Mechanical Engineering Aspect

Engines :

1. Classification:

(a) According to type of used, they are classified into petrol Engine, Diesel engine and Engine.

(b) According to number of strokes required to complete the cycle, they are classified into four stroke and two stroke engine.

Four stroke : Cycle completes in two revolution of crankshaft.

- There is one power stroke in every four strokes.

Two stroke : Cycle completes in one revolution of crankshaft.

- There is one power stroke in every two in every two strokes.

(c) According to cycle of operation, they are classified into two types.

Otto cycle :- Combustion of fuel takes place at constant volume. Eg. petrol engine, gas engine.

Diesel cycle :- Combustion of fuel takes place at constant pressure. Eg. diesel engine

(d) According to methods of ignition, they are classified into types.

Spark Ignition Engine :- The mixture of fuel and air is ignited with the help of an air is ignited with the help of an electric spark. Eg. petrol engine.

Compression Ignition Engine :- Fuel is ignited with the help of compressed hot air. Eg. Diesel engine.

(e) According to method of cooling, they are classification into two types.

Air cooled Engine :-Cooling is provide by air. Eg. Scooter and motor engine.

Water cooled Engine :- Cooling is provided by water. Eg. bus and truck engine.

(f) According to method of governing used, they are classified into two types.

Quality Governing :- Air-fuel ratio is constant but air and fuel content can be changed. Eg. petrol engine.

Quantity Governing :- Air-fuel ratio is not constant but air and fuel content changed as per requirement. Eg. diesel engine.

2. Comparison of two stroke and four stroke :

· Two stroke engine develops 1.7 to 1.8 times the power developed by four stroke engines as some power is used for compressing the charge in crank case and due to scavenging.

· Two stroke engine is lighter, less bulky and occupies less floor area then 4-stroke engine.

· The torque is uniform in two-stroke engine compared with four stroke engine so it requires lighter flywheel and lighter foundation.

· Two stroke engine is mechanically simpler.

· Two-stroke engine has higher mechanical efficiency.

· The starting of two-stroke engine is easy compared with four-shaped engine.

· The weight per H.P. capacity of two-stroke engine is less than four-stroke engine.

· The overall efficiency of two-stroke engine is less than four-stroke engine as some charge is lost to atmosphere during scavenging.

· The fuel consumption per kilometer and the running cost of two-stroke engine is higher than four-stroke engine.

3. Petrol Engine :-

· A four stroke petrol engine has four strokes such as suction stroke, compression stroke. Expansion stroke and Exhaust stroke.

·Air fuel ratio is controlled by carburettor in petrol engine. Air ratio is ratio is generally 15 : 1.

· The compression ratio in compression stroke of petrol engine is 6 : 1 to 10 : 1.

· Thermal efficiency of petrol engine is 25% to 30%.

· Compressed fuel and air mixture is ignited with the help of electric spark at the beginning of expansion stroke, so it is commonly called as spark ignition engine.

4. Diesel Engine :-

· During suction only air is taken inside the cylinder.

· Compression ratio of diesel engine varies from 14 : 1 to 25 : 1.

· Thermal efficiency of Diesel engine is about 65% to 70%.

· Diesel is sprayed just before completing the compression stroke, diesel is burnt with the help of hot, compressed air, so it is also known as compression ignition Engine.

5. Different terms of IC (Internal Combination) Engine :-

i. Indicated Horse Power (IHP) :-

- Power developed inside the cylinder of an IC engine.

ii. Brake Horse Power (BHP) :-

- Power available at the shaft of an IC engine.

- This power gives the output to drive the load.

iii. Frictional Horse Power (FHP) :-

- It is loss of power while transferring from cylinder to shaft.

- FHP = IHP - BHP

iv. Indicated Thermal Efficiency (η_i):-

(η_i)= IHP/(heat supplied to engine)

v. Brake Thermal Efficiency (η_b):-

(η_b)= BHP/(heat supplied to engine)

vi. Mechanical Efficiency (η_m):-

(η_b)= (BHP/IHP)= (η_b)/(η_i)

6. Renewable and Non-Renewable Energy Resources :

i. Renewable energy Resources :- They are not depleted and available in long term in periodic basis. Eg. Biomass, Solar Energy, Wind Energy, Hydropower, Geothermal Energy, Ocean Tidal Energy Biofuel, etc.

ii. Non-Renewable energy Resources :- They are depleted with continuous use. Eg. Fossil fuels, Radioactive fuel/Nuclear Energy, etc.