**6. Airfreight**

The steadily growing world trade is the reason for the rapid increase in air cargo volume in recent decades. This transport method offers many advantages such as speed, safety, and reliability. The short transport times over long distances are particularly attractive for goods with a high urgency and high value. Airfreight records the highest growth worldwide compared to other modes of transport [47]. Another advantage is the precisely planned organization in air traffic. Flight plans

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*Energy Efficiency Management: State of the Art and Improvement Potential Analysis…*

fuel than, for example, seagoing vessels [48] per tonne kilometer.

future annual growth rate of ~7% is expected on average [4, 47].

export orders have been rising fastest for more than 7 years [49].

rose by 30.3% and capacity by as much as 9.2% [49].

**6.1 Solar energy systems: solar kerosene**

are minutely adhered to under very high safety standards, thus ensuring a smooth supply chain. Compared to other transport methods, the transport costs, due to the high fuel consumption, are relatively high. Aircraft consume about 12 times more

Based on the assessment basis for specific CO2 emissions, air traffic is a significant contributor to climate change. In most cases, energy consumption is related to transport performance, such as passenger kilometers or tonne kilometers. This includes the consumption from the departure terminal to the arrival terminal and therefore also the movements that take place on the ground. Between 1990 and 2011, freight transport services quadrupled in Germany, and on a global scale, a

In December 2017, the International Air Transport Association (IATA) published updated data for the global airfreight market. It showed that demand (measured in freight tonne kilometers, FTK) increased by 5.9% compared to the previous year. Freight capacity, measured in available freight tonne kilometers (AFTKs), also

Alexandre de Juniac (IATA Director General and CEO) said: "Demand for air freight increased by 5.9% in October. And tightening supply conditions in the fourth quarter should be the air cargo industry delivering its strongest operational and financial performance since the post-global financial crisis rebound in 2010" [49]. In the Asia-Pacific region, airlines increased their cargo volumes by 4.4% and capacity by 3.9%. Freight demand exceeds the record high reached in 2010 by

Airlines in North America recorded an increase in cargo volume of 6.6% in 2017 compared to 2016. The increase in capacity was 3.8%. In recent years, the market for inbound freight transport has increased due to the strength of the US economy and

In Europe, the 5-year average of 4.9% was exceeded, and freight demand rose by a total of 6.4%. Capacity grew by 2.5%. Compared to other continents, European

Middle Eastern carriers' freight volumes increased 4.6%, and capacity increased

In the last half of 2017, seasonally adjusted international freight volumes continued to rise at a rate of 8–10%. Airlines in Latin America, like all other major regions, posted positive growth in freight demand (7.2%) and capacity (4.4%). By far the largest increase over the previous year was seen by African carriers. Freight demand

Decarbonization attempts in aviation concern passenger and freight transport alike. Engine improvements have a very strong leverage on energy efficiency. There

For many years countless research activities have been dealing with the topic of solar energy and where it can be used. The EU Commission announced in 2014 that an experiment had succeeded in producing kerosene with the help of sunlight [51]. In the process, synthesis gas is generated under the action of sunlight, which consists of hydrogen (H2) and carbon monoxide (CO). Andreas Sizmann from the Bauhaus Luftfahrt (participant in the research project) explained two major advantages of this method. First, the harmful climate gas CO2 would be used and not fossil hydrocarbons such as oil. Although the kerosene produced in this way will also release CO2 through combustion, CO2 can be obtained directly from the air over the long term. Therefore, the process is on the whole potentially CO2 neutral,

is a trade-off between NOx emissions and turbine energy efficiency [50].

*DOI: http://dx.doi.org/10.5772/intechopen.86552*

increased by 3.7% compared to 2016 [49].

around 3%.

the US dollar.

3.4% in 2017 [49].

#### *Energy Efficiency Management: State of the Art and Improvement Potential Analysis… DOI: http://dx.doi.org/10.5772/intechopen.86552*

are minutely adhered to under very high safety standards, thus ensuring a smooth supply chain. Compared to other transport methods, the transport costs, due to the high fuel consumption, are relatively high. Aircraft consume about 12 times more fuel than, for example, seagoing vessels [48] per tonne kilometer.

Based on the assessment basis for specific CO2 emissions, air traffic is a significant contributor to climate change. In most cases, energy consumption is related to transport performance, such as passenger kilometers or tonne kilometers. This includes the consumption from the departure terminal to the arrival terminal and therefore also the movements that take place on the ground. Between 1990 and 2011, freight transport services quadrupled in Germany, and on a global scale, a future annual growth rate of ~7% is expected on average [4, 47].

