Why Turbine Engines Are Better Than Reciprocating Engines?

Turbine Engines are also known as Turboshaft Engines. The age of Turbine engines started in 1951 when Charles H. Kaman, an American aeronautical engineer developed a new kind of engine for his K-225 Helicopter. This engine was later known as the Turboshaft Engine. Consequently, the K-225 helicopter became the first helicopter powered by a turboshaft engine.

In the first half of the 20th century, major improvements were done in fuels and the efficiency of engines. This led to the infrastructural development in the aviation world, mainly in helicopters. In the second half, improvements were done mainly to produce faster, bigger, and more powerful engines.

Design Analysis of Turbine Engines

A turbine engine consists of three main parts.

  1. Combustion Section
  2. Compressor Unit
  3. A Turbine (or a set of turbines)

Every turbine engine has these three components. The combustion section and compressor unit are collectively known as Gas Generator Section. This gas generator section creates the input for the turbines i.e. hot expanding gases.

In most advanced engines, the gas generator section (combustion section + compressor unit) and turbine are physically separated from each other. The reason for this is to let these units move freely at different speeds. This type of design is known as Free Turbine Turboshaft.

Free Turbine Turboshaft model can be very useful in vehicles than the current reciprocating model of engines as it can minimize the heavyweight and cost overheads of transmission and clutch-system.

In the figure shown below, Combustion Section is represented by red color, the Compressor Unit by cyan, and the Turbine is shown by a purple color. Image Source: NASA

Turbine Engine
Turbine Engine Demonstration

Working Principle

Turbine engines are of different types for example

  1. Turbojet Engines: the ones used in jets and rockets.
  2. Turbofan Engine: the ones used in airplanes.
  3. Turboshaft Engine: the ones used in helicopters.

The working of these types is similar up to some extent but still, they have some distinguishable features.

The animation below shows how a turbine engine runs. Image Source : Nasa

Turbine Engines Animation
Turbine Engine Animation

The air in the turbine engine goes through 4 stages. Intake, Compress, Power Generation, and Exhaust. Let’s discuss each of these stages in detail.

Intake, Compress, Generate Power, Exhaust

1. A Large Amount of air is drawn from the surroundings and is brought into the engine inlet. This stage is also widely known as Intake Stage. These inlets are of different shapes and sizes as per the needs of the airplane/jet.

2. At the backside of the inlet, there is a compressor. The main function of the compressor is to compress the air and increase the air pressure. This compression is achieved by a series/rows of airfoils, with each row contributing to the net increase in air pressure. When the air leaves the compressor, it has much more pressure than it had, when it entered the inlet. This stage is also known as Compress Stage.

Turboshaft Engine Diagram
A Turboshaft Engine

3. After leaving the compressor, the compressed air now becomes the input for the Burner. In the burner, this compressed air is mixed with a small amount of fuel and ignited. This stage is Power Generation Stage.

4. When the hot exhaust leaves the burner, it is then passed through a turbine. The turbine here works similarly to a windmill. In turbojet and turbofan engines, the turbines use a very small part of the exhaust power and use the major part of the power to create the thrust.

Whereas, in turboshaft engines, the turbine is connected to a rotor shaft, which uses the majority of power as no thrust is needed in turboshaft engines. This stage is the Exhaust stage.

Reasons Why Turbine Engines Are Better

1. High Power Output

Turbine Engines provide greater power than reciprocating engines. This is the reason why many military helicopters and utility helicopters use turbine engines. However, turbine engines cost a bit expensive and are costly to maintain. Therefore, smaller and lesser expensive helicopters use reciprocating engines.

Robinson R44 is an example of helicopter which is powered by a reciprocating engine.

2. Lesser Vibrations

The turbine engines produce very less vibrations during flight. As a result, turbine engines account for greater reliability and comfort during the flight.

In reciprocating engines, the vibrations are very high, which spoils the smoothness of the flight and also contributes to the wear and tear of the engine.

3. Small Size

Turboshaft Engines are more compact in size as compared to the legacy piston engines/ reciprocating engines. Smaller size means that less space is required for the engine and therefore the overall size of the aircraft can be reduced as per the needs.

Helicopters with smaller sizes are easier to land and easier to maintain when used for personal use.

4. Lightweight

Lightweight with compact size and a large amount of horsepower is an obvious advantage of the turbine engines. Due to this, turbine engines are used in helicopters, ships, tanks, etc.

Lower weight penalty and increased power in turbine engines increase the payload capacity of the Helicopter. The lightweight of the aircraft also makes it easier to handle the aircraft during the flight.

5. Ease Of Operation

Aircraft which use turbine engines are easier to operate and have fewer engine failures as compared to reciprocating engines.

Sometimes, while driving a car, due to minor failure in the engine, the engine stops working and the car shuts down. Suppose, if same engine failure happens when you are in mid-air, even for 1-2 seconds. Nightmare!

That could be fatal and led to a possible aircraft crash. This thing never happens with the turbine engines. So this is one of the main reasons why turbine engines are more useful.

6. Reliable

Turbine Engines are more reliable than reciprocating engines. Turbine engines are less prone to engine breakouts and the functioning of the engine is very smooth. The reason for this is the 98% to 100% combustion efficiency of the engine.

At sea level take-off conditions, the combustion efficiency is close to 100% and it decreases non-linearly as the altitude increases. So, a pilot tends to be happier when flying a turbine-powered helicopter rather than a helicopter with a reciprocating engine. ­čśü

For these reasons, it seems obvious that these turbine engines are much better than reciprocating/piston engines. But, this does not mean that reciprocating engines are inefficient and poor in performance. They have their own advantages and functions which may or may not be achieved by turbine engines.

To learn more about engines and machines, read articles @FlyingMack

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