Fuel efficiency in the context of Potential energy

Sustainable transport is transportation sustainable in terms of their social and environmental impacts. Components for evaluating sustainability include the particular vehicles used; the source of energy; and the infrastructure used to accommodate the transport (streets and roads, railways, airways, waterways and canals). Transportation sustainability is largely being measured by transportation system effectiveness and efficiency as well as the environmental and climate impacts of the system. Transport systems have significant impacts on the environment. In 2018, it contributed to around 20% of global CO₂ emissions. Greenhouse gas emissions from transport are increasing at a faster rate than any other energy using sector. A 2023 study published in Journal of Transport Geography found that shared electric bicycle systems reduce urban transport-related carbon emissions by about 108–120 grams per kilometre, particularly in non-central urban areas and when powered by low-carbon electricity sources.Road transport is also a major contributor to local air pollution and smog.

Sustainable transport systems make a positive contribution to the environmental, social and economic sustainability of the communities they serve. Transport systems exist to provide social and economic connections, and people quickly take up the opportunities offered by increased mobility, with poor households benefiting greatly from low carbon transport options. The advantages of increased mobility need to be weighed against the environmental, social and economic costs that transport systems pose. Short-term activity often promotes incremental improvement in fuel efficiency and vehicle emissions controls while long-term goals include migrating transportation from fossil-based energy to other alternatives such as renewable energy and use of other renewable resources. The entire life cycle of transport systems is subject to sustainability measurement and optimization.

The energy efficiency in transport is the useful travelled distance, of passengers, goods or any type of load; divided by the total energy put into the transport propulsion means. The energy input might be rendered in several different types depending on the type of propulsion, and normally such energy is presented in liquid fuels, electrical energy or food energy. The energy efficiency is also occasionally known as energy intensity. The inverse of the energy efficiency in transport is the energy consumption in transport.

Energy efficiency in transport is often described in terms of fuel consumption, fuel consumption being the reciprocal of fuel economy. Nonetheless, fuel consumption is linked with a means of propulsion which uses liquid fuels, whilst energy efficiency is applicable to any sort of propulsion. To avoid said confusion, and to be able to compare the energy efficiency in any type of vehicle, experts tend to measure the energy in the International System of Units, i.e., joules.

Air-breathing jet engines typically feature a rotating air compressor powered by a turbine, with the leftover power providing thrust through the propelling nozzle—this process is known as the Brayton thermodynamic cycle. Jet aircraft use such engines for long-distance travel. Early jet aircraft used turbojet engines that were relatively inefficient for subsonic flight. Most modern subsonic jet aircraft use more complex high-bypass turbofan engines. They give higher speed and greater fuel efficiency than piston and propeller aeroengines over long distances. A few air-breathing engines made for high-speed applications (ramjets and scramjets) use the ram effect of the vehicle's speed instead of a mechanical compressor.

Pair trawling is a fishing activity carried out by two boats, with one towing each warp (the towing cables). As the mouth of the net is kept open by the lateral pull of the individual vessels, otter boards are not required. With the towing power of two boats and no otter boards, a larger net may be worked than would otherwise be possible, or alternatively, the two boats can share increased fuel efficiency.

As doors are not necessary, the gear arrangements are simplified, with the warps attaching directly to the wings of the net. Setting and hauling of the nets are carried out by one boat, while the other is only used for towing; usually each will take turns at these operations.

A four-engined jet, sometimes called a quadjet, is a jet aircraft powered by four engines. The presence of four engines offers increased power and redundancy, allowing such aircraft to be used as airliners, freighters, and military aircraft. Many of the first purpose-built jet airliners had four engines, among which stands the de Havilland Comet, the world's first commercial jetliner. In the decades following their introduction, their use has gradually declined due to a variety of factors, including the approval of twin-engine jets to fly farther from diversion airports as reliability increased, and an increased emphasis on fuel efficiency.

A vertical and/or short take-off and landing (V/STOL) aircraft is an airplane able to take off or land vertically or on short runways. Vertical takeoff and landing (VTOL) aircraft are a subset of V/STOL craft that do not require runways at all. Generally, a V/STOL aircraft needs to be able to hover. Helicopters are not considered under the V/STOL classification as the classification is only used for aeroplanes, aircraft that achieve lift in forward flight by planing the air, thereby achieving speed and fuel efficiency that is typically greater than the capability of helicopters.

The main advantage of V/STOL aircraft is closer basing to the enemy, which reduces response time and tanker support requirements. In the case of the Falklands War, it also permitted high-performance fighter air cover and ground attack without a large aircraft carrier equipped with aircraft catapult. V/STOL was developed to allow fast jets to be operated from clearings in forests, from very short runways, and from small aircraft carriers that would previously only have been able to carry helicopters.

