AIR CONDITIONING IN AIRPLANE

Previous Air Conditioning in commercial plane :

Ford 5AT

•  Introduced in 1928, accommodated 13 passengers in its earliest model and was modified to seat up to 17. 

• With no air conditioning and little heating, the plane was hot in summer and cold in winter, and with no circulation system, its environment was made even more unpleasant by the smell of hot oil and metal, leather seats, and disinfectant used to clean up after airsick passengers Opening a window was the only way to escape the smell At high altitudes. 

• Conditions are not in conformity with the physiological requirement of human being As the atmospheric pressure drops, the quantity of oxygen, CO2 and water in each lungful of air decreases proportionally Reduction in pressure causes irregularities like Bleeding through nose, ears, eyes etc.

The TEMPERATURE goes up due to the following reasons:-

CLASSIFICATION OF AIRCRAFT REFRIGERATION  SYSTEM-

1. Basic or Simple air-refrigeration system

Without evaporative cooling

With evaporative cooling

2. Bootstrap air-refrigeration System

Without evaporative cooling

With evaporative cooling

3. Regenerative air-refrigeration system

4. Reduced ambient air-refrigeration system

BASIC AIR- REFRIGERATION SYSTEM:

 

Air comes in due to ramming effect.

A part is bypassed to HE.

Remaining get compressed by compressor.

A part of this compressed air goes to combustion chamber, then turbine and finally expands through nozzle for propulsion of the aircraft.

Compressed air get cooled in HE by bypassed air.

 

Advantages of  Air-Cycle for Aircraft Refrigeration:

1. Air is used as cooling medium. Minor leakage can be avoided. Non toxic. Non flammable.
2. Main compressor do all compression work.
3. By direct use of cooling air the evaporator unit is eliminated.
4. Direct mixing of hot and cold air happens in HE.
5. The ducting system is easy.
6. Low maintenance cost.
7. Light weight compared to VCS.

 

 

FUEL INJECTION SYSTEMS

• Introduction :

•         Fuel injection system is a well-designed mechanism for admitting fuel into an I.C. engine.

•         It has become the primary fuel delivery system used in automotive petrol engines, having almost completely replaced carburetors in the late 1980s.

•         A fuel injection system is designed and calibrated specifically for the type(s) of fuel it will handle. Most fuel injection systems are for gasoline or diesel applications.

•    The basic function of a fuel injection system is to inject fuel to the engine cylinders in proper quantity, at correct time and at a pre-determined rate.

 

Requirements  Of Fuel Injection System:

The injection system of the compression ignition

  engine should fulfill the following objective

s consistently and precisely:

1.Meter the appropriate quantity of fuel, as 

demanded by the speed of, and the load on, the 

engine at the given time.

 

2.Distribute the metered fuel equally among

 cylinders in a multi-cylinder engine.

 

3.Inject the fuel at the correct time (with respect to 

crank angle) in the cycle.

 

4.Inject the fuel at the correct rate (per unit time or

 crank angle degree).

 

5.Inject the fuel with the correct spray pattern and

 sufficient atomization as demanded by the design

the combustion chamber.

 

6.Begin and end injection sharply without dribbling.

There are two major divisions of Fuel Injection systems:

•       Solid Injection systems, which inject only the liquid fuel through the injectors.

•        Air Injection systems, which inject air along with the liquid fuel.

    However, the air injection systems have proved to be less efficient and costlier than other systems and hence, is now obsolete.

 

 Air Injection Systems 

Fig. Show the schematic diagram of an air injection system. 

The fuel is metered and pumped to the fuel valve by a camshaft driven fuel pump.
The fuel valve is opened by means of a mechanical linkage operated by the camshaft which controls the timing of injection.
The fuel valve is also connected to a high pressure air line fed by a multi-stage compressor which supplies air at a pressure of about 60 to 70 bar.

Advantages of air injection system:

 

The main advantage of the air injection system is the good atomization obtained.

1.        A high mep can be attained as rapid combustion results due to good mixing of fuel and air.
2.        Heavy and viscous fuels, which are cheaper, can also be injected.
3.        The fuel pump is required to develop only a small pressure.

 Disadvantages of air injection system:

1.It require a high pressure multi-stage compressor .

2.The large number of parts, the inter-cooler , etc.

3. make the system complicated and expensive.

4.A separate mechanical linkage is required to time the operation of the fuel valve.

5.Reduced bhp due to power loss in operating  the compressor and the linkage.

6.The fuel in the combustion chamber burns very near to the injection nozzle which many times leads sto overheating and burning of the valve and its seat.

 

Solid Injection System:

 

•      The commonly used types of Solid Injection system are:

•     Individual pump system: This consists of a separate metering and compression pump for each cylinder.

•   Common rail system: A single pump for compressing the fuel, plus a metering element for each cylinder.

Advantages of CRS(common rail system)

•     It increases fuel economy.

•     It lowers emission.

•     It delivers less noisy operation.
•     The system can be easily integrated in wide variety of  engines.
•     It is relatively simple in construction & needs less maintenance.