Experiment on combustion characteristics of n-heptane droplets in micro-tube

To understand the effect of micro-tube on the droplet formation and combustion stability, the following researches were performed by using the n-heptane as fuel in 4 mm internal diameter quartz tube. Firstly, without heating, the stability of the flame and quartz tube drips was studied. The results showed that without heating, quartz tube was easy to form droplets, and when the n-heptane volume flow rate was lower than 40 μL /min, the flame stability was influenced by dripping easily, the evaporation rate of the droplets was mainly affected by the flame position under the influence of the effect of air volume flow rate; when the fuel volume flow rate was larger than 40 μL/min, the flame stability was not affected easily by the dripping of droplet due to the formation of liquid film. Secondly, the influences of heating on the droplet formation and the combustion characteristic were studied. It was found difficult to form droplets when the n-heptane volume flow rate was lower than 60 μL/min, and when the n-heptane volume flow rate was greater than 60 μL/min, the droplet could drip, and film didn't appear when the wall temperature was 180℃. Droplet evaporation was greatly influenced by air velocity; under the influence of air velocity and the droplet dripping, the temperature of micro burner had a greater impact on evaporation rate of droplet. The flame was more easily formed under fuel-rich condition than fuel-lean condition. Hence, air velocity has strong impact on the tube wall temperature, the lower air velocity means the higher wall temperature, the higher evaporating rate of fuel droplet and lower droplets dripping frequency.