Dresden research facility produces Audi E-diesel

Af­ter a com­mis­sion­ing phase of just four months, the re­search fa­cil­ity in Dres­den, German, started pro­duc­ing its first batches of high‑qual­ity diesel fuel a few days ago. To demon­strate its suit­abil­ity for every­day use, Fed­eral Min­is­ter of Ed­u­ca­tion and Re­search Prof. Dr. Jo­hanna Wanka put the first five liters into her of­fi­cial car, an Audi A8 3.0 TDI clean diesel quat­tro*. “This syn­thetic diesel, made us­ing CO2, is a huge suc­cess for our sus­tain­abil­ity re­search. If we can make wide­spread use of CO2 as a raw ma­te­r­ial, we will make a cru­cial con­tri­bu­tion to cli­mate pro­tec­tion and the ef­fi­cient use of re­sources, and put the fun­da­men­tals of the “green econ­omy” in place,” de­clared Wanka.

The Dres­den en­ergy tech­nol­ogy cor­po­ra­tion sun­fire is Au­di’s pro­ject part­ner and the plant op­er­a­tor. It op­er­ates ac­cord­ing to the power‑to‑liq­uid (PtL) prin­ci­ple and uses green power to pro­duce a liq­uid fuel. The only raw ma­te­ri­als needed are wa­ter and car­bon diox­ide. The CO2 used is cur­rently sup­plied by a bio­gas fa­cil­ity. In ad­di­tion, ini­tially a por­tion of the CO2 needed is ex­tracted from the am­bi­ent air by means of di­rect air cap­tur­ing, a tech­nol­ogy of Au­di’s Zurich‑based part­ner Clime­works.

Reiner Man­gold, Head of Sus­tain­able Prod­uct De­vel­op­ment at Audi, sees Audi e‑diesel and Audi e‑fu­els in gen­eral as an im­por­tant com­po­nent that com­ple­ments elec­tric mo­bil­ity: “In de­vel­op­ing Audi E-diesel we are pro­mot­ing an­other fuel based on CO2 that will al­low long‑dis­tance mo­bil­ity with vir­tu­ally no im­pact on the cli­mate. Us­ing CO2 as a raw ma­te­r­ial rep­re­sents an op­por­tu­nity not just for the au­to­mo­tive in­dus­try in Ger­many, but also to trans­fer the prin­ci­ple to other sec­tors and coun­tries.”

Pro­duc­tion of Audi e‑diesel in­volves var­i­ous steps: First, wa­ter heated up to form steam is bro­ken down into hy­dro­gen and oxy­gen by means of high-tem­per­a­ture elec­trol­y­sis. This process, in­volv­ing a tem­per­a­ture in ex­cess of 800 de­grees Cel­sius, is more ef­fi­cient than con­ven­tional tech­niques be­cause of heat re­cov­ery, for ex­am­ple. An­other spe­cial fea­ture of high-tem­per­a­ture elec­trol­y­sis is that it can be used dy­nam­i­cally, to sta­bi­lize the grid when pro­duc­tion of green power peaks.

In two fur­ther steps, the hy­dro­gen re­acts with the CO2 in syn­the­sis re­ac­tors, again un­der pres­sure and at high tem­per­a­ture. The re­ac­tion prod­uct is a liq­uid made from long‑chain hy­dro­car­bon com­pounds, known as blue crude. The ef­fi­ciency of the over­all process – from re­new­able power to liq­uid hy­dro­car­bon – is very high at around 70 per­cent. Sim­i­larly to a fos­sil crude oil, blue crude can be re­fined to yield the end prod­uct Audi e‑diesel. This syn­thetic fuel is free from sul­fur and aro­matic hy­dro­car­bons, and its high cetane num­ber means it is read­ily ig­nitable. As lab tests con­ducted at Audi have shown, it is suit­able for ad­mix­ing with fos­sil diesel or, prospec­tively, for use as a fuel in its own right.

The Fed­eral Min­istry of Ed­u­ca­tion and Re­search is sup­port­ing the sun­fire pro­ject, which started in May 2012. Con­struc­tion work on the fa­cil­ity in Dres­den‑Re­ick kicked off in July 2013 and the plant was com­mis­sioned on No­vem­ber 14, 2014. The plant is set to pro­duce over 3,000 liters (792.5 US gal) of Audi e‑diesel over the com­ing months. Audi is sun­fire’s ex­clu­sive part­ner in the au­to­mo­tive sec­tor.

Over and above the part­ner­ship with sun­fire, Audi has been ac­tive in the de­vel­op­ment of CO2‑neu­tral fu­els – Audi e‑fu­els – since 2009. The Audi e‑gas plant in Werlte, Lower Sax­ony, al­ready pro­duces Audi e‑gas (syn­thetic methane) in a com­pa­ra­ble man­ner; dri­vers of the Audi A3 Sport­back g‑tron* can fill up on it us­ing a spe­cial fuel card. Audi is also con­duct­ing joint re­search into the syn­thetic man­u­fac­ture of Audi e‑gaso­line with Global Bioen­er­gies, of France. In a fur­ther pro­ject, Audi has joined forces with the U.S. com­pany Joule, which uses mi­croor­gan­isms to pro­duce the syn­thetic fu­els Audi e‑diesel and Audi e‑ethanol.

Fuel consumption of the models named above:

Audi A8:
Com­bined fuel con­sump­tion in l/​100 km: 5.9 (39.9 US mpg)**; 
Com­bined CO2 emis­sions in g/​km: 155 (249.4 g/​mi)**

Audi A3 Sportback g-tron:
CNG con­sump­tion in kg/​100 kilo­me­ters: 3.3 – 3.2 (71.3 – 73.5 US mpg)**; 
Com­bined fuel con­sump­tion in l/​100 km: 5.2 – 5.0 (45.2 – 47.0 US mpg)**; 
Com­bined CO2 emis­sions in g/​km (CNG): 92 – 88 (148.1 – 141.6 g/​mi)**; 
Com­bined CO2 emis­sions in g/​km (gaso­line): 120 – 115 (193.1 – 185.1 g/​mi)**

**The fuel con­sump­tion and the CO2 emis­sions of a ve­hi­cle vary due to the choice of wheels and tires. They not only de­pend on the ef­fi­cient uti­liza­tion of the fuel by the ve­hi­cle, but are also in­flu­enced by dri­ving be­hav­ior and other non-tech­ni­cal fac­tors.