Four-stroke cycle petrol engine

Four-stroke cycle operation in automobile engines is common nowadays. The four strokes in the operation of a four-stroke cycle petrol engine are suction stroke, compression stroke, power stroke and exhaust stoke. The inlet valve should keep open and exhaust valve closed during suction stroke. Downward movement of piston creates a partial vacuum inside the cylinder. This leads to sucking of the mixture of air and petrol into the cylinder. Both the inlet and exhaust valves are closed during the compression stroke. The compressed mixture gets vapourized and a spark is produced in the spark plug igniting the mixture during this stroke. Inlet and exhaust valves remain closed during power stroke. But the burning of gas forces exhaust valve to open. During the exhaust stroke, the inlet valve is closed and the exhaust valve is open. Here the burnt gas is pushed out of the cylinder which forces exhaust valve to close and inlet valve open.

Water logging

Water logging is the situation when the productivity of agricultural land gets affected by the high waterablity. Water logging results in ill-aeration of plants. Water logging also makes tilling and ploughing processes difficult. Water logging also leads to the growth of unwanted plants like grass, weeds etc. and affects the growth of the crops. Water logging is responsible for bacterial activity retardation. Water logging also leads to salinity of soils. A saline soil reduces osmotic activity of the plants. Thus crop yield is very much affected by water logging. Some important causes for water logging are intensive irrigation, seepage of water from the adjoining high lands, inadequate surface drainage, inadequate natural drainage, impervious obstruction, seepage of water through canals, irregular topography, submergence due to the floods and excessive rains. The important measures employed for water logging control are introduction of lift irrigation, reducing the intensity of irrigation, provision of intercepting drains, introduction of crop rotation, lining of canals, provision of an efficient drainage system, improving the natural drainage and optimum use of water.