2 stroke diesel engine - practical PDF

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Experiment no 10 Objective: To study the cut model of two storke deisel engine.

Apparatus: Two stroke diesel engine. A two-stroke diesel engine is a diesel engine that works in two strokes. All diesel engines use compression ignition, a process by which fuel is injected after the air is compressed in the combustion chamber, thereby causing the fuel to self-ignite. The two stroke engine employs both the crankcase and the cylinder to achieve all the elements of the Otto cycle in only two strokes of the piston.     

Intake. ... Crankcase compression. ... Transfer/Exhaust. ... Compression. ... Power.

A two-stroke, or two-cycle, engine is a type of internal combustion engine which completes a

power cycle with two strokes (up and down movements) of the piston during only one crankshaft revolution. This is in contrast to a "four-stroke engine", which requires four strokes of the piston to complete a power cycle.

Working of two stroke diesel engine: One big difference between two-stroke and four stroke engines is the amount of power the engine can produce. The spark plug fires twice as often in a two-stroke engine -- once per every revolution of the crankshaft, versus once for every two revolutions in a four-stroke engine. This means that a two-stroke engine has the potential to produce twice as much power as a fourstroke engine of the same size. At the top of the cylinder are typically two or four exhaust valves that all open at the same time. There is also the diesel fuel injector (shown above in yellow). The piston is elongated, as in a gasoline two-stroke engine, so that it can act as the intake valve. At the bottom of the piston's travel, the piston uncovers the ports for air intake. The intake air is pressurized by a turbocharger or a supercharger (light blue). The crankcase is sealed and contains oil as in a fourstroke engine. The two-stroke diesel cycle is as follows: 1.

When the piston is at the top of its travel, the cylinder contains a charge of highly compressed air. Diesel fuel is sprayed into the cylinder by the injector and immediately ignites because of the heat and pressure inside the cylinder.

2.

The pressure created by the combustion of the fuel drives the piston downward. This is the power stroke.

3.

As the piston nears the bottom of its stroke, all of the exhaust valves open. Exhaust gases rush out of the cylinder, relieving the pressure.

4.

As the piston bottoms out, it uncovers the air intake ports. Pressurized air fills the cylinder, forcing out the remainder of the exhaust gases.

5.

The exhaust valves close and the piston starts traveling back upward, re-covering the intake ports and compressing the fresh charge of air. This is the compression stroke.

6.

As the piston nears the top of the cylinder, the cycle repeats with step 1. The two stroke engine is a reciprocating engine in which the piston does two time movement ( i.e. TDC to BDC and BDC to TDC ) to produce a power stroke.

When the piston moves from TDC to BDC or BDC to TDC then this movement of piston from TDC to BDC and vice versa is called one stroke.

Cycle of two stroke diesel engine: The main strokes of the two stroke diesel engine are the following. INTAKE: The fuel/air mixture is first drawn into the crankcase by the vacuum that is created during the upward stroke of the piston. The illustrated engine features a poppet intake valve; however, many engines use a rotary value incorporated into the crankshaft.

CRANKESE COMPRESSION: During the downward stroke, the poppet valve is forced closed by the increased crankcase pressure. The fuel mixture is then compressed in the crankcase during the remainder of the stroke.

EXHAUST: Toward the end of the stroke, the piston exposes the intake port, allowing the compressed fuel/air mixture in the crankcase to escape around the piston into the main cylinder. This expels the

exhaust gasses out the exhaust port, usually located on the opposite side of the cylinder. Unfortunately, some of the fresh fuel mixture is usually expelled as well.

COMPRESSION: The piston then rises, driven by flywheel momentum, and compresses the fuel mixture. (At the same time, another intake stroke is happening beneath the piston).

POWER: At the top of the stroke, the spark plug ignites the fuel mixture. The burning fuel expands, driving the piston downward, to complete the cycle. (At the same time, another crankcase compression stroke is happening beneath the piston.)

The two strokes of a two stroke engines are described as follows:

1. Upward stroke:    

During upward stroke, the piston moves from BDC to TDC and compresses the charge (air-fuel mixture) in the combustion chamber of the cylinder. Because of the upward movement of the piston a partial vacuum is created in the crankcase and this allows the entry of the fresh charge into the crankcase through uncovered inlet port. The exhaust port and the inlet port remains covered when the piston at the TDC. The ignition of the fresh charge is takes place through fuel imjector.

Downward stroke:       

As soon as the combustion of the fresh charge takes place, a large amount of the hot gases is produced which exerts a very high pressure force on the top of the piston. Due to this high pressure force, the piston moves downward and rotates the crankshaft and does useful work. During this stroke the inlet port is covered by the piston and the new charge is compressed in the crankcase. Further downward movement of the piston uncovers first the exhaust port and the transfer port and the exhaust starts through the exhaust port. As soon as the transfer port opens, the charge through it is forced into the cylinder. The charge strikes the deflector on the piston crown, rises to the top of the cylinder and pushes out most of the exhaust gases. The piston is now at BDC position. The cylinder is completely filled with the fresh charge but it is somewhat diluted with the exhaust gases. Finally the cycle event is then repeated. We get two strokes for the single revolution of the crankshaft.

Parts of Engine:  Piston: The piston is moved up and down by a crankshaft, which is connected to it via the connecting rod. When the piston reaches the top the spark plug then lights the air mixture burning it and sending the piston back down .It is free to move. It compresses the air fuel mixture and converts the fuel energy into the mechanical energy. It transmit the power to the crankshaft.

 Crankshaft: It is located in the bottom end of the cylinder block. It transmits the reciprocating motion of the piston into rotary motion. This rotary motion used to rotate wheels of the vehicle.

