The valve timing analysis is one of the most important studies in IC engine development. Based on Valve timing analysis, engine performance, fuel requirement and stock timing can be studied and improved. the following experiment shows the study of valve timing study for petrol and diesel engine.
EXPERIMENT NO: 01
AIM: To study valve timings for four-stroke petrol/Diesel Engines.
APPARATUS:
Models and cut sections of four-stroke petrol/Diesel Engine.
Measuring tape
Chalk
Piece of paper
Theory and Description:
The diagram which shows the position of the crank of a four-stroke cycle engine at the beginning and at the end of suction, compression, expansion, and exhaust of the engine are called the Valve Timing Diagram.
The extreme position of the bottom of the cylinder is called "Bottom Dead Centre". In the case of horizontal engines, this is known as "Outer Dead Centre". The position of the piston at the top of the cylinder is called "Top Dead Centre". In the case of horizontal engines, this is known as "Inner Dead Centre".
In an ideal engine, the inlet valve opens at TDC and closes at BDC, The exhaust valve opens at BDC and closes at TDC. The fuel is injected into the cylinder when the piston is at TDC and at the end of compression stroke but in actual practise it will differ.
Procedure:
Remove the cylinder head cover and identify the inlet valve, exhaust valve and piston of the particular cylinder.
Mark the BDC and TDC position of the flywheel. This is done by rotating the crank in the usual direction of rotation and observing the position of the flywheel when the piston is moving downwards at which the piston begins to move in the opposite direction. I.e. from down to upward direction. Make the mark on the flywheel with reference to the fixed point on the body of the engine. That point is the BDC for that cylinder. Measure the circumference. That point is TDC and is diametrically opposite to the BDC.
Insert the paper in the tappet clearance of both inlet and exhaust valves.
Slowly rotate the crank until the paper in the tappet clearance of the inlet valve is gripped. Make the mark on flywheel against a fixed reference. This position represents the Inlet valve open (IVO). Measure the distance from TDC and tabulate the distance.
Rotate the crank further, till the paper is just free to move. Make the marking on the flywheel against the fixed reference. This position represents the inlet valve close (IVC). Measure the distance from BDC and tabulate the distance.
Rotate the crank further, till the paper in the tappet clearance of the exhaust valve is gripped. Make the marking on the flywheel against a fixed reference. This position represents the exhaust valve open (EVO). Measure the distance from BDC and tabulate.
Then convert the measured distances into an angle in degrees.
4-STROKE SINGLE CYLINDER DIESEL ENGINE:
The working of a 4- stroke single cylinder Diesel engine is based on using a very high compression ratio.
It is based on the Diesel cycle. The compression ratio used for diesel engines is 14:1 to 20:1. Liquid fuel is injected into the cylinder in the form of spray by an Injector. The working cycle is completed in the four strokes named suction stroke, compression stroke, power or expansion stroke and exhaust stroke.
4-STROKE SINGLE CYLINDER PETROL ENGINE:
The working of a 4- stroke single cylinder Petrol engine is based on using a low compression ratio. It is based on the Otto cycle. The compression ratio used for petrol engines is 6:1 to 12:1.
The air-fuel mixture is injected and ignited with the help of spark plugs placed at the top of the cylinder.
The working cycle is completed in the four strokes named suction stroke, compression stroke, power or expansion stroke and exhaust stroke.
2-STROKE SINGLE CYLINDER PETROL/DIESEL ENGINE:
CONCLUSION:
As per valve timing diagram total process is done before the timing which we assume theoretically. This timing diagram is very helpful for practical studies and actual efficiencies.
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