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Comment by notfed | Hacker News Reader

What really is sustainable aviation fuel (SAF)? Is it one thing?

It's specified by IATA: https://www.iata.org/en/programs/environment/sustainable-avi...

Apparently they have identified seven different ways to produce fuels that meet this specification. Including bio fuels and synthetic fuels.

I first heard about it from United Airlines ads that feature Oscar the Grouch (yes, of Sesame Street):

https://m.youtube.com/watch?v=akOq47EZZpU

Interestingly, that ad takes care to mention what can’t be turned into SAF (skip to 0:32).

The ad also mentions that United uses less than 0.1% SAF as part of their fuel consumption.

there's a bunch of chemical pathways for turning plant matter into jet fuel

https://afdc.energy.gov/fuels/sustainable_aviation_fuel.html

As far as I can tell it’s basically used cooking oil and waste fats.

And the planes will smell delicious

I have noticed that bio-diesel cars smell like burning french fries... so maybe you're not that far off...

Interesting. I've been running that for years in my diesel truck. A mechanical diesel will run basically whatever you can pump through its fuel system. I assume jet engines are roughly the same. However they have some major standards, and can't risk running recycled fryer oil from the Chinese restaurant down the street.

What truck do you have, how did you modify it, and whats your opinion on why it's not more common?

1994 Toyota pickup with a Om617 swap. I bought a kit for the engine swap then did all the work to swap it.

I did nothing to handle the oil. It just works. You pour it in the tank and go. However, it doesn't work in the winter without a heater or additives.

It's not more common because a) mechanic diesels are old technology and means you'll be driving an old vehicle. b) WVO is a hit or miss in your area. Lots of restaurants will get paid for their old oil by recycling centers so most wont give it away. c) processing it is tough until you get a system in place

As well you can run on so many different fluids. Waste motor oil, waste transmission fluid, brake fluid, etc.

Can you just pour used motor oil into the tank of such an engine? It's always a hassle to dispose of at home.

It will happily burn in the cilinder, however catalytic converters and other parts will not be so happy. And of course, its awfully contaminant.

Motor oil burns more rapidly than diesel. You'll get more "power" but also less durability.

Burning motor oil happens when your turbo breaks down and puts all your oil via the air inlet to your engine. It's hard to stop that engine until all the oil is used.

Didn't find an article in English, so here's a random one in Polish: https://www.autobaza.pl/page/news/choroba-szalonych-diesli-c...

https://en.wikipedia.org/wiki/Diesel_engine_runaway

You need a multi-fuel engine for that to work without special care.

But yes, you can pour motor oil into the tank of your Deuce and a Half and let it rip.

The Caterpillar diesel engine manual says you can burn up to 5% used motor oil without affecting the warrantee. It does say to make sure you filter the used oil so as not to gunk up your fuel system.

For a large engine that produces many buckets of oil at each change, this is a good way to get rid of the stuff.

You absolutely can and I have before. However, I blended it 70% WMO and 30% diesel. Used motor oil WILL carbon up everything. It's so full of ash that it'll pool up internally.

You need to used a centrifuge to pull out the carbon. Sounds intense but it's not.

You can pour it entirely in your tank without any filters but your fuel filters only go to about 10-30 which will not pull out the tar. Small amounts like that won't do any damage really.

I ran my 1999 Nissan Primera 2.0 turbo diesel on virgin vegtable oil for a couple of years (I had about 400L in the back when taking the channel ferry to to drive around Europe). It cost 0.40p/l instead of 1.20/l in the UK. Bought it from a farmer from an ad on eBay. No modification needed, but you need to have a couple of fuel filters and a tool to change it handy, in case you have a blockage (more common when first starting to run on oil). In winter add 5-10% petrol to keep the viscosity down. You can always add diesel to the tank without issue.

I think many 90s indirect-injection diesels can run vegtable oil without modification, but some ppl add a fuel heating system or a dual-fuel switchover system.

There were newspaper stories of ppl going into Tescos and filling their trollies with 5L bottles of vegtable oil, then going to the parking and filling their tanks. Later (virgin) vegetable oil became more expensive than diesel, used oil is a different story.

