The effect of hydrogen and propane addition on the operation of a natural gas-fired pulsed combustor

Abstract

A commercialy available nonpremixed pulsed combustion room heater designed to burn natural gas has been used to study the effect of gas composition on the operational characteristics of the combustor. Three parameters have been monitored as fuel flowrates and gas composition were varied, viz., the amplitude of the pressure oscillations, the operating frequency and the phase difference between the pressure and heat release oscillations. When burning methane only, an increase in fuel flowrate caused a decrease in the phase difference which led to an increase in chamber pressure. This is attributed to an increase in the ignition delay time as the fuel flowrate increases. Addition of hydrogen, however, caused a sharp drop in pressure, and increases in the operating frequency and in the phase difference. This is due to a decrease in the ignition delay time arising chiefly from the far higher burning velocity of hydrogen compared with methane. For hydrogen contents of over 20 vol%, the phase difference approached 90°, which means that Rayleigh's criterion is no longer satisfied. Under such conditions the combustor emitted large quantities of carbon monoxide and had clear difficulties in sustaining combustion. This explains previous reports that pulsed combustors are intolerant of hydrogen in the fuel gas. Addition of propane to the fuel gas has a much less marked effect; slight increases were recorded in phase difference, pressure and operating frequency, which were attributed to the marginally higher burning velocity of propane compared with methane.