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Valve timing diagram on four stroke diesel engine model


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This type of analysis on the valve timing diagrams of a engine gives a clear view of how the engine valves are fixed and it gives a clear picture of how the fuel is being consumed



Valve timing diagram on four stroke diesel engine model

To draw the valve timing diagram on the given four stroke diesel engine is the main intention behind doing this experiment. The apparatus required for this experiment are engine model, thread, steel rule and chalk.

The co-efficient operation of the engine require the inlet and exhaust valves pen and close of proper time. Theoretically the valves are to open and close at proper time. But in practical the suction as well as exhaust valve open early and close late. So that gas velocities are reduced and hence their flow resistance reduces intake and exhaust manifolds.

The suction or inlet valve opens slightly before top dead center in vertical engine (or inner dead center in horizontal engines) so that the charge is not restricted at the dead center position. The valve continues to be opened. Well beyond the bottom dead center or outer dead center in horizontal engines to admit more charge due to high velocity at charge in the inlet manifold. The charge air from atmosphere enters the cylinder due to suction stroke. The angle between inlet valve opening and closing gives the suction process in crank angles in degrees.

Exhaust valve opens considerably before the end of the working stroke that is before bottom dead center. This no doubt reduces the power output from the engine. But this reduces the work to be expanded to force the piston during its return stroke. Hence the exhaust valve is made to open before bottom dead center or products of combustion are not expanded completely inside the engine cylinder is made near to atmosphere pressure to reduce pumping losses.

Pumping losses consists of the power spend in solution and exhaust when the engine acts as a pump and losses consists of the power spend in suction and exhaust when the engine acts as a pump and losses consists of the power spend in suction and exhaust when the engine acts as a pump and losses vary from five to ten percent in four stroke engine

In four stroke engines one cycle will be completed in two revolutions of the crank shaft that is 720 degrees of exhaust travel. In actual engines the suction stroke and exhaust takes place for about 235 degree of crack where as compression stroke requires less than ISO degrees of the crank.

During suction stroke air enters the engine cylinder through inlet valve opening while exhaust valve is closed. Pistion moves from top dead center to bottom dead center. The charge compressed during compression stroke while piston moves from bottom dead center to top dead center and both the valves are closed. Just before the completion of compression stroke fuel injected in to the combustion chamber. The fuel injected burns with air with the assistance of high temperatures and pressure. The combustion products are sent out of the cylinder in the exhaust stroke pistion. Moves from top dead center to bottom dead center then the combustion products re sent out of the cylinder in the exhaust stroke when the exhaust valve opens and piston moves from bottom dead center to top dead center.

Procedure

When the fly wheel is turned in its usual direction and the points of opening and closing of inlet and exhaust valve are marked on the flywheel. When the valve is about open the push becomes rod tight. Then the valve timing diagram is drawn. The angles are tabulated. Marks on the flywheel rim are made when the valves start opening and when they are fully closed


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