An Airbus A380 was flown on fuel derived from cooking oil | Hacker News Reader

An Airbus A380 was flown on fuel derived from cooking oil

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59 pointsprostoalex95 comments

The obvious question is whether we could switch all aviation from jet fuel to cooking oil. Commercial aviation consumes about 200 million tons of jet fuel per year. The world annual production of palm oil (by far the highest yielding vegetable oil crop) is about 75 million tons. Can we expand this by a factor of 3.5?

Currently palm trees for palm oil are planted on about 50 million acres of land. For comparison, in the US about 30 million acres are planted with corn for ethanol production.

They can fly an A380 on cooking oil, but can't phase out avgas? How does this make sense?

The issues are totally unrelated. Jet turbines have always been capable of running on almost any fuel. I would hazard a guess that what Airbus did here was mostly certifying that the alternative fuel wouldn't cause any major problems, maybe also things like tweaking the engine management systems to ensure consistent power output and throttle responsiveness with the new fuel. The problem with avgas is that there are a huge number of aviation piston engines still in use that were built with 1930s-1960s era technology (in some cases the engines themselves are literally that old) that were designed to use leaded gasoline. Getting those engines to run on unleaded gas would at best require extensive modifications to the engine and at worst just isn't possible. In the cases where it's possible, someone has to foot the bill to figure out how to modify the engines and get the changes certified with the FAA, both incredibly expensive propositions. Once that's done all of the owners will have to drop the money to upgrade their engines.

The death of avgas is inevitable but unfortunately it's probably going to take some sectors of general aviation with it. Those older planes are still flying in large part because newer planes have gotten so incredibly expensive. Also from what I've read the warbird community is working on the problem but many of them aren't very optimistic about being able to get those big WW2 era engines to run unleaded.

I am not a chemist so maybe I am naive here. My understanding is that lead additives were necessary to "fake" higher octane content (and the 0.1% lead additive is much cheaper than the 99% octane). Why can't we just go back to expensive high-octane fuels instead of adding lead (or just use the various alternative additives used in other high-performance engines)?

Edit: an internet search tells me that avgas has an octane rating of 100... So why can't we just use actual pure octane in these engines?

Knock resistance isn't the only factor in leaded vs. unleaded. From Wikipedia, valve wear is also a factor (the lead deposits apparently act as a kind of lubricant):

"Meanwhile, Teledyne Continental Motors indicates (in document X30548R3 most recently revised in 2008) that leaded avgas is required in their engines: "Current aircraft engines feature valve gear components which are designed for compatibility with the leaded ASTM D910 fuels. In such fuels, the lead acts as a lubricant, coating the contact areas between the valve, guide, and seat. The use of unleaded auto fuels with engines designed for leaded fuels can result in excessive exhaust valve seat wear due to the lack of lead with cylinder performance deteriorating to unacceptable levels in under 10 hours."[8]"

https://en.wikipedia.org/wiki/Avgas#Properties

This seems like such a cop-out excuse. We'd rather harm potentially millions of people with toxic materials rather than inconvenience a few dozen aviation enthusiasts. Progress moves forward, if these old engines can't function in this new world they should be scrapped and replaced with something that can do the job.

And BTW, general aviation has been asking for leaded avgas to be dropped for decades now. The holdup is not the pilots or plane owners but the goddamn FAA [0].

[0] https://www.avweb.com/insider/faa-continues-to-stall-on-g100...

Do you know of any research focused on lead-related health issues from areas of popular general aviation? Or around the supply chain for leaded fuel?

There are a few studies done. Here is one carried out by the NIH around NC. [0]

In summary they are noticeably elevated but not as high as, an example, Flint Michigan. Lead blood levels do fall off precipitously after ~2km.

[0] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3230438/

This is really good thank you. Worthy of a follow-up submission on HN of its own since we're pretty deep into comments here.

Note that this study is specifically focused on North Carolina. I'm curious if similar research has been done in the Western US. California in particular is very popular for GA. Here's the top 10: https://generalaviationnews.com/2020/02/03/top-10-busiest-ge...

edit: Another link: Santa Clara, CA recently banned sale of leaded fuel https://grist.org/transportation/california-county-bans-toxi...

To save people the full read, here is the most relevant sentence:

> children living within 500 m, 1,000 m, or 1,500 m of an airport had average blood lead levels that were 4.4, 3.8, or 2.1% higher, respectively, than other children.