In December 2017, the International Air Transport Association (IATA) published updated data for the global airfreight market. It showed that demand (measured in freight tonne kilometers, FTK) increased by 5.9% compared to the previous year. Freight capacity, measured in available freight tonne kilometers (AFTKs), also increased by 3.7% compared to 2016 [49].

Alexandre de Juniac (IATA Director General and CEO) said: "Demand for air freight increased by 5.9% in October. And tightening supply conditions in the fourth quarter should be the air cargo industry delivering its strongest operational and financial performance since the post-global financial crisis rebound in 2010" [49].

In the Asia-Pacific region, airlines increased their cargo volumes by 4.4% and capacity by 3.9%. Freight demand exceeds the record high reached in 2010 by around 3%.

Airlines in North America recorded an increase in cargo volume of 6.6% in 2017 compared to 2016. The increase in capacity was 3.8%. In recent years, the market for inbound freight transport has increased due to the strength of the US economy and the US dollar.

In Europe, the 5-year average of 4.9% was exceeded, and freight demand rose by a total of 6.4%. Capacity grew by 2.5%. Compared to other continents, European export orders have been rising fastest for more than 7 years [49].

Middle Eastern carriers' freight volumes increased 4.6%, and capacity increased 3.4% in 2017 [49].

In the last half of 2017, seasonally adjusted international freight volumes continued to rise at a rate of 8–10%. Airlines in Latin America, like all other major regions, posted positive growth in freight demand (7.2%) and capacity (4.4%). By far the largest increase over the previous year was seen by African carriers. Freight demand rose by 30.3% and capacity by as much as 9.2% [49].

Decarbonization attempts in aviation concern passenger and freight transport alike. Engine improvements have a very strong leverage on energy efficiency. There is a trade-off between NOx emissions and turbine energy efficiency [50].

#### **6.1 Solar energy systems: solar kerosene**

For many years countless research activities have been dealing with the topic of solar energy and where it can be used. The EU Commission announced in 2014 that an experiment had succeeded in producing kerosene with the help of sunlight [51]. In the process, synthesis gas is generated under the action of sunlight, which consists of hydrogen (H2) and carbon monoxide (CO). Andreas Sizmann from the Bauhaus Luftfahrt (participant in the research project) explained two major advantages of this method. First, the harmful climate gas CO2 would be used and not fossil hydrocarbons such as oil. Although the kerosene produced in this way will also release CO2 through combustion, CO2 can be obtained directly from the air over the long term. Therefore, the process is on the whole potentially CO2 neutral,

*Transportation Systems Analysis and Assessment*

*5.7.3 Biofuels and blends with petrodiesel*

the fueling and the hydrogen storage capacity [34].

*5.7.2 Natural gas locomotives using liquefied natural gas (LNG)*

ballast. In the case that the temperatures of the batteries are too high, a pressure relief device can be activated. This process ventilates the batteries as well as the hydrogen fuel cells. With this model, the air pollution and the noise pollution at the stations are reduced. The problem with this variant is the limited range between

Liquefied natural gas (LNG) is an interesting alternative fuel for locomotives [39, 40]. Westport Innovations is working with Caterpillar to develop a natural gas fuel system for locomotives [34]. This project uses high-pressure direct injection technologies for combustion. The main objective was defined as the production of emission compliant long-haul locomotives with interchangeable tender vehicles. With this technology, 95% of the diesel fuel is replaced by natural gas and thus only 5% diesel fuel used for combustion to bring the locomotive to full capacity. Energy Conversions Inc. is working with Burlington Northern Santa Fe (BNSF) to develop a convertible engine with a dual-fuel system. This system uses low-pressure direct injection (LPDI) with no pump being required. The NOx emissions caused by premixed combustion are reduced. This system can save up to 1.1 million liters of diesel per year per locomotive, equivalent to a possible replacement of 92% [34]. According to BNSF, the economy and technology have been improved so much that

natural gas in long-haul locomotives becomes operationally feasible [34].

number facilitates combustion in compression ignition engines [34].

Bioethanol is more a fuel of choice for smaller (gasoline) engines. Other biofuels are, e.g., biobutanol and biomethanol [3, 46].

For two recent reviews on biodiesel, see [43–45] for biodiesel in railway use.

