The working of two strokes CI engine is very similar to two stroke SI engine. The main difference is that in CI engine supercharged air is used through the inlet port and in place of exhaust ports exhaust valves are used. Pressurized air is inducted through the inlet port which expels the combustion gases through exhaust valve during the expansion stroke. Inlet and exhaust valve is closed during the compression stroke, piston moves from BDC to TDC. At the end of compression fuel is injected inside the cylinder and ignites and piston is forced to move from TDC to BDC. The same process is repeated again and again. The cut model of two stroke CI engine is shown in Figure 6.10 and the working strokes are shown in Figure 6.11.
Figure 6.10 Cut-section of Two Strokes CI Engine
Figure 6.11 Working of Two Strokes CI Engine
6.4.5 Comparison Between Four Strokes and Two Strokes Engines
Table 6.1 Comparison Between Four- and Two-strokes Engine
| Four-stroke engines | Two-strokes engines |
|---|---|
| The thermodynamic cycle is completed in four strokes of the piston and two revolutions of the crankshaft. Thus, one power stroke is obtained in two revolutions of crankshaft.Turning moment is not so uniform during all the four strokes and hence heavier flywheel is required.The power produced for same size engine is less than two strokes engine due to one power stroke in two revolutions of crankshaft. Or for same power output engine required is heavier and bulkier.Lesser cooling and lubrication is required due to one power stroke in two revolutions and hence less wear and tear occurs.It consists of valves and valve actuating mechanism such as cam, camshaft, rocker arm, spring, valve and valve sheet.It has higher volumetric efficiency as the time available for induction of charge is more.It has higher thermal efficiency due to complete combustion of the fuel. | The thermodynamic cycle is completed in two strokes of the piston and one revolution of the crankshaft. Thus, one power stroke is obtained in one revolution of crankshaft.Comparatively, turning moment is more uniform and hence lighter flywheel can be employed.The power produced for same size engine is more than the four stroke engine due to one power stroke in each revolution of crankshaft.Larger cooling and lubrication is required due to one power stroke in each revolution and hence more wear and tear occurs.It has ports in place of valves.Volumetric efficiency is lower due to lesser time available for induction.It has lower thermal efficiency due to partial wastage of fuel through the exhaust port and incomplete combustion. |
Leave a Reply