An apparatus including an air blower; a rotary airlock; a receptacle having an inner chamber supplied with a plurality of colorant particles; a water supply; and a mixing chamber. The air blower blows air into a bottom section of the rotary airlock, and the rotary airlock receives colorant particles from an output of the receptacle. A rotor shaft of the rotary airlock rotates to cause colorant particles to be transported to the bottom section of the rotary airlock. Air blown into the bottom section of the rotary airlock mixes with colorant particles transported into the bottom section of the rotary airlock to form an air and colorant particles mixture, which is blown out of a first output of the rotary airlock and combined with water to form a water, air, and colorant particles mixture, which is mixed with material in a mixing chamber. The material may be natural mulch.

A dust injection system for engine testing and related methods are provided. The system includes a carrier pipe that defines a fluid flow path between an inlet and an outlet and an injection nozzle disposed within the carrier pipe between the inlet and the outlet. The injection nozzle receives a slurry comprising dust particulates and a carrier liquid, and injects the dust particulates and the carrier liquid into the fluid flow path. The carrier liquid is atomized and evaporates in the fluid flow path prior to the outlet to enable dried version of the dust particulates to exit the outlet.