Investigating the Effects of Natural Gas Preheating on Soot Formation, Flame Luminosity, and NOX Emissions: A Combined Experimental and Numerical Approach

One of the most problematic aspects of gas-fired furnaces is their poor luminosity and radiative characteristics which are directly affected by the carbon percent of the fuel molecules. This study investigates the soot content, flame temperature, and efficiency of a 120 kW boiler resulting from inlet gas (natural gas) preheating. A probability density function (PDF) being parameterized by the mean and variance of mixture fraction was used to model chemical reactions. To describe the effects of turbulences on soot formation, a Moss-Brooks model and a beta-PDF in terms of normalized temperature is employed. Using Nickel-Chrome electrical heaters, the fuel was preheated to more than 573 K. Radiations emitting from the flame were measured by a laboratory pyranometer with a photovoltaic sensor; moreover, a Testo 350 XL gas analyzer was used for recording the temperature and combustion species. Results revealed that gas preheating up to about 510 K has no considerable effect on the flame luminosity. On the other hand, preheating the inlet gas up to 700 K increases the soot content of the flame up to 300% resulting in a serious augmentation of flame luminosity. This increase causes a significant reduction in flame temperature (150 K) and NO emission. The predicted results have good agreement with measurement results. (C) 2016 Wiley Periodicals, Inc.