Presumably 'valve gear components' could be designed to function without reliance on a toxic lubricant. Ultimately this comes down to being cheap.

Absolutely for new equipment that would be the case. Safely retrofitting existing equipment is quite a bit more challenging, and my suspicion (without having actual numbers) is that the vast majority of the fleet that would require those retrofits is quite old. Some of the manufacturers don’t exist anymore, so having them sign off on “this retrofit kit will safely transport you in the air for thousands of hours” wouldn’t be possible.

It’s not an unsolvable problem, but it’s thorny for sure both from a safety perspective and a cost perspective. You call it “being cheap” but my gut feeling is that retrofitting existing 40-year-old kit to handle unleaded Avgas safely would be capital-E Expensive.

General aviation is expensive certainly and for a select few very wealthy individuals. I call it cheap because there is a way to solve it, but owners of small planes are choosing not to do so (and they're not compelled to do so despite the known externalities of their outdated machinery).

Maintaining a beautiful car from the days of the Cold War is also not cheap, but it can be retrofitted to pass emissions tests. If you don't, you can't legally drive it. I don't see why the same doesn't apply to aircraft.

The trick is that there’s two tiers of expensive for GA:

- People buying, say, a new SR22 for $779,000

- People buying, say, a 1976 Cessna 172 for $72,000 and splitting it with 3 friends

Having Cirrus work on, say, regular Mogas by contracting Continental to develop a new engine would be expensive but the buyers aren’t particularly price sensitive and amortized across the typical lifetime of an aviation engine design (the IO-550 in the SR22 was first delivered in 1983) likely wouldn’t hurt much.

Trying to come up with an engine swap for the O-320 in that ‘76 172 is a whole other can of worms. Who’s going to even sign off on it? The whole aircraft is 50 years old and designed and certificated for that specific engine. There’s no financial incentive for Cessna to do it, and even if they did, the cost to do the swap would likely significantly exceed the financial capacity of many owners.

I absolutely would love to see a financially viable way to get past this! The use of LL fuel in 2022 is tragic. On the other hand, killing off a big chunk of the GA industry and leaving it solely in the purview of the Wealthy and not just dedicated hobbyists… that sucks.

For context, my family has an old Piper J3 sitting in a hangar on a farm. It definitely needs an overhaul, but to get it back in the air would likely be a low 5-figure bill; retrofitting a Mogas engine onto it in such a way that it doesn’t need to be categorized as “experimental” would be… prohibitive.

Thanks for this context. I'm not a pilot but I can absolutely relate to the joy such a machine could give.

I'd like to ask one thing further: Do you think the existence of these older cheaper planes is holding back the development of upstart companies aiming for a price point that's closer to the Cessna 172 than the SR22? If leaded fuel engines were banned by the FAA today, would that create an opportunity for new entries, maybe with EV/hybrid engines? Or are there fundamentally different manufacturing economics to safely put something like that up in the air at that price point today?

There are already alternative engines in wide use (particularly on ultralights and light-sport aircraft) that can run on regular, unleaded gasoline, like the Rotax 912[0]. The issue, as others have pointed out, is getting these newer engines certified for use on existing, older planes. This would require extensive testing to get a Supplemental Type Certificate (“STC”) to allow the engine to be installed on a certified aircraft (think anything manufactured, like a Cessna 172 or Piper Cub.)

0 - https://en.wikipedia.org/wiki/Rotax_912

I wonder if this extensive testing could be funded by a tax on leaded fuel. Seems like this would benefit everyone.

Sure, or the FAA could just go ahead and approve G100UL[0] and save everyone the trouble of an engine swap.

0 - https://www.avweb.com/insider/faa-continues-to-stall-on-g100...

Except the people who have to pay for an engine swap.

> Do you think the existence of these older cheaper planes is holding back the development of upstart companies aiming for a price point that's closer to the Cessna 172 than the SR22?

Things in aviation are incredibly expensive because of how much it costs to have things certified by the FAA for safety and reliability. I'm no legal expert but I don't think an upstart company has much wiggle room to get around that if they want to legally sell their aircraft in the US. As an example Cessna 172s are still made and AFAIK the modern ones haven't required leaded fuel for some time. A 172 is just about the most basic small airplane you can get but today a new one costs as much as a house, about $400k.

