THE ABC OF THE GAS TURBINE

[Music] [Applause] [Music] let's suppose you lived at the time when the steam engine was the main source of power for turning the shafts and wheels of industry and transportation in power generating plants and in railroad locomotives the heat energy from the burning fuel is converted into mechanical energy by using the expanding power of steam to drive a piston and rod the back-and-forth or reciprocating motion is converted to rotary motion by linking the piston rod to an off-center point on the flywheel the cranking action thus produces rotary motion for turning shafts and wheels rotary motion can also be produced by taking the steam right out of the boiler putting it through a nozzle to increase its velocity and directing it against blades on a wheel thus converting heat energy into mechanical energy so the steam turbine was born it provided instant direct rotary motion this is an external combustion engine with the fuel burned outside the part where the output power is produced gasoline and diesel engines are internal combustion engines with the fuel burning inside their crank linkages convert the reciprocating piston action to rotary shaft motion internal combustion can be combined with direct rotary motion it is done by taking a combustion chamber burning fuel in it and directing the hot expanding gasses onto blades on a wheel converting the heat energy into mechanical energy a gas turbine the turbine shaft turns a compressor a bladed wheel air pump that supplies the large quantity of the engine uses in developing its power or thrust as in a piston engine the process begins with the intake of air then compression power and exhaust in the gas turbine they all occur continuously this compressor is a centrifugal type the rotor takes in outside air at the center and throws it outward giving it velocity and energy a diffuser converts this energy to increased pressure for use in the combustion process some engines use an axial flow compressor the air is drawn in parallel to the axis of the shaft usually through stationary guide vanes two blades on a rotating wheel the rotating blades like those on an ordinary fan accelerate the air adding energy and velocity to it the compressor also has stationary blades they decrease the airs velocity raising its pressure axial type compressors usually have several stages they add more pressure to the air which is then directed into the combustion chamber a fuel nozzle sprays the fuel usually a kerosene type into the chamber when the engine is first started a spark plug fires igniting the fuel which then burns continuously supplying gases to the turbine at a temperature as high as 2500 degrees Fahrenheit there may be one combustion chamber or two or more equally spaced about the shaft the engines turbine wheels are usually of the axial type they may be single stage with stationary guide vanes and one rotating wheel or multistage with stationary guide vanes between them because shaft speed may be as high as 50,000 revolutions per minute the blades and wheels must be made of special heat-resistant and high tensile strength alloys this simple way of converting heat energy into rotary mechanical energy with only one moving part basically provides smooth action that is virtually free of vibration the gas turbine has many useful applications for example if you taper the exhaust pipe so that it acts like a nozzle and speeds up the velocity of the gases you have a turbojet engine for airplanes the turbine extracts only enough energy to drive the compressor and accessories leaving as much energy in the gas as possible to utilize for thrust turbojet components are easily recognized compressor combustion chambers and turbine and tail pipe together they provide the thrust that drives the airplane the thrust does not come from pushing against the outside air behind the engine thrust is developed inside the engine for a somewhat simplified explanation of what happens take a balloon when you let it go it flies by jet action or rather by reaction as you know if you hold the stem closed nothing happens in this case the air inside is pressing with equal force on all sides in all directions the pressure force at any point is offset by the pressure force on the opposite side but when you let the air escape the pressure and the force at that point decreases to less than the pressure force on the opposite side the result is an unbalanced force that pushes the balloon on the inside misting it forward and that's the jet principle in an engine then it's the pressure force of the gas inside the engine that sets up a reaction that sends the engine and the airplane forward the same principle holds for rocket engines they can operate in outer space where there is no and therefore nothing for the exhaust gases to push against it's the reaction of the gas pressure forces inside that does it reaction also makes a thrust reverser work on a turbojet engine when the plane is touched down the reverser is moved so that it deflects the exhaust gasses reversing their direction the thrust now opposes the forward motion of the airplane and slows it down not only saving the brakes but also providing additional safety on slippery runways some turbo jets are equipped with an afterburner that provides extra thrust for short periods when fuel is injected it combines with the unused oxygen in the exhaust the extra burning increases the exhaust gas temperature and velocity substantially increasing the energy and the thrust the pan jet is a turbojet with modifications the compressor has a set of fan blades that take the incoming air and that increased pressure drive some of it out through an opening surrounding the engine the nozzle shape of the opening increases the velocity of the air and reactive thrust is produced a second turbine is added to the engine to drive this fan in the remainder of the incoming air the pressure is increased even higher by the compressors other set of blades the air then flows into the combustion chambers through both sets of turbines and the jet action produces additional thrust more of the engines total thrust is supplied by the fan than by the exhaust gases and overall efficiency is higher than in a standard turbojet another modification as the gas turbine combined with a propeller producing the turboprop engine its turbine extracts a much greater portion of the energy from the gas to drive the compressor accessories and propeller the engine incorporates a gear train that reduces the high speed of the turbine shaft to the relatively low speed of the propeller which produces most of the thrust turboprop engines are well suited for long-range flights at moderate air speeds gas turbines can also be used to drive the rotor system of a helicopter the design is usually called a turbo shaft engine other versions of the turbo shaft are rapidly-growing sources of power in industry in highway trucks and buses electric power generators boats and heavy duty mining and oil field equipment the engine in each of these examples is compact efficient and relatively quiet it has certain features that contribute to superior performance let's examine them the basic components are the usual compressor combustion chamber and turbine this system is called the gas generator in addition there is a separate power turbine or free turbine driven by the gases leaving the gas generator system a speed reduction gear drives the load shaft the engine also has a power transfer feature a gear hydraulic clutch and torque control this mechanism connects the two turbines improves the engines operating efficiency and provides a braking action in vehicles for increased safety the clutch can be operated partially engaged that is with slippage or fully engaged providing transfer of mechanical energy from the gas generator to the load the torque control responds to load changes and adjusts the clutch settings for maximum efficiency in the braking action the clutch is fully engaged so that the energy that the vehicle puts into the shaft is absorbed by the gas generator system the engines operating efficiency is also heightened by a regenerator or heat exchanger it is a rotating flat disc of porous steel the exhaust gases pass through it and give up a good part of their heat to the disk eat that would otherwise be wasted in the exhaust gas the compressor discharge air also flows through the disc rotation moves the heated portion into the path of the incoming compressed air preheating it this conservation of heat reduces the amount of fuel burned and thus improves fuel economy the fuel consumed by a regenerative turbine is much less than that used by a non regenerative turbine of the same power the engines components include a starter motor driven by a battery that is kept charged by an alternator a high voltage coil for the spark a fuel pump supplying fuel to the nozzles a fuel control for scheduling the proper amount of fuel to the engine an air pump supplying compressed air to the nozzles for amaizing the fuel sprayed into the chamber a torque control that controls the power transfer system a control system that provides protection against exceeding engine limits a pump to supply oil to the engine shaft bearings and an engine oil cooler of the radiator type this industrial type gas turbine engine is in the 300 to 800 horsepower size class it is of symmetrical design with a single combustion chamber and two regenerators for maximum recovery of the turbine waste heat air enters the intake is compressed by the compressor preheated as it passes through the regenerator and supports combustion of the fuel sprayed into the combustion chamber the hot expanding gases give up most of their energy to the gas generator and power turbines and give up some of their remaining heat to the regenerator and flow out of the exhaust the gas turbine is making great strides as a versatile power source it's many advantages in simplicity durability light weight in pounds per horsepower output freedom from vibrations and it's very low exhaust emissions and thus low pollution account for the growth and the importance of the gas turbine engines