Chinese astronauts make rocket fuel and oxygen in space

Why aren't we engineering plants to produce automotive fuel? We ought to at least be able to do diesel.

We do this for some plants. Hybrid palms are used for palm oil production due to the favorable yields and properties compared to parental species. One might ask why there are no cars powered off palm oil seeing as we can readily grow it across the world?

Plants have very low sunlight conversion efficiency compared to solar farms. If you need chemical fuel instead of electricity, it would still be more efficient to use solar electricity to turn carbon dioxide and water into simple liquid fuels like methanol (usable in spark ignition engines) or dimethyl ether (usable in diesel engines).

There are. Millions of them. Most any diesel can run just fine on veg oils, even used cooking oil. (Some very modern cars might need the electronic control systems tweaked.) There have been times/places where grocery stores put limits on oil once it became cheaper than diesel.

Mythbusters: https://youtu.be/QEX1YFXYTdI

TopGear: https://youtu.be/GOFbsaNeZps

Biodiesal is already a thing. Also, we (the US) already blend a portion (about 10%) of corn-derived ethanol to our gasoline. There are problems with it though, one of which is that overall, it probably has a higher carbon footprint (fertilizer, harvesting, processing, etc.) than just not using it.

Corn ethanol is a farm subsidy. It gets greenwashed as something positive because plant=natural=good.

Solar panels have a manufacturing cost, though, while you could imagine a renewable plantation of diesel trees that needs no raw ingredients other than a handful of seeds. It could even be self-seeding, though there are some good reasons we don't usually produce GE crops with viable seeds.

I'm sure the economics don't work out for it: solar panels are already cheap, the land could grow other crops, etc. But photosynthesis being lower-yield than photovoltaic generation isn't enough to rule it out. Perhaps as science fiction, on a future mission to an Earthlike planet that doesn't have the right resources to produce semiconductors at scale.

So now, on top of clearing forests and destroying ecosystems for farmland and infinite suburbia, we should clear even more forests to get fuel for cars, so we can drive them through the infinite suburbia.

we already do have plants that produce (sort of) high-energy-density liquids for us. So if you want gas to be as expensive as maple syrup then... sure. :)

> Plants have very low sunlight conversion efficiency compared to solar farms.

Measured how? If nothing else, they seem to be good at carbon capture. And I don't see how you it could account for engineered for plants engineered to store more of their energy as oil.

Over 1% of US land is devoted to biofuels. If we replaced those corn fields with solar, it would produce 4x the electricity currently consumed in the US.

The forests are cleared because they are allowed to be sold for clearance. Doesn't matter if its palm oil or for cows or sugarcane or ranch homes or solar panels or data centers. People tend to want a return on their investment in land vs spending serious capital to not do anything with a jungle. If you want to limit this you need to prevent land from being sold to entities that would like to profit from it. The specific thing being grown is basically irrelevant.

We do and call it canola oil - which should give you an idea of whether eating canola oil is a good idea

It’s not great for the environment, but it keeps a food surplus available in crisis instantly by just turning off the ethanol production facilities

Internal combustion engines and humans fundamentally use the same chemical process to generate energy. The fact that something can be used as automotive fuel alone says nothing about whether or not it is safe for human consumption.

Or if we just put those panels on any other land. Land isn't the constraint here.

Measured by the fraction of incident sunlight that gets transformed to usable energy. Solar farms generate about 30 times as much power per hectare as corn farms, assuming that you can use electricity directly:

"Ecologically informed solar enables a sustainable energy transition in US croplands"

https://www.pnas.org/doi/full/10.1073/pnas.2501605122

As a rough estimate, you'd lose 2/3 of that energy if the electricity had to be turned into liquid fuels. That would still mean 10 times greater usable energy produced per acre.

Plants genetically engineered for fuel production might be somewhat more efficient in the future, but future solar farms are also probably going to be more efficient.

It's my understanding that corn produces the most (edible) calories per square metre of any of our farmed plants

edit: Looked it up - Rice has the highest number of calories per square metre of farmland, just that it requires marshy/swamp land to grow.

