Aircraft Fuel Consumption: 7 Answers You Should Know


Aircraft Fuel Consumption

In general, fuel is a material that is burned to produce energy or heat. Fuel is a term used in aviation to refer to kerosene, which is used to power aircraft engines. The amount of fuel burnt during a flight is referred to as aircraft fuel consumption, though the reserves processes are not included in the fuel consumption for this project. The mass difference between the aircraft’s take-off and landing weights equals the aircraft’s fuel weight.

Let us briefly learn about aircraft fuel first.

Aircraft Fuel | Aviation Fuel

There are a few different types of aircraft fuel that are employed. Jet A and Jet A-1 are kerosene-based fuels that are colorless and easily flammable and are used in turbine engine airplanes. Another form of fuel is aviation gasoline (AVGAS), which is only used in tiny piston-engine planes. Large planes utilize kerosene-based fuels because kerosene has a higher flash point than gasoline. Gasoline is inefficient and does not provide the same amount of electricity as kerosene. The average national price of Jet-A fuel is $4.42 per gallon as of May 2021, though prices fluctuate frequently depending on various factors.

This article focuses on the calculation of aircraft fuel usage to expose the best-hidden secret in today’s commercial aviation. The aircraft’s fuel usage per passenger and 100 kilometers flown falls fast as the range increases until it reaches a near-constant level around the average range. Fuel consumption rises dramatically at greater ranges when cargo reduction is required.

Influence of range and payload on aircraft fuel consumption per nautical mile

Aircraft Specific Fuel Consumption

Fuel consumption is shown on engine performance chart as a fuel flow-rate/hr and fuel consumption is stated as specific fuel consumption in engineering process (SFC). Its definition is as follows:

[latex]SFC = \frac{Fuel\, flow\, rate\, in\, Newton\, per\, hour}{BHP\, in\, kW}[/latex].

A piston or turbo prop engine’s output is obtainable as power at the engine shaft position. When the FPS system is utilized, it is referred to as BHP and is measured in HP, for SI unit measurement kW is used. The thrust produced by a turbofan or turbojet engine, on the other hand, is measured in ‘lbs.’ in the FPS system and Newton in SI units.

A jet engine’s specific fuel consumption is defined as follows:

[latex]SFC = \frac{Fuel\, flow\, rate\, in\, Newton\, per\, hour}{Thrust\, in\, Newton}[/latex]

Let us recall what thrust is and understand what role it plays in aircraft fuel consumption efficiency.

The force that propels the airplane thru the air is known as thrust, is the force that allows the plane to fly by overcoming the drag. Because the thrust equals the drag in cruise flight, the aircraft does not accelerate. Thrust is generated by accelerating gas masses in air-breathing engines. According to Newton’s 3rdlaw, the force is generated in the reverse direction of the acceleration directions. Fuel is burned in the combustion chamber, and heat is added to the gas. The gas expands and accelerates as it exits the engine’s back, propelling the plane forward.

How to calculate Aircraft Fuel Consumption?

Specific Fuel Consumption Propeller Aircraft

The propeller transforms the engine’s output into thrust. This may have 2-4 blades, depending on the engine power and operational conditions. When necessary, specialized propeller with 5/6 blade also utilized for some applications.

The Specific Fuel Consumption of jet engine is known as BSFC and denoted as follows to distinguish the particular fuel consumption of a piston or turbo prop engine from that of a jet engine.

[latex]BSFC = \frac{Fuel\, flow\, rate\, in\, Newton\, per\, hour}{BHP\, in\, kW}[/latex] ; with unit of N/kW-h.

BSFC is often expressed in metric term as mg/W-s.

Brake Specific Fuel Consumption (BSFC) | Power Specific Fuel Consumption (PSFC)

Any prime mover fuel efficiency that burns fuel and provides rotational or shaft power is measured by BSFC, utilized to analyze the efficiency of IC engine with shafts o/p. This is calculated by dividing the rate of fuel consumption by the amount of energy produced. For this reason, it’s also known as power-specific fuel consumption. The Brake Specific Fuel Consumption can be employed for the direct analysis or comparison studies of the fuel efficiency of various engines in industries.

Jet Aircraft Fuel Consumption

Air-breathing propulsion systems, known as jet engines, are used to power and propel aircraft. A compressor compresses the air, and heat is supplied in the combustion chamber before the air exits through a turbine that drives the compressor. Excess energy is converted into thrust. The Brayton Cycle is the thermodynamic principle.

The turbine also powers fan blades in turbofan engines, accelerating surrounding air masses that bypass the engine. The by pass ratio is the ratio of air masses that by pass the engine compared to air mass that pass thru it, as high by pass ratio engines are happened to be more fuel efficient, they are going to be increasingly popular in future.

