Monday, May 27, 2024

Red Bull Powertrains RBPTH001

The Red Bull RB18, which won the 2022 F1 Constructors’ and Drivers’ Championships, was powered to its dominant success by a Red Bull Powertrains (RBPT) RBPTH001. This power unit is a derivative of the Honda RA621H, used by the Japanese manufacturer during the 2021 F1 World Championship campaign. Red Bull Powertrains was created in 2021 to supply power units to Oracle Red Bull Racing and Scuderia AlphaTauri for the 2022 F1 season and beyond after Honda announced it would exit F1 at the end of the 2021 season.

Although Honda’s participation in F1 was officially over, the 2022 Oracle Red Bull Racing and Scuderia AlphaTauri power units were Honda-produced, assembled, maintained, and trackside supported, despite their RBPT designation.  Between 2021 and 2022, there were significant FIA-implemented development restrictions in place for the power unit manufacturers, limiting the spec changes for the 2022 season ahead of an internal combustion engine (ICE), MGU-H, turbocharger, fuel and oil freeze from 1 March 2022, and the MGU-K, energy store and control electronics freeze from 1 September. After these dates, power unit specifications were frozen until the end of the 2025 season, before a new power unit era starts in 2026.

Despite the limited development scope, Honda engineers in Japan were busy making detailed but essential design changes to the RA621H to produce its successor’s specifications. Without Honda’s commitment, Red Bull would have started the new era at a significant disadvantage, as the other manufacturers developed their power units before those freeze dates. Honda developed the 2022 RBPTH001 power unit at its research and development centre in Sakura City, Tochigi prefecture, run by Honda’s racing subsidiary, HRC (Honda Racing Corporation). In charge of the development there is Tetsushi Kakuda, executive chief engineer, automobile racing development division and F1 project leader.

The E10 issue

The most significant development area for the 2022 Formula 1 power unit specification was around the new fuel introduced for 2022, which includes 10 per cent ethanol, up from the previous 5.75 per cent bio-content. There are pros and cons to running any engine on E10. The construction of the ethanol molecule means it carries a lower quantity of joules per kilogram as a combustible vapour compared to the equivalent volume of petrol, making the combustion process less potent. However, engineers can adjust several elements of the engine configuration, as well as running parameters, to exploit some beneficial characteristics of the higher ethanol content. For example, compression ratio, if permissible by regulation, can increase and drive combustion efficiency higher.

Honda tested several E10 formulations proposed by its fuel partner, ExxonMobil, before choosing the one with the most desirable characteristics. ‘Because E10 has very different characteristics from the previous fuel generation, we had to develop the combustion-related elements to work with that,’ Kakuda explains. ‘The calorific value of E10 is lower than the previous fuel, which would reduce engine output if we could not address it. We adjusted the ignition timing for the 2022 engine compared to 2021, and peak cylinder pressure is higher in the 2022 engine.’ There was no change to the pre-chamber ignition systems coinciding with the fuel evolution, though the MGU-H ERS was tuned to the E10 exhaust gas entropy. Honda and ExxonMobil conducted detailed investigations into the fuel and lubricant interaction with combustion chamber geometry. Not all the fuel injected into the combustion chamber burns to generate power, thanks to crevice losses around the pre-chamber ignition, valve seats and piston top land. Formula 1 engines typically have low crevice volumes, but still, roughly two per cent of the injected fuel escapes combustion by residing in them.

Top Secret

Kakuda would not be drawn to expose the details of the changes, calling them ‘top secret’. However, he admits that ‘we explored many different paths in developing this area and tried many different configurations. We have also developed very accurate simulations to prove our concepts before implementing them into a mechanical system.’ The RBPTH001 takes advantage of a significant amount of additive-manufactured (AM) parts. Kakuda emphasises the fact that additive manufacturing allows engineers to create components with the structure only where load transfers through the part, which is obviously efficient.

