Efficiency

Any discussion of energy whether it be of fuels, alternative sources such as solar or Hydrogen, or an engine, which is a device that transforms energy into power or work, needs to include a simple yet thorough explanation of efficiency. This topic is important because it relates the costs of equipment, fuel, and power produced. For example, if a device or a system of devices has a low efficiency then the cost of the fuel to provide power must be very inexpensive because the system would require a great deal of fuel to produce a given amount of power.

In the examples, if one injected 5Kw (5*3412btu* 5) worth of fuel and the engine is 20% efficient you would receive 1/5ofthe amount of fuel in power out of the system or 1Kw. Conversely, if you wanted to get 10Kw of power out of the system and the engine were 33% efficient you would need (10Kw*3412Btu*3) of fuel to get 10Kw out of it.

5Kw --à  20%  -à 1Kw -----1/5

5Kw-  à 33%   -à1.6Kw----1/3

10Kw  ß 33%  ß  30Kw-----300%

In any energy conversion system all the energy must be accounted for either as converted to power or wasted unused in some manner.

If the fuel is inexpensive and the system is inefficient then one needs a large amount a of fuel input as heat and there is also a large amount of waste. As the price for the fuel or the price for the equipment becomes more expensive so does the price for power. These relationships are true for every engine, fuel or power source.

Most thermal cycle fall under one of two descriptions: OPEN or CLOSED.

OPEN SYSTEMS inject a working fluid under pressure either air or water as steam into a device, which converts this fluid to cause a piston into rotary or linear motion. When the working fluid has finished its work, it is ejected into the to the atmosphere as waste heat. CLOSED SYSTEMS operate similarly except that the working fluid is not ejected into the atmosphere. Instead, the heat left in the working fluid is taken out after it finishes its work. Upon exiting the turbine or engine the fluid is passed over a cooling coil, which caused the fluid to condense and then precipitate as a liquid. Compressors and pumps return the fluid to a boiler for reheating to the gaseous /pressurized state.

The efficiency of these systems relies, to a certain degree, on the efficiencies of its component parts:

1-      The efficiency of the system to convert the fuel to heat.

2-    The efficiency of the system to accept the heat and convert its working fluid to a pressurized fluid ready to do work.

3-  The efficiency of the conversion device-reciprocating engine or turbine to convert the energized/pressurized fluid to work …motion and then to power or electricity.

These efficiencies are usually determined by the relationship between the engines hot side and its cool side. This relationship is usually called its Carnot efficiency and is defined by the following equation:

                H₁-C₁   = Efficiency

                  H₁

By definition, this usually applies to engines that have air as a working fluid which are usually OPEN system. We also apply this number to closed systems that use steam as working fluid. The temperatures that are used are either Rankine degrees or degrees Kelvin these two temperature measurements are referred to as absolute temperatures. They are calculated as follows:

     Degrees Rankine= 459+ temperature in degrees Fahrenheit

     Degrees Kelvin= 273+ temperature in degrees Celsius