The steadily growing world trade is the reason for the rapid increase in air cargo

volume in recent decades. This transport method offers many advantages such as speed, safety, and reliability. The short transport times over long distances are particularly attractive for goods with a high urgency and high value. Airfreight records the highest growth worldwide compared to other modes of transport [47]. Another advantage is the precisely planned organization in air traffic. Flight plans

Biofuels are derived from renewable and (in principle) non-exhaustive sources of energy. To produce biofuels, biological (plant or animal) materials are converted into liquid fuel composed of fatty acid methyl esters (FAME). Instead of fossil fuels, organic waste (e.g., waste cooking oil) can also be used for production [41, 42]. Biodiesel fuel is obtained from transesterification of fatty acids. In this chemical process, glycerol is separated from fat or vegetable oil, and methanol is consumed. Biodiesel is made from a variety of products, such as animal fat, vegetable oil (rape seed, soy bean, palm oil, etc.), or recycled restaurant fat. Petroleum diesel can be blended with biodiesel to any percentage. In these biodiesel blends, the percentage of biodiesel is always clearly marked. For example, B10 contains 10% of biodiesel, with the remaining 90% being made from fossil sources. Pure biodiesel is known as B100. Blends containing more than 20% biodiesel require special handling or even modifications of the equipment. Biodiesel is biodegradable and nontoxic, reduces air pollutants, and provides better lubricity due to its viscosity. The high cetane

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**6. Airfreight**

according to Sizmann. Second, the energy for the entire process is generated from solar energy. The process is very efficient and does not compete with food production as opposed to the production of other (mainly first-generation) biofuels [52].

#### **6.2 Electric motors: environmentally friendly flying**

The use of electric motors is already well advanced in parts of the transport sector. Soon, electric flying should become possible. In this regard, Siemens and Airbus announced a development cooperation in 2016 in which hybrid technology is used. In the presented test aircraft, the jet engine was replaced by a 2 megawatt electric motor (produced by Siemens), which drives the large air impellers. The 2 megawatt electric motor is only 30 centimeters long and weighs 175 kilos. To get power from the electric engine, several steps are necessary. With a gas turbine burning kerosene, an electric generator is powered, which feeds the power into a 2 tonne lithium-ion battery. Finally, the lithium-ion battery supplies the built-in electric motor. Since starting up an aircraft requires a great deal of energy, the lifting can be supported by generator and battery. During the descent, the engine blades, which work like small windmills, can be used to generate electricity. This principle is similar to that of electric cars or locomotives, which carry power back into the battery while braking. The representatives of this project are of the opinion that with their concept they can reduce the consumption of kerosene by double-digit percentages compared to conventional jet engines. Flying would therefore also become more environmentally friendly and more quiet [53, 54]. Electric power for a two-seat aircraft is discussed in [55]. The more electric aircraft (MEA) concept is discussed in [56]. Light pureelectric and hybrid-electric aircraft are presented in [57]. The MEA concept essentially aims at replacing conventional non-electric power (pneumatic, hydraulic, and mechanical) by electric power to drive aircraft subsystems more efficiently. An all-electric 180-passenger commercial aircraft is discussed in [58].

### **6.3 Aerodynamics: winglets and riblets**

In aviation, aerodynamics focuses on two main forces: lift and drag. The power of lifting makes an airplane fly. This is caused by the uneven pressure on a wing's top and bottom. The drag represents the resistance that arises during movement through the airflow. Due to the high pressure under the wings, air flows over the wing tips upward and rolls off in the form of a vortex. This vortex is also called induced drag and can be so strong that it disturbs other planes. Wake turbulence can become a safety concern particularly for small aircraft. Induced air drag degrades performance and reduces the range and speed of the aircraft [59].

Winglets are more than just a striking and aesthetic design feature; they are among the most visible fuel-saving and performance-enhancing technologies in aviation introduced in recent years. According to Whitecomb, winglets can reduce induced drag by about 20% and improve carrying capacity by 6–9%. The design of the winglets can be very different. Aviation Partners Boeing (APB) has developed a special form: the Blended Winglet. The Blended Winglet's design fuses the wing into a smooth upward curve. Other winglets are shaped more like a fold or kink. Through this smooth transition, optimal efficiency can be achieved [59].

Riblets are micro- and nanostructured surface structures that cause drag reduction. This technology comes from the field of bionics, which works by transferring phenomena from nature to technology. Riblets resemble the skin of a shark and are characterized by fine grooves on the surface. The so-called sharkskin effect causes a reduction of the friction resistance of up to 8% compared to aircraft without this coating [60].

