AN ASHLESS, FUEL SUPPLEMENT was found to typically reduce diesel particulate emissions by over 30% while significantly improving fuel economy and power output without any modifications to existing diesel engines or fuels. The treating cost is an order of magnitude less than the estimated cost of reducing aromatic content at the refinery to achieve particulate reductions. The particulate reduction is virtually all from the carbon (soot) fraction. The reduced soot formation translates into less abrasives and less soot-loading stress on the engine oil.The patented fuel supplement is completely ashless, containing a highly stable system of organic combustion catalyst, an organic detergent, and a stable organic acid. The supplement disperses immediately into diesel fuel. The effects on diesel emissions, fuel economy, and horsepower are instantaneous, even in a new engine.Diesel tests were conducted in: a laboratory engine; a diesel car; conventional diesel trucks and buses in the field; and in controlled engineering diesel trucks by the SAE J1321 fuel economy road test procedure.