Editing Diesel engine (section)

===Torque control===
To control the torque output at any given time (i.e. when the driver of a car adjusts the [[accelerator pedal]]), a [[governor (device)|governor]] adjusts the amount of fuel injected into the engine. Mechanical governors have been used in the past, however electronic governors are more common on modern engines. Mechanical governors are usually driven by the engine's [[Serpentine belt|accessory belt]] or a gear-drive system<ref name="buckman" /><ref name="Rochester" /> and use a combination of springs and weights to control fuel delivery relative to both load and speed.<ref name=buckman/> Electronically governed engines use an [[electronic control unit]] (ECU) or electronic control module (ECM) to control the fuel delivery. The ECM/ECU uses various sensors (such as engine speed signal, intake manifold pressure and fuel temperature) to determine the amount of fuel injected into the engine.

Due to the amount of air being constant (for a given RPM) while the amount of fuel varies, very high ("lean") air-fuel ratios are used in situations where minimal torque output is required. This differs from a petrol engine, where a [[throttle]] is used to also reduce the amount of intake air as part of regulating the engine's torque output. Controlling the timing of the start of injection of fuel into the cylinder is similar to controlling the ignition timing in a petrol engine. It is therefore a key factor in controlling the power output, fuel consumption and exhaust emissions.