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Comment by masta | Hacker News Reader

I'll be blunt. This sounds very fishy to me. Diesel creates about 2.6kg of CO2 per litre burned. So for a typical 500 litre tank of a Semi truck, you'll create 1.3tons of carbon. How exactly do you plan on storing that? How do you release it from its storage? When you store it under pressure, the release of the gas will create problems due to freezing. Not to mention the problems and energy requirements of pressurising 1t of carbon.

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I appreciate the fish pun! This is why we're currently offloading the CO2 every 600 miles. Luckily, offloading only takes a couple mins, and drivers are legally mandated to stop every 8 hours (< 600 miles of driving), so they can just offload while they stop, or at the end of the day. 600 miles worth of driving creates about 1,800 lbs of CO2, which is very doable to store onboard a truck.

To offload, the driver attaches a hose, which connects to an offloading tank, and the CO2 is pumped from the tank inside our device to the much larger offloading tank. We liquefy the CO2 as it comes off the truck for storage in the tank. Luckily, the pump doesn't use much energy, and our early partners are using renewable energy to power the pump! We plan to continue using

Is this likely to go on container ships and help them become more eco friendly?

potentially yes that could be a market we expand to. We want to capture all the engine exhaust CO2 we can! So maybe trains as well.

There are different exhaust compositions for the engines on these different vehicles, in part because they use slightly different fuels. So there will be some research and work to do before jumping into the next market, but we love developing technology that has never existed before, we are so excited!!

Does the weight of the CO2 negatively impact the fuel efficiency of the truck in any appreciable way?

We think the impact to fuel efficiency will be < 3%, but we'll be doing more testing over the next couple months to get an exact figure. We'll capture those extra carbon emissions, and we'll more than pay for the extra fuel cost by sharing the revenue from selling the carbon dioxide.

18 wheelers get about 5 to 6 mpg, with a us gallon being 3.785 liters (corrected) . Each mile thus is 0.63 or more liters of diesel.

A truck can do at least 100k to 120k miles per year.

So 63k to ~76k liters per year per truck. 63k * 2.6kg equals about 163.6 metric tons per year on the low end.

It's 3.785 litres per US gallon.

Corrected, thank you!

Down thread it's explained that the device weighs 1000+ lbs more when full, after 600 miles.

600 miles isn't the full tank of combustion. Sound like driver is swapping tanks or something at one of their stops.

That makes for about 470 k per km captured, and they're not claiming 100% efficiency. So it passes that sniff test, at least. Weight is also plausible.

Final q (other than cost): how much exhaust backpressure?

This is a crucial question! To our surprise, our beta testing of our prototype has actually shown that this is creating < 0.5 psi back pressure on the engine (negligible) and we believe we can get it down to essentially 0 by the time we deliver our first units to customers this summer.

Are you saying 1 litre (about 0.71 kg) of fuel creates 2.6 kg of CO2? :-)

You're taking a bunch of `C` in the tank (AMU: 12) and 2x `O` out of the atmosphere (AMU: 16). This means the expected mass goes from 12 -> 44, or an increase of 3.6. My trusty calculator says that takes .71kg to 2.6kg.

This is just approximate, since fuel has a bunch of H and S and other crap, so it's not 100% C. But, yes, these figures are in the right ballpark.

You are correct of course. I was intending to make an alchemy joke about a particular phrasing of the parent poster (the part about creating 1 tons of "carbon"), but misread the entire message and commented on the wrong part. :-/

Now the jokes' on me.

Ah, my bad, yes obviously it creates ~1ton of CO2, not Carbon. :)

It certainly does. The O2 comes from the air and is heavier than carbon. The carbon comes from the fuel, which is its main content by weight.

1 kg of carbon from fuel + 1.75 kg of O2 from aith = 2.75 kg of CO2.

Meanwhile the hydrogen in a hydrocarbon is somewhere in the range of 1/7th of the weight, so the fact that it all goes up the exhaust pipe in the form of water doesn't really subtract all that much weight from the input.

There's more energy in the hydrogen bonds, not the carbon-carbon bonds, right? Just adds insult to injury, if you ask me.

When you mix each 1 kg of fuel with around 3 kg of O2 during combustion, why do you think that outcome is impossible?

On the surface, it seems like you're only burning fuel in an engine. People forget, or may not even know that you're burning mostly air, and the fuel is there to help burn the air. I think this was a legit question to ask, as it's going to be a common misunderstanding for a lot of people.

I think some of the replies are missing your little s/carbon/CO2 sleight of hand there :)

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