1885

Supercharger and Turbocharger

Gottlieb Daimler (1834–1900)

Think about what is happening inside the cylinder of a diesel or gasoline engine. During the intake stroke, the piston moves downward and sucks in a volume of air. Let’s say the amount of air is one liter. Now the question is: How much fuel can burn using that one liter of air? The amount is limited by the number of oxygen atoms in the cylinder. The oxygen will combine with the carbon and hydrogen atoms in the fuel to create CO2 and H2O. Adding too much fuel is a waste—it can’t burn because of the limited oxygen.

Engineers look at this situation and ask an obvious question: Is there a way to get more oxygen into the cylinder? One way is to boost the pressure of the incoming air. If incoming air arrives at double the normal pressure, then twice as much oxygen gets crammed in the cylinder and twice as much fuel can burn. The 2x boost roughly doubles the power available. Engineers can radically improve the power-to-weight ratio of the engine as long as the boosting equipment itself doesn’t weigh too much.

A supercharger, patented by German industrial engineer Gottlieb Daimler in 1885, is the standard way to boost air pressure. It is an air pump attached to the engine’s crankshaft with a belt. Three types of superchargers are in common use: centrifugal, screw, and roots types.

If you take a centrifugal supercharger and power it with an exhaust turbine instead of a belt attached to the crankshaft, you have created a turbosupercharger, or turbocharger. The advantage: a turbocharger uses less engine power. The disadvantage: increased complexity and less boost at low rpm.

In big engines, superchargers can be a no-brainer. Dragsters using four-stroke nitromethane engines, and locomotives using two-stroke diesel engines always use them. But in smaller engines, the size, weight, cost, and complexity of the supercharger, plus the beefier design requirements for the engine, may cancel the benefits. Engineers analyze the tradeoffs to decide if the benefits outweigh the disadvantages.

SEE ALSO Two-Stroke Diesel Engine (1893), Nitrous Oxide Engine (1978), Bugatti Veyron (2005).

Close up of supercharger on the engine in a customized 1968 AMX by American Motors Corporation (AMC), a two-seat GT-type car.