by Chris Kjel­gaard
Aviation.com

As con­cerns about glob­al warm­ing inten­si­fy through­out the world, avi­a­tion is receiv­ing a dis­pro­por­tion­ate lev­el of scruti­ny for its con­tri­bu­tion to total glob­al pro­duc­tion of green­house gas­es.

Even though avi­a­tion emits only about one-ninth as much car­bon diox­ide (CO2) as do motor vehi­cles, its high-vis­i­bil­i­ty nature as an activ­i­ty, its rapid growth as an indus­try and the fact that avi­a­tion emits most of its CO2 and par­tic­u­late emis­sions in the upper atmos­phere has made it a par­tic­u­lar tar­get for envi­ron­men­tal­ists.

Eliz­a­beth Bar­ratt-Brown, a senior attor­ney with the Nation­al Resources Defense Coun­cil, told last week’s Eco-Avi­a­tion Con­fer­ence in Wash­ing­ton, D.C. that in the Unit­ed States, unless the indus­try achieves enor­mous effi­cien­cy increas­es, “by 2050 avi­a­tion emis­sions are expect­ed to almost equal the amount from auto­mo­biles” because of avi­a­tion’s growth. The event, spon­sored by Air Trans­port World mag­a­zine and Lee­ham Com­pa­ny, was the first avi­a­tion envi­ron­men­tal forum to be held in the Unit­ed States.

Luck­i­ly for Earth, per­haps, the soar­ing price of oil has made the search for sus­tain­able, CO2-neu­tral alter­na­tives an imme­di­ate eco­nom­ic imper­a­tive as well as an envi­ron­men­tal­ly crit­i­cal focus for many human com­mer­cial activ­i­ties — with avi­a­tion fore­most among them. Eco­nom­ic experts are now view­ing high oil prices as a long-term fact of life rather than a short-term blip, and say avi­a­tion in its present form sim­ply can’t live with the pos­si­bil­i­ty of the price of a bar­rel of oil lev­el­ing at $200.

Research into fos­sil-fuel alter­na­tives is snow­balling. Even­tu­al­ly, a clean fuel such as hydro­gen may be the answer for avi­a­tion — but the tech­nolo­gies that will allow it to be used safe­ly and eco­nom­i­cal­ly to pow­er large air­craft are gen­er­al­ly regard­ed as being 40 or more years away.

For avi­a­tion, it increas­ing­ly appears that bio­fu­els — jet fuels made from plants or algae using any one of a vari­ety of process­es — rep­re­sent by far the best medi­um-to-long-term hope for the eco­nom­ic and envi­ron­men­tal sur­vival of the indus­try. One of the main advan­tages of bio­fu­els is that the plants used to make the fuels need lots of CO2 to grow, poten­tial­ly mak­ing it pos­si­ble for the avi­a­tion indus­try to achieve true car­bon-neu­tral­i­ty.

“Boe­ing Com­mer­cial Air­planes and its part­ners are active­ly accel­er­at­ing devel­op­ment of sec­ond-gen­er­a­tion bio­fu­els because they present an eco­nom­i­cal­ly viable oppor­tu­ni­ty to sus­tain­ably pow­er the world’s com­mer­cial air­craft fleet,” said Boe­ing in a recent brief­ing doc­u­ment enti­tled ‘What is the future of jet fuel?’

Avi­a­tion’s ‘proven track record’

Avi­a­tion’s “proven track record” in reduc­ing its “car­bon foot­print” on a per-pas­sen­ger basis already is excel­lent, with a 70 per­cent improve­ment in fuel-effi­cien­cy and CO2 emis­sions per pas­sen­ger mile in the last 50 years, said Rolls-Royce senior envi­ron­men­tal ana­lyst Nuno Tabor­da.

“Avi­a­tion spends rel­a­tive­ly more than any oth­er indus­try on CO2 reduc­tion,” he said. Oth­ers not­ed that dur­ing the last 30 years, the U.S. auto­mo­bile indus­try did not improve the fuel-effi­cien­cy and CO2 emis­sions of its prod­ucts at all.

But civ­il avi­a­tion is only just start­ing. “The IATA (Inter­na­tion­al Air Trans­port Asso­ci­a­tion) goal is for a 25 per­cent emis­sions reduc­tion per pas­sen­ger by 2020,” from an aver­age of 4 kilo­grams of CO2 per 100 pas­sen­ger kilo­me­ters to 3 kilo­grams, said Bil­ly Glover, Boe­ing Com­mer­cial Air­planes’ man­ag­ing direc­tor of envi­ron­men­tal strat­e­gy. In the U.S., “the Air Trans­port Asso­ci­a­tion goal is for 30 per­cent by 2025.” These goals do not include any pos­i­tive effects from using sus­tain­able bio­fu­els which might be avail­able by then, Glover added.

Var­i­ous part­ner­ships have been estab­lished to fos­ter the devel­op­ment of alter­na­tive fuels and oth­er ways to improve avi­a­tion’s envi­ron­men­tal effi­cien­cy. It is one area on which Air­bus and Boe­ing coop­er­ate will­ing­ly. One lead­ing forum is the Com­mer­cial Avi­a­tion Alter­na­tive Fuels Ini­tia­tive (CAAFI), which includes part­ners from the avi­a­tion indus­try, fuel sup­pli­ers, uni­ver­si­ties, and var­i­ous U.S. gov­ern­ment agen­cies.

