Coal Engine: Tank to Engine Fuel Delivery
One large difference between coal and conventional fuels is the state of the matter. Coal is a solid and Gasoline and diesel are liquids. This makes for difficulty in storing and transporting the fuel from storage to the engine. Coal fuel would most likely be used in a diesel engine.
Two ideas come to mind in how to handle this; an auger system and a coal slurry. In both scenarios the coal would need to be crushed up into a fine powder. A powder behaves somewhat like a liquid in that the powder will take on the shape of its container – it’s much easier to handle than in rock form.
The first idea is to use an auger system to transport the coal from storage to engine. An auger is basically a screw that rotates inside of a pipe. It is also typically called the Archimedes’s Screw for the credited inventor of this technology. This is 2000 year old technology. (1)
An auger system would require several moving mechanical parts. Anywhere you have a moving part leads to loss of efficiency, sources of failure, and extra complexity. It is possible to route an auger system but, it would require break points – not a continuous flow. This is also a loss of efficiency because 1) the changing direction of a material takes energy and 2) the requirement of support machinery – gearboxes, motors to turn each auger, timing the mating augers.
The benefit of such a system, in comparison to coal slurry, is that the engine is being delivered raw coal – which is effectively pure carbon. The only exhaust would be CO2. The fuel is in its purest form, no extra processing, aside from powderizing.
The second method would be to make the powdered coal into slurry. This could be as simple as combining coal powder with water in a 1:1 ratio. Doing so would eliminate the need for any major changes in the standard fuel delivery system. The pumps, sensors and nozzles may need to be more robust to handle the coal particles, depending on the size of the particles.
The downside to using a water-coal mix is that a good chunk of the energy in coal is captured by the water to steam process.
From a conceptual stand point, it appears that the best method of fuel delivery is as a coal water slurry. The system is much simpler and less likely to break down however this is at the cost of available work energy.
Some further readings on the subject: