PAT SYMONDS
FORCE-FED: HOW A TURBO WORKS
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 which 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.
Now 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