I mean, there's being cheap and then there's getting a new aviation engine FAA certified. Those aren't exactly the same thing and Bob the dentist who likes to take his Cessna 172 up on weekends can't simply approve a new engine.

This is why buying a new spec Cessna 172 from the factory floor today will still come with the good old Lycoming O-360 engine, introduced in 1955.

Cessna sells ~250 172s per year, nowhere near enough to justify new engine approval.

I'm no expert, but I'll express a wish: that modern supply constraints mean Lycoming O-360 engines may be noncompetitive to an engine design conceived today. Perhaps these old engines are suppressing the investment into an invention that turns a 250 person market into a 25,000 one?

> a select few very wealthy individuals

Whenever I see comments like this I always remember the airplane owner (Cessna 152) I used to know who drove a beat up old Toyota Corolla with the bumper sticker "My Other Car is an Airplane."

> Meanwhile, Teledyne Continental Motors indicates (in document X30548R3 most recently revised in 2008) that leaded avgas is required in their engines: "Current aircraft engines feature valve gear components which are designed for compatibility with the leaded ASTM D910 fuels. In such fuels, the lead acts as a lubricant, coating the contact areas between the valve, guide, and seat. The use of unleaded auto fuels with engines designed for leaded fuels can result in excessive exhaust valve seat wear due to the lack of lead with cylinder performance deteriorating to unacceptable levels in under 10 hours."

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

Aviation moves very slowly because of the safety and reliability requirements. This is a blessing and a curse as far as things like that go. Generally speaking, equipment gets certificated under very specific conditions and deviating from those conditions is strongly discouraged (if nothing else, by your insurer). If the POH (Pilot Operating Handbook) says that your 1967 Cessna 172 has to run on 100LL, you run 100LL and not some unleaded 100-octane equivalent.

I don’t have the exact numbers, but outside of doctors and nouveau-riche tech folks, I would suspect that most of the North American GA (general aviation) fleet is 30-40 years old. There’s new GA aircraft coming to market, but they’re eye-wateringly expensive compared to perfectly serviceable older aircraft that can get an electronics upgrade.

Jet fuel is a fuel oil more like kerosene. High octane aviation fuel is for piston engine aircraft like a Cessna or a p-51.

There are actually very strict regulations on the maximum amount of biodiesel (fatty acid methyl esters) allowed in jet fuel. They are much more prone to microbial blooms than petroleum based fuel oils and the fungal films can clog filters, starving an engine.

Lead also has lubricant properties for things like mechanical fuel pumps and injection, valve seats and stems, so it's not just for octane boosting you need to replace the lubricant too.

Are there unique design constraints for engines used in general aviation that these components couldn't have a lubrication strategy akin to engines that work with unleaded fuel?

Nope it's just all the old planes flying around that require it. As the engine in a plane could be considered to be fairly safety critical people are extremely resistant to trying new things on it.

For sure, Thank you. I meant it 100% with a not toward the regulatory/economic constraints at stake and have zero interest in the physical workings of engines.

There is G100UL which seems to be promising as a 1:1 replacement for the current 100LL. Though regulatory inertia seems to be delaying a large scale rollout: https://www.avweb.com/insider/faa-continues-to-stall-on-g100...

I'm not aware of any experiences of G100UL with warbird engines.

Gas turbines (which includes jet engines) can potentially use a lot of different fuel sources. For example, the M1 Abrams tank can run off a variety of different fuels. If it’s liquid and burns, it’ll probably work.

Turbofan engines may need to be redesigned to accommodate a different fuel source, but there isn’t any reason you can’t use automotive gasoline to power a jet. It’s just not a good idea because it vaporizes more readily on the ground, has less power per volume, and freezes in the temperatures jet operate in.

Piston engines aren’t as flexible. They don’t inject fuel in a constant stream, they compress and explode it.

Vastly different fuels.

Jet engines run on a Jet A1, kinda like diesel or kerosene, ignites under pressure with oxygen.

Avgas is a high octane (100) petrol that requires a spark for ignition.

Last time I was reading about unleaded avgas it seemed to be mostly a regulatory inertia problem, though I'm not well versed in aviation engine requirements.

In the case of cooking oil, it is (I assume, didn't check) a trial and neither the engine nor the oil are certified for regular flight. Even if ao, it most likely would be the specific engine that would be recertified, not the cooking oil derived fuel.