> same chemical process

Our digestive systems heat and oxidize hydrocarbons to generate kinetic energy? You sure about that?

We do. It is called biodiesel. You can make it from any organic matter.

For anyone wanting to learn more - the holy grail of Ag engineering would be to increase the efficiency of rubisco, which is the rate-limiting enzyme in photosynthesis - so understandably there’s a ton of research at doing just that.

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

True. But it might be cheaper to store the corn for a year and then dispose of it, replace it with fresh corn.

Sure if we could magically transport and store it. Like we can for liquid fuels.

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There are many varietals of rice. Most do not grow in marsh land. Farmers often do flood the fields at the beginning of a rice growing season in order to drown out any competing plants. Flooding is not necessary though. Rice will grow with normal irrigation.

We do use oxidation to generate energy.

Of glucose, not a hydrocarbon, but there are plenty of organisms that use hydrocarbons directly.

We don't because we use glucose as our easily transportable fuel, which we evolved because plants happened to produce glucose when we evolved. If there were plants producing some hydrocarbon in fruits we'd have evolved mitochondria to use that instead.

>corn-derived ethanol to our gasoline

Stupidest possible thing to do with food. Especially since in some operations you put in more diesel than take ethanol out.

what goes through my mind is the fact plants aren't low maintenance, the land has to be tended.

growing the fuel plant is probably easy.

How do you get it OUT of the plant?

Solar panels just sit there (they do need cleaning i admit) and produce electricity that we can manipulate very cheaply already.

What machine collects diesel from plants? Can you safely dispose of the plant matter?

I’d rather farm food where plants grow well and put up panels where they don’t..

See https://www.aircela.com/ and many other e-fuel startups, that one makes a very pretty image of a "personal fuel synthesizer" which makes about a gallon of gas a day which is about what my wife and I use.

Ok, yeah, if your reference for biofuel is corn, where you can only use a tiny fraction of the plant, no kidding it'll look bad.

A somewhat less (but still!) ambitious project is to retrofit C4 photosynthesis into rice. It's something like 50% more efficient, and has evolved independently dozens of times, so it's probably a lot more feasible.

Surely you can make cornstarch from it, and that problem only lasts a year.

They are used for all sorts of things we eat, corn nuts, hominy, grits, corn meal/flour and all the things those are used in. Personally, I find it far more palatable than sweet corn and it is far more useful/versitile/nutritious than sweet corn; it is a traditional cereal grain and can be used for all those things we use wheat and rye for.

Do you want plants you grind up into fuel or are you thinking Niven style Booster Trees?

If you are disposing of the corn anyway, why not turn it into Ethanol and then burn it as car fuel?

The only real issue with Ethanol IMO is that corn Ethanol is preventing progress in advanced synthesis made out of, ex: switchgrass cellulose. There are better sources of ethanol if we invest into them.

Why do we need more efficient photosynthesis in plants? Is it for indoor cultivation?

Yes. Rice tolerated flooding better than weeds so it is used as a cheap and easy weed control. Also some places grow fish alongside rice in the same land, getting some extra pest control and fertilizer for free.

Which plant do you estimate is a much better pick?

Something like 40% of the corn grown in the US is turned into biofuel:

https://www.ers.usda.gov/publications/pub-details?pubid=1057...

Cool! They have the numbers, too. Their system needs electricity for electrolysis, 75kWh per gallon of fuel. Compare to 0.24-0.87 kWh/mi for electric cars.

Either a perennial with oily fruit (someone mentioned palm oil down below), or something where you can relatively easily use the entire plant. The idea I keep coming back to is algae bred or engineered for oil content, but I'm not actually sure how feasible that is.

You wrote it like „diesel trees” would be working in a way where you simply chop it down and put it in your gas tank.

Making and then using „diesel trees” would definitely require special equipment and manufacturing pipelines that might be the same cost or more than those for solar panels.

My guess: (in the US, at least) brains focussed on profits have taken less delight in exploration/invention. (Somewhat similar to what's been happening in science.)

> I'd rather farm food where plants grow well and put up panels where they don’t..

False dichotomy. There are places where food does not grow at all and can be used to grow fuel crops. Say, the ocean.

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

> But it might be cheaper to store the corn for a year and then dispose of it, replace it with fresh corn.

I don't think any food crisis scenario in the US involves a road bump that spans a single year and doesn't disrupt existing crops.

So many incorrect statements... you know the world is bigger than your (presumably US) backyard.

I suggest travelling around the world a bit and visiting ie Borneo how entire rainforest ecosystem is being reduced to nothing just due to palm oil plantations, mostly for biofuel and cheap&bad for health food additive.

Similar sight across many places out there. What you wrote ain't valid for a single one.

It's my science fiction story, so I'm going to say the tree we engineered for this was the sugar maple: you can put a tap in it and collect highly pure diesel fuel with a pre-Columbian level of technology.

Plants get more energy, so they generate more food.

> Mayali says that growing phytoplankton outdoors with natural light and finding a less energy-intensive method of powering production would help microalgae-based diesel compete.

I'm sorry, were they measuring the carbon footprint of growing algae by what it takes to grow it inside with artificial light?

Any? That's even more optimistic than me.

No no, you integrate the pump directly into the tree. Skip the farms, just plant the trees at the station in place of the current pumps.

Forest fires would definitely get a lot more exciting.

We kind of are but we are also in the process of stopping burning stuff to create energy for ourselves, as usually burning creates CO2.

Strongly recommend for one of the light-dependent reactions from before that enzyme: https://youtu.be/WhCczIqADuI

We literally make ethanol from corn and sugar cane. And biodielse from soy.

It doesn't make economic and enviromental sense in most parts of the world (especially corn). In some places they are net-positive on carbon emissions compared to oil-derived gasoline. Tilling the fields, growing, harvesting, processing and transporting often emits more CO2 than the equivalent gasoline produced. Especially the initial tilling of the land to convert it to farmland releases A LOT of CO2 into the atmosphere (this is a one-time thing though).

In the US all (ground vehicle) gasoline sold needs to have 10% ethanol (corn-based), in Brazil it is 20% (sugar cane based). In Brazil almost all cars support 100% ethanol fuel and it is quite common to fuel with ethanol only.

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

The whole bio-fuel industry is a very complex mix of economics (often requires subsidies to make sense), geopolitical (less imported oil), environmental concerns (mass scale farming soil degradation and CO2 emissions derived from it) and logistical (completely different transportation and refining process).

Fun fact ethanol freezes at a fairly high temperature and mixes with water which makes it not ideal for cold climates and boats. It is quite common for unaware boat owners to f-up their engines by buying car-grade fuel-station gasoline in Brazil.

No need for diesel trees when there's wood gas, which was successfully used to power vehicles:

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

It's wildly inefficient though and not worth the trouble compared to solar panels and batteries.

Different process, same outcome: hydrocarbons are broken down and oxidized into CO2. We just do it with some enzymes in the Krebs cycle instead of doing a high temperature reaction.

Depends on the context? Could be used in facitilies to produce biochar for production of terra preta/black earth/chernozem which counts as carbon-sink and is very productive soil. Doubly dual-use, so to speak. On-demand. Either biochar, or wood gas. Maybe even both.

Magically transporting and storing liquid fuels involves an unbelievably massive supply chain of trucks and refineries and storage tanks and gas stations.

If we need infrastructure to make use of energy we can ‘magic’ it up.

No magic required: the tech for transporting electricity predates writing, and that by about six millenia; while reusable storage was only about 27 years after dynamo generators, 1859 vs. 1832.

Both have since been improved upon somewhat.

If you had a widely applicable improvement, you’d be able to grow fruit trees in Canada or have two harvests in one season for food crops, or grow much denser species of wood, much more quickly for construction lumber. It would be massively world changing — but it is a 4 billion year old enzyme so is pretty entrenched..

IIRC, diesel engines can run directly on vegetable oil.

> in Brazil it is 20% (sugar cane based)

30% in 2025 for cars (from 27%), 15% biodiesel in diesel for trucks (from 14%).

Source: https://www.em.com.br/politica/2025/06/7183470-governo-aumen...

> The whole bio-fuel industry is a very complex mix of economics (often requires subsidies to make sense), geopolitical (less imported oil), environmental concerns (mass scale farming soil degradation and CO2 emissions derived from it) and logistical (completely different transportation and refining process).

Don't forget lobyying by the relevant sectors!

Oh interesting! Is photosynthesis the main thing limiting growth speed?

I would have expected there to be multiple processes with similar or aligned timings, or some built in limiting mechanism or something... it's not like giving humans higher calorie food makes them become adults faster.

And the social implications of converting farmland from growing food to growing sugar cane/corn/soy. It is a VERY complex topic, but it seems overall it is a marginally positive thing for Brazil (even in emissions). While a very negative thing in the US because of all the subsidies required to make corn ethanol viable and overall negative emissions impact compared to oil gasoline.

Biodiesel is an oil plus an alcohol (usually 80% vegetable oil + 20% methanol) reacted using an alkaline catalyst like lye.

Methanol is also known as "wood alcohol", and can be made at ~40% yield by cooking down wood ("destructive distillation") in a specific fashion, or made from too-cheap-to-meter natural gas if you've got it. Anything you can do with natural gas can also be done with anaerobically fermented methane. You can also use ethanol (fermented from any carbohydrate crops) instead of methanol, creating a biodiesel with slightly different but still usable properties.

...

Sunflower, rapeseed, and soybean oil have very well-established agricultural workflows which require very little labor input.

Palm oil is substantially higher yield, but more labor intensive and is associated with tropical rainforest destruction.

...

You don't necessarily even need to react your vegetable oil. The original Diesel Cycle demonstration engines ran on straight peanut oil, and there are some truck engines out there (like the 12 valve Cummins) that will happily run on filtered waste fryer oil all day long. It's just a matter of tuning, viscosity, compression ratios, seal materials, and the like, being slightly different from petrochemical diesel fuel. Reacting vegetable oils into fatty acid esters ("biodiesel") does attain some modest engine benefits, but mostly it's to match compatibility with petrochemical diesel grades so that you don't, eg, need to replace your fuel lines & pumps with different diameter fuel lines & pumps.

For a car that gets 30mpg that is 2.5 kWh/mi which is 3x worse than the the least efficient electric car, 10x worse than the best.

Still people will want to keep classic cars running in the future and there will be some market, enthusiasts will be willing to pay upwards of $8/gallon. Methanol-to-gasoline fuel is very high octane, around 96, which should keep old engines happy.

The most significant market, I think, for e-fuels are large vehicles such as construction trucks and farm tractors. California has absolutely terrible air quality not just in cities but in ag areas and it would be ideal to synthesize

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

which burns without any soot because it has no C-C bonds.

Improving rubsico would be more along the lines of improving your metabolism so that you can process 4,000 calories per day with the loose analog of supplying more CO2 being the ‘higher calorie food’. It’s the single largest bottleneck in photosynthetic efficiency. TBH, it would likely take several more breakthroughs for plants to make use of an improved rubisco but it’s still a massive target for ag research.

Maybe that's quite the reason why we didn't do it :)

The issue is once again the forest is allowed to be sold. If you open up land for development, that is typically what tends to happen. People will seek out whatever use case makes sense with that land. No one wants to lord over a nature preserve. Everyone wants to make their buck into a buck fifty. Clearcutting of the rainforest in Borneo could be solved with a pen stroke by the government in charge but it seems they are more interested in supporting industrialization than preservation.

Thanks! very interesting space that i barely understand lol. hope it didn't come off as know it all, just questions.

What are you referring to? Copper?

"If you are disposing of the corn anyway, why not turn it into Ethanol and then burn it as car fuel?"

It costs more money and has a higher carbon footprint than simply using gasoline.

More money yes.

The carbon footprint thing doesn't past review of the overall literature. There's one outspoken guy who has to bend over backwards and publishes media articles rather than keeping things academic who tries to make the public believe what you say, but I'm not convinced he's arguing in any serious manner.

Mostly, but gold and silver are also simultaneously antiquity-era metals and great electrical conductors.

No generators to connect to a power grid, nothing to use the power for, but they could still transport electricity in the time before writing.