is because the flow-bench experiments have been carried out on a specific geometry. On the other hand, the simulations related to the moving geometry consider a geometry closer to the one currently used by the company for a specific project.

The RANS approach is the one chosen for all the simulations.
Documents such as data graphs and images have been normalized and overshadowed in order to meet Ilmor’s confidentiality criteria.

Masters thesis doing a deep dive on comparison of CFD programs against experimental (flowbench) data on what is a TJI racing racing engine (presumably Merc’s F1 engine or very similar to). Published circa 2019.

Much of the values have been normalized or blocked off, but this paper does a great job of explaining flow structures, turbulence, measuring mass flow, in cylinder motion, some TJI injector work, etc. as part of defining the measurements. The author looked at static values, cold motored values, and motored values with the TJI spraying. There is A LOT to learn from reading this, even just from a fluid dynamics standpoint.

* for the record, both programs have had big code updates. This paper is great but the results would be even more useful to Ilmor in 2023. Software changes fast.

[Tommy Cookers]

.... but still has a really strong focus on combustion efficiency .....

the significant matter isn't combustion efficiency CE - it's indicated thermal efficiency ITE

combustion efficiency is simply the percentage of fuel burnt (eg 95%) without any regard to conversion of heat to work
there's no reason to think the CE of these cars is outstanding (even though there can be a bit of post-cylinder burning)

the ITE is outstanding - and yes that's largely due to the novel and nearer-to-ideal combustion rate behaviour
ITE is the ratio of work developed in cylinder (ie work at piston crown) to the heat released in-cylinder
(it is derived from the continuous measurement of in-cylinder' pressure and volume)

what science types parrot as 'thermal efficiency' is correctly known by engineers as brake thermal efficiency BTE
BTE is the ratio of work (at the crankshaft nose) to the heat (lower heating value LHV) of the fuel taken
(LHV ignores the fuel heat heat 'trapped' as latent heat in exhaust water and fuel vapours)