This equation is used to calculate the input power of an engine used to drill for oil and gas.
Where
Thermal efficiency is the measure of the efficiency and completeness of combustion of the fuel, or, more specifically, the ratio of the out- put or work done by the working substance in the cylinder in a given time to the input or heat energy of the fuel supplied during the same time. Two kinds of thermal efficiency are generally con- sidered for an engine: indicated thermal efficiency and overall thermal efficiency. Since the work done by the gases in the cylinder is called indicated work, the thermal efficiency determined by its use is often called IN- DICATED THERMAL EFFICIENCY (ite). If all the potential heat in the fuel could be delivered as work, the thermal efficiency would be 100%. Because of the various losses, however, this per- cent is not possible in actual installations. If the amount of fuel injected is known, the total heat content of the injected fuel can be deter- mined from the heating value, or Btu per pound, of the fuel; and the thermal efficiencies for the engine can then be calculated. From the mechanical equivalent of heat (778 foot-pounds equal 1 Btu and 2545 Btu equal 1 hp-hr), the number of foot-pounds of work contained in the fuel can be computed. If the amount of fuel injected is measured over a period of time, the rate at which the heat is put into the engine can be converted into potential power. Then, if the ihp developed by the engine is calculated, as previously explained, the indicated thermal effi- ciency can be computed by the following expression: ite = hp × 2545 Btu per hr per hp Rate of heat input of fuel in Btu per hr × 100 For example, assume that the same engine used as an example in computing ihp consumes 360 pounds (approximately 50 gallons) of fuel per