The performance of fuel additive candidates to mitigate soot particulate emissions in turbine engines was assessed in a T63 helicopter engine. Seventeen additives, including commercial compounds to reduce emissions in internal combustion engines, diesel cetane improvers, and experimental/proprietary additives, were evaluated. The additives were individually injected into the JP-8 fuel feed to the engine, and evaluated at a minimum of three concentration levels. The engine was operated at two conditions, idle and cruise, to investigate additive effects at different power settings or equivalence ratios. Particulate samples were collected from the engine exhaust using an oil-cooled probe, and analyzed using a suite of particulates instrumentation, which included a condensation nuclei counter (CNC), scanning mobility particle sizer (SNIPS), laser particle counter (LPC) and a tapered element oscillating microbalance (TEOM). Results indicate that the diesel cetane improvers and commercial smoke abatement additives tested had minimal impact on particulate emissions in the T63 turboshaft engine. One proprietary additive was shown to reduce particle number density (PND) by up to 67% at the relatively high concentration of 3000 mg/l. These benefits were observed only at cruise condition, which may provide some insight into the mechanisms by which the additive suppresses the formation or enhances the oxidation of soot particles. Test results with blends of JP-8 and Norpar-13 (normal paraffins) show significant reductions in particulate emissions for both idle and cruise conditions demonstrating the potential environmental benefits of using blends of clean (low aromatic and low sulfur) fuels with JP-8. Comparisons of mass determination with different instruments and preliminary results of chemical characterization of particulate emissions with and without additives are also presented. (C) 2004 Elsevier B.V All rights reserved.