Why does an internal combustion engine have to run on liquid fuel?

I have a full knowledge of how petrol and diesel engines work so I know that it is far easier to get a liquid fuel into the combustion space than it would be a solid fuel. However this does not mean that that it would be impossible to introduce a solid chemical fuel broken down into a light powder. The problems would be to identify a suitable fuel and its costs. It would obviously be necessary to dispose of combustion by-products with minimal polluting effects. Does anyone have thoughts on this or do you think its a non starter?
I would appreciate any thoughts.


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Actually, coal slurry fired engines have been operated. And the original design for the SR71 P+W engines were supposed to be slurry fired.

The killer of course is wear
+1 Yep, I remember reading about IC engines running on Coal dust. Big problem with coal dust is it is explosive, as well as the ash exhaust and the wear factors.

Just about any dust made from something flammable can explode. Grain elevators sometimes blow up from the grain dust igniting.

Mythbusters made a giant fireball from coffee creamer powder. It even surprised them how explosive it was.
beanjay1 (author) 5 years ago
Thanks once again for all the interesting and thought provoking comments. I believe that eventually some modifications or changes to the way internal combustion engines operate will be found. This may mean a move away from conventional design, like the rotary engine.I appreciate that you cannot get something for nothing but there has to be cheaper alternatives to the present fossil fuels. Hydrogen and electricity are not without their limitations!

Prfesser5 years ago
It doesn't *have* to run on liquid fuel.  That being said, the challenges of a solid fuel are considerable.  If a student of mine were attempting such a project I might suggest that it's far too broad to be solved in a reasonable amount of time, so the project should be broken down into manageable parts.  One part might be "make a powder (ANY powder) that will flow as rapidly as a liquid fuel, and describe what is necessary (preparation and properties needed) to make that powder."

Once that part is solved, then go to another part, for example, "Design a method to remove noncombustibles from wood/coal/other suggested fuel."  Etc.  Etc.

I won't say that the project is impossible, but considering the necessary physical and chemical properties of the proposed solid fuel, I suspect that it's a multi-lifetime project for one person...
lemonie5 years ago
If it were practical people would have got it to work by now.
Here's something you probably haven't though of:
> Powder fouling the valve-seats and piston-bore before it burns.

beanjay1 (author) 5 years ago
Thanks for all of the comments. It seems you all feel that the idea is not practical. I think the problem would be identifying a cheap substance that would ignite easily. After that ways of controlling the rate of burning and introducing the fuel could be worked out. The key is the fuel. Thanks once again.

Most solid fuels leave behind unused particles (ash). Any combustion chamber you have will quickly get a buildup ash quite fast. How would you prevent this buildup? Some sort of vacuum system? How would you go about injecting the powder into the engine?
rickharris5 years ago
You can run an IC engine on a gas easily - Liquid propane or even air.

A solid fuel would need to be a very fine dust in order to burn quickly - efforts have been made to run IC engines on gun powder for example. Not very cost effective.
Re-design5 years ago
If you could find/design a suitable solid fuel there would be ignition problems. Solid fuels are going to be much harder to ignite than fuels in a vapor state. I know that dust such as in a flour mill can ignite but only under the correct conditions. You would have to create those correct conditions every power stroke and many times a second.

You will find that you have a very difficult problem designing a working delivery system.