Injection Characteristics of Coal-Water Slurries in Medium-Speed Diesel Equipment

The injection characteristics of several micronized coal-water slurries (CWSs, where “s” implies plural) were investigated at high injection pressures (40 to 140 MPa, or 6,000 to 20,000 psi). Detailed spray characteristics including drop-size distributions and cone angles were measured using a continuous, high-pressure injection system spraying through various hole shapes and sizes into a continuous, elevated-pressure air flow. Penetration and cone angle were also measured using intermittent injection into an elevated-pressure quiescent chamber. Cone angles and fuel-air mixing increased rapidly with the relatively constant cone angles of diesel fuel. However, even at high injection pressures the CWSs mixed with air more slowly than diesel fuel at the same pressure. The narrower CWS sprays penetrated more rapidly than diesel fuel at the same injection pressures. Increasing injection pressure dramatically reduced drop sizes in the CWS sprays, while increasing injection pressure reduced drop sizes in the diesel fuel sprays more gradually. The CWSs produced larger average drop sizes than the diesel fuel at all conditions, except for some hole shapes at the highest injection pressures where the average sizes were about the same. Varying the hole shape using converging and diverging holes had a minimal impact on the spray characteristics. A turbulent jet mixing model was used to predict the penetration rate of the CWS fuel jets through different orifice sizes and into different air densities. The jet model also computes the liquid fuel-air ratio through the jet. The work reported here was abstracted from the more complete report by Schwalb et al. (1991).