Question

Qa. Mention 3 application  of Prime mover                   

               

    b.Brielfy explian the sequence of events in a cycle of a diesel engine   

                                               

    c. Using a  simple sketch to explian the working sequence of a steam engine

                                                                  

    d. Briefly explain the basic principle on how generators generate electricity 

Answer 1

1) Diesel engine works on diesel cycle which is the constant pressure cycle. It can be four stroke or two stroke. It is an internal combustion engine since the working fluid is not seperated from the combustion process. Everything happens inside the cylinder.

During suction stroke, atmospheric air is drawn into the cylinder of the engine. This air is compressed during the compression stroke to high temperature and pressure. This temperature would be above the ignition temperature if the fuel used. Before the ending of compression stroke , a sufficient quantity if fuel is injected in the form of spray by a fuel injector. Since athe air inside is of high temperature and pressure, the fuel ignites and the gas thus formed expands, thereby thr pistons moves. This is the expansion or working stroke. After this, the burnt gases escape through exhaust valve, which is the exhaust stroke.Diesel engines are also called compression ignition engines since here ignition takes place due to heat of compressed air.

In four stroke engine, the piston takes 4 strokes, ie the shaft rotates 2 times for 1 cycle of operation while in two stroke engine, the piston takes 2 strokes, ie the shaft rotates only 1 time for 1 cycle of operation since it eliminates seperate suction and exhaust strokes.

2) A steam engine is an engine which can do mechanical work by using steam as its working fluid. Steam engines were widely and mainly used in locomotives. Given is a brief layout of a steam engine.

slide value High pressure steam in Exhaust steam Valye rod INT n cylinder Piston

Here we have the slide valve connected to the valve rod for the high pressure steam to come inside. The high pressure steam is shaded in green in the picture. The piston which is attached to the flywheel reciprocates inside the cylinder due to the high pressure steam and thereby the steam engine works. We have the exhaust steam( which is shaded in blue in the picture) going out while the piston moves back and froth.

Steam engines are external combustion engines since the working fluid is seperated from the combustion process. Rankine cycle is the ideal thermodynamic cycle which explains the process of a heat engine, ie conversion of heat into mechanical work. The performance of steam engine is explained by rankine cycle.

3)A generator works on the principle of electromagnetic induction. Whrn there is a relative motion between armature and field flux, a voltage will be induced in the conductors. We have bith DC generator and AC generator. In DC generators, we have rotaing armature and stationary field, while in AC generators we have a stationary armature, which is the stator and rotating field winding, which is the rotor.

When rotor is rotated by a prime mover, the stator conductors cut the magnetic field produced by the rotor poles. Therefore, by Faraday's law of electromagnetic induction, an emf is induced in the stator conductors. This is how electricity is generated.

The prime movers of generators can be different like steam turbines, water turbines etc depending on the power plant.