The development of the Stirling engine started with the aim of being an alternative to the machine of value due to certain advantages that it had with respect to the then popular steam engine.
Over time, certain disadvantages compared to internal combustion engines have left the Stirling engine in the background.
Advantages of the Stirling engine compared to internal combustion engines
The main advantages of a Stirling engine compared to an Otto engine, a diesel engine or a steam engine are:
- The maintenance facility
- They are quieter engines
- Stirling engines offer better performance than alternative internal combustion engines.
- Greater fuel versatility.
Ease of maintenance. The Stirling engine is an external combustion engine, which means that the heat is transmitted to the working fluid through an exchanger; the absence of direct contact between the combustible gas mixture and all moving mechanical parts reduces the wear, the need for lubrication and the consequent maintenance of the Stirling engine.
Less noise. The Stirling engine also does not have valves or explosions, so it is constructively simpler. The vibrations generated are easier to control and much less noisy than an internal combustion engine.
Better performance The Stirling engine is the only one capable of approaching the theoretical maximum performance known as Carnot performance, in fact, it theoretically achieves it, so as far as thermal engine performance is concerned, it is the best option.
The Stirling engine offers a good response to low temperatures. This alternative engine works better with cold ambient temperatures, in contrast to internal combustion, which start easily in a warm temperature, but with problems in cold temperatures.
Fuel versatility. The Stirling engine can work with any source of heat, for example, burning wood, coal, gas, biogas, liquid fuels and even solar energy, nuclear energy: there are commercial examples that use some of the sources mentioned. By contrast, internal combustion engines are limited to the use of gasoline in the Otto engine, or diesel in the diesel engine.
Disadvantages of the Stirling engine compared to internal combustion engines
The main disadvantages of a Stirling engine compared to an alternative internal combustion engine are the following:
- Greater volume and greater weight
- Higher economic cost of the engine
- The Stirling engine have a slower start
- More dangerous
More voluminous and heavy. External combustion, which requires heat exchangers at both hot and cold points, makes the Stirling engine generally more bulky and heavier than a generic internal combustion engine with the same output power.
High cost. Stirling engines require inlet and outlet heat exchangers, which contain the high-temperature working fluid, and must withstand the corrosive effects of the heat source and the atmosphere. This involves the use of materials that significantly address the machine.
Slower start. The inherent thermal inertia of an external combustion engine makes it slower to start. For this reason the Stirling engine is not suitable for applications that require fast starts or rapid changes in speed.
More dangerous. The mixture of air and lubricating combustible fluids inside the engine can produce explosive mixtures due to the oxygen contained in the air, a danger that is accentuated in high-pressure engines. The problem was solved using reducing (hydrogen) or neutral (helium, nitrogen) working gases or without the use of conventional lubricants.
