The hidden danger lurking in controversial alleged F1 engine trick

The thorny issue of compression ratio, and its measurement by the FIA, has not yet been definitively resolved, although single-seater technical director Nikolas Tombazis is optimistic it will be before the season-opener.

It has been alleged that Mercedes High Performance Powertrains (HPP) and Red Bull Powertrains (RBPT) have developed a system to potentially run a higher compression ratio than allowed by the rules, so it is worth examining why rivals Audi, Ferrari, and Honda are unhappy. 

Essentially, it is claimed that HPP and RBPT will be able to generate a compression ratio of 18:1 through the use of heat-expanding metals when the car is on track, although this has yet to be demonstrated in the specific conditions of using an F1 power unit. 

A higher compression ratio results in more engine power due to an increase in the thermal efficiency of the engine - more energy being unleashed from the same amount of fuel. 

In simple terms, it must by compressing the air-fuel mixture before combustion, a higher compression ratio will create a more powerful explosion, allowing the pistons to move faster, increasing power.

A higher compression ratio means that the air-fuel mixture is compressed into a smaller space, creating higher temperatures and pressures. A cleaner combustion is thus reached, creating higher thermal efficiency - the conversion of heat into mechanical energy. 

With the higher ratios, during the expansion (combustion) phase, the gases created in combustion can expand over a greater distance, leading to more mechanical energy, with a more efficient combustion cycle, thus increasing pressure and improving torque, especially at low and medium speeds.

A good rule of thumb is that each additional percentage point of compression ratio can generate an estimated 3-4% increase in power.

However, compression ratio cannot be increased indefinitely. 

In gasoline engines, too high a ratio carries the risk of uncontrolled detonations before the optimum combustion point - known as knock. This can cause major damage to the engine.

For this reason, high-octane fuels are used to manage temperatures, wit the FIA's 16:1 limit for compression ratio safer than the 18:1, with the sophistication of the fuel mixtures also important in how they can delay the detonation point.

It makes the additional challenge facing the F1 fuel suppliers with the fully sustainable mix for 2026 all the more important, especially with the now 50-50 split in power generation between the internal combustion engine and battery power.