Partially premixed combustion systems were widely used for the household hot water supply system.The purpose of this study is to investigate the combustion oscillation in a new gas storage water heater

which utilizes primary

secondary and tertiary air supply.The effect of each air stage is investigated by observing flow changes.The pressure fluctuation in combustion chamber is one of the characters of combustion oscillation that are visible most easily.Hence

the pressure was observed to determine the oscillation.Experimental result shows that the pressure fluctuation is larger than 400 Pa during the oscillation.The total air excess ratio and primary air excess ratio are the most important parameters affecting the combustion oscillation.In the experiment

seven zones appeared at different operation parameters.The oscillation occurred between two normal combustion zones as the primary air excess ratio increased from 0.4 to 0.8.With the CH4 concentration measured directly

the range of primary air excess ratio could be determined.It shows that combustion oscillation will occur when the primary air excess ratio is from 0.44 to 0.93

consistent with those measured directly.The investigation shows that the occurrence of combustion oscillation is influenced by the primary air excess ratio directly.