AvGas is different, there it is not individual engines that get re certified for using lead free fuel (faster for each engine but impossible due to the agevand obsolescense of these old engines), so the fuel has to certified for all engines at the same time.

I wonder how viable it is to synthesize Kerosene or some other carbon fuel using renewable energy and some carbon source (stored factory exhaust?). Renewables are intermittent, but if the fuel synthesis process can also be intermittent then isn't that fine? Viola: you got a form of storage. Why does this not seem to be viable despite dropping costs of renewables?

It is possible, the search keywords are "synthetic fuels" or "e-fuels" ("electro-fuels). Currently it's a lot more expensive than fossil fuel, which is why it's mostly a research project and not a large-scale commercial business.

One problem is that while you can get an unlimited amount of hydrogen via electrolysis of water, you have to get the carbon from somewhere to produce hydrocarbons. There is a lot of CO2 in the atmosphere, but it's still a pretty low concentration so it takes a lot of energy to filter it out. And yes, using factory exhaust etc. is an easier option, but if we're gonna solve climate change most CO2 exhaust sources have to be replaced at some point so that might not be a very long term plan.

Is CO2 capturing the biggest problem that prevents it from being cost-effective?

Energy input is the other. It takes at minimum the combustion energy to reconfigure the molecules but most of the processes happen at high temperature and pressures which takes energy to do.

I understand input is an issue, but why aren't renewables cheap enough to solve the energy input part of the problem? Don't solar panels cost next to nothing nowadays?

How much must renewables decrease in cost in order for such fuels to be economically competitive?

Gasoline is maybe 5 dollars a gallon and contains some 35kwh of energy. When burning gas in an engine we don't get 35kwh [1], but that is what is there.

Lets imagine we are building a gallon of gas with perfect efficiency. 35kwh is already about $3.15-10.50 depending on the market [2]. Lets assume however, we are willing to take the capital risk and invest in our own solar plant which gives us a price of $2.10-2.80. We can take this even further.

Lets say we buy our own panels, and don't even connect it to the grid. These panels are only used for this, and we only make gas during the day. Here we pay $1.2/watt of capacity [0]. Solar panels have a life of about 10 years. 8x265x10 -> 29.2Kwh/dollar if we use the energy from the panels entirely efficiently. This is about $1.2 on the absolute low end. Note that panels require some maintenance, and don't just die after 10 years.

Now that we have the energy, lets get our raw materials. Gasoline has a chemical formula of C8H18, a ratio by weight of 96:18 or 16:3. A Gallon of gas weighs about 6 pounds, meaning about 5 pounds of carbon to 1 pound of hydrogen.

Hydrogen is not cheap [4], Electrolysis costs some 2.4K USD per ton, 1.2 dollars a pound. Electrolysis is more than energy in, hydrogen out. It uses up electrodes for instance. If we are allowed to use fossil fuel derived hydrogen the price comes down to 0.2 dollars a pound [5].

Carbon is $35/ton, but this increases to $75/ton if we want beverage grade [6]. You could argue that we will need to purify the CO2 ourselves either way so we can use the cheaper carbon. Carbon to oxygen by weight is 12 : 30 or 2 : 5. So for 1 pound of carbon we need 3.5 pounds of CO2. This brings our cost to $122.5/ton or about 0.12 cents a pound.

Thus our material cost, including no synthesis is already in the ball park of $2 -> $12.9 per gallon.

We should also consider that gasoline has costs that our hypothetical fuel would also need. Additives make up 30-70 cents per gallon. Distribution another 30-60 cents a gallon. Taxes another 40-60 cents a gallon [7].

Adding these costs, our hypothetical fuel now costs $3 -> $14.8 per gallon. But we still need to actually add the costs for turning the ingredients into fuel. We also don't have any labor costs, or costs of capital.

[0] - https://a1solarstore.com/solar-panels/panasonic-solar-panels... [1] - https://physics.stackexchange.com/questions/98966/maximum-th.... [2] - https://www.electricrate.com/electricity-rates-by-state/#:~:.... [3] - https://homeguide.com/costs/solar-panel-cost#:~:text=Residen.... [4] - https://oilprice.com/Energy/Energy-General/The-Green-Hydroge.... [5] - https://www.chemanalyst.com/Pricing-data/hydrogen-1165 [6] - http://www.dotyenergy.com/Economics/Econ_Physical_CO2_Market.... [7] https://voltaoil.com/what-makes-up-retail-price-for-gasoline....

now the only meal served in flight will be french fries with fried chicken

A significant improvement over most current in-flight meals...

