Aircraft and Energy Use
JOOSUNG J. LEE, STEPHEN P. LUKACHKO, and IAN A. WAITZ
Massachusetts Institute of Technology Cambridge, Massachusetts, United States
1. Introduction
2. Economic Growth, Demand, and Energy Use
3. Energy Use, Emissions, and Environmental Impact
4. Trends in Energy Use
5. Energy Consumption in an Aircraft System
6. Historical Trends in Technological and Operational Performance
7. Technological and Operational Outlook for Reduced Energy Use in Large Commercial Aircraft
8. Industry Characteristics, Economic Impacts, and Barriers to Technology Uptake
Glossary
bypass ratio The ratio of air passed through the fan system to that passed through the engine core. contrail The condensation trail that forms when moist, high-temperature air in a jet exhaust, as it mixes with ambient cold air, condenses into particles in the atmosphere and saturation occurs. drag The aerodynamic force on an aircraft body; acts against the direction of aircraft motion. energy intensity (EI) A measure of aircraft fuel economy on a passenger-kilometer basis; denoted by energy used per unit of mobility provided (e. g., fuel consumption per passenger-kilometer)
energy use (EU) A measure of aircraft fuel economy on a seat-kilometer basis (e. g., fuel consumption per seat - kilometer).
great circle distance The minimum distance between two points on the surface of a sphere. hub-and-spoke system Feeding smaller capacity flights into a central hub where passengers connect with flights on larger aircraft that then fly to the final destination. lift-to-drag ratio (L/D) A measure of aerodynamic efficiency; the ratio of lift force generated to drag experienced by the aircraft.
load factor The fraction of passengers per available seats. radiative forcing A measure of the change in Earth’s radiative balance associated with atmospheric changes;
positive forcing indicates a net warming tendency relative to preindustrial times. structural efficiency (OEW/MTOW) The ratio of aircraft operating empty weight (OEW) to maximum takeoff weight (MTOW); a measure of the weight of the aircraft structure relative to the weight it can carry (combined weights of structure plus payload plus fuel). thrust A force that is produced by engines and propels the aircraft.
thrust specific fuel consumption (SFC) A measure of engine efficiency as denoted by the rate of fuel consumption per unit thrust (e. g., kilograms/second/Newton). turbofan engine The dominant mode of propulsion for commercial aircraft today; a turbofan engine derives its thrust primarily by passing air through a large fan system driven by the engine core.
An aircraft is composed of systems that convert fuel energy to mechanical energy in order to perform work—the movement of people and cargo. This article describes how aircraft technology and operations relate to energy use. Historical trends and future outlook for aircraft performance, energy use, and environmental impacts are discussed. Economic characteristics of aircraft systems as they relate to energy use are also presented.
1. INTRODUCTION
The first powered passenger aircraft were developed at the turn of the 20th century. Since then, there has been rapid growth in aviation as a form of mobility and consequently significant growth in energy use. In 2002, aviation accounted for 3 trillion revenue passenger-kilometers (RPKs), or approximately 10% of world RPKs traveled on all transportation modes and 40% of the value of world freight shipments. Among all modes of transport, demand for air travel has grown fastest. If, as expected, strong growth in
air travel demand continues, aviation will become the dominant mode of transportation, perhaps surpassing the mobility provided by automobiles within a century. This evolution of transportation demand also suggests an increase in per-person energy use for transportation. Minimizing energy use has always been a fundamental design goal for commercial aircraft. However, the growth of air transportation renders ever-increasing pressures for improvements in technology and operational efficiency to limit environmental impacts.
In the analysis presented here, trends in aviation transportation demand, energy use, and associated environmental impacts are examined (Sections 2-4). In Sections 5 and 6, aircraft systems from an energy conversion perspective are introduced and key performance parameters of aircraft technology and operation are discussed. A technology and operational outlook for reduced aircraft energy use is presented in Section 7, followed by a summary of industry characteristics and economic impacts that affect energy use of individual aircraft and the fleet as a whole in Section 8.
