As most people know, not all animals on earth benefit from humans driving vehicles that warm the globe and produce horrible chemicals, such as Carbon dioxide and Nitrogen oxide.

My question

What chemicals can be used as fuel (with or without a catalyst) as a potential substitute for hydrocarbon fuels (Petroleum & Diesel), that are more environmentally friendly?

Requirements for this fuel go as follows:

  • The fuel must be sourced from the continent on which it is used.
  • The fuel must be able to be stored as a liquid (including if mixed with water)
  • The fuel must be more environmentally friendly than Hydrocarbons (either producing less CO2 and NOx chemicals, or by them being renewably sourced- eg, via crops that offset any carbon dioxide produced.)
  • $\begingroup$ FYI, carbon dioxide is produced by any aerobic organism as long as it lives and breath. $\endgroup$ – L.Dutch - Reinstate Monica May 3 '19 at 13:38
  • $\begingroup$ And last but not least, what is the worldbuilding problem here? $\endgroup$ – L.Dutch - Reinstate Monica May 3 '19 at 13:39
  • 1
    $\begingroup$ Hydrogen. Period. There's water everywhere to produce it, it "burns" back to water, and using renewables to produce it it's rather environmental friendly. $\endgroup$ – Erik May 3 '19 at 13:41
  • $\begingroup$ I'm with @L.Dutch, there doesn't seem to be a worldbuilding problem here. What rule or system of your world are we talking about? This seems to be a question better suited for Chemistry. VTC OT:NAW. Also, Erik's suggestion of Hydrogen along with bio-diesel are likely the only chemicals that meet your expectations - and you could have learned that with a little research. Keep in mind that combustion is destructive, which means there's always an undesirable consequence to its use. $\endgroup$ – JBH May 3 '19 at 14:24
  • $\begingroup$ Yeah, sounds like you're looking for bio-diesel. The alternative, which doesn't fit the parameters of your question, is an electric engine where all the batteries are charged by purely sustainable means like solar and wind. $\endgroup$ – Cyn says make Monica whole May 3 '19 at 14:31

Liquid is not the way to go, period. They are pretty much all going to contain extra pollutants compared to stored energy or gas based fuels. If you lift these restrictions and just focus on what is more environmentally friendly, that can be utilized to replace liquid fuels, I can think of 3 options, but they all have trade-offs.

1 - Electric: As long as you collect your power from a force of nature such as solar, wind, hydroelectric, or geothermal, you get virtually no emissions from use. However, in most cases, electric cars are powered from the main power grid which mostly burns fossil fuels anyway and could even be more harmful since so much power is lost in the process of converting kinetic energy to electricity, then transferring it through miles of cabling, then storing it to batteries which drain a bit while waiting to be used, then back to kinetic. Batteries also make electric cars heavier meaning it takes more energy to move them. Also, the batteries are made from highly toxic materials which need to be occasionally replaced. The toxicity of battery mass production and use could in some ways be just as bad as vehicle emissions.

2- Hydrogen Fuel: This has a lot of the same advantages and disadvantages as electric. Pure Hydrogen does not naturally exist in this world. The processes to refine it require more power than you get form fueling your car with it meaning, if you don't refine it using renewable power, you're wasting your time. Also, pressurized hydrogen can be pretty dangerous stuff. The plus side is that hydrogen powered cars use less toxic materials to make than electric, but the needed materials are still rare which limits mass production.

3 - Methane Fuel: While technically this is a hydrocarbon and not a liquid fuel, this might actually be your winner. It's way more environmentally friendly than other hydrocarbons because it only burns into CO2 and H2O without releasing any of the much more harmful CO or NHx gases and it can be stored and transferred between tanks much the same way that liquid fuels are stored. Methane is also a renewable resource which can be gathered as a byproduct of agricultural waste and landfills. This means that you could renewably supply a lot of the worlds needs within the natural carbon cycle making it just as carbon neutral as solar despite having a burning emission. Once in the atmosphere it will safely decompose into CO2 and H2O just like it would have naturally if you never collected it. Also, a methane engine can be made from roughly the same materials as a traditional car meaning you can mass produce them just as cleanly. Lastly, methane does not need to be shipped or pumped. Because gasses dissipate, you can transfer them over great distances using passive forces and underground pipes. By building this infrastructure up, you could virtually eliminate the carbon footprint of distribution

As an added bonus, methane stored in a fiberglass tank is less dangerous than petroleum in an accident. Methane only burns under certain pressures and oxygen saturations meaning if the tank ruptures, the fiberglass won't fragment and the gas will dissipate too much before it mixes with enough O2 to burn, so no risk of fire or explosions.

As for tradeoffs, methane needs to be compressed first. This requires a fair amount of extra energy right now, but recent advancements in multi-stage emulator systems have shown a lot of promise in the direction of significantly reducing this overhead in future compression systems. The second concern is fracking. While methane is safe, many companies still insist on utilizing toxic chemicals to mine for it instead of utilizing the resources we already create ourselves.

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