Why is such a high energy density needed for a ICE?

Question

What is the purpose of having a gas with such a high energy density? Couldn't we use more available gases with less density?

Answer 1

Energy density is what makes vehicles efficient at transporting mass, like people or objects. The lower the energy density, the more energy gets used for simply moving the fuel itself, and less is left over for whatever the vehicle is designed to move.

Answer 2

I'm not sure I understand the question. Common fuel types include a host of petrochemicals such as Petroleum (Gasoline), Diesel #2 (DERV), Liquefied Petroleum Gas (LPG), Diesel #1 (Kerosene 28) plus a host of blended fuels like Ethanol 85, Biodiesel, Momentum99 (a branded high performance fuel but formulated in a different way to premium unleaded).

In order for a regular road car to run anything not listed above, it would have to be adapted (I accept LPG is usually a conversion but there are models available from the show room with LPG). So your choice as a fuel station owner is to stock a selection of fuels that covers 99.9% of vehicles on the road or give up forecourt space, a storage tank and a pump to your new low density fuel. The shear economics state you aren't going to bother, which means vehicles designed to run on this new fuel won't sell in any great quantity.

If you want a new type of fuel, the bottom line is it has to work in existing cars otherwise no one will adopt it. This link shows that in the UK in 2014 there were around 17 million petrol cars on the road, 10 million diesel cars and less than 1 million alternative fuel cars (LPG / Electric). I accept that there will likely be an uplift in alternative fuel cars as people adopt electric vehicles but the chances of making a successful introduction of an alternative lightweight gas fuel that won't work in either petrol or diesel vehicles is low because you'd have to spend probably billions and you'd be going up against the oil companies.

Answer 3

Even if the oil industry would want to cooperate is would be hard to create another, better form of fuel. That's because there are a lot of requirements to fuel. Energy density is just one of the most important requirements. The flamespeed and temperature, vapour pressure, freezing and boiling point, auto-ignition point, knock-resistance, availability, shelf life, emissions, corrosivity and toxicity all have to be within reasonable limits. And these are just a few requirements i could come up with; there are a lot more.

Petrol is pre-eminently suitable for the purpose of being combusted in engines. It evaporates quite easily at all the temperatures that you can expect on earth, while still not freezing or boiling at ambient pressure and temperature. On top of that, it also contains a huge amount of energy per both volume and weight.

Out of all mediums, hydrogen is IMO the most interesting sustainable carrier of energy. But it has a lot more complications compared to petrol. It contains a huge amount of energy per mass unit, but not per volume unit. You need to cryogenically cool it to keep it liquid, or you need a gas tank that can withstand the extreme pressure at which hydrogen is stored. It also tends to leak through the tank walls. You'll understand that transport and storage will be very difficult. And there are a lot more reasons why one would choose petrol over hydrogen.

Unfortunately, as with almost all things on earth, costs are seen as the utmost importance. If petrol is only a dime cheaper per 10000 litre, they will favour that over anything else. No matter the other advantages on environment and such.

I expect them to keep using petrol or another similar petrochemical fuel until we're really close to the point of running out of oil.

We need at least another one hundred Elon Musk's to beat the development of the combustion engine. But i don't see that happening anytime soon.