2-STROKE INTERNAL COMBUSTION ENGINE.pptx

“A two-stroke engine is a type of internal combustion engine that completes a power cycle with two strokes of the piston during only one crankshaft revolution.”

Two Stroke engine are classified as-
2-stroke petrol engine
2-stroke diesel engine

1. Fundamentals of Mechanical Engineering (BME-101/201) UNIT-2 2-STROKE ENGINE PREPARED BY ER. PEEYUSH CHAUHAN ASSISTANT PROFESSOR DEPARTMENT OF MECHANICAL ENGINEERING

2. “A two-stroke engine is a type of internal combustion engine that completes a power cycle with two strokes of the piston during only one crankshaft revolution .” Two Stroke engine are classified as- 2-stroke petrol engine 2-stroke diesel engine INTRODUCTION

3. Key Points: In two stroke engine the suction and exhaust strokes are eliminated . There are only two remaining strokes – these are the Compression stroke (Upward stroke) Expansion or power stroke (Downward stroke). Instead of valves, the two stroke engine consists of inlet and exhaust ports.

4. 1. Piston- The piston transfers the expanding force of gases to the mechanical rotation of the crankshaft through a connecting rod. 2. Crankshaft- It converts the reciprocating motion to rotational motion. 3. Connecting Rod- It transfers motion from a piston to the crankshaft and acts as a lever arm . 4. Flywheel – It is a mechanical device that is used to store energy. Construction of A Two-Stroke Engine

5. 5. Spark Plug – It delivers electric current to the combustion chamber and in turn ignites the air-fuel mixture leading to abrupt expansion of gases. 6. Counter Weight – Counterweight on the crankshaft is used to reduce the vibrations due to imbalances in the rotating assembly. 7. Inlet and Outlet Ports – These ports allow fresh air with fuel to enter and exit from the cylinder . 8. Transfer Port- The compressed air fuel mixture is transferred from the crankcase to the combustion space through the transfer port.

6. 2-Stroke Petrol Engine

7. 1 . Upward stroke: P iston 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 the 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 by the spark plug. Working of A Two-Stroke Petrol Engine

8. 2 . 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 (TDC to BDC) 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 .

9. 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 the 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. Note:- In SI (Petrol) Engine spark plug are used.

10. Working in short:- During Upward stroke- Piston move from BDC to TDC. Inlet port are open. Air & Fuel Mixture enter in crankcase. Air & fuel mixture are compressed by piston. Charge (Air &Fuel Mixture) are burn by spark plug. Crankshaft rotate 0 to 180 .

11. During Downward stroke- Piston move from TDC to BDC. Burn Gases force on the piston. First exhaust port uncover after that transfer port are uncover. Exhaust gases leave out from the exhaust port & same time fresh charge enter in crankcase. Crankshaft rotate 180 to 360 .

12. 2-Stroke Diesel Engine

13. 1 . Upward stroke: When piston move from BDC to TDC a partial vacuum is created in the crankcase and this allows the entry of the fresh Air into the crankcase through the uncovered inlet port . The fresh air move on the top of the cylinder through transfer port. The exhaust port and the inlet port remains covered when the piston at the TDC . When piston reach at TDC its compressed the fresh air due to which temperature of air rise. In the end of upward stroke fuel is injected by fuel injector. Working of A Two-Stroke Diesel Engine

14. 2 . Downward stroke: As soon as the combustion of the fresh air 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 (TDC to BDC) and rotates the crankshaft and does useful work. During this stroke the inlet port is covered by the piston and the new air 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 fresh air through it is forced into the cylinder .

15. The fresh air 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 the BDC position. The cylinder is completely filled with the fresh air but it is somewhat diluted with the exhaust gases. Finally, the cycle event is then repeated.

16. Working in short:- During Upward stroke- Piston move from BDC to TDC. Inlet port are open. Fresh Air enter in crankcase. The fresh Air is compressed by piston. Fuel injected by fuel injector. Fuel burn by compressed air. Crankshaft rotate 0 to 180 .

17. During Downward stroke- Piston move from TDC to BDC. Burn Gases force on the piston. First exhaust port uncover after that transfer port are uncover. Exhaust gases leave out from the exhaust port & same time fresh air enter in crankcase. Crankshaft rotate 180 to 360 .

18. Two stroke engine gives a working stroke for each revolution of the crankshaft. The four stroke engine gives a working stroke for each two revolutions of the crankshaft. Power developed by the two-stroke engine is twice that developed by the four-stroke engine for the same engine speed and volume. Lighter flywheel is required in two stroke engine because of the more turning moment on the crankshaft. For the same power, a two stroke engine is more compact, light and requires less space than a four stroke engine, therefore is used in motorcycles and scooters . Advantages of A Two-Stroke Engine

19. It is simpler in construction and mechanism. There is no valve and valve mechanism in it. The ports can be easily designed and covered and uncovered by the movement of the piston itself. It has high mechanical efficiency. It requires fewer spare parts due to its simple design.

20. It has high fuel consumption. Thermal efficiency is less than four stroke engine. The charge is diluted by the burnt gases due to incomplete scavenging. It produces greater noise & vibrations. It does more consumption of the lubricating oil. There is a greater wear and tear of moving parts . Scavenging problems. Incomplete combustion, carbon deposit on the piston head and exhaust port. Disadvantages of A Two-Stroke Engine

21. Two-stroke engines are still found in a variety of small propulsion applications, such as- O utboard motors S mall on- and off-road motorcycles Mopeds Scooters Tuk-tuks Snowmobiles Go-karts U ltralight and model airplanes. Applications of A Two-Stroke Engine

22. Q:1 What is 2-stroke engine? Q:2 What is 2-stroke petrol engine? Q:3 What is 2-stroke Diesel engine ? Q:4 Write the applications of 2-stroke engine. Q:5 How 2-stroke SI engine works? Explain with neat & clean diagram. Also w rite its merit & demerits. Q:6 How 2-stroke CI engine works ? Explain with neat & clean diagram. Also write its merit & demerits . Questions