Education

The growth of green aviation

 By RP Siegel

The UN Civil Aviation Organization recently announced new targets for greenhouse gas emissions from aircraft. RP Siegel looks at the background of this issue, put it in context and look at various approaches underway to address the problem. Included the efforts to reduce weight in aircraft, the growing movement to use biofuels, the use of fuel cells to power planes taxiing on runways, to early prototypes of electric planes and the Solar Impulse effort to fly around the world on sunshine…

(Cover photo by www.zastavki.com)

As our climate continues to break temperature records, most governments, industries and consumers are scrambling to cut the emissions that have been linked to the problem in whatever ways they can. The utility sector is undergoing massive change as solar and wind power are grabbing the lion’s share of new capacity. In transportation, electric vehicles are no longer a novelty, while hybrids are now seen on every street. Buildings are undergoing massive “performance upgrades” with new materials, equipment, and smarter control systems.

One industry that’s been relatively slow to respond has been aviation. That’s not because of an unwillingness to change. It’s just the basic physics of flight. Aircraft must be extremely lightweight, while at the same time, requiring a great deal of energy to remain airborne. Those two constraints pose a challenge beyond the reach of many of the technologies that fit more easily into other sectors.

At the moment, air travel contributes 2-3% of total GHG emissions, but it is projected to increase to as much as 5% by 2050. This is because air travel is becoming ever more popular. Revenues doubled between 2004-14. According to UN spokesman Stephane Dujarric, “Carbon emissions from aviation are growing rapidly, with the number of flights worldwide expected to double in the next 15 years.”

(Microlattice is the lightest metal ever made)

Several governing bodies have become involved. The UN’s International Civil Aviation Organization (ICAO) has been seeking new rules for trans-Atlantic flights that could soon render certain aging aircraft, like the Boeing 747-8, obsolete. At the same time, the International Air Transport Association (IATA) has set targets to address climate change including: fuel efficiency improvements of 1.5% per year through 2020, a cap on net carbon emissions beginning 2020, and a 50% reduction in emissions (based on 2005 levels) by 2050. The US EPA is expected to follow suit, once an international standard has been set.

So how will these targets be achieved, especially the ambitious long-range ones? There is plenty of low-hanging fruit. For example, weight reduction initiatives are getting a great deal of attention. Boeing recently announced a new micro-lattice material, which is 99.99% air by volume, and is considered the lightest metal ever produced. Other areas, including engine modifications, winglets, improved routing and air traffic control systems will all contribute. But the biggest opportunities almost certainly lie in the area of propulsion technology.

The idea of electric airplanes seems far-fetched when you consider that the energy-density of today’s batteries is about a hundred times less than that of fossil fuel. That’s a hundred times the weight for the same amount of energy. Yet that hasn’t stopped the Solar Impulse, an extraordinary demonstration aircraft, flying on nothing but sunlight (and carrying minimal load), from flying halfway around the world, storing enough solar electricity in batteries each day, to last through the night. Airbus has successfully tested their single-seat E-Fan all electric prototype on a test flight across the English Channel and on dozens of other flights. They expect to have a 2-seater on the market relatively soon, followed by a 4-seater a few years later. The company envisions a 75-seat electric regional aircraft on the horizon, but that is still many years off. A number of significant advances in battery technology as well as aircraft design will likely be required before that becomes a reality.

Nearer to the ground, EasyJet has begun developing a system in which an electric motor will drive the wheels for low speed ground operation, which, according to the airline, constitutes 4% of total energy consumption. Perhaps inspired by the E-fan, which uses a similar approach, this concept utilizes regenerative breaking to capture energy dissipated upon landing, and stores it for later use.

EasyJet is developing fuel cell hybrid aircraft

In the mean time, a great deal of effort has been going into the development of lower carbon fuels for aviation use. Biofuels are a crucial component of the decarbonization of the aviation industry, where significant levels of electrification are still decades away. Not only is the existing infrastructure entirely based on liquid fuel, but the ever-important question of energy density weighs heavily on the issue.

A number airlines including United, Qantas, Continental, Japan Airlines, Alaska Airline and Air China as well as a number of military programs have run demonstration flights using low-carbon biofuels. Boeing is now participating in a consortium of companies aiming to produce biofuels from forestry waste in British Columbia. United recently began a regular service out of LAX with planes using a 50% blend of Honeywell Green Jet Fuel, produced by AltAir in a converted diesel refinery with a 30 million gallon annual capacity. The process technology for this plant was developed by Honeywell/UOP. This drop-in green fuel will not only cut lifecycle emissions by between 65-85% compared to conventional jet fuel, but it also boasts an increased energy density. At the same time, the fuel meets the ASTM HEFA certification standard.

UOP develops refinery technology for producing fuels from both conventional and alternative sources. Fully 60% of the world’s gasoline is produced using UOP technology. Veronica May VP/GM of UOP’s Renewable Energy and Chemicals business, describes the flexibility of the process in accommodating a wide variety of feedstocks including algae, non-edible fats, such as grease or tallow, oil rich plants, and even woody biomass, which is converted to an oil through a rapid pyrolysis process. The beauty of this use of woody biomass is that it qualifies for cellulosic RIM credits under the Renewable Fuel Standard (RFS) program in the US, under which cellulosic fuel volumes are expected to double in 2016.

(Imagine by www.nasa.gov)

The 50% blend limit, says May, is due to the aromatics contained in the conventional fuel but not in the green version. Today’s engines require them for lubrication purposes, but, says May, research is being done to overcome that. The company is also exploring, with Boeing, the possibility of blending diesel into jet fuel. Honeywell’s Green Diesel™, says May, is inherently low in Sulphur, which is another advantage.

Any of these feedstocks go through an identical Ecofining™ process which involves deoxygenation, removal of water and acid gas, then isomerization and hydrocracking, at which point any of a number of fuel products including Green Jet Fuel™ or Green Diesel™ can be produced. The process won the 2015 Process of the Year Award from Biofuels Digest. Production is going on already, not only at the AltAir refinery in California, but also by Petrixo in the UAE, and by SG Preston in the Midwest. In 2014, UOP partnered with Eni in the revamping of an existing refinery for Ecofining™ in Venice.

The aviation industry and the massive supply chain that supports it are working to respond to climate change with a host of emerging technologies. Only time will tell which of these initiatives will truly take off.

 

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about the author
RP Siegel
Skilled writer. Technology, sustainability, engineering, energy, renewables, solar, wind, poverty, water, food. Studied both English Lit.and Engineering at university level. Inventor.