Valve Timing Diagram of Four Stroke Cycle Petrol Engine

ME6412

THERMAL ENGINEERING LABORATORY – I I

2015

1. VALvE TIMING DIAGRAM OF FOUR STROKE CYCLE PETROL ENGINE Exp. No. :

Date:

Aim :

To draw the valve timing diagram of the given four stroke cycle petrol engine.

Apparatus Required :

1. Four stroke petrol engine 2. Measuring tape 3. Chalk 4. Piece of paper. 5. Polar Graph

Theory and Description :

The diagram which shows the position of crank of four stroke engine at the beginning and at the end of suction, compression, expansion and exhaust of the engine are called as valve timing diagram. The extreme position of the piston at the bottom of of the cylinder is called “Bottom Dead Centre” [BDC]. In the case of horizontal engine, this is known as “Outer Dead Center”(ODC). The extreme position position of the piston at the top of the cylinder is called “Top Dead Centre” (TDC). In the case of horizontal engine this is known as “Inner Dead Centre” (IDC). In an ideal engine, the inlet valve opens at TDC and close at BDC. The exhaust valve opens at BDC and close at TDC. The charge is ignited when the piston is at TDC at the end of compression stroke. But in actual practice it will differ.

A

1

PREPARED BY BIBIN.C and S.GOBINATH, AP/MECH, RMKCET

ME6412

A

2



2015

ME6412


2015

Inlet valve opening and closing :

In an actual engine, the inlet valve begins to open few degrees before the piston reaches the TDC during the exhaust stroke. This is necessary to ensure that the valve will be fully open to allow the more amount of air fuel mixtures into the cylinder as soon as the piston starts to move TDC during the suction stoke. If the inlet valve is allowed to close at BDC, the cylinder would receive less amount of air-fuel mixture than its capacity and the pressure of the mixture at the end of suction stroke will be below, the atmosphere pressure. To avoid this, the inlet valve is 0

0

0

kept open for 40 to 50 rotation of the crank after the BDC for high speed engine and 20 0

to 25 for low speed engine. Exhaust valve opening and closing :

Complete clearing of the burned gases from the cylinder is necessary to take in more air-fuel mixtures into the cylinder and also to avoid the dilution of the fresh 0

0

mixture. To achieve this the exhaust valve is open at 25 to 45 before the piston reaches the BDC during the power stroke. In order to completely remove the burned products, the exhaust valve is remain 0

0

open for 5 to 10 after the TDC during the suction stroke. It is clear the diagram, for certain period both inlet valve and exhaust valve remains in open condition. The crank angle for which the both the valves are open are called as over lapping. This overlap must not be excessive enough to allow the burned gases to be checked into the intake manifold or the fresh charge escape through the exhaust valve. Ignition:

There is always a time between the spark and ignition of mixture. The ignition starts some time after giving the spark, therefore it is necessary to produce the spark before piston reaches the TDC to obtain proper combustion without losses. The angle through which the spark is given earlier is known as “Ignition Advantage” or Angle of 0

0

Advance. It may ranges from 35 to 40 before the piston reaches the TDC during the compression stroke.

A

3


ME6412


2015

Observation

1. Circumference of flywheel = ................. cm Formula used:

1. Crank angle = Distance of flywheel 2. Time duration =

x 360 Circ Circum umfe fere renc nce e

of flywhe flywheel el

Crank Crank angle angle displa displacem cement ent 360 360 x Engin Engine e spee speed d in sces sces

Tabulation

Sl. No

Event

Position of crank w.r.to Nearest Dead centre

1

IVO

Before TDC

2

IVC

After BDC

3

EVO

Before BDC

4

EVC

After TDC

5

IG

Before TDC

Distance from their respective dead centres in „cm‟

Model calculation:

A

4


Angle in degrees

ME6412


2015

Procedure:

1. Remove the cylinder head cover and identify the inlet valve exhaust valve and piston of particular cylinder. 2. Mark the BDC and TDC position of flywheel. This is done by Rotating the crank in the usual direction of rotation and observe the position of the fly wheel. When the piston is moving downwards at which the piston, begins to move in opposite direction. i.e from down to upward direction. Make the mark on the flywheel with reference to fixed point on the body of the engine. That point is the BDC for that cylinder. Measure the circumstance of the flywheel and mark the point from BDC at a distance of half of the circumference. That point is TDC and is diametrically opposite to the BDC. 3. Insert the paper in the tappet clearance of both inlet and exhaust valves. 4. Slowly rotate the crank until the paper in the tappet clearance of inlet valve is gripped .make the mark on fly wheel against fixed reference. This position represent the inlet valve open (IVO). Measure the distance from TDC and tabulate the distance. 5. 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 exhaust valve is gripped. Make the marking on the flywheel against fixed reference. This position represents the exhaust valve open (EVO). Measure the distance from BDC and tabulate. 6. Then convert the measured distances into angle in degrees

Result: The valve timing diagram for the given four stroke Petrol engine was drawn.

A

5



Duration of suction stroke

= ....................



Duration of compression stroke

= ....................



Duration of expansion stroke

= ....................



Duration of exhaust stroke

= ....................


Valve Timing Diagram of Four Stroke Cycle Petrol Engine

Recommend Documents