‘Additive manufacturing has allowed us to optimise many components, including pistons and the turbocharger housing,’ he says. ‘Although Formula 1 has many restrictions on the materials teams are allowed to use, we have tried many different materials and combinations that fit within the regulations to give us the performance we want for our additive manufactured components.’ Honda also adjusted the crankshaft and cylinder block geometry to ensure reliability with the new E10 combustion conditions, while a specialised cylinder liner coating was applied at Honda’s Kumamoto factory. ‘We developed the whole combustion loop to exploit E10 in the most profitable way, including the injection system, exhaust system and turbocharger compressor and turbine efficiencies,’ Kakuda notes.

‘The RBPTH001 power unit weighed more than the RA621H [2021 version] thanks to beefed-up components to aid reliability, but the dimensions are almost identical in terms of the outside shape and volume. ‘However, several points of the chassis installation are different. For example, the exhaust and intake pipework and the electrical system loom layout.’

Close collaboration

Of note is the fact the RBPTH001 power unit was not solely a Honda F1 department venture. The broader Honda company was involved in various activities. The Honda aircraft division, which developed the HF120 turbofan engine in conjunction with GE, the motorcycle division and the automotive division assists wherever necessary. ‘If the F1 division would like expertise from any others then the working relationship is there, and vice versa,’ Kakuda explains. ‘We collaborated closely with the jet engine division to develop our compressor and turbine for the Formula 1 project.

‘The jet engine division also has very efficient and precise manufacturing processes that we were able to exploit in Formula 1, including additive manufacturing. Additionally, we reached out to the motorcycle division to implement the cylinder wall coating. The engine life would be significantly reduced if we wanted to run this high cylinder pressure without using the specialised coating.’ The investigation into the cylinder wall coating was triggered by Technical Directive 37, implemented in September 2020, which forces teams to only use one power mode for the power unit during the race weekends. Some teams decided to sacrifice reliability for outright performance as they could come back and improve reliability during the season as the regulations allowed for reliability improvements within the specification freeze.

In contrast, Honda’s power units from late 2020 onwards have focussed equally on reliability and output.  ‘With the implementation of Technical Directive 37, it meant we couldn’t run our qualifying mode any more, and at the time our engine wasn’t strong enough to run that mode throughout the whole race weekend,’ Kakuda says. ‘This is when we started to focus on developing reliability for a higher average output from the power unit.’

Reliability Target

‘The RBPTH001’s reliability target is to cover eight grands prix with a single power unit, as it has been for the last few years. That is a base position. It’s a fine balance to strike but, ultimately, we want to achieve the three power unit regulation without incurring penalties. ‘The 2022 power unit achieved a higher thermal efficiency than in 2021, even with the lower calorific value of the E10 fuel. I can confidently say it’s well above 50 per cent, but that is all I can say. This is thanks to the many detailed changes and developments around the new combustion regime.’

Running the 2022 power unit also saw a number of significant changes made to the calibration. ‘After securing the reliability, we did some testing to see how high we could run the engine temperature,’ Kakuda says. Running the power unit at a higher temperature means it needs less cooling, which has a series of knock-on effects for other elements of the car.’ A higher nominal running temperature means the cars don’t require as much mass airflow through coolers, meaning fewer intakes, slots and louvres are required on the bodywork to extract temperature.

This aids the aerodynamic department’s scope for developing the car, the most performance-dependent factor in current Formula 1. The ability of the oil to carry heat away from the engine is just one of the essential lubricant’s critical functions. The latest engine oil can withstand significantly higher temperatures than its predecessor, and that affects the design of many other parts of the car, giving Honda the scope to design a smaller, more efficient engine. ‘We studied the ambient race conditions, including moisture, oxygen content, temperature and pressure the power unit will experience during the race season so that we could optimise the calibration for everywhere we go,’ Kakuda expands.

‘We measure the ambient conditions in great detail to set up the power unit to be most performant in the conditions we see at the track during the race weekend. The level of precision we went into in 2022 is higher than ever before. ‘Throughout the season, there were several occasions where we could change the software, as far as input from the driver and output from the power unit are concerned. We introduced new software when we had driveability challenges and to support different driving styles and circuits. This has coincided with the car finding more grip with the team developing the mechanical set-up and the drivers becoming more confident in the car. ‘Part of these software upgrades was optimising energy management. With the 2022 chassis regulations, F1 cars are significantly heavier than the previous generation, which widened the options for energy management to and from the ERS on more of the lap.’