Yes. To be fair the last time I flew it was clear that the packaging had more nutritional value than the food.

[Cue the 'We are the Millers' Meme] You guys got food?

Cooking oil is in such short supply (Ukraine produced much of the world's seed-derived cooking oil) that UK fish and chip shops were unable to get supplies.

I've seen news reports of cooking oil thefts here in the US - restaurants being broken into for their frying or cooking oil.

Trying to push these "solutions" is beyond irresponsible. People in many countries can't afford to eat, and we're turning food into fuel?

The fuel is made from used, waste oil. Not something you can cook with. The article explains this.

Same is true when you read about cars and buses powered by cooking oil. They aren't going to the grocery store to buy the oil.

> Ukraine produced much of the world's seed-derived cooking oil

Best I can find is that Ukraine accounts for as much as 50% of exported sunflower seed oil, which is different from "much of the world's seed-derived cooking oil" since almost all countries produce cooking oil domestically, and american imports are most likely from canada.

https://www.ifpri.org/blog/impact-ukraine-crisis-global-vege...

There's still cooking oil available but there's definitely less of it and at a higher price. The local stores here are out of the cheaper brands of rapeseed and sunflower oil.

The intent is to use waste oil, so, the oil remaining after shits been cooked in it. Usually this is referred to as WVO (waste vegetable oil).

Similar to how people process WVO from fish and chip shops into biodiesel for vehicles by reacting it with methanol and potassium hydroxide after some cleanup steps.

At the moment disposing of WVO is costly and wasteful.

> restaurants being broken into for their frying or cooking oil

If that were happening, I'd expect to see shortages of cooking oil on store shelves. I don't recall that ever being the case.

Diesel fuel thefts from road work equipment and farm machinery here in Australia have also recently spiked.

It runs on used cooking oil.

Biofuel from forest byproducts seems like a much more reasonable source than to use anything edible.

The problem with biofuels in general is that they're always sold as "from byproducts". But of course as soon as you set up a market for fuel it becomes a product in its own right. So they tend to drive the conversion of natural habitat into land managed like agricultural land, which has all the same problems as normal agriculture (habitat destruction, use of ecosystem-destroying pesticides, pollution from fertilizer runoff, soil erosion, etc.) and it's not even producing food. Land usage for food crops (destruction of tropical rainforest habitat for soy and palm oil, destruction of atlantic rainforest for sheep farming, etc.) is already contributing to a rate of species lost three orders of magnitude higher than the expected background rate. And there's a limit to how much we can eat; the amount we can burn as fuel is almost unlimited.

"Sustainable" solutions that incentivise turning over more land to agriculture are nothing of the sort. And it's really the incentives that matter more than whether the initial prototypes are using existing byproducts.

My personal perspective growing up in Sweden is basically that there are thousands of trees per capita and the tragedy is that forests are slowly taking over old farmland. In the northern half of the country you can’t grow wheat due to the short season. It’s wildly different from the more densely populated parts of Europe, but in Russia and Canada there are probably tons of similar areas with spruce and pine forests the size of small countries have always grown, and where the climate is perfect for forests and bad for food crops. I don’t think there is ever a demand for forest byproducts where it would be profitable to grow trees where corn or wheat could be grown instead.

It's just that we use 2B litres of cooking oil every year. They're always looking for something useful to do with used cooking oil.

Used cooking oil is a great product use because it’s basically waste. It’s a logistics nightmare though because it’s distributed and must be collected. Even if it’s free, it’s expensive.

does the used cooking oil gas station in berkeley still exist?

Biofuel Oasis, yes! They still sell biodiesel.

I suppose one could say that the flight was well done, a rare achievement indeed.

With farmers being attacked, there won't be cooking oil for this soon enough...

> an Airbus A380 airliner was flown solely on fuel derived from cooking oil.

Clickbaity, derived from cooking oil is a little different than flying on straight up cooking oil (like what diesel engines are capable of, just dump it in).

I doubt there is enough [used] cooking oil on earth to power all the jet engines on a daily basis. Cool as a PoC, though.