Thrust Specific Fuel Consumption stands for specific fuel consumption of a turbofan or turbojet engine.

[latex]BSFC = \frac{Fuel\, flow\, rate\, in\, Newton\, per\, hour}{Thrust\, in\, Newton}[/latex].

Having unit in hr-1 .

Thrust Specific Fuel Consumption (TSFC)

The fuel economy of an engine design in terms of thrust output is known as the thrust-specific fuel consumption (TSFC).

Because fuel mass is unaffected by temperature, it is utilized instead of volume (gallons or liters) for the fuel measurement. At maximal efficiency, the SFC of air jet engines is approximately proportional to exhausting speed.

TSFC characteristics of typical aircraft engines (Mattingly 1996, p.29)

Effect of Altitude on TSFC

The temperature of the air declines with altitude until it reach to the tropo-pause layer and the temperature difference between the maximum internal temperatures (limited by engine material) and the outside air temperature benefits jet engines. As a result, jet engine efficiency will rise with altitude until it reach the tropo-pause layer and as a result, a decrease in TSFC increasing altitude is to be predicted. The literature evaluation, however, did not reflect this.

Furthermore, because jet transport planes often fly in the stratosphere, where the temperature remains constant with altitude, minor fluctuations in TSFC with height are expected in the stratosphere where these planes fly.

Effect of Speed on TSFC

Air flight speed is also a significant factor for jet engines. The jet’s exhaust speed is counteracted by air flight speed. Furthermore, mechanical power is force times speed because work is force (i.e., push) times distance.

Though the nominal SFC is one of the helpful metric of fuel efficiency, this must be divided by speed if compared various speed engines and maximum range speed is achieved at constant propulsive efficiency when the ratio between velocity and drag is low, while maximum endurance is achieved at the best lift-to-drag ratio.

Aircraft Fuel Consumption per Hour | Aircraft Fuel Consumption Rate

Fuel usage is about 3 to 4 liters per passenger per 100 kilometers, making it the airline’s most expensive expenditure (representing around 30 percent of total costs). As a result, one of the most critical challenges in airline management is how much fuel per passenger an airplane consumes. To begin, the many indicators used to quantify transportation fuel efficiency are often compared to industry “production” metrics. By comparing an airline’s production to the amount of fuel burned, fuel efficiency can be determined.

Industry Indicator

Airlines’ conventional business is to carry people from point A to point B. The number of seats (or passengers) transported multiplied by the distance is a traditional indication of productivity. Let’s have a look at some examples of these indicators in more depth.

Aircraft Fuel Consumption Formula

  1. Revenue Passenger km (RPK). / Passenger Kilometer Performed. (PKP): The revenue passenger earns compensation from the airline and 1- RPK represent the transport of one person over a distance of 1 km.
  2. Available Seat Kilometer (ASK): One ASK equates to one seat flown per kilometer.
  3. Passenger Load Factor (PLF): PLF equates to the fraction of RPK and ASK.
  4. Passenger ton kilometers: Let us understand this using the reference below.
  5. Freight ton kilometers: Let us understand this using the reference below.

From 1968 to 2014, the average fuel burn of new airplanes decreased by 45 percent, a compounded yearly drop of 1.3 percent with a varied reduction rate. In 2018, CO2 emissions from passenger transportation were 747 million tons, equating to 8.5 trillion revenue passenger kilometers (RPK), or an average of 88 gram CO2 per RPK. A CO2/km of 88 g corresponds to 28 g of gasoline per kilometer or fuel consumption of 3.5 L/100 km (67 mpg-US).

Every second, a Boeing 747 consumes around 1 gallon of fuel (about 4 liters). It may consume 36,000 gallons of fuel during the course of a 10-hour journey (150,000 liters). According to Boeing’s website, the 747 consumes about 5 gallons of fuel each mile (12 liters per kilometer).

Consider that a 747 can transport up to 568 passengers. Let’s call it 500 people to account for the fact that most planes don’t have all of their seats filled. A 747 uses 5 gallons of fuel to transport 500 people 1 mile. Given that the 747 is flying at 550 miles per hour (900 km/h), the plane uses 0.01 gallons per person each mile. As a result, the Boeing 747 usually consume around 4 lt/sec, or 240lt/min and 14,400 lt/hr and for example, this might consume 187,200 lt/13hr for travelling from Tokyo to New York City.

Aircraft Fuel Consumption Table | Aircraft Fuel Consumption Comparison

Airline TypeLiters per 100 passenger kilometers
Low-cost Aircraft3.18
Regional Aircraft3.469
Charter Aircraft4.47
Flag carrier Aircraft3.405
Aircraft Fuel Consumption Table

Low-cost airlines have the best performance in terms of liters per 100 kilometers per passenger. Typically, because low-cost vehicle is one of the best in term of filling rate, they use the least amount of fuel per passenger.

