Cooler - IC engines

Explain cooler?

Cooler:

The cooler which is placed in between stages is called Intercooler. With the object of removing moisture, coolers are sometimes fitted after the last stage, and for this reason are called ‘After-coolers’, but it should be understood that after-coolers cannot influence the work done in compression.4mechtech

Coolers are simple heat exchangers in which heat is removed from air which has been compressed and its temperature has risen as a result of compression. The cooling water passes through the tubes which are secured between two tube plates, and the air circulates over the tubes through a system of baffles.

working of two stroke diesel engine

Explain working of two stroke diesel engine?

WORKING OF TWO STROKE DIESEL ENGINES:

Working of two stroke diesel engines is similar to that of petrol engines except the following differences:

a) Fuel injector is provided in the cylinder head in place of spark plug.

b) Only air enters the crank case. After slight compression, it is passed to cylinder and compressed in the cylinder.

c) At the end of compression strokes fuel injector injects diesel into compressed air. Due to high temperature of air, diesel starts burning.

Explain working of 2 stroke petrol engine

Explain working of 2 stroke petrol engine?

WORKING OF TWO STROKE PETROL ENGINE:

Two stroke and four stroke engines are different in the method of filling the cylinder with fresh charge and also in the removal of burnt gases from the cylinder. In a four stroke engine these processes are performed by the movement of piston during suction and exhaust stroke. In four stroke engines these are suction and exhaust valves where as suction (inlet) and exhaust (outlet) ports are cut in the walls of cylinder.

Whole process of has been shown in Figure. The Figure shows a three channel system in which the fresh charge is compressed in the crank case of the engine. This is also called crank are compression system. Figure shows all working of two stroke petrol engine in three stages.

Exhaust and Transference:

Figure shows the exhaust and transfer process. When the piston moves from TDC to BDC, i.e. downwards after expansion of gases, the piston uncovers the exhaust port. The burnt gases start going out of the cylinder. Simultaneously the slightly compressed charge in the crank case is forced into the cylinder through transfer port. The deflector on the piston crown deflects this charge and the fresh charge moves in the upward direction. This fresh charge pushes the burnt gases out of cylinder. During this process, some fresh charge may also leave the cylinder through exhaust port.4mechtech

Compression

When the piston moves upwards from BDC to TDC, transfer port and exhaust ports are closed. Compression of charge, present in the cylinder takes place. During this motion the inlet valve open and fresh charge enters the crank case. When the piston reaches TDC, compression process is completed.

Ignition and Expansion

After compression, spark plug generates spark and ignition of fuel takes place. Rapid rise in pressure and temperature takes place at constant volume. At this stage both transfer port and exhaust port are closed. Expansion of burnt gases takes place at the piston moves downward from TDC to BDC. The gases push the piston with great force and power is obtained during this process. Simultaneously, slight compression of fresh charge, present in crank case takes place.

After this process i.e. exhaust and transfer of charge takes place and cycle is repeated again. Thus, the cycle is completed in two strokes of piston and one revolution of crank shaft. In case of petrol engines, fresh charge consists of air petrol mixture which comes from carburetor after mixing.

PRINCIPLE OF CARBURETOR

PRINCIPLE OF CARBURETOR:

Both air and gasoline are drawn through the carburetor and into the engine cylinders by the suction created by the downward movement of the piston. This suction is due to an increase in the volume of the cylinder and a consequent decrease in the gas pressure in this chamber. It is the difference in pressure between the atmosphere and cylinder that causes the air to flow into the chamber. In the carburetor, air passing into the combustion chamber picks up fuel discharged from a tube. This tube has fine orifice called carburetor jet which is exposed to the air path. The rate at which fuel is discharged into the air depends on the pressure difference or pressure head between the float chamber and the throat of the venturi and on the area of the outlet of the tube. In order that the fuel drawn from the nozzle may be thoroughly atomized, the suction effect must be strong and the nozzle outlet comparatively small. In order to produce a strong suction, the pipe in the carburetor carrying air to the engine is made to have a restriction. At this restriction called throat due to increase in velocity of flow, a suction effect is created. The restriction is made in the form of a venturi to minimize throttling losses. The end of the fuel jet is located at the venturi or throat of the carburetor.4mechtech

Normally, The spray of gasoline from the nozzle and the air entering through the venturi tube are mixed together in this region and a combustible mixture is formed which passes through the intake manifold into the cylinders. Most of the fuel gets atomized and simultaneously a small part will be vapourized. Increased air velocity at the throat of the venturi helps the rate of evaporation of fuel. The difficulty of obtaining a mixture of sufficiently high fuel vapour-air ratio for efficient starting of the engine and for uniform fuel-air ratio in different cylinders (in case of multicylinder engine) cannot be fully met by the increased air velocity alone at the venturi throat.

CLASSIFICATION OF IC ENGINES

CLASSIFICATION OF IC ENGINES

There are many different types of IC engines and they can be classified on the following basis:

a. Thermodynamic Cycle:

1. Constant Volume or Otto Cycle-the heat energy is added to the system at constant volume
2. Constant Pressure or Diesel Cycle-the heat energy is added to the system at constant pressure. Limited Pressure or Dual cycle the heat energy is added to the system partly or constant volume and partly at constant pressure.
3. Joule or Brayton Cycle-heat energy is added at constant pressure and the heat energy is rejected also at constant pressure whereas in Otto, Diesel and Dual cycles, the heat energy is rejected at constant volume.

b. Number of Strokes per Cycle:

1. 4-stroke engines the thermodynamic cycle is completed in four strokes of the piston.
2. 2-stroke engines the thermodynamic cycle is completed in two strokes of piston.

c. Ignition System:

1. Spark Ignition (SI) a combustible homogeneous air fuel mixture prepared by the carburetor and sucked inside the cylinder is Ignited with the help of a spark plug.
2. Compression Ignition (CI) the fuel is injected inside the system and it automatically ignites in presence of high temperature and high pressure air (compressed within the system prior to the injection of fuel) present inside the system
3. Pilot injection of fuel oil in gas engines.

d. Fuel Used:

1. Petrol engine the engine uses petrol or gasoline as the source of energy
2. Oil engine uses diesel oil, mineral oil etc., as fuel
3. Gas engines uses gaseous fuel (coal gas, natural gas, coke oven gas, producer gas etc.,
4. Multi fuel engines use gasoline or diesel oil for starting purpose and kerosene or biogas as primary fuel.

e. Cooling Arrangement:

1. Water cooled cylinder walls are cooled by circulating water
2. Air cooled walls of the system are cooled by blowing atmospheric air over hot surfaces (motor cycles. scooters, aircrafts have air cooled engines).

f. Arrangement of Cylinders:

Multi-cylinders engines are invariably used in automobiles. The upper limit on the size of the cylinder is determined by the dynamic considerations, i.e., when the reciprocating masses of the piston and connecting rod are accelerated and decelerated, inertia forces develop and they put a limit on the speed of the engine and thus on the power output. Therefore, the displaced volume is distributed amongst several smaller cylinders. By this means, the Inertia forces per cylinder are reduced and the forces in one cylinder can easily be balanced by an appropriate arrangement of other cylinders.