The secrets of F1 turbocharging explained

Turbocharged engines are now de rigueur as the industry adopts engine downsizing to increase efficiency. While they are thought of as a relatively new development, the first patent for such a device was granted in 1905.

Although the idea was sound, the materials available to engineers at the time weren’t suitable for such arduous conditions, and while a Liberty aero engine was turbocharged in 1918, it wasn’t until the 1950s that the first production turbo-diesel engine went into production. This was followed in 1962 by a pair of turbocharged petrol General Motors models (albeit running very low boost): the Chevrolet Corvair Monza and Oldsmobile F-85 Jetfire. Poor reliability led to them going out of production within two years.

In Formula 1, Renault introduced turbocharging in 1977 but reliability was still problematic – the car retired 19 times out of the 26 races it started between 1977 and 1979. So, with so many difficulties why was turbocharging pursued? The answer lies in two important aspects of engine design: power production and efficiency.

Firstly, a petrol engine operates under a cycle of operations known as the Otto four-stroke cycle (after combustion-engine pioneer Nicolaus August Otto). The first part of the cycle draws air into the cylinder as the piston moves down the bore. The second part compresses that air as the piston moves up, while the third action is where the work is produced as the fuel that has been injected is burned, causing a rapid increase in pressure which drives the piston back down the bore – and, via the connecting rod, turns the crankshaft. Finally, the piston travels back up the bore, expelling the exhaust gases ready for the cycle to start again.

The more air you can introduce in the first part of the cycle, the more fuel you can inject and the more energy is released. For any given engine speed this can be done by both smoothing the entry path for the air or pushing it in under pressure. In the early days of pressure charging this was done with a supercharger and some engines still use this method. A supercharger is an air compressor, in effect a big pump, which is driven mechanically by the engine.

Any compressor requires power to drive it and the amount of power required by a supercharger is considerable, around 60kW at full boost and high revs for an F1 engine. This power drain can be reduced by not relying on a mechanical drive but to use the exhaust gases to drive the compressor. This is what is known as a turbocharger and consists of two main parts: the turbine which is spun up by the hot exhaust gases, and the compressor which is connected on the same shaft as the turbine and takes in cool air and compresses it to a high pressure before it’s fed into the cylinder.

Modern F1 turbochargers are complex and finely-tuned components of the hybrid powertrain

Photo by: Giorgio Piola

The turbocharger helps improve engine efficiency since much of the power to drive the compressor comes from the exhaust gases spinning the turbine, and therefore using energy that would otherwise be wasted. Unfortunately, nothing comes for free as the law of conservation of energy states that energy in a closed system remains constant so an amount of energy must be taken from the exhaust.

Some of this doesn’t matter – for example the exhaust gas loses some heat as it expands through the turbine, but it also causes a back pressure into the engine which robs it of some power. Overall, though, it’s a good way to pressure-charge an engine.

Mechanically a turbocharger is a design challenge. The exhaust gas enters the turbine at over 1,000 degrees so the turbine wheel is made of a special steel called Inconel, which is a material developed for jet engines. The turbocharger is also rotating at up to 150,000rpm, so the centrifugal forces on the wheel are immense and the bearings must cope with both this high speed and high temperature.

A Formula 1 turbo is slightly different from most turbochargers since the shaft that joins the turbine and compressor is also the rotor of an electric generator which sits between the two. This further increases efficiency by harvesting exhaust energy, turning it into electrical energy, which can be stored in the battery for later use.

The compressor is very large for such a small engine. One reason for this is that the engine requires a lot of air owing to its high rpm and the high boost pressure it runs

A problem with turbocharging is that when the driver demands torque from the engine, the turbocharger may be spinning too slowly to produce the boost required. It takes time to come up to speed and this is known as turbo lag. Now, the generator mentioned above can also act as a motor if voltage from the battery is applied to it. This unit, now acting as a motor, can spool the turbo up, thereby eliminating lag.

In fact, when generating electricity the system doesn’t have to send it to the battery. The rules allow it to be sent straight to the other motor of the hybrid power unit which is connected directly to the crankshaft, thereby delivering power by a more direct route. Whichever route, it will take energy out of the system and slow down, so the control systems get extremely complex with very high frequency switching to optimise energy recovery with the need for instant response.

The other thing you’ll notice with a Formula 1 turbocharger is that the compressor is very large for such a small engine. One reason for this is that the engine requires a lot of air owing to its high rpm and the high boost pressure it runs. More surprisingly, it’s oversized because a Formula 1 engine runs slightly differently to a road engine. Firstly, it uses a modified Otto cycle called the Millar cycle and secondly, it runs very lean, meaning its combustible mixture has a lot more air than normal. Both these factors require a large compressor.

As with many things in F1, the turbocharger isn’t simple, but is highly developed.

Minimising turbo lag is vital for F1 powertrains to work effectively

Photo by: Simon Galloway / Motorsport Images