Humanity's main fuel for eons was wood, which has a carbon-to-hydrogen ratio of 10 to 1 when burned; by comparison, that ratio is 2 to 1 for coal and 1 to 2 for oil.

For the combustion of dry coal, the results with varying air fuel ratio are similar to those for the combustion of high moisture coal.

The results show that, double injection system can get high replacement ratio of coal liquids fuel and good operation performance of the engine.