MECHANISMS RUNNING THE WORLD

Ever wondered what happens when you press the starter button of your vehicle; switch on the refrigerator; switch on the Air conditioning system of your automobile or home? You are at the right place where you will get to know about these interesting things in a simple and interesting way.

There are ‘Mechanisms’ which work behind these devices. In this article we will be learning about mechanisms behind ‘Engine & Compressor’ because these are some devices with which we deal daily & we are unaware about them.

A mechanism is a combination of linkages (rigid bodies) which is a means of transmitting, controlling, or constraining relative movement.

This particular principle is used in every machine & then the word ‘Machine’ comes into picture. A machine is a combination of mechanisms in which one link is fixed.

So let’s see the Mechanism used in ‘Engines & Compressors’ which makes them a ‘Machine’.

1.   RECIPROCATING ENGINE MECHANISM:

The term ‘Reciprocating Engine’ tends to refer to Internal Combustion Engine in which combustion is intermittent. In the seventeenth century, Sir Samuel Morland, an English inventor, used gunpowder to drive water pumps, creating the first rudimentary internal combustion engine. In 1879 Karl Benz designed and built the four-stroke engine that powered the first automobiles.

The important components of this mechanism are as follows:

A.Crank: It is the rotating part of the mechanism.

B.Connecting Rod: It is the oscillating part of the mechanism.

C.Piston:It is the sliding part of the mechanism.

D.Cylinder: It is the fixed or stationary part of a mechanism.

As in the mechanism, there is one sliding and one rotating element, it is commonly known as Single Slider Crank Mechanism.

The working of this 4-Stroke Engine Mechanism occurs in 4 Stages, hence called 4-Stroke Engine. The four stages are as follows:

A.  SUCTION STROKE:

When the starter motor or kick of a vehicle is operated it pushes the piston in downward direction by means of a crank and vacuum is created inside the cylinder.

This suction occurs due to pressure difference inside the cylinder and the surrounding pressure. It is similar to that of a syringe in which the medicine is sucked from the container.

During this stroke, the charge that is the air-fuel mixture in case of petrol engines also called Spark-Ignition Engines (S.I Engines) and only air in case of diesel engines also called Compression Ignition (C.I Engines)is sucked inside the cylinder through the inlet valve.

B.COMPRESSION STROKE:

During this process, the charge sucked in the cylinder is compressed by the piston which increases the pressure inside the cylinder. The pressure and temperature of the charge goes on increasing.

C.POWER STROKE:

At the end of compression stroke, a spark is ignited in case of S.I engines and fuel is sprayed in case of C.I engines which produces a tremendous pressure inside the cylinder, thus causing the crank to rotate. This power is transmitted from piston to crankshaft through connecting rod which is the desired output.

D.EXHAUST STROKE:

After the power stroke, the burned gases present inside the cylinder are pushed out of the cylinder by piston through exhaust valve which then goes through muffler(silencer) & then to the surrounding. The upward movement of piston after power stroke occurs due to inertia which is transmitted from crankshaft, to crank & then to piston via connecting rod.

If we see carefully in this engine mechanism, it can be noticed that out of the four links named Crank, Piston, Connecting Rod & Cylinder, the cylinder is fixed one while the other three are movable which satisfies the definition of ‘Mechanism’.

2.RECIPROCATING COMPRESSOR MECHANISM:

From the name itself the word ‘compressor’ can be interpreted that it is a device which compresses something. Depending upon applications, the fluid inside the compressor may vary.Compressors have a variety of engineering applications.

In case of an automobile application, it is used for compressing air which is further used to inflate tyres.In case of HVAC application it is used to compress the refrigerant which is further allowed to flow through the system.

Also, in case of the domestic refrigerators the black cylindrical portion at the bottom of the refrigerator is nothing but a hermetically sealed compressor.

The mechanism used in reciprocating compressor is the same as that used in the internal combustion engine as discussed earlier. It is the slider crank mechanism

The components of the Reciprocating Compressor are same as that of internal combustion engine.

Now, the question arises what is the difference between them then. The fundamental difference between is that in case of I.C engine the input is provided in the form chemical energy (fuel) which is converted to mechanical work. But in case of compressor, the input is supplied in the form of electrical energy that is electricity.

This means an electric motor is connected at the input of the compressor which compresses the fluid and passes to the required application.

Conclusion:

In many applications, a desired motion is required at the output and that motion needs to be constrained within a defined boundary which can be achieved by arranging some linkages (rigid bodies) in a particular manner as per the requirement which we call a ‘MECHANISM’.

References:

1.     R.S Khurmi, J.K Gupta. "Theory of Machines".

2.     Rowland S. Benson, N.D Whitehouse. "Internal Combustion Engines".