Bonus: when reversing, or at the lights with a breeze, you often notice an odour like fried chips. :)

It probably wasn't more common because it was some hassle with the fuel filters and potential damage to fuel pump (some are built better than others). The Nissan had a license-built Bosch design that was solid.

If I’m at the lights, and you floor it and take off to leave my car smelling of battered haddock I guess you could call it…

Rolling Cod

Thanks. Here all week!

https://en.m.wikipedia.org/wiki/Rolling_coal

Shame on you for not going with Rolling Sole [1]

[1] https://en.wikipedia.org/wiki/Sole_(fish)

Yeah this would have been better

Perhaps you need to consider when you want to buy a switchover system from eBay: If caught, obviously by police with a nose for chips. They will take your car milage multiply that by the amount of fuel tax you did not pay, double it as punishment and give you a set fine while they are at it.

Can you prove beyond a reasonable doubt that this vehicle was operated under illegal conditions for the entirety of that duration? What if it were imported? Used?

In my country the tax law has a reversed proof clause. Meaning, you are guilty until proven innocent. This clause is activated after you get caught, or even when you did not comply with administrative requirements. Other countries have similar clauses.

So in this case, if you have hard proof, meaning a proper administration, fuel tickets, etc. Which you all don't have, there is basically only a central milage database and ownership records that can hedge your damage.

If he's doing less than 2,500 miles per year using the biofuel, that's not the case.

https://www.gov.uk/guidance/biofuels-and-other-fuel-substitu...

According to that link it's actually if you use > 2500 litres/year, which is a lot. Assuming 40 MPG (UK), that would do you about 35k miles in a year.

That's absolutely fucking insane.

In Poland at least, people were doing it - mostly rural in their tractors - but just straight using cooking oil for your trucks&tractors is illegal - too much pollution.

Of course SAF is cleaned up to different standards. Also, SAF is not just cooking oil, they use various kinds of tech.

Running personal cars on cooking oil was legal in the UK up to a certain number of litres/year. I think it was more an issue of taxation, I'm not aware that it creates additional polution.

I just checked and you're right. In Poland it's also during taxation - the penalties for using that are due to taxation laws, not environmental laws.

In the USA (and other countries) there's something called "red dye" which is dyed diesel for use on off-road farm equipment, much less taxes on it.

If they catch you with it in your truck (by dipping the tank) you get big tax-evasion fines.

Not a truck, but my buddy had an old 300SDL (1984, I think)

He would just run whatever in that. I think my favorite was peanut oil, it made the neighborhood smell like Chinese food.

> A mechanical diesel will run basically whatever you can pump through its fuel system. I assume jet engines are roughly the same.

This is very much not the case. They run on kerosene which is highly refined and pure. It has a lower freezing point, higher flash point and lower viscosity, which are obviously positive characteristics when flying in -45C temps high in the atmosphere.

Those are requirements of the use case, not the underlying technology. Turbines are famously adaptable to different fuels.

Mechanical diesels will run on bunker fuel.

Yes, of course, but we're talking about jet engines, as per the comment I was responding to. No jet engine runs on "whatever".

I think you overread it and OP meant turbines generally, but yes, if you mean only jets, that’s different.

> A mechanical diesel will run basically whatever you can pump through its fuel system.

Not really true. They won't even run on gasoline, and if you put it in your tank by mistake it's probably going to be expensive.

In practice it's mostly that, but to a way lesser degree it's other kinds of tech - even direct CO2 capture (although that one is very expensive).

Here is a definition from EASA: https://www.easa.europa.eu/eco/eaer/topics/sustainable-aviat...

Lufthansa's Compensaid originally had a whole portfolio of projects that delivered SAF, but I can see that they mostly switched to cooking oil by now.

https://lufthansa.compensaid.com/projects/sustainable-aviati...