Kerosene freezes at -47°C. Cooking oil freezes at temperature ranges you're more likely to experience in an aircraft. I don't think we'll see any straight cooking oil jet aircraft.

The accent should be on the "solely".

Mixing small quantities of fuel derived from cooking oil has been done before, even at industrial level:

https://www.newscientist.com/article/2181821-how-to-make-jet...

A jet turbine is a diesel engine; you could run one on straight up cooking oil the same as any other diesel engine. The same principles apply you just have a combustion chamber instead of a cylinder.

Jet engines aren’t actually Diesel engines though. They don’t use a Diesel cycle but a Brayton cycle. The principles are different - a Diesel engine works by having a fuel which ignites when compressed in a confined space, while a Brayton engine specifically avoids that and ignites its fuel via a heat source.

But the fuel known as “Diesel” is pretty close to jet fuel, both of them being almost kerosene, so it should burn just fine in a jet engine.

Right, but compression itself is not an ignition source; all the compression does is generate heat, so really it's no different!

You can also run diesel cars and trucks on kerosene. The winter blend of diesel fuel in cold climates is a mixture of diesel and kerosene (which has a lower freezing temperature).

Straight kerosene would work, but it is less lubricating that diesel fuel, so you need to mix some engine oil in with it to avoid damaging the engine. And on a modern car you are probably going to destroy any emissions control system, as kerosene has much higher sulfur than diesel.

> You can also run diesel cars and trucks on kerosene. The winter blend of diesel fuel in cold climates is a mixture of diesel and kerosene (which has a lower freezing temperature).

I know that Mercedes diesel sedans here in Asia has "NO ADDITIVES" written multiple times all around its inner fuel lid.

I don't know for sure if Germany is considered to have cold climate, but if it is, I wonder if their diesel has kerosene and how that plays out with these engines.

As I understand, Mercedes diesels are ubiquitous in some European countries (atleast as a taxi)?

In terms of the length of the hydrocarbon chains, winter diesel has shorter chains than summer diesel (to reduce the gelling temperature), which moves it towards a kerosene-like composition. So in that way you could say it's a blend of (summer) diesel and kerosene. However, it's a product made to diesel specifications at a refinery, and has to satisfy all the other properties of diesel fuel standards like sulphur content, cetane number etc etc.

Here's one winter diesel fuel I know is used in Germany (though this page is speaking to the Austrian market): https://www.omv.com/en/news/omv-maxxmotion-best-winter-diese...

It seems to include a "HVO bio component" (Hydrotreated Vegetable Oil).

Many years ago, one (among many others) of the reasons why Caterpillar earth moving equipment was ubiquitous was that their diesels could be tuned to burn almost any fuel. probably not cooking oil, but the diesel fuel available in some countries was more like what is called "bunker"[0] than anything else.

On the other hand up to the '80's it was a common practice to add in cold climates some 5%-10% gasoline or kerosene to diesel fuel directly in the tank of trucks and building site machines.

[0] https://en.wikipedia.org/wiki/Fuel_oil#General_classificatio...

I remember a 70s? book speculating that jet engines could run on a wide variety of sources, eg. shredded straw (intended for tractors and combine harvesters). I don't think that idea was well received... don't see too many jet tractors around.

The old Tornado jet engines can run, basically, everything. For a while that is, the need serious overhaul after running on Diesel for example after low singel diggit flight hours. The reasoning back the, at the hight of the cold war, was to be able to move the squadrons quickly to dort strips an roads and out of harms way, and back to an airfield, in case nuclear strikes and stuff. For that purpose using Diesel is helpful I guess. It was never done, exept for trials as far as I know.

> A jet turbine is a diesel engine

I though jet engines used heat to ignite the fuel? Diesel engines use compression alone to ignite it.

compression itself is not an ignition source; it's the heat the compression generates that ignites the fuel.

Commercial aircraft engines run on kerosene formulations, not diesel.

Common automotive Diesel fuel is a paraffin, just like JP-8/Jet A1. They're chemically pretty similar.

Would you just dump used cooking engine into your engine? I’d imagine there’s a few particles that don’t burn off super cleanly and gunk up the pistons or valves or something

If you filter it well, you actually can run a diesel engine from waste cooking oil directly (but it's not great for it, which is why it's often converted to biodiesel or HVO/HEFA).

