AIRCRAFT PROPULSION : RAMJET ENGINE

Gas turbines are particularly suited for aircraft propulsion because they are light and compact and have a high power-to-weight ratio. Aircraft gas turbines operate on an open cycle called "Jet propulsion Cycle", as explained below . It can be of turbojet, turbofan or turboprop type.

RAMJET ENGINE :

A particularly simple type of engine known as ramjet engine requires neither a compressor or a turbine. A sufficient pressure rise is obtained by decelerating the high speed incoming air in the diffuser (ram effect) on being rammed against a barrier. For the ramjet to operate , the aircraft must already be in flight at a sufficiently great speed. The combustion products existing the combustor are expanded through a nozzle to produce the thrust.

In each of the engines mentioned so far, combustion of the fuel is supported by air brought into the engines from the atmosphere. For very high altitude flights and space travel, where this is no longer possible, rockets may be employed. In a rocket , both fuel and an oxidizer ( such as a liquid oxygen ) are carried on board of the craft. High pressure combustion gases are expanded in a nozzle. The gases leave the rocket at very high velocities, producing the thrust to propel the rocket.

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Advantages And Disadvantages Of Air Refrigeration System :

Advantages Of Air Refrigeration : 1. The refrigerant used namely air is cheap and easily available. 2. There is no danger of fire or toxic effects due to leakages. 3. The weight to ton of refrigeration ratio is less as compared to other systems. Disadvantages Of Air Refrigeration : 1. The quantity of Refrigerant used per ton of refrigeration is high as compared to other systems. 2. The COP of the system is very low. Therefore running cost is high. 3. The danger of frosting at the expander valves is more as the air contains moisture content.

ELECTRICAL COMPARATORS AND ITS WORKING

Electrical Comparators are used as a means of detecting and amplifying small movements of a work contacting elements. An electrical comparator consists essentially of a pick-up head or transducer for converting a displacement into a corresponding change in current and a meter or recorder connected in the circuit to indicate the electrical change, calibrated to show in terms of displacement. Generally, an amplifier is needed to provide the requisite sensitivity and to match the characteristics of different parts of the circuit. Electrical comparators can be classified according to the electrical principle used in the pick-up head. Most of the comparators use either a differential transformer, an inductance bridge, a strain gauge or a capacitor as a means of detecting movement of the gauging element. There are different types of electrical comparators. One kind called an electrolimit gauge is used to check or measure the outside diameter of a roll. The objec...

THROTTLE GOVERNING OF STEAM TURBINES

Steam Pressure at inlet to a steam turbine is reduced by throttling process to maintain the speed of the turbine constant at part load and hence this method of governing is called "Throttle Governing". Construction : Throttle governing system consists of a centrifugal governor, a lever , an oil pump , a pilot piston , control valve , a relay piston and a throttle valve. The throttle valve is moved by a relay piston. The relay piston is actuated by pilot piston control valve. There are two piston valves covering ports in the pilot piston control valve without any overlap. These piston valves are operated by lubricating oil supplied by a gear pump at 2 to 4 bar. The oil returns to the drain from this chamber. Working : When the turbine works on full rated load, the throttle valve will remain open. When the load is decreased, the energy output of the turbine becomes in excess and the turbine shaft speed increases. Hence, governor sleeve will lift. The upward movemen...

Mechinopedia For Mechanical Engineers

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