CH-2268 -- Developments in Automatic Fuel/Air Ratio Controls for Fuel Preservation and Pollution Prevention PDF

The precious gas and oil fuel supplies that can be saved annually by maintenance of closer to correct fuel/air ratio in our boilers and other space-heating and process heating devices can help our energy crisis. Fig. 1 shows that trimming the fuel/air ratio can produce savings to not only conserve our energy supply, but,also save on fuel bills; this accounts for fuel only used to heat excess air. In actuality, cutting back to only 10% excess air would give a flame temp about 200 deg hotter than the 30% excess air, greatly improving heat transfer efficiency. Hence it can be said that precise fuel/air ratio control is beneficial to air conservation because it will insure that the equipment is being operated at the best level for minimized pollution.

The traditional reason for using excess air is that extra air was needed to assure complete combustion. In this respect, gaseous and liquid fuels were a great improvement over solid fuels. However, developments in gas and oil burners over this last decade have made it possible to assure complete combustion with closer to correct fuel/air ratio. It is a common error to evaluate combustion systems using performance data based on the high fire rate. Because most installations spend most of their operating life at some fraction of full rating, it is important to have fuel/air ratio controls and burners that can hold operations close to correct fuel/air ratio all up and down their firing range