Explain "SAF" To Me

Synthetically prepared jet fuel on the other hand, is like playing with Legos (TM).  You start with one thing, like carinata oil, and you do something to tear it all apart.  Then you take the parts you want and put them together in a way you like.  In the case of synthetically prepared, there is a lot of chemistry going on and it can get complicated. Sometimes you get something that is pretty close when you start and you do not have to do a lot to make it acceptable all by itself.  Other times it is close, but not quite, so you can only use it reliably when you blend it with conventional jet fuel.  And sometimes, it is not intended to be a fuel all by itself, it is used to add something, either to existing conventional jet fuel, or to other synthetically prepared jet fuels that need a little something more.

This brings me to the final product.  The efforts inside the aviation fuel community are to identify and standardize synthetically prepared blend components or final fuel.  Our job is to test it, to evaluate it, to specify it, and to make sure that it can be safely used in all turbine engines to the best of our ability.  Outside of our community, there is a, surely laudable, goal of making aviation cleaner and more sustainable.  That goal is to move to using 100% sustainable aviation turbine fuel as quickly and as extensively as is possible.  People often ask, why we cannot just start using 100% SAF, right now?  In a recent CAAFI presentation, Andac Gurhan of General Electric explains the challenge in a straightforward and clear way (https://caafi.org/resources/pdf/3.10_100_Percent_SAF_Andac_Kramer.pdf) which I whole-heartedly recommend.  In short, sometimes the SAF process gets us so close that we have a fuel that is safe to use at 100% in almost every aircraft.  Sometimes it is close, but needs the blending with conventional jet fuel to get the rest of the way.  And sometimes, it just is not close at all. 

Then why do we see reports about successful flights in the news, where the aircraft is successfully fueled and flown with 100% SAF?  Have you noticed that these aircraft are usually brand new models with the newest engines?  The truth is that our industry is an iterative one.  We make technology advances in engines.  We make advances in the fuel.  The engineers take advantage of the improvements and tweak the engine/aircraft/flight profiles to take advantage of the improvements.  And we baby step our way to some very impressive modern systems and some very clean burning new fuels.  But our industry does not leave the legacy systems behind, they must be able to fly safely also.  So while the latest and greatest airframes and engines may be able to quite happily use 100% sustainable aviation fuel, we inside the industry have to make sure that the oldest systems can too. 

 

Okay, you may say, but can't we start using the 100% SAF in the aircraft that can use it and keep letting the older aircraft get the conventional fuel?  Ah, but the way we certify aircraft and the way we move and sell aviation turbine fuel means that all the fuel has to be the "same".  Only Jet A/Jet A-1 compliant with ASTM D1655 may be used on an aircraft.  And the way it is moved, it ALL has to be compliant with D1655, without record keeping or separate tanks, or a confirmation system that prevents "misfueling".  So this ends up being an all or nothing proposition, at least in the U.S.

So we will continue to be cautious, methodical, and considerate.  We want to get there too, but we do not want to see an aircraft full of people trying to pull over to the side of the road because of an issue with the fuel... 

 

Until next time, be safe out there, keep washing those hands, and be nice.

Here comes July!  As I sit and prepare this update, I find myself in awe that half the year has slid from under me.  While the running theme is that 2020 just didn't exist, I am finding that for me personally, January and February 2021 didn't seem to exist either.  Because Baere is a support company, the belt tightening in the aviation industry has not hurt us, yet at least.  We have continued to pick up the slack at places where downsizing, remote work, and just a loss of market have meant there are even less of us aviation fuel specialists out there.  And this has happened at a time where the emphasis on synthetic and sustainable aviation fuels is ramping up to a new pitch.  Baere has been busy attending webinars and conferences related to the renewed interest in not only synthetic jet fuels, but looking forward to the hydrogen economy, and to the electrification of aviation.

Explain SAF to me...  One of the topics that has really slapped me in the face is SAF terminology.  After no less than three professional sessions since I last shared with you, I have come to the realization that we are on the cusp of having a "failure to communicate" with my apologies to Cool Hand Luke.  Many of you have seen the growing media exposure of "SAF"  All you have to do is type "Sustainable Aviation Fuel" in your favorite search engine to see the plethora of articles on the topic.  And as anyone who has been following this page or is involved in the industry knows, the technical people have been working hard for a decade to get new, cleaner, non-petroleum kerosene jet fuel approved for safe use in aircraft.  We have talked about Fischer Tropsch fuels, canola, carinata, green waste, yellow grease, algae, alcohol to jet, Green Diesel (TM)...  The ASTM community has approved seven different pathways to alternatively prepared jet fuel components.  All these synthetically prepared fuels are acceptable blending components which are now permitted to be used in conventional aviation jet fuel.  

So, you may be asking, where is the miscommunication?  It comes from short-hand.  Within the fuel community and the standardization community, we have a tendency to refer to all these synthetically prepared blending components as SAF.  Yep, the same acronym.  But within the community, synthetically prepared does not necessarily mean it came from only "green" sources.  Fischer Tropsch (F.T) processes are used on many sources - coal, natural gas, old tires, etc., many of which would not meet the contemporary focus on "sustainable".  The point is, all current "green" sourced aviation fuels are synthetically prepared, but not all synthetically prepared fuels are from "green" sources. 

What do I mean by "synthetically prepared" anyway?  Conventional jet fuel prepared from crude oil is, in its simplest form, distilled from the barrel of crude oil.  Just like moonshine mash, the crude oil is heated up until it vaporizes (boil the mash).  The vapor is run through a condensing tower and cooled off.  The desired product is collected on the other end (but I wouldn't drink it!).  Different ranges of petroleum products turn into vapor and turn back into liquid at different temperatures.  By controlling the temperatures, the refiner can separate the barrel of crude into everything from tar to naphtha.  Here is a classic film from Shell if you are interested in the details, https://www.youtube.com/watch?v=hC1PKRmiEvs.  To be honest, most conventional jet fuel also has some "chemistry" done to it; like hydrogenation where hydrogen is added.  But again, at its simplest, it is boiled, cooled, and collected.