Variable Swept Volume and Downsizing

The passenger cars during city driving operate at light loads when high pumping losses, poor fuel efficiency and high HC and CO emissions are obtained. Operation of the engine with lower swept volume would be at a higher mean effective pressure which would result in better fuel economy and lower CO and HC emissions.   For the 6- and 8-cylinder engines, the effective engine swept volume has been varied by deactivating the valve operation of half of the cylinders during city operation. This technology although has been applied to 4-cylinder engines as well but is better suited for the large engine having 6- and 8-cylinders. On high driving all the cylinders come into operation. The   cylinders are electronically switched on and off without the sudden acceleration and deceleration of vehicle being felt.  When operating only on half the number of cylinders, friction losses are also reduced as overhead camshafts of the two cylinders are not in operation.
Using a lower displacement engine and develop the required full throttle torque and power by supercharging is another approach to improve fuel economy and reduce emissions particularly the HC. A lower swept volume engine would operate at higher mean effective pressures and would have lower fluid and mechanical friction losses. At part loads, the supercharged and downsized engine  can result in fuel economy improvements of  upto 25% and accompanied benefits related to lower CO, HC and CO₂ emissions.