Internal Combustion Engine.
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Construction of I.C engine:
The figure shows the mechanical elements of the reciprocating I.C engines. The piston which reciprocates in the cylinder is made a very close fit in the cylinder. The cylinder is bored in the cylinder block which may be cast integral with the crankcase or the cylinder block may be bolted on the top of the crankcase. The combustion space is provided in the top cylinder head. In the passages of cooling medium are shown cast in walls of the cylinder block round the cylinder and also cast in the cylinder head the combustion space.
The reciprocating motion of the piston is converted into the rotary motion of the crankshaft by means of connecting rod and crank. The pin, which connects the piston and connecting rod, is known as the gudgeon pin or wrist pin. The crankshaft rotates in the main bearings that are set in the crankshaft. The flywheel is fitted on the crankshaft in order to smoothen out the uneven torque.
A mechanical cycle for an I.C engine can be completed in one revolution of the crankshaft or in two revolutions. The opening and closing of the valve is controlled by means of cams which are fixed to the crankshaft. The control of admission and exhausted by means of ports in two-stroke cycle.
Four stroke cycle engine principle:
In I.C engine the following events take place in the cyclic order:
1. The quantity of air mixture of air and fuel must be taken in the engine.
2. If the charge contains only air, the fuel must be injected at the end of compression.
3. The charge in the engine cylinder must be compressed to the desired pressure.
4. The charge must be ignited at proper time.
5. The combustion of the fuel should be complicated.
6. The energy developed in the engine must be transferred to the crankshaft.
7. Brunt gases should be removed.
Two stroke cycle engine principle:
The figure illustrates diagrammatically the two stroke cycle petrol engine. Employing crank case compression of the type used in say an ordinary motor cycle.
In two stroke cycle engine we have parts instead of valve through the inlet parts the mixtures in taken in to the crank case of the engine the exhaust ports serve the purpose of exhausting the gases from the engine cylinder a mixture of air and fuel slightly compressed in the crank case enters through the transfer ports and drives the burnt gases out of the cylinder through the exhaust ports for the remainders of the upward stroke the charge after the piston has covered the transfer and exhaust ports.
When the piston reaches the end of its strokes the entire charge is compressed in the clearance space and the ignited charge exerts pressure on piston the down ward movement of the piston causes the compression of the charge taken in to crank case of cylinder when the piston moves further the transfer ports are open an so are exhaust ports and the stroke is completed when the piston reaches the end of the down ward stroke.
It should be clearly seen that in two stroke engine both the side of the piston are effective.
Comparison between Two-stroke cycle engine & Four-stroke cycle engine:
1. In two stroke cycle engine every revolution has active strokes hence in four stroke cycle one power stroke in four strokes.
2. In two stroke cycle engine gives one working stroke per revolution and thus for the same speed and a given size increases of power is obtained over the four stroke cycle engine.
3. Four stroke cycle engines generally gives higher efficiency due to the positive scavenging action during the exhaust.
4. The quantity of burnt gauges left in the two stroke cycle engine is greater than that in the four stroke.
5. One reason for lower efficiency of two stroke.