Conversion of Liquid to Gaseous Fuels for Lean Premixed Combustion

Abstract

The lean premixed combustion of gaseous fuels is an attractive technology to attain very low NOx emission levels in gas turbine engines. If liquid fuels are converted to gaseous fuels by vaporization, they also can be used in premix gas burners and similar low NOx emissions are achievable. Experiments were carried out in a test rig in which the three main process steps of liquid fuel combustion (vaporization of fuel, mixing of air and fuel vapor and combustion reaction) can be performed successively in three separate devices and examined independently. A wide range of liquid fuels (methanol, ethanol, heptane, gasoline, rape oil methyl ester and two diesel oil qualities) was vaporized in an externally heated tube in the presence of superheated steam. These fuel vapors were led to a Pyrocore® radiant burner operating in fully premixed mode at atmosperic pressure. For all fuels without bound nitrogen, NOx levels below 15 mg/m3 at 3% O2 in the dry exhaust gas (2.5 ppm at 15% O2) were measured at lean combustion conditions. However, the nitrogen particularly bound in higher boiling fuels like diesel oil was converted completely to NOx under these conditions. The fuel bound nitrogen (FBN) proved to be the major source of NOx when burning vaporized diesel oil.