The widely accepted definition of an engine is a machine which converts energy into mechanical motion with the purpose of performing useful work. A turbine engine achieves this by converting the stored or potential energy in a flow of combustion gas into mechanical motion. This mechanical motion is achieved by directing the high pressure gases from the combustion of a fuel and air mixture over a set of turbine blades. These turbine blades are attached to a shaft which turns a set of compressor blades at the opposite or intake side of the engine to supply the compressed air for the combustion cycle. Within their arena of application turbine engines have several noteworthy benefits over conventional piston engines although there are some disadvantages.
The turbine engine, although strictly an internal combustion engine, is far simpler than its piston-operated counterpart in that it basically has only one major moving part in its power conversion section. An internal combustion piston engine has dozens of moving parts while a turbine engine has only a central shaft with a turbine at the exhaust end and a compressor fan at the intake end. A basic turbine engine functions by igniting a fuel/air mixture in a combustion chamber located towards the rear of the engine and directing the resultant high pressure combustion gas over a set of turbine blades. These blades are attached to a central shaft that runs the entire length of the engine structure. This shaft is fitted with a large set of compressor blades at the intake end which draw in and compress air into the combustion chamber to sustain the work cycle.
As long as the combustion process continues, the turbine section of the engine will turn the compressor which will continue to sustain the combustion cycle and so forth. The turbine engine generally operates at higher speeds than piston engines with a typical aircraft jet engine operating at approximately 10,000 revolutions per minute (RPM) and smaller micro turbines in the region of 100,000 RPM. The work done by a turbine engine may be derived from a direct connection to the central shaft or the thrust developed by the exhaust gas. Turbine engines have many different applications including aircraft propulsion, ships, helicopters, military tanks, and road vehicles.
The turbine engine has several distinct advantages over a reciprocating or piston engine. These include:
- Lower operating pressures
- Better performance at extreme altitudes
- Higher operational speeds
- Fewer operating parts
- Better lubrication characteristics
- High power to weight ratios
- Smaller physical dimensions for any given output
- Single axis of operation
- Low vibration characteristics
Some of the limitations and disadvantages of turbine engines include:
- Low efficiency at idle
- Slower power demand response
- Construction cost
- Longer start-up times