The hydro-processing that HEFA/HVO (the kind of fuel used in the above trial) goes through is mostly for cold handling properties, viscosity, etc. - it actually makes it basically chemically identical to the fossil derived hydrocarbons that are normally used, which is pretty cool and interesting.

The tricky part of cooking oil in engines is that it's higher viscosity / thicker than diesel. So straight cooking oil only really works well in the types of diesel engines that use glow plugs and swirl chambers...where the fuel gets fully atomized despite the high viscosity. Direct injection diesel engines have more trouble with cooking oil, with lots of deposits and gummy build up.

The dirty bits aren't a big issue, other than for any fuel filters if you don't filter it first.

Car Throttle had a good video about it a few years ago:

https://youtu.be/WNJH1rikujI

The most important point is you need an older car with mechanical injection (before ~2005). Modern diesels with electronic injection are much more sensitive to the fuel used, as they run at much higher pressure and components have tighter tolerances.

On an older car, yes you can just dump it in after some crude filtering (e.g. with cheesecloth). I have a neighbour with an old Land Rover and he has been running it for years on cooking oil. Some people start on diesel then switch to cooking oil later. It has a higher viscousity at room temperature than diesel, so it works better once everything is warmed up.

It can be done: https://www.popsci.com/diy/article/2009-09/taking-chances/

it's well known enough that the grease bins behind McDonalds and places now have locks, people were looting the oils

Why wouldn't McDonald's and places be thankful that somebody is disposing of their waste for them? Or do they do something productive with the contents of the grease bin?

It seems recycling grease is profitable enough that it's offered as a free service to restaurants. See, e.g.,

> > What does it cost me to be a DAR PRO Solutions customer? > In most cases, there is no signup or administrative fee for becoming a DAR PRO customer, though depending on market conditions, store location or other special circumstances, there may be a small delivery fee. This would be disclosed prior to finalizing any agreement. Normally, we provide the oil storage equipment and grease pick up at no charge to our customers under normal yellow grease market and operational conditions.

Source: https://www.darpro-solutions.com/about-dar-pro-solutions/faq...

I wouldn't be surprised if a large company like McDonalds is able to recoup some of their costs by selling grease. Alternatively, even if the service is a net cost, as with residential recycling the service fee might offset by what the recycler can make from the waste, and so the recycler might require measures to safeguard their supply. Also, you might not want strangers rummaging through your bins as some of them might make a mess.

Very american answer: maybe somebody sues mcdonalds after stealing the used oil and it breaks their engine

They get money for it

Sewer oil industry will be booming

Could you ever grow enough crops on Earth to replace jet fuel at current usage, without starving everyone to death? I have no idea how to evaluate this. How realistic is it?

Since plants are very bad at converting sunlight to oil, I would assume that it will always be much more space efficient to use solar panels and synthesize the fuel. But there is waste biomass, including oils, that can supplement a small fraction of our energy demands with little extra effort.

I think it's a bad idea. But I saw a statistic saying the waste oil collected now could satisfy about 2% of the demand, and I think if we looked at thermal depolymerisation and hydroprocessing of other biodegradable waste we could possibly get up to a decent chunk, maybe 20-30%? If done with zero emissions energy that would be pretty carbon neutral.

Not sure where we go after that for aviation, it's definitely one of the most tricky applications for alternate fuels. Maybe efuels would be next for some portion. Hopefully electric aircraft can eventually do regional short haul but I'm not holding my breath on energy densities getting competitive for that to take a huge chunk of aviation any time soon...

I think the idea is to use waste cooling oil, meaning oil that was already used for cooking, then blended with whatever to make it more usable as jet fuel and reused. So it wouldn't be a waste of crops, but reuse of a waste product already manufactured and used for other things.

That's nice in theory, but in practice most biofuels in use today are manufactured from food crops. So worries that producing kerosene from cooking oil might worsen the already existing food crisis are not completely unfounded.

Related article from today: https://www.theguardian.com/environment/2022/jul/13/halt-use...

around fifteen years ago at the start of the synthetic biology boom, there was lots of talk of genetically engineered algae as a potential stand in for fossil fuels. i haven't heard much in a while so i'm guessing there were problems with it, but it always sounded like the most elegant of solutions to me....

Algae fuels have been researched at least since the 1970'ies. In principle they are very promising, but it seems it's almost impossible to make these theoretical yield predictions work out in practice.

Did the smoke detector go off? /s

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