The Turbocharger: The Exhaust Drives the Compressor

US 1,006,907, 'Hydrocarbon Power Plant', Alfred Büchi, filed 30 October 1906, granted 24 October 1911. The drawing shows piston cylinders, a working turbine fed by their exhaust, and *"a turbine-compressor"* that *"draws"* the charging mixture and *"forces"* it into the cylinders. The specification talks of the charging mixture being *"cooled"* — the charge-air cooler is in the idea from the start.

Take a turbocharger compressor wheel and measure it with calipers: the **inducer** (the small diameter where air enters, at the nose), the **exducer** (the full diameter at the back), and the blade height at each. Look at the blades from the front. They lean into the direction of rotation at the inducer, to scoop the air in, and at the exducer they sweep backward — a backward-curved centrifugal wheel, like the pump impeller in batch 150 but made for air and for enormous speed. Count the full blades and the shorter splitter blades between them: splitters add blade area at the rim without choking the inlet. Put the exducer diameter into the notebook's speed table.

**US 1,006,907, 'Hydrocarbon Power Plant', Alfred Büchi; filed 30 October 1906, granted 24 October 1911.** Büchi went on to apply exhaust turbocharging to large diesel engines, where it became standard; aircraft engines used turbochargers to hold their power at altitude; and today most car and truck diesels are turbocharged. **Honest limits.** Turbo lag: at low engine speed there is little exhaust and little boost. The turbine side runs very hot and the bearings depend on clean oil. Boost raises cylinder pressures and temperatures, so the engine must be built for it. **A running turbocharger is a hazard** — its wheels can suck in a hand-held object or fingers and fail explosively.