CARBURETION AND IGNITION IN INTERNAL COMBUSTION ENGINE

 CARBURETION OF INTERNAL COMBUSTION ENGINE

As we know that engine works on fuel (may be petrol, diesel or any other gasoline product).
The fuel is supplied into the combustion chamber of engine where it is burned under high pressure.

Now a question arises that can engine breathe any amount of fuel and air mixture to its cylinder?

The answer is NO. This is because an engine work efficiently only at certain ratio of fuel and air mixture.

Hence carburetion is technique of providing exact amount of fuel and air mixture to combustion chamber of cylinder of an engine, and the device used for it is called carburetor.

Fig:-Carburetor

DESCRIPTION:-

The air from the atmosphere is sucked in air filter chamber and filtered. Then it passes through choke valve. The air then comes to narrow passage called venturi.The venturi section increases the speed of air (as the diameter decreases at the section). This enables good quality carburetion effect.At this point the air is mixed with fuel which is coming from another channel having nozzle at the tip. The fuel channel has a device called float,which regulates the amount of fuel entering the chamber.

The fuel-air mixture is then passed through the throttle valve. This valve regulates the amount of fuel-air mixture entering the engine cylinder and finally the mixture is released in combustion chamber.

VARIOUS FACTOR THAT AFFECT CARBURETION

Factor that has influence over carburetion are as fallows:-

• Air temperature at inlet.

• Fuel properties and its nature.

• Operational speed of engine.

• Shape,size,outline or blueprint of carburetor.

As the temperature of inlet air increases good quality of carburetion is achieved. This is because with increase in temperature, vaporization of fuel occurs and good homogeneity is obtained.The fuel properties has vast effect on carburetion process. The properties like melting point, boiling point, viscosity etc effect vaporization and intern proper carburetion.When engine operates at high speed, large amount of air-fuel mixture is to be supplied from carburetor.The construction of carburetor is also a major criteria where performance of device lies. The construction should be such that it should be most efficient in making exact mixture and in exact amount.

The best mixture ratio of air/fuel is 12/1.
 According to the demand of engine a carburetor should must fulfill the fallowing criteria. These are:-

• During high power (full load) and ideal (no load) condition it should provide enriched mixture of air and fuel.
• It should be economical and safe.

IGNITION IN INTERNAL COMBUSTION ENGINE

Curiously you would be imagining how combustion is initiated inside engine cylinder.

The process of ignition is initiated by propagation of flame which provides enough energy for beginning of burning of fuel till combustion gains momentum.

Suppose there are two electrodes,a spark is introduced between them at high voltage. This spark has capability to ignite the entire fuel and air mixture. There is critical voltage beyond which only spark is produced. This critical voltage is based on:-

• Air-fuel ratio.
• Gap between two electrodes.
• Gas pressure.

Requirement of good ignition system:-

• Should produce spark at correct time. This will help to reduce ignition delay or pre ignition. Hence will effect efficiency of engine.
• Work over varying engine speed.
• Easy to use and low in cost.

TYPES OF IGNITION SYSTEM

• Older ignition system.

1. Battery ignition system.
2. Magneto ignition system.

• Modern ignition system.

1. Electronic orTransistorized ignition system.
2. Capacitive type system.

1.  BATTERY IGNITION SYSTEM:-

BATTERY USED IN THIS TYPE OF SYSTEM

• ALKALINE BATTERY used in commercial vehicle (heavy duty).
• LEAD ACID BATTERY used in light vehicle (light duty).

FIG:-BATTERY IGNITION SYSTEM

CONSTRUCTION:-

The basic parts of battery ignition system are:-

• Battery
• Coil for ignition
• Breaker
• Distributor
• Spark plug

The battery provides constant power (6V-12V) without any variation.The source is connected to a coil which acts as transformer.When the circuit is complete,the current flows through the circuits and enters into the coil.

The coil has primary and secondary winding, the primary winding is of approx 300 turns and secondary winding is of around 22000 turns. These winding are generally made up of copper. This difference in number of turns produces large potential difference.

Contact breaker is a tungsten made hard switch which is used to break circuit by cutting flow of current coming from ignition coil. It is operated by cam arrangement.

Distributor is a device that has arrangement of spark plug designed to fire in proper sequence and in accurate time.

MAGNETO IGNITION SYSTEM:-

In magneto ignition system there is no need of battery. Current is obtained by magneto system.Such engine requires less space.

No battery discharge problem in this system.