ENERGY CONSUMPTION IN AN AIRCRAFT SYSTEM
Energy intensity can be related to specific measures of technological and operational efficiency in the air transportation system. The rest of this article takes a more detailed look at trends in these efficiencies and
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options for controlling energy use. The first step is a simplified description of the energy conversion within an aircraft engine. An aircraft engine converts the flow of chemical energy contained in aviation fuel and the air drawn into the engine into power (thrust multiplied by flight speed). Overall engine efficiency is defined by the ratio of power to total fuel energy
flow rate. Only one-fourth to one-third of fuel energy is used to overcome drag and thus propel the aircraft. The remaining energy is expelled as waste heat in the engine exhaust. A parameter that is closely related to the overall engine efficiency is the specific fuel consumption (SFC). When judging the efficiency of an aircraft system, however, it is more relevant to
consider work in terms of passengers or payload carried per unit distance. Energy intensity is an appropriate measure when comparing efficiency and environmental impact to other modes. Ei consists of two components—energy use, EU, and load factor, a, as described by Eq. (1). Energy use is energy consumed by the aircraft per seat per unit distance traversed and is determined by aircraft technology parameters, including engine efficiency. EU observed in actual aircraft operations reflects operational inefficiencies such as ground delays and airborne holding. The fleet average EU is of interest because it is the fleet fuel efficiency that determines the total energy use. Load factor is a measure of how efficiently aircraft seats are filled and aircraft kilometers are utilized for revenue-generating purposes. increasing load factor leads to improved fuel consumption on a passenger-kilometer basis.
MJ = MJ, RPK = Eu I RPK ASK=ASK a ’ 1 1
of seats.
