Objective: To give a brief introduction to aero engines.
Desired Learning Outcomes:
1. Understand the origin of aero engine.
2. Analyse (broadly outlined) types of engines.
3. Revise basic Gas laws.
4. Understand the derivation of chemically correct mixture.
History of Engine
1. The industrial revolution, which took place in the late eighteenth century and continued into part of the twentieth century, was largely a result of the ability of human beings to find ways of using energy sources to develop power. Development of the internal-combustion engine took place largely during the nineteenth century. A French inventor named Jean Lenoir built the first practical gas engine in 1860. However, the first four-stroke-cycle engine was built by August Otto and Eugen Langen of Germany in 1876. Otto and Langen also built a two-stroke cycle engine. The first truly successful gasoline engine, operating according to the four stroke-cycle principle, was built in Germany in 1885 by Daimler, who had previously been associated with Otto and Langen. Karl Benz of Germany built a similar gasoline engine in the same year. The Daimler and Benz engines were used in early automobiles, and the engines used today are similar in many respects to the Daimler and Benz engines.
... piston engine is called a four stroke cycle. These strokes are: 1. The Intake Stroke also called Induction Stroke 2. The Compression Stroke 3. The Combustion Stroke, also ... auto-engine thus marked the dawn of the automotive era in the world. Most cars in Europe began to be built by ... hand in the early 1900s. As the auto-engine improved, the automobile industry also ...
2. The first powered flight in an airplane was made by the Wright brothers on December 17, 1903; it is safe to say that the first successful gasoline engine for an airplane was the engine used in the Wright plane(fig 1-1).
It was a four cylinder, water-cooled, 12 horsepower engine producing ignition by means of a high-tension magneto.
Types of Energies
3. Energy is the capacity for doing work. There are mainly two types of energies: kinetic and potential. Kinetic energy is the energy of motion, such as, that possessed by a moving cannon ball, falling water or a strong wind. Potential energy or stored energy, is the energy of position. A coiled spring has potential energy. Likewise, the water held by the dam of a reservoir has potential energy and gasoline has potential energy.
Law of Conservation of Energy
4. This law state “Energy can neither be created nor can it be destroyed.” But, energy can be transformed from one form to another to carry out useful work. For example, heat energy can be transformed into mechanical energy, mechanical energy can be transformed into electrical energy, and electrical energy can be transformed into heat, light or mechanical energy.
5. An engine is a device which coverts chemical energy of fuel into heat energy. Subsequently this heat energy is converted into mechanical energy to get useful work done. There are basically two main types of heat engines: –
(a) Internal combustion engines.
(b) External combustion engines.
Internal Combustion Engine
6. In the internal combustion engine, the transformation of chemical energy into thermal energy and then thermal energy into mechanical energy takes place within the engine cylinder, where hot expanding gases act directly on the piston.
Types of Internal Combustion Engines
... either case, because the combustion takes place within it, the engine is called an internal-combustion engine. Modern transportation relies heavily upon internal-combustion engines. All airplanes and ... the fuel is converted to useful power. Most of the energy becomes heat that must be removed by a cooling system. Usually ...
7. Internal combustion engines are sub-divided into three categories:-
(a) Reciprocating Engines.
(i) Petrol engine
(ii) Diesel engine
(b) Rotary Engines.
(i) Turbo jet
(ii) Turbo fan
(iii) Turbo prop
(c) Direct Engines.
(i) Ram jet
(ii) Pulse jet
(iii) Rocket engines
External Combustion Engine
8. External combustion engine (fig 1-8) is also known as steam engine in which the conversion of chemical energy into thermal energy and subsequently into mechanical energy takes place in separate chambers.
Internal Vs External Combustion Engine
9. Separate chambers in external combustion engine results in having greater volume and greater weight as compared to internal combustion engine. This engine also has lower efficiency as compared to internal combustion engine. Due to these reasons, this class of engine is not used for aircraft propulsion. On the other hand high efficiency, absence of auxiliary parts like furnaces, boilers and condensers, make the internal combustion engine light, more compact and reliable, making it suitable for propulsion of aircraft.
Requirements of Aero Engines
10. The following are the requirements of aero engines:-
(a) Low specific fuel consumption
(b) Lesser weight.
(c) High Thrust /Power to weight ratio.
(d) Capability to operate at high altitudes.