**127**

metalworking [62].

*Energy Efficiency Management: State of the Art and Improvement Potential Analysis…*

In the research project FAMOS (management system for the automated application of multifunctional surface structures) of Lufthansa Technik, Airbus Operations GmbH, BWM GmbH, and the Fraunhofer Institute for Production Technology, it has been possible to develop an automatic guidance system for the application of riblets to the outer shell of the test aircraft [61]. Tests from this research project have shown that riblets, despite minor wear of the microstructures, significantly reduce the frictional drag in the air. For riblets, lacquer is first applied to a UV-transparent mold or matrix. This matrix contains the negative impression of the riblet shape. The resulting negative mold is then pressed into fresh paint and thus cured with UV light. After removing the negative mold, the positive of the sharkskin structure stops at the surface. The application of the riblets is possible on any aircraft models; they are attached in the form of strip tracks on the surfaces parallel to the flow direction. In the laboratory of the project FAMOS, the longevity as well as the efficiency of the sharkskin structure was confirmed. Depending on the area applied, airlines can use this technology to save about 1.5% of fuel [61].

**6.4 Composite materials to optimize fuel consumption and CO2 emissions**

The processing of composite materials is becoming increasingly important for aircraft construction. Even though planes are themselves tonnage heavy, every single kilogram counts. The manufacturing and processing costs of carbon fiberreinforced plastics (CFRP) in aircraft far exceed the costs of traditional metal construction. In the long term, however, the cost advantage outweighs due to the low weight and the resulting reduced fuel consumption. Nowadays, fuel consumption is a top priority for airlines because less fuel means less CO2 emissions and lower operating costs. Thus, something good is done for the environment while saving money, too. For many years CFRP has been installed on models such as the Airbus A380 (28%) or the Airbus A350 XWB (53%). Predecessors, such as the A330, weigh almost 10 tonnes more and consume more fuel than the Airbus A350 XWB with

CFRP consist of hair-thin layers of carbon fibers, which are embedded in a resin matrix (thermoset). The material scores with a very high specific strength and low weight. Mechanically, this composite material is extremely difficult to deal with, so millimeter-thin CFRP tapes have to be stacked on top of each other for the outer hull of the skin in a day-long process and then baked together under pressure and heat. Due to the extreme hardness of the material, particularly high-quality and expensive cutout drills and cutters (e.g., for external connections, doors, windows, and holes for rivets) must be used. Because of the high abrasion when drilling, even modern tools with diamond-like coating last on average only half as long as tools in

**6.5 Aircraft engines: current technology and energy-efficient developments**

Aircraft engines must be reliable and efficient. The technology behind them is explained quickly and easily. Engines work in a similar way as rockets: The intake air is compressed and fuel is injected. The combustion of the fuel creates an exhaust gas jet, which emerges at the back. The exhaust jet drives the actual turbine (a wheel with blades). The turbine finally generates the drive for the compressor at the engine entrance. The compressor increases the pressure of the air and consists of several stages. Each of these stages includes a rotor and a stator wheel. The turbine part is also constructed like that. Depending on the engine, between 8 and 14 stages are used today. Particularly modern engines achieve compressions of 45 times the input pressure. The developments in aircraft engines initially focused on sending

*DOI: http://dx.doi.org/10.5772/intechopen.86552*

comparable payload capacity and range [62, 63].

*Energy Efficiency Management: State of the Art and Improvement Potential Analysis… DOI: http://dx.doi.org/10.5772/intechopen.86552*

In the research project FAMOS (management system for the automated application of multifunctional surface structures) of Lufthansa Technik, Airbus Operations GmbH, BWM GmbH, and the Fraunhofer Institute for Production Technology, it has been possible to develop an automatic guidance system for the application of riblets to the outer shell of the test aircraft [61]. Tests from this research project have shown that riblets, despite minor wear of the microstructures, significantly reduce the frictional drag in the air. For riblets, lacquer is first applied to a UV-transparent mold or matrix. This matrix contains the negative impression of the riblet shape. The resulting negative mold is then pressed into fresh paint and thus cured with UV light. After removing the negative mold, the positive of the sharkskin structure stops at the surface. The application of the riblets is possible on any aircraft models; they are attached in the form of strip tracks on the surfaces parallel to the flow direction. In the laboratory of the project FAMOS, the longevity as well as the efficiency of the sharkskin structure was confirmed. Depending on the area applied, airlines can use this technology to save about 1.5% of fuel [61].