CAAFI has estab­lished a fuel-cer­ti­fi­ca­tion roadmap that envis­ages achiev­ing cer­ti­fi­ca­tion of jet fuels made entire­ly from bio­mass-derived pure hydro­genat­ed oils in 2013. CAAFI also has set sev­er­al inter­me­di­ate tar­gets, begin­ning this year with the planned cer­ti­fi­ca­tion of a fuel made from a 50 per­cent blend of bio­mass-derived syn­gas and con­ven­tion­al jet fuel. (Syn­gas is a mix­ture of car­bon monox­ide and hydro­gen and is cre­at­ed from feed­stock by the Fis­ch­er-Trop­sch process, which was dis­cov­ered in 1923. Syn­gas can be processed into jet fuels.)

Find­ing the right bio­fu­el feed­stock

Key to the entire avi­a­tion bio­fu­el issue is just what type of bio­mass is most suit­able for fuel pro­duc­tion. Sev­er­al vital issues must be tak­en into account. First is the den­si­ty and ener­gy con­tent of the fuel: It must take up a suf­fi­cient­ly small space that it can be car­ried in an air­craft and, sim­i­lar­ly, a giv­en vol­ume of the fuel must pro­duce enough ener­gy so that an air­craft can car­ry enough in its tanks to com­plete its flight.

Sec­ond is the “car­bon life­cy­cle” of the bio­fu­el: that is, the net amount of CO2 pro­duced dur­ing pro­duc­tion and burn­ing of the fuel, less the amount the bio­mass feed­stock for the fuel absorbs while grow­ing.

Third is the amount of sul­fur and oth­er par­tic­u­lates pro­duced. Fourth is the huge­ly sen­si­tive polit­i­cal issue of mak­ing sure the land and bio­mass used to make bio­fu­el does not reduce the amount of food avail­able to human­i­ty and the Earth­’s fau­na.

These con­sid­er­a­tions imme­di­ate­ly rule out “first-gen­er­a­tion bio­fu­els” such as ethanol pro­duced from corn and soy­beans. Not only does ethanol not con­tain enough ener­gy per unit vol­ume to be suit­able as an avi­a­tion fuel, but grow­ing enough corn or soy­beans to pow­er all the world’s air­lin­ers would require an area just about the size of the Unit­ed States, accord­ing to Boe­ing. Nor does ethanol have suit­able boil­ing and freez­ing points for avi­a­tion use.

Sec­ond-gen­er­a­tion bio­fu­els

Experts believe “sec­ond-gen­er­a­tion bio­fu­els” derived from the wood and nuts of plants such as Jat­ropha cur­cas (Bar­ba­dos Nut) and babas­su, which grow strong­ly in arid areas unsuit­able as arable land and which (in jat­ropha’s case) are poi­so­nous any­way, rep­re­sent a good inter­im solu­tion.

These Latin Amer­i­can plants, as well as oth­er flo­ra such as switch­grass and salt-water-tol­er­ant plants known as halo­cytes (among them marsh grass­es found in parts of the Mid­dle East), could be grown for fuel pro­duc­tion in non-arable areas suit­ed to their par­tic­u­lar growth require­ments. Dif­fer­ent parts of the world would grow dif­fer­ent bio­fu­el-pro­duc­ing plants, depend­ing on their local cli­mat­ic and soil con­di­tions.

How­ev­er, there is a prob­lem: Although their oils offer much high­er ener­gy con­tent and much bet­ter boil­ing/freez­ing-tem­per­a­ture char­ac­ter­is­tics than ethanol, these plants would­n’t yield enough oil per hectare to be able to serve the avi­a­tion indus­try’s fuel require­ments unless, again, very large areas were giv­en over to their cul­ti­va­tion.

Algae a like­ly long-term answer

There is broad con­sen­sus through­out the indus­try that, longer-term, algae rep­re­sent the opti­mum solu­tion to avi­a­tion’s fuel needs. A num­ber of basic prob­lems need to be solved, such as ensur­ing enough light gets to every part of an algae tank to enable all the cells to grow prop­er­ly; and dry­ing algae cells suf­fi­cient­ly to enable the oil they con­tain to be extract­ed and cracked into jet fuel.

But Boe­ing and Air­bus are con­fi­dent these prob­lems can be solved — and the ben­e­fits that algae offers as a “third-gen­er­a­tion bio­fu­el” are immense. Algae can pro­duce an oil yi
eld 15 times that of sec­ond-gen­er­a­tion bio­fu­el plants: The world’s entire air­lin­er fleet could be pow­ered from a cul­ti­vat­ed area just the size of West Vir­ginia, or Bel­gium, says Boe­ing.

Addi­tion­al­ly, because algae can be grown in tanks any­where, bio­fu­el-pro­duc­ing algae farms could be sit­ed next to facil­i­ties pro­duc­ing jet fuel from coal or nat­ur­al gas using the Fis­ch­er-Trop­sch process. These “coal-to-liq­uid” or “gas-to-liq­uid” process­es gen­er­ate large amounts of CO2 from fos­sil fuels, mak­ing them unsuit­able as sus­tain­able fuel sources. How­ev­er, if the CO2 they gen­er­ate is piped off and used to grow algae in near­by farms, the two forms of fuel pro­duc­tion togeth­er could cre­ate an effi­cient, car­bon-neu­tral sym­bio­sis for jet fuel pro­duc­tion.