The NACA cowling is a type of aerodynamic fairing used to streamline radial engines installed on airplanes. It was developed by Fred Weick of the National Advisory Committee for Aeronautics (NACA) in 1927. It was a major advancement in aerodynamic drag reduction, and paid for its development and installation costs many times over due to the gains in fuel efficiency that it enabled. NACA won the 1929 Collier Trophy for its development.

The 2010s oil glut was a significant surplus of crude oil that started in 2014–2015 and accelerated in 2016, with multiple causes. They include general oversupply as unconventional US and Canadian tight oil (shale oil) production reached critical volumes, geopolitical rivalries among oil-producing nations, falling demand across commodities markets due to the deceleration of the Chinese economy, and possible restraint of long-term demand as environmental policy promotes fuel efficiency and steers an increasing share of energy consumption away from fossil fuels.

The world price of oil was above US$125 per barrel ($790/m) in 2012, and remained relatively strong above $100 until September 2014, after which it entered a sharp downward spiral, falling below $30 by January 2016. OPEC production was poised to rise further with the lifting of international sanctions against Iran, at a time when markets already appeared to be oversupplied by at least 2 million barrels (320,000 m) per day.

A six-stroke engine is one of several alternative internal combustion engine designs that attempt to improve on traditional two-stroke and four-stroke engines. Claimed advantages may include increased fuel efficiency, reduced mechanical complexity, and/or reduced emissions. These engines can be divided into two groups based on the number of pistons that contribute to the six strokes.

In the single-piston designs, the engine captures the heat lost from the four-stroke Otto cycle or Diesel cycle and uses it to drive an additional power and exhaust stroke of the piston in the same cylinder in an attempt to improve fuel efficiency and assist with engine cooling. The pistons in this type of six-stroke engine go up and down three times for each injection of fuel. These designs use either steam or air as the working fluid for the additional power stroke.

A thermoelectric generator (TEG), also called a Seebeck generator, is a solid state device that converts heat (driven by temperature differences) directly into electrical energy through a phenomenon called the Seebeck effect (a form of thermoelectric effect). Thermoelectric generators function like heat engines, but are less bulky and have no moving parts. However, TEGs are typically more expensive and less efficient. When the same principle is used in reverse to create a heat gradient from an electric current, it is called a thermoelectric (or Peltier) cooler.

Thermoelectric generators could be used in power plants and factories to convert waste heat into additional electrical power and in automobiles as automotive thermoelectric generators (ATGs) to increase fuel efficiency. Radioisotope thermoelectric generators use radioisotopes to generate the required temperature difference to power space probes. Thermoelectric generators can also be used alongside solar panels.

The atmospheric engine was invented by Thomas Newcomen in 1712, and is sometimes referred to as the Newcomen fire engine (see below) or Newcomen engine. The engine was operated by condensing steam being drawn into the cylinder, thereby creating a partial vacuum which allowed atmospheric pressure to push the piston into the cylinder. It is significant as the first practical device to harness steam to produce mechanical work. Newcomen engines were used throughout Britain and Europe, principally to pump water out of mines. Hundreds were constructed during the 18th century. James Watt's later engine design was an improved version of the Newcomen engine that roughly doubled fuel efficiency. Many atmospheric engines were converted to the Watt design. As a result, Watt is today better known than Newcomen in relation to the origin of the steam engine.

Cutty Sark is a British clipper ship. Built on the River Leven, Dumbarton, Scotland in 1869 for the Jock Willis Shipping Line, she was one of the last tea clippers to be built and one of the fastest, at the end of a long period of design development for this type of vessel, which ended as steamships took over their routes. She was named after the short shirt of the fictional witch in Robert Burns's poem Tam o' Shanter, first published in 1791.

After the big improvement in the fuel efficiency of steamships in 1866, the opening of the Suez Canal in 1869 gave them a shorter route to China, so Cutty Sark spent only a few years on the tea trade before turning to the trade in wool from Australia, where she held the record time to Britain for ten years. Continuing improvements in steam technology early in the 1880s meant that steamships also came to dominate the longer sailing route to Australia, and the ship was sold to the Portuguese company Ferreira and Co. in 1895 and renamed Ferreira. She continued as a cargo ship until purchased in 1922 by retired sea captain Wilfred Dowman, who used her as a training ship operating from Falmouth, Cornwall. After his death, Cutty Sark was transferred to the Thames Nautical Training College, Greenhithe, in 1938 where she became an auxiliary cadet training ship alongside HMS Worcester. By 1954, she had ceased to be useful as a cadet ship and was transferred to permanent dry dock at Greenwich, London, for public display.