We continue to develop resources related to the COVID-19 pandemic. See COVID-19 initiatives on Appropedia for more information.
Comparison of motors
This article compares motors, primarily on their efficiency and usability in a given location.
Comparison of the engine types
|Type||Efficiency||Fabrication requirements||Difficulty of production||Durability||Difficulty of repair||Production cost|
|Engines using a (modestly) heated/compressed liquid (ie water)|
|Piston steam engine||15%?||?||?||??||?|
|Steam turbine (bladed rotor)||35%||?||?||??||?|
|Steam turbine (Tesla)||40%||?||?||??||?|
|Engines using a (cold) compressed gas (ie expanding air, wind, ...)|
|Compressed air engine||26%||?||?||??||?|
|Bladed rotor (wind harvester or solar heat harvester)||42-48%||?||?||??||?|
|Engines using a modestly heated (non-deflagrative) gas (ie air, nitrogen, ...)|
|Stirling engine||upto 40%||?||?||??||?|
|Engines using a very hot (deflagrative) liquid/gas (ie gasoline, hydrogen, ...)|
|Internal combustion engine (Otto)||30%||?||?||??||?|
|Internal combustion engine (Diesel)||35-50%||?||?||??||?|
|Engines using electricity|
|Electric engine (Brushed motor)||40-80%||?||?||??||?|
|Electric engine (Brushless motor)||85-90%||?||?||??||?|
|Electric engine (squirrelcage_rotor_induction_motor)||90%||?||?||??||?|
|Electric engine (Switched reluctance motor)||between 90 and 100%||?||?||??||?|
The appropriate use of the different engines
A lot of inefficient (fuel-burning) engines generally have very little efficiency and lose most energy in the form of heat. Ie internal combustion (IC) engines lose 70% of their energy in the form of heat, which makes them insuitable for tasks such as transport, ... In applications where this generated heat can be reused (ie for space heating), the 70% inefficiency can be recovered. This means that these engines are most suitable as a combined heat and power system, ie for use in greenhouses, ... The same is true with a multitude of different engines (see above).
Internal combustion engines can be fed using various fuels; ie diesel and petrol but also biofuels and wood gas. Fuels alternative from diesel and petrol reduce the efficieny of the system since energy is lost in the fuel production. For example, with wood gas, we find that we lose 25% efficiency (production is 75% efficient).
Thus, if ie IC-engines were to be used for inappropriate tasks as transport, the system will attain a efficiency of 3/4_X_30%= 22,5%. The production of the other fuels (ie pure plant oil, produced from waste vegetable oil) may be even less efficient. From an ecologic and a appropriate standpoint, these supplemental losses are irrelevant, and the system used for these inappropriate tasks will still be much more ecologic than by using diesel/petrol for the same tasks, simply because plants are already in the ecosystem where fossil oils are not. However, appropriately seen, we can never justify their use for inappropriate uses as transport, even if it is already better than their same use using fossil fuels.
- Steam turbine efficiency between 10-40%, efficiency calculated between fuel and energy produced by turbine (so including efficiency losses through extra conversion of heat to steam)
- When the efficiency is calculated between the energy in the steam and the turbine, it's a lot higher, upto some 70-80%
- 70 to 80% of Betz' law limit
- Extraction efficiency of the kinetic wind energy depends heavily on the size of the blades use, doubling the size quadrupels the kinetic energy extraction and vice versa, 42-48% extraction is the upper limit
- [http://www.sesusa.org/types.htm Working gas of Stirling engines is either air, nitrogen, helium or hydrogen
- [http://www.wbdg.org/resources/microturbines.php Efficiency of gas-powered turbines (microturbines)
- Gas turbine efficiency also depends on size (microturbines being less efficient), but primarily on the heat of the gas (not all heat can be extracted by the time the gas leaves the engine)
- The higher end of the efficiency range (30%) can only be attained using recuperated turbines, unrecuperated turbines are but 15% efficient
- To extract more heat (and increase efficiency), turbines with more sets of blades can be used (spaced at some end apart), and the tube guiding the heat can be elongated, the whole thus acting more like a "multi-stage unit"
- An additional method to extract more heat is to place the tube upwards (rather than horizontal ie as for jet-powered vehicles -a horizontal stance is only useful for propulsive purposes, not ie electricity generation)- and offcourse to burn a very limited amount of fuel, this would in effect make a fuel-powered updraft tower
- Efficiency range depends on the cycle (2 or 4-stroke) and the compression ratio. Large low-speed (2-stroke) diesel engines typically having a efficiency of 50%, medium/high speed 4-stroke stroke engines have a efficiency of 35%
- Effiency varies greatly under the load, at optimal speed, they can be as efficient as brushed motors
- The efficienct of both brushed and brushless motors differs greatly upon the design as well, the more poles the more efficient the engine is, the number of poles if often less with smaller motors
- http://www.gizmag.com/go/4936/ , http://www.cleanpowertechnologies.com/ , and http://www.guardian.co.uk/environment/2008/aug/27/alternativeenergy.energy : solution to reclaim energy from waste heat by means of liquid matter cooling; original design not efficient though (steam engine=15% efficient, stirling upto 40%)
- Marine IC engine liquid matter cooling with stirling engine