OPERATION AND EFFICIENCY OF CYCLIC COAL BURNING ENGINES

ABSTRACT

A method of burning porous solid fuels in a fixed bed and in pellet or chunk form is described wherein compressing the fuel with air forces oxygen deep into the fuel pores where primary reaction occurs. Subsequent expansion brings the primary re action gases out of the fuel pores where secondary reaction with additional oxygen can occur. Useful mechanical work can be produced by carrying out this compression-reaction-expansion process within a piston engine or within a gas turbine engine. Maximum useable engine speeds are not limited by burning rates but by pressure drop due to gas flow into and out of the fuel pores. Approximate thermal efficiency relations are presented which show the piston engine process to be less efficient than the turbine engine process due to incomplete expansion in the piston engine. Engines using this cyclic porous burning are somewhat less efficient than engines using constant volume burning at minimum volume, as in Otto engines, or constant pressure burning at maximum pressure as in Brayton engines. This latter efficiency difference is due to the cyclic burning being distributed throughout the compression and expansion rather than occurring all at the end of compression.