Abstract: Various implementations include a combustor system including an inner wall, a fuel grate, an ash grinder, an igniter, and a fan. The inner wall defines a combustion chamber and has a longitudinal axis and first and second ends. The inner wall defines primary and secondary air inlets. The primary air inlets are defined closer than the secondary air inlets to the first end. The fuel grate is disposed within the combustion chamber between the primary and secondary air inlets and is configured to support fuel disposed within the combustion chamber. The ash grinder is disposed between the fuel grate and the secondary air inlets and is rotatable about the longitudinal axis relative to the fuel grate. The igniter provides energy to the combustion chamber. The fan is configured to cause air to flow from the primary and secondary air inlets through the second end of the combustion chamber.