Development Scope

Kakuda says there is no change to the power band because the friction losses are still there, despite significant improvement in this area over the course of the eight years F1 has been running this power unit regime. A percentage of the chemical energy delivered to the combustion chamber in the form of fuel is lost to mechanical friction between components, most notable of which are the piston ring and cylinder interface and the connecting rod and big end bearing assemblies.

Developing an oil to provide a higher performing lubrication regime with less friction in these areas therefore offers a contribution to engine performance. Reducing friction also has a knock-on effect in other areas of efficiency, such as reducing the amount of energy required to carry out the non-firing strokes, known as pumping losses. Additionally, wear on the engine is reduced, giving it the ability to run in a higher performing mode for more miles.

In the Honda-developed RBPTH001 power unit, the friction losses are small and so have only a minor influence on the rpm range it uses. Fuel flow, on the other hand, is the limiting factor. This has been a significant influence in the useable power band since the hybrid power unit regime started in 2014. The current 100kg/h fuel flow limit means it is challenging to extract more power at a higher rpm, considering the additional fuel consumption required. For this reason, most of the power units in the Formula 1 field produce peak output at around 10,500rpm. 

Kakuda says the Honda-developed RBPTH001 power unit is at 98 per cent of the absolute optimum power unit potential under the current regulations in terms of reliability, performance and driver ability. ‘Of course, there are many areas of development where we can incrementally improve, but the gains at this point are extremely small. If the fuel regulations evolve again towards an even higher bio-content, it will open up more areas of development for us to explore. We have some reliability issues that we are addressing but, from a dynamometer perspective, that won’t  change anything, as we are very close to optimising most of the power unit.’

Gear Change

The technical support programme between Red Bull Powertrains and Honda Racing Corporation will continue until the end of 2025. In 2026, Red Bull Powertrains will  run a power unit developed in collaboration with American automotive giant, Ford,  which will work with RBPT to develop the next-generation hybrid power unit and supply them to both Oracle Red Bull Racing and Scuderia AlphaTauri. The 2026 season will see the 1.6-litre, 90-degree V6 engine architecture remain unchanged, with a similar rpm limit. However, fundamental changes to the formulae include the removal of the MGU-H, an increase in output for the MGU-K and much tighter constraints on ICE design.

The internal combustion engine will run on 100 per cent sustainable fuel by 2026, which must be sourced from non-food bio sources, municipal waste or certified carbon capture schemes. The new technical regulations specify that the fuel energy flow rate must not exceed 3000MJ/h, which equates to approximately 65kg/h, compared to the current fuel flow rate of 100kg/h. The FIA has applied this reduced fuel energy flow rate in a bid to reduce ICE output to approximately 400kW (536bhp), representing a drop of approximately 35 per cent in performance when compared to the ICE  of the current era. The MGU-H absence will necessitate a total re-design of the ICE as the combustion regime of the existing engines is permitted by the charge air control the MGU-H provides. The next generation ICE rules will provide greater freedom for combustion system design, but will outlaw features such as variable inlet trumpets on cost control grounds. Conversely, the bottom end components – reciprocating parts, pumps and other ancillaries – will be subject to more restrictions compared to the current regime.

The FIA will also enforce standardised injectors and many other ICE sensors, as well as expanding the authorised materials list to exclude many high-cost options. MGU-K peak output will increase to 350kW, with full power permitted up to around 300km/h. After that speed, the regulations specify the following equation for deployment: P(kW) = 1850 – [5 x car speed (km/h)] when the car speed is below 340km/h. At or above 340km/h, the rules limit MGU-K power to 150kW. The MGU-K will also have to be mounted within the battery volume in the chassis to ensure all high-voltage cables are within the car’s main crash structure. The Red Bull Ford deal is a long-term strategic technical partnership that will continue until at least 2030. The FIA states that the 2026 regulations are designed to increase the road relevance of the energy recovery and electrical components, with battery cell chemistry and technology open to development. This is where Red Bull Ford’s power unit will draw on Ford’s EV knowledge and depth of resources, including battery cell design, electric motor technology and power unit control software and analytics.

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