The Stirling engine applications can be divided into three main categories:
- Mechanical propulsion
- Heating and cooling
- Power generation systems
A Stirling engine is a thermal engine that works by cyclic compression and expansion of air or other gas, the working fluid. During the Stirling cycle there is a net conversion of heat to mechanical work. The Stirling cycle engine also operates in reverse, using a mechanical energy input to drive the heat transfer in a reverse direction (ie, a heat pump or refrigerator).
Generation of electrical energy by a Stirling engine
There is a potential for Stirling nuclear propulsion engines in power generation plants. Replacing the steam turbines of nuclear power plants with Stirling engines could simplify the plant, produce greater efficiency and reduce radioactive byproducts. Several designs of breeder reactors use liquid sodium as a coolant. If the heat is to be used in a steam plant, a water / sodium heat exchanger is required, which generates some concern since sodium reacts violently with water. A Stirling engine eliminates the need for water in any part of the cycle. This would have advantages for nuclear facilities in dry regions.
The Stirling engine is located in the center of a parabolic mirror, a Stirling engine can convert solar energy into electricity with better efficiency than non-concentrated photovoltaic cells, and comparable to concentrated photovoltaics.
Combined heat and power
In a combined heat and power (CHP) system, mechanical or electrical energy is generated in the usual way, however, the residual heat emitted by the motor is used to supply a secondary heating application. This can be virtually anything that uses heat at a low temperature. It is often a pre-existing energy use, such as commercial space heating, residential water heating or an industrial process.
The thermal power plants in the electricity grid use fuel to produce electricity. However, there are large amounts of waste heat that are often not used. In other situations, the high quality fuel is burned at high temperature for a low temperature application. According to the second law of thermodynamics, a thermal engine can generate energy from this difference in temperature. In a CHP system, the high temperature primary heat enters the Stirling engine heater, then part of the energy is converted into mechanical energy in the engine and the rest goes to the cooler, where it comes out at low temperature. The "residual" heat actually comes from the main engine cooler, and possibly from other sources such as the burner exhaust, if there is one.
The power produced by the engine can be used to run an industrial or agricultural process, which in turn generates waste biomass waste that can be used as a free fuel for the engine, which reduces the costs of waste disposal. The general process can be efficient and profitable.
Motor Strirling for mechanical output and propulsion
It is often claimed that the Stirling engine has a too low power / weight ratio, too high a cost and too long starting time for automotive applications. They also have complex and expensive heat exchangers. A Stirling cooler should reject twice as much heat as an Otto engine or a diesel engine radiator.
The heater must be made of stainless steel, exotic alloy or ceramic to withstand high heating temperatures necessary for high power density, and to contain hydrogen gas that is often used in Stirling cars to maximize power. The main difficulties involved in the use of the Stirling engine in an automotive application are the starting time, the acceleration response, the shutdown time and the weight, which do not all have ready-made solutions.
Stirling engines may be theoretically promising as aviation engines, if high power density and low cost can be achieved. They are quieter, less polluting, gain efficiency with altitude due to lower ambient temperatures, are more reliable due to fewer parts and the absence of an ignition system, produce much less vibration (fuselages can last longer) and use safer and less explosive fuels. However, the Stirling engine often has a low power density compared to the commonly used Otto engine and the Brayton cycle gas turbine. This problem has been a source of discord in automobiles, and this performance characteristic is even more critical in aircraft engines.
Stirling engines as part of a hybrid electric drive system can avoid the design challenges or disadvantages of a non-hybrid Stirling car.
In November 2007, the Precer project in Sweden announced a prototype hybrid car with solid biofuel and a Stirling engine.
The Stirling engine could be suitable for submerged energy systems where electrical or mechanical work is required at an intermittent or continuous level. General Motors has carried out a considerable amount of work on advanced Stirling cycle engines that include thermal storage for subsea applications. United Stirling, in Malmo, Sweden, is developing an experimental four-cylinder engine that uses hydrogen peroxide as an oxidant in underwater power systems.
Stirling engines can drive pumps to move fluids such as water, air and gases. For example, Stirling Technology Inc.'s ST-5 output power of 5 horsepower (3.7 kW) that can operate a 3 kW generator or a centrifugal water pump.
Heating and cooling
If supplied with mechanical power, a Stirling engine can work in reverse as a heat pump for heating or cooling. In the late 1930s, the Philips Corporation of the Netherlands successfully used the Stirling cycle in cryogenic applications. The experiments have been carried out using wind energy driving a Stirling cycle heat pump for domestic heating and air conditioning.