If you wonder where all this cooking oil comes from? Go to China. Regularly you see old, small trucks with open containers and a worker collecting the oil straight from the sewer. If you pass them you automatically go to the other side of the street because of the smell. (This probably exists everywhere, but the capture system used in my country is more or less invisible for the bystander)

Apparently there is a lot of oil produced by all the restaurants.

Dirty fact, when I lived in China, the scandal of the day was counterfeit oil (underground oil). The original idea was to use this oil for fuel. However these fuel converter factories went bankrupt because another industry found a higher value: refine the oil and distribute it as new in counterfeit containers.

Are you sure that’s the sewer? Even in China, the goal of sewer management is to keep things flowing at reasonable cost.

In the US, there are two widespread solutions:

1. The ultimate in cost reduction: a 55 gallon drum out back. When it’s full, someone collects it. It’s far more cost effective to dump your oil in a 55 gallon drum than to dump it in a sink and hope you don’t immediately have to call a plumber to clean up the mess.

2. A grease trap: a not-particularly-expensive device like this:

https://www.webstaurantstore.com/4235/grease-traps.html

Are you sure the tricks weren’t collecting oil from drums and grease traps?

I’ve never looked at oil collection in China. But here’s a Wikipedia article showing what looks like 55 gallon drums:

https://en.m.wikipedia.org/wiki/Gutter_oil

Grease traps are required in all commercial kitchens here in Michigan. AFAIK they're more intended to protect the sewer system rather than for day-to-day grease disposal.

I think they’re required in California too.

In any case, there are multiple companies that will compete to collect your kitchen grease out of that 55 gallon drum, for free. Maybe they’ll even pay if the kitchen makes enough grease — that mess is valuable!

I suspect that most kitchens pay for grease trap service, as it’s more labor and equipment intensive and the resulting extracted crud may be more of a mess than a valuable commodity.

This was a whole Simpsons episode.

> Are you sure that’s the sewer?

It are always grease traps, but it is the same pipe that is used by the toilet, so I would say it is technically just the sewer. And ss the saying goes: if it looks like sewer, smells like sewer, it probably is sewer :-)

Huh? Why on earth would anyone plumb their toilet into the grease trap? There’s probably some cross-contamination from sewage getting into the grease trap outlet, but that doesn’t mean that toilet waste flows through it. There’s also lots of contamination from people washing their hands, cleaning meat and fish, washing dirty vegetables [0], etc in the kitchen sink.

Certainly one ought not to eat anything extracted from the grease trap, but one also ought not to eat anything extracted from the grease collection barrel.

These containers are allll over the place, but you probably don't notice them. Most commonly, I see them as the tiny little dumpster next to the main dumpster. Can be hard to spot since most of them are in a dumpster corale.

Are you sure it wasn't just a stinky tofu stand? :-D

Don't get me started. If you ever have eaten that, don't click on this link and surely don't scroll down to the stinky tofu paragraph (1)

(1) don't click: https://en.wikipedia.org/wiki/Food_safety_incidents_in_China

Look up Gutter Oil on YouTube. Supposedly people clean it up and resell it to restaurants.

We should be so lucky that they only resell it for burning for heat and engines.

> If you wonder where all this cooking oil comes from? Go to China.

I think that your local McDonalds is much closer.

Just the other day I saw for the first time in my life, a "vetboer" (Dutch for fat farmer) truck parked outside the local bar/cafe, and as I turned the corner they were leaving the bar with a big blue barrel.

According to their website [1], the fats and oils they collect are recycled into biofuel for vehicles and green power for households.

Maybe in the future they'll mention aircraft as well...

[1] https://www.devetboer.nl/

See also "Conversion of VW Jetta Diesel to Burn Vegetable Oil":

* https://www.builditsolar.com/Projects/BioFuel/WVOConcersion/... * https://www.caranddriver.com/features/a15129612/how-to-conve...

* https://www.theglobeandmail.com/life/my-volkswagen-runs-on-v... * https://archive.li/ONJo1

Some analysis:

* https://www.consumerreports.org/cro/2012/05/diesel-vs-biodie...

In a more official capacity:

* https://www.carscoops.com/2022/02/tdfrying-oil-audi-makes-it...

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