A study on soot formation in premixