What is a Sterling Engine?

The Stirling engine was invented by British physicist Robart Sterling in 1816, so it was named "Stirling engine". The Stirling engine outputs power through a cycle of cooling, compression, heat absorption, and expansion in the working medium (hydrogen or helium) in the cylinder, so it is also called a hot gas engine. The Stirling engine is an external combustion engine, and its effective efficiency is generally between gasoline and diesel engines.

In 1816, the Rev. Robert Stirling of London proposed the concept of a piston-type hot gas engine and a Stirling engine, which is an externally heated closed-cycle engine. This cycle consists of two isothermal processes and two constant volume regenerative processes, which belong to one of the generalized Carnot cycles. The key to achieving the Stirling cycle is to achieve heat recovery. The heat engine conceived by Sterling consists of two cylinder-piston clamps and a regenerative regenerator. The working principle of the refrigeration process is as follows:

Compared with internal combustion engines, hot air engines have the advantages:

1. Suitable for all kinds of energy. Whether it is liquid, gaseous or solid fuel, when using a heat carrier system (such as a heat pipe) for indirect heating, almost any high temperature heat source can be used, such as biomass energy (wood fire, etc.), and the engine itself (except the heater ) No need to make any changes at the same time, the hot air engine does not need a compressor to pressurize, using a general fan can meet the requirements, and allows the fuel to have a higher impurity content; solar energy, which is one of the more common uses of Stirling engines; radioisotopes , Common in submarine, deep space

1. High requirements for materials. The maximum gas temperature of the internal combustion engine is much higher than Stirling, but the internal combustion engine relies on heat dissipation to control the temperature of the cylinder at about 90 degrees, while the heater and expansion cavity of the Stirling engine need to be kept at a higher temperature for a long time. Higher requirements are placed on the materials.

2. Large heat loss. It is also because of the high temperature maintained for a long time, which causes a lot of heat to be lost through direct transfer and heat radiation. Therefore, a series of measures need to be taken to reduce heat loss, such as making the piston into a hollow structure, and setting multiple "thermal barriers" inside.

3. Large volume. This is caused by a series of measures to reduce heat loss, to be insulated,

The designed and manufactured hot air machine has various structures and can use various energy sources, and has been applied in various fields such as aerospace, land, water and underwater. The power transmission mechanism of the test hot gas engine is divided into crank-link transmission, diamond transmission, swash plate or wobble plate transmission, hydraulic transmission and free piston transmission. Successful examples include the civil 25KW external combustion engine of the American STM Company and the Stirling engine used by the Japanese pro-tidal submarine, and the Chinese submarine also has a self-developed and mature Stirling engine. The future development of hot air engines will use more new materials (such as ceramics), which can further increase the heater temperature, and the theoretical effective efficiency can be increased to 42%. The Stirling engine has been reported that it has begun to use it on the cooling fan of the computer motherboard. The heat of the Northbridge chip is used to drive the Stirling engine to cool the hardware. The research is still in the research stage. ^[2]

With the increasingly severe global energy and environmental protection situation, the Stirling engine has been paid more and more attention due to its extensive adaptability to a variety of energy sources and excellent environmental characteristics.It is used in underwater power, solar power, space station power, and heat pump air conditioners. Power, vehicle hybrid propulsion and other aspects have received extensive research and attention, and have been successfully applied. The three directions for Stirling machine promotion include:

(1) Small-scale distributed cogeneration system: The Stirling engine can be applied to cogeneration systems based on its characteristics. The cogeneration system is divided into small distributed cogeneration systems and large cogeneration systems based on thermal power plants. The small distributed cogeneration system has the characteristics of equipment miniaturization and fuel diversification. The small-scale distributed cogeneration system is mainly composed of a power unit, a heating device and other auxiliary devices. The power unit is the core component of the entire system. Natural gas first enters the burner for combustion. The high-temperature flue gas generated is first used to heat the high-temperature hot cavity (area) of the engine, and then exchanges heat with the heat exchanger to obtain hot water flowing into the storage tank as domestic hot water. Exhaust from the exhaust pipe. At the same time, the low temperature cold chamber (zone) of the cold water-cooled engine is also heated to obtain hot water. The working fluid circulates between the high-temperature hot cavity and the low-temperature cold cavity, pushing the piston to reciprocate to perform external work, driving the engine to generate electricity.

(2) Low-level waste heat recovery: The Stirling machine is also particularly suitable for recycling low-level waste heat, such as factory waste heat, geothermal heat, solar energy, etc., in order to obtain good energy-saving benefits.

(3) Mobile power source: After miniaturizing and lightweighting the Stirling engine, and improving its control performance, it can also be used as a power source for pushers, rollers, and even submarines. ^[2]