What is an engine dynamometer?

Answer 1

It's a machine that determines the power output of an engine by measuring the rotation rate and torque. It can be adjusted to load the engine as desired, thus imposing a particular desired load torque. In the U.S., many states require that engine pollution be measured with dynamometer loading that is varied to simulate a typical road trip. The car is placed with its drive wheels resting on a pair of cylinders, in front of and behind the wheels, which couple the car's power to the loading and measurement mechanisms. In an engine/fuel test lab, the engine is more likely directly coupled to the dynamometer. Loading may be provided by a brake mechanism (e.g., a Prony brake) or by electrically loading a generator driven by the engine.