Cylinder deactivation is used to reduce the fuel consumption and emissions of an internal combustion engine during light load operation. In typical light load driving the driver uses only around 30 percent of an engineâ€™s maximum power. In these conditions, the throttle valve is nearly closed and the engine needs to work to draw air. This causes an inefficiency known as pumping loss. Some large capacity engines need to be throttled so much at light load that the cylinder pressure at top dead centre is approximately half that of a small 4 cylinder engine.
Low cylinder pressure means low fuel efficiency. The use of cylinder deactivation at light load means there are fewer cylinders drawing air from the intake manifold which works to increase its fluid (air) pressure. Fuel is continuously pumped into each cylinder and combusted even though maximum performance is not required. By shutting down half of an engine's cylinders the amount of fuel being consumed is much less. Between reducing the pumping losses which increase pressure in each operating cylinder and decreasing the amount of fuel being pumped into the cylinders. Fuel consumption can be reduced by 8 to 25 percent in highway conditions.
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