For example, suppose we assume an airline flying a 2-hour medium-haul flight with a 200-seat narrow-body aircraft. In that case, the efficiency is roughly 3.5 liters per 100 kilometers with an 80% load ratio, but 3.15 liters per 100 kilometers with a 90% load factor. The liters per 100 km per passenger measure is not the most appropriate for measuring fuel efficiency since, as previously stated, the fig. is impacted by the loading factor.

The number of miles an airplane can go on a gallon of fuel is referred to as fuel economy. This is frequently mentioned in debates about global warming and the long-term aims of keeping average warming below 2°C. To meet this goal, emissions from all sectors has to be drastically reduced and the number of available seats on planes has increased by more than 25% in the last 20 years, and demand is expected to climb at a rate of roughly 5% each year.

Aircraft Fuel Consumption Chart

aircraft fuel consumption
Aircraft Fuel Consumption Chart; Image Source: IEA

What changes do modern aircraft make to lower fuel consumption?

The worldwide fleet is predicted to rise by 20,930 aircraft by 2032, bringing the total number of aircraft to almost 40,000. According to estimates, aviation fuel demand r the aircraft fuel consumption is expected to rise by 1.9% to 2.6% each year through 2025. The Non presence of extra mitigation system, the aviation industry’s planned development could push its proportion of global emissions to 22% by 2050. The present aviation world is on the lookout for innovative technologies, designs, and materials that can boost fuel efficiency long-term. By engine up-gradation, increasing aerodynamics features, and by using lighter materials, planes emit less carbon dioxide.

Winglets :

Winglets is a little device which connected to the tips of the wings, are utilized to improve the aerodynamics efficiency of a wing by creating additional push thru the flow-around the wing tip. They have the potential to boost airplane performance by 10% to 15%. A wing-let placed at a modest angle to the coming wind and surrounded by a swirling stream creates “lift” on the wing-let, which is coordinated internally along the wing and onward. Finally, they can reduce emissions by 6% by lowering drag.

Why do blended wing aircraft have lower fuel consumption?

The Boeing blended wing board (BWB) with a broad fuselage combined with high aspect-ratio wings is aerodynamically more efficient because the whole aircraft contributes to lift generation and has less surface area. It induces lesser drag and reduces weight due to lower wing loading.

Image Source: NASA/The Boeing Company, Boeing advanced blended wing body concept 2011 (cropped), marked as public domain, more details on Wikimedia Commons

For the super-regional 110-130 position, Dzyne Technologies reduces the thickness of the blended wing body, usually too thick for a slim body substitution and more suitable for large aircraft, by placing the airplane in the wing-roots, enabling the aircraft fuel consumption to be reduced by 20%.

Flexible Navigation System

By substituting the current airplane navigation system with more real time up-gradation, aircraft might  confront unfavorable weather circumstances such as storm, high wind, and other hazardous situation while improving the performance of favorable weather and according to different studies, employing a flexible navigation system may saves around 1.4 tons of CO2 per flight.

Continuous Climb Operation | Continuous Descent Operation

The working tactics include continuous climb and descent operation (CCO and CDO), allow airplanes to follow a flexible and optimum flying route that provides significant environmental and cost benefits. These include reduced aircraft fuel consumption, greenhouse gas emissions, noise, and fuel expenses, all of which negatively influence human well-being.

What is Double D8 ?

Double D8

In 2008, the Aurora Flight Science, MIT, and Pratt & Whitney has stated working on a design conceptualization for commercial aircraft entitled as DoubleD8 (do not have an engine beneath the wings) in a project of NASA-N+3. In this concept, designers has selected to positioned the engine toward the tail on top of the plane’s body.

Image Source: NASA/MIT/Aurora Flight Sciences, MIT and Aurora D8 wide body passenger aircraft concept 2010, marked as public domain, more details on Wikimedia Commons

This modification minimizes drag and improves fuel efficiency by reducing emissions by up to 66% over 20 years. It will also use 37% less fuel than passenger jets, reduce community noise by 50%, and reduce nitrogen oxide emissions by 87% during the landing and take-off cycle.

Learn about aircraft fuel storage systems in previous articles here.

Esha Chakraborty

I have a background in Aerospace Engineering, currently working towards the application of Robotics in the Defense and the Space Science Industry. I am a continuous learner and my passion for creative arts keeps me inclined towards designing novel engineering concepts. With robots substituting almost all human actions in the future, I like to bring to my readers the foundational aspects of the subject in an easy yet informative manner. I also like to keep updated with the advancements in the aerospace industry simultaneously. Connect with me with LinkedIn - http://linkedin.com/in/eshachakraborty93

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