 Connecting Rod: It connect piston to the crankshaft and transmit the motion of the piston to crankshaft. The lower end is connected to piston and the upper end to crankshaft.

 Cylinder Head: The top end of the cylinder is closed by means of a removable cylinder head. The inlet valve, exhaust valve, spark plug and injector are bolted on the cylinder head. The main function of the cylinder head is to seal the cylinder block and not permit entry and exist of gases on the cover of head.

 Cylinder block: The main function of the cylinder is to guide the piston. It is in direct contact with the products of the combustion so it must be cooled. For cooling of cylinder a water jacket or fin are situated at the outer side of the cylinder. So at the upper end of it cylinder head and at the bottom crankcase is bolted.

 Carburetor: A device for mixing vaporized fuel with air to produce a combustible or explosive mixture, as for an internal combustion engine.

 Fuel injector: It is used to inject fuel into the system through which the combustion process starts.

 Piston Rings: Piston rings provide a sliding seal between the outer edge of the piston and the inner edge of the cylinder. The rings serve two purposes:

 They prevent the air mixture in the combustion chamber from leaking into the sump during compression and combustion.  They keep all oil in the sump from leaking into the area, where it would be burned and lost.

 Piston Pin: It is the parallel spindles fitted through the piston and connecting rod small end. It connects the piston to the connecting rod. In the internal combustion engines, the gudgeon pin connects the piston to the connecting rod and provides a bearing for the connecting rod to pivot upon as the piston moves.

 Fly wheel: A flywheel is a rotating mechanical device that is used to store rotational energy. The amount of energy stored in a flywheel is proportional to the square of its rotational speed. To keep the crankshaft. The flywheel is a disk that is about 30 to 40 cms in diameter.

 Dead Centre: In a reciprocating engine, the dead centre is the position of a piston in which it is farthest from, or nearest to, the crankshaft. The former is known as top dead center while the latter is known as bottom dead centre.

 Stroke: Distance covered by piston from top dead centre to bottom dead centre or bottom dead centre to top dead centre is called stroke. The length of stroke is called stroke length.

Advantages of 2-Stroke Diesel Engines:        

Two stroke engines do not have valves which are easy to construct and lowers their weight Two stroke engines fire once every revolution. Power is produced once during 2 strokes of the piston .This gives a significant power boost. This two stroke engines lower output in horse power Two stroke engines can work in any position, since oil flow is not a concern with any valves to worry about. 2 stroke engines are lighter comparatively. Since the power produced by the two-stroke engine is higher, these engines are small and compact in size. The torque produced on the crankshaft is more uniform because the power is produced during every alternate stroke of the piston. These Engines often provide high power-to-weight ratio, usually in a narrow range of rotational speeds called the “power band”.

Disadvantages of 2-Stroke Engines:     

Two stroke engines do not last as long as four stroke engines; there is no lubrication system in a two stroke engine so parts wear out a lot faster. Two stroke oil is expensive; you would burn a gallon every 1000 miles if it were in a car Two stroke engines are Less Efficient. Two stroke engines produce a lot of pollution, and the way the engine is designed that part of the air/fuel leaks out of the chamber through the exhaust port. The exhaust gases often get trapped inside the combustion chamber. This makes the fresh charge impure. Therefore maximum power doesn’t get delivered because of improper incomplete combustion.



Since in two-stroke engines power stroke is produced after every stroke, a large amount of heat is generated within them. To reduce the temperature of the engine and keep the moving parts well-lubricated, good lubrication and cooling systems for the engine are required.

Uses: A two stroke engine is most commonly used for small load applications such as pumps, lawn movers, chain-saws, snowmobiles, snow-blowers etc. They also were used in automobiles but due to the introduction of the much more clean breathing 4 stroke engines and also the introduction of strict emission norms, the 2 stroke engine had to let go off the automotive world.

Difference Between Two storke Deisel/Four Deisel storke engine: S. No.

1. 2. 3.

4.

5. 6.

7. 8. 9. 10. 11. 12.

Two Stroke Engine

Four Stroke Engine

It has one revolution of crankshaft within one power stroke. It can generate high torque compare to 4 strokes engine. It used port to inlet and outlet of fuel. 2 stroke engines require lighter flywheel compare to other engines because it generates more balanced force due to one revolution for one power stroke. The charge is partially burn and mix with the burn gases during inlet. It is due to port mechanism. Easy lubrication due to lubrication oil mix with the fuel.

It has two revolution of crankshaft between one power strokes. It generates less torque due to 2 revolution of crankshaft between one power strokes. It used valve to inlet and outlet.

More lubricating oil requires because some oil burns with fuel. These engines give less thermal efficiency. It has high power to weight ratio compare to others. It creates more noise. Two stroke engines are less efficient and generate more smoke. These engines are comparatively cheaper.

It requires heavy flywheel because it generates unbalance force due to two revolutions for one power stroke. In four stroke engine charge is fully burn and does not mix with burn charge in ideal condition. Comparatively complicated lubrication.

Comparatively less lubricating oil requires. These engines give more thermal efficiency. 4 stroke engines have less power to weight ratio. It is less noisy. Four stroke engines are more efficient and generate less smoke. These engines are expansive due to valve

13.

These engines are easy to manufacture.

14.

These engines are generally lighter. These are mostly used in ships, scooters etc. Due to poor lubrication more wear and tear occurs

15. 16.

and lubrication mechanism. These engines are comparatively hard to manufacture. These engines are comparatively heavier than 2 strokes due to heavy flywheel and valve mechanism. These engines mostly used in car, truck, and other automobiles. Less wear and tear occurs....