Q.1.What is advantage And Disadvantage of turbo-jet-engine ?

Advantages of Turbo-jet engines:

1. Construction much simpler (as compared to multi-cylinder piston engine of comparable power).
2. Engine vibrations absent.
3. Much higher speeds possible (more than 3000 km/h achieved).
4. Power supply is uninterrupted and smooth.
5. Weight to power ratios superior (as compared to that of reciprocating type of aero-engine).
6. Rate of climb higher.
7. Requirement of major overhauls less frequent.
8. Radio interference much less.
9. Maximum altitude ceiling as compared to turbo-prop and conventional piston type engines.
10. Frontal area smaller.
11. Fuel can be burnt over a large range of mixture strength.

Disadvantages of turbo-jet engines:

1. Less efficient.
2. Life of the unit comparatively shorter.
3. The turbo-jet becomes rapidly inefficient below 550 km/h.
4. More noisy (than a reciprocating engine).
5. Materials required are quite expensive.
6. Require longer strip since length of take-off is too much.
7. At take-off the thrust is low, this effect is overcome by boosting.

Q.2.What is advantages and disadvantages of a stirling engines vis-a-vis conventional I.C. engine ?

Advantages and disadvantages

The following are the advantages and disadvantages of a stirling engines vis-a-vis conventional I.C. engine.

Advantages :

1. Since it is an external combustion engine, it possesses multi-fuel capability.
2. Owing to rhombic drive (this mechanism consists of two crankshafts rotating in opposite directions, each having a crank on it ; two synchronising gears are used to time these crankshafts which in turn drive the output shaft), it is a perfectly balanced engine.
3. Reduced exhaust emission (due to overall lean mixtures and exhaust gas circulation).
4. Part load efficiency considerably higher.
5. The engine can be safely overloaded for a brief period.
6. Higher thermal efficiency (Typical value is 45% at 100 bar and 300°C).
7. Noise-free engine (because combustion takes place outside the engine).
8. The starting of the engine is reliable (because it depends only on the ignition of fuel in the burner).
9. Suitable for a variety of applications (e.g. automobiles, ship propulsion or power generation) since a stirling engine has almost constant torque characteristics over the entire range of speed.
10. No lubricating oil required (the use of rollsock seal has eliminated the use of lubricating oil).

Disadvantages :

1. Complex engine design (due to rhombic drive, regenerator, heater and cooler).
2. Requires large quantity of cooling water and bigger radiator.
3. The engines requires a blower to force the air through the preheater and the combustion chamber. This reduced the engine efficiency, and increases the noise.
4. The major disadvantage of a stirling engine is its high cost.

Q.3.What is advantages and Applications of Rotary Combustion Engines ?

Advantages and Applications of Rotary Combustion Engines

Advantages :

1. Lighter in weight, High power to weight ratio.
2. Compact, occupies less space.
3. Engine completely balanced, hence free from vibration and inertia forces.
4. Less noise.
5. Low grade petrol can be used, as it is less knock prone.
6. Low maintenance requirements.
7. The size of the engine is appreciably smaller than conventional I.C. engines for the same output.
8. It generates power after every rotation whereas 4-stroke engine develops power after every two revolutions.

Applications :

1. High performance motor cycle (Comotor, Luxemberg)
2. Snow mobile (Outboard marine in USA)
3. Outboard engine (Yanmar)
4. Helicopter engine (Curtis Wright)
5. General purpose engines
6. Industrial engines (Ingersoll-Rand, USA)
7. Passenger Cars (Several models in Japan and Germany).

Q.4.What is advantages and Disadvantages of Free-piston Engine Arrangement ?

Advantages of Free-piston Engine Arrangement

Advantages :

1. Less air rate as compared to a conventional gas turbine.
2. It is possible to achieve efficiency more than 40 percent.
3. Lighter and smaller than a diesel engine of the same capacity.
4. The gas turbine is about one third the size of the turbine for a simple open gas turbine plant.
5. The free-piston is vibrationless.
6. The thermal efficiency is considerably higher than simple gas turbine unit.
7. Higher volumetric efficiency can be obtained than conventional diesel engine.
8. Highly simplified system (since connecting rod, crankshaft, valves and valve mechanism required for conventional engine are absent).
9. The starting of a free piston engine is easier compared with conventional diesel engine as air required for starting is hardly 50 percent of the conventional diesel engine of the same capacity.
10. Since a free piston engine has little thermal as well as mechanical inertia, its acceleration characteristics are much superior compared to diesel engine.

Disadvantages of Free-piston Engine Arrangement :

1. Starting and control problems.
2. Synchronisation problem not yet full overcome.
3. The specific fuel consumption is higher than conventional diesel engine, particularly at part load conditions.
4. The fuel supply can be varied only in a limited range. Any fluctuation in the fuel supply will make the operation unstable.

Q.5.What is advantages and Disadvantages of Multi-stage compression ?

Multi-stage compression:

Multi-stage compression is very efficient and is now a days almost universally adopted except for compressors where the overall pressure rise required is small. The method is not only advantageous from a thermodynamic point of view, but also has mechanical advantages over single-stage compression.

Advantages :

The important advantages of multi-stage compression can be summed up as follows :

1. The air can be cooled at pressures intermediate between intake and delivery pressures.
2. The power required to drive a multi-stage machine is less than would be required by a single-stage machine delivering the same quantity of air at the same delivery pressure.
3. Multi-stage machines have better mechanical balance.
4. The pressure range (and hence also the temperature range) may be kept within desirable limits. This results in (i) reduced losses due to air leakage (ii) improved lubrication, due to lower temperatures and (iii) improved volumetric efficiency.
5. The cylinder, in a single-stage machine, must be robust enough to withstand the delivery pressure. The down pressure cylinders of a multi-stage machine may be lighter in construction since the maximum pressure there in is low.

Disadvantages :

1. Inspite of all these advantages, a multi-stage compressor with intercoolers is likely to be more expensive in initial cost than a single-stage compressor of the same capacity.

Q.6.What is advantages and Disadvantages of centrifugal compressors over axial flow compressors ?

Advantages of centrifugal compressors over axial flow compressors :

1. Smaller length.
2. Contaminated atmosphere does not deteriorate the performance.
3. Can perform efficiently over wide range of mass flows at any speed.
4. Cheaper to produce.
5. More robust.
6. Less prone to icing troubles at high altitudes.

Disadvantages :

1. Large frontal area.
2. Lower maximum efficiency.

Uses : The centrifugal compressors are used in : (i) Superchargers (ii) Turbo-prop.