The mechanical design of the internal combustion engine has not changed since its conception in 1876, mainly because it works. The problem is, that it has been invented long before there was thorough understanding of thermodynamics or of the chemical reactions during combustion process. Further cheap and plentiful fuel -- Gasoline was easily available and until few years ago there was no concern with conservation or pollution.

As a result the internal combustion engine is an energy efficiency dinosaur that refuses to die.

To give you some idea why that is so, let’s consider this:

Gasoline contains about 42 to 43.5 Mega-Joules of energy in one Kilogram that is equal to about 18,060 to 18,705 Btu per pound.

The pie chart on next page will show you where all that energy that is available in Gasoline goes:

Car manufacturers are constantly playing with all of the following variables to make an engine more powerful and/or more fuel efficient.

1.      Increase displacement - More displacement means more power because you can burn more gas during each revolution of the engine. You can increase displacement by making the cylinders bigger or by adding more cylinders. Twelve cylinders seems to be the practical limit.

2.      Increase the compression ratio - Higher compression ratios produce more power, up to a point. The more you compress the air/fuel mixture, however, the more likely it is to spontaneously burst into flame (before the spark plug ignites it). Higher-octane gasolines prevent this sort of early combustion. That is why high-performance cars generally need high-octane gasoline -- their engines are using higher compression ratios to get more power.

3.      Stuff more into each cylinder - If you can cram more air (and therefore fuel) into a cylinder of a given size, you can get more power from the cylinder (in the same way that you would by increasing the size of the cylinder). Turbochargers and superchargers pressurize the incoming air to effectively cram more air into a cylinder. SeeHow Turbochargers Work for details.

4.      Cool the incoming air - Compressing air raises its temperature. However, you would like to have the coolest air possible in the cylinder because the hotter the air is, the less it will expand when combustion takes place. Therefore, many turbocharged and supercharged cars have an intercooler. An intercooler is a special radiator through which the compressed air passes to cool it off before it enters the cylinder. See How Car Cooling Systems Work for details.

5.      Let air come in more easily - As a piston moves down in the intake stroke, air resistance can rob power from the engine. Air resistance can be lessened dramatically by putting two intake valves in each cylinder. Some newer cars are also using polished intake manifolds to eliminate air resistance there. Bigger air filters can also improve air flow.

6.      Let exhaust exit more easily - If air resistance makes it hard for exhaust to exit a cylinder, it robs the engine of power. Air resistance can be lessened by adding a second exhaust valve to each cylinder (a car with two intake and two exhaust valves has four valves per cylinder, which improves performance -- when you hear a car ad tell you the car has four cylinders and 16 valves, what the ad is saying is that the engine has four valves per cylinder). If the exhaust pipe is too small or the muffler has a lot of air resistance, this can cause back-pressure, which has the same effect. High-performance exhaust systems use headers, big tail pipes and free-flowing mufflers to eliminate back-pressure in the exhaust system. When you hear that a car has "dual exhaust," the goal is to improve the flow of exhaust by having two exhaust pipes instead of one.

7.      Make everything lighter - Lightweight parts help the engine perform better. Each time a piston changes direction, it uses up energy to stop the travel in one direction and start it in another. The lighter the piston, the less energy it takes.   

The load on the piston due tocombustion of fuel in the combustion chamber is transmitted to crankshaft through the connecting rod.One end of connecting rod known as small end and is connected to the piston through gudgeon pin while the other end known as big end and is connected to crankshaft through crank pin.

Connecting rods are usually made up of drop forged I section.In large size internal combustion engine,the connecting rods of rectangular section have been employed.In such cases,the larger dimensions are kept in the plane of rotation.

In petrol engine,the connecting rod's big end is generally split to enable its clamping around the crankshaft.Suitable diameter holes are provided to accommodate connecting rod bolts for clamping.The big end of connecting rod is clamped with crankshaft with the help of connecting rod bolt,nut and split pin orcotter pin.

Generally,plain carbon steel is used as material to manufacture connecting rod but where low weight is most important factor,aluminium alloys are most suitable.Nickel alloy steel are also used for heavy duty engine's connecting rod.

Function-Inlet valve allow the fresh charge of air-fuel mixture to enter the cylinder bore.Exhaust valve permits the burnt gases to escape from the cylinder bore at proper timing.

It controls the speed of engine at a different load by regulating fuel supply in diesel engine. In petrol engine, supplying the mixture of air-petrol and controlling the speed at various load condition.

It converts petrol in fine spray and mixes with air in proper ratio as per requirement of the engine.

This device supplies the petrol to the carburettor sucking from the fuel tank.

This device is used in petrol engine only and ignite the charge of fuel for combustion.

This device is used in diesel engine only and delivers fuel in fine spray under pressure.

Connects the piston with small end of connecting rod.

This pin connects the piston with small end of the connecting rod,and also known as piston pin.It is made up of case hardened steel and accurately ground to the required diameters.Gudgeon pins are made hollow to reduce its weight,resulting low inertia effect of reciprocating parts.

This pin is also known as "Fully Floating" as this is free to turn or oscillate both in the piston bosses as well as the small end of the connecting rod.There are very less chances of seizure in this case but the end movement of the pin must be restricted to score the cylinder walls.This can be achieved by using any one of the following three methods,

A) One spring circlip at each end is fitted into the groove in the piston bosses.

B) On spring circlip is provided in the middle.

C) Bronze or Aluminium pads are fitted at both ends of the pin,which prevents the cylinder walls from being damaged.

The gudgeon pin may also be semi-floating type,in which either the pin is free to turn or oscillate in the small end bearing but secured in the piston bosses or it may secured in the small end bearing and allowed a free oscillating movement in the piston bosses.This method provides more bearing area at the bosses and hence no need for providing bushes there in,is preferred.

Hand over the power and motion to the crank shaft which come from piston through connecting rod.