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Comment by bragr | Hacker News Reader

One important thing to call out about these fuels, and is often neglected in the reporting, is while they might be carbon neutral, they aren't environmentally neutral. At the very least, these fuels will still emit NOx and particulate pollution, so you cannot simply wave away all environment concerns of flying with "synthetic fuels".

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That's not really true, at least for particulates. Most of those problems occur because the fuels have impurities or longer-than-normal hydrocarbon chains. It's harder to filter out existing impurities and long chains from fossil hydrocarbons than it is to not introduce them with synthetic hydrocarbons.

Will the NOx and particulate emission be the same as with traditional fuels? Is there a way to refine this process or an additional process to reduce or eliminate these emissions?

They are making kerosene for aviation. It will replace kerosene made in a refinery, and be burned in the same engines that move the aircraft today. Thus the exhaust will be the same as today.

You seem to be an expert on this topic. I wouldn't expect them to have the exact same characteristics. Kerosene as it is used in aviation today is distilled from crude oil extracted from the ground. This is synthesized gas that is then refined. My question is how much of NOx and particulate emission is from impurities and what the differences are between the synthetic and conventional kerosene.

Is there a way to make a kerosene with less NOx and particulate emission that simply isn't practical today? Since we need to ramp up renewable energy sources to synthesize this fuel can that economy of scale justify some currently impractical process?

The way I read the Wikipedia article on NOx [1] it sounds like NOx comes from nitrogen in the fuel. Is it possible to reduce or eliminate this nitrogen and then emit less NOx? I also parse the Wiki article to suggest the nitrogen is from coal and oil based fuels, which the technology in the article is not.

[1]: https://en.wikipedia.org/wiki/NOx#Fuel

Syngas can be made from various sources, and of course the feedstock can affect the resulting composition. Atmospheric chemistry also plays a role. So reduction in NOx and in particular SOx are possible. But they are also high pressure, high temperature reactions, in particular in a turbine, and the principal component of the atmosphere is N2. So I think we’d have to see what happens.

On particulate pollution: soot and other particulates result from incomplete combustion, so I doubt there would be much change.

Note that particulate and SO2 pollution in the upper atmosphere reflect sunlight before it reaches the surface of the earth. So reduction in SOx and soot has actually allowed the earth to heat more! (It still was good that action was taken, and continues to be taken, on those pollutants)

This is a really complex question and I don't think chemists completely know the answer. If nothing else because we can directly control the molecules coming from this process we can design an engine and the fuel around each other such that we minimize what is produced.

The only way to complete remove NOx production is some sort of N2 filter in the air intake. While it is easy to propose such a thing on the internet, it is not known how to create such a thing in the real world.

It will not be, because the content of 'artificial' kerosene can be controlled exactly. E.g., there is no way even trace amounts of sulfur could enter manufactured kerosene.

That means it won't emit sulfur oxides. But those are already heavily controlled and not a big problem. NOx and ozone are created from the chemicals on the atmosphere, and particulate emissions are created by every kind of fire.

There is even a trade-off here in that adjusting the engine for creating less NOx and ozone makes it emit more particulate matter.

I’m still hung up on the NOx. From what I can tell this doesn’t come from atmospheric nitrogen. It’s from nitrogen in the fuel. I’m not sure if this can be controlled or reduced in the synthetic fuel.

It comes from both. How much of it comes from the atmosphere depends on the burning temperature.

Cool fires produce almost none of it from the atmosphere, so all the NOx comes from the fuel. Hot fires produce so much of it from the atmosphere that the fuel is almost irrelevant.

High-efficiency engines, that produce the least CO2, CO, and particulate matter run on very high temperatures, and produce a lot of NOx and ozone.

Thanks for the clarification.

Did you not realize that various NOx compounds are also generated naturally in the atmosphere with no humans involved. And of course when humans start causing high P-T reactions those reactions happen a lot too.

I don’t see how that is relevant in a conversation about marginal human-caused emissions. Natural NOx is the baseline. The question is the specific delta-NOx between conventional and synthetic kerosene.

Yes, but the high-pressure/high-temperature environment of the turbine will spew NOx compounds out too — as I said we’ll have to see the result.

I’m neutral on this plan (scale up will have to be seen) but since you brought up this issue I’m responding.

also papering over the need to invent cost competitive green hydrogen production and massively scale it really fast.

also hydrogen is a leaky greenhouse gas https://energypost.eu/hydrogen-is-also-a-greenhouse-gas-so-l...

wish them luck, not trying to be negative, we need solutions asap, situation is dire.

The facility mentioned in the article is generating hydrogen on site - the feedstocks are water and CO2. I imagine this reduces the leakage problem quite a bit, since you don't need to pipe it around.

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