Stirling Engine – The Dream Pollution-Free Engine for Greener Tomorrow!

Ever dreamed of an engine totally free from pollution? Well, we’re not talking about low emission levels, but rather concept of a totally pollution-free engine! The vehicle manufacturers have been on the quest for developing engines with less vibration, high torque, high power, and most necessarily without any pollution ever since the invention of engine. One step ahead towards the objective of creating pollution-less engine is the development of Stirling engine.

Stirling engine is a heat engine, which is vastly different from an internal combustion engine. It makes use of a fixed quantity of gas packed within the cylinder. The gas expansion as well as contraction using the heat from an external source forms useful work. Using this kind of engine offers an advantage… i.e. it is capable of using any kind of emission and fuel without exhaust gases.
stirling engine
Parts of Stirling Engine

The different parts of this pollution less engine are listed below:

Main chamber: This is the compartment wherein a fixed quantity of gas gets packed at first. Only gas expansion or compression takes place within this chamber.

Output shaft: This horizontal shaft is mounted a few inches over main chamber that we saw above. The shaft end that is centered above this main chamber features a connecting rod and a crank to drive the displacer piston.

Displacer: The displacer is a large piston that is quite free in the cylinder. Thus air can travel effortlessly between the engine’s cooled and heated parts as this piston shifts downwards and upwards.

Power piston: The power piston is smaller when compared to the displacer and can be seen on the engine’s top. This firmly sealed piston shifts upwards as the sealed gas within the engine starts expanding.

Crankshaft: It is made of steel and moves via the bearing before receiving crank disc.

Regenerator: It is designed using a material that conducts heat readily and features a high surface region. When heated gas gets shifted to the cold cylinder, it first moves through the generator, wherein a part of heat is set down. When cooled-down gas is moved back, the heat is regained. As a result, the regenerator achieves its task of pre-cooling and pre-heating the working gas, thus drastically enhancing its efficiency.

Principle of Working

The principle of working of this pollution-less engine is that a fixed quantity of gas is sealed within the engine. There is a series of events involved in the Stirling cycle that changes the gas pressure within the engine, making it to function.

Stirling engine makes use of two cylinders, out of which one gets heated by an external source of heat, while the other gets cooled by an external source of cooling. A connection that decides how they will shift in relation to each other bonds the gas chambers of both these cylinders mechanically.

Stirling Cycle

The two pistons in the stirling engine create a 90-degree phase angle and 2 diverse temperature spaces. The working gas within the engine is sealed perfectly and cannot move in or out to the atmosphere. The engine uses a Stirling cycle, which is not like the cycles in the typical internal combustion engine. The way in which the Stirling cycle proceeds is explained below.

Expansion: During expansion, most of the gases in the system get driven into the hot cylinder, where it heats and expands. This pushes both the pistons inwards. Once the gas gets expanded, around 2/3rds of the gas is still placed in the hot cylinder. The flywheel momentum moves the crankshaft for the following 90 degrees, this shifting most of the gas to the cool cylinder.
Contraction: Following the expansion, the expanded gas is shifted to the cool cylinder, where it gets cooled and contracted, pulling both the pistons outwards. The contracted gas is now placed in the cool cylinder. The flywheel momentum shifts the crank to another 90 degrees, moving the gas back to the hot cylinder to finish the cycle.
Power is generated only during the first phase of cycle.

Types of Stirling Engines

Stirling engine can be classified into two types:
• Two piston type Stirling engine: This kind of engine makes use of 2 power pistons. Out of these two pistons, the first is a hot piston that is utilized in hot chamber, while the second is a cold piston that is utilized in cold chamber. The gap over the hot piston is heated by a source of heat always, while the gap over the cold piston is always cooled by cold air.

• Displacer type Stirling engine: This kind of engine utilizes a displacer and a power piston. The gap under the displacer piston is heated by a source of heat always, while the gap over the displacer piston is always cooled by cold air. This way, the displacer piston displaces cold air and hot air.


The offered advantages of a Stirling engine are listed below -

• Since the quantity of gas in the chamber is fixed, gases are not exhausted as in the case of the typical piston engines. This it turns out to be a pollution-less engine.
• Stirling engines operate quieter than the normal engines.
• The gas within the engine does not leave the engine.
• Combustion does not take place within the engine’s cylinder. Thus there is no explosion.
• The external source of heat can be anything.

Stirling engine exhibits a higher potential when compared to any other kind of engine today due to its ability to use any kind of fuel and its pollution-free nature. As a result, this is the most preferred engine in the automobile division, finding application from hybrid cars to submarines. Few of the recent applications are Stirling thermal motor, 4-piston wobble yoke machine, and 4 cylinders free piston Alpha engine.

On account of the wide range of advantages that it offers, this pollution-less engine gives a cutting-edge to the other types of engine in today’s world and proves to be a great solution for the present day energy crisis & global warming. But, it’d still take quite some time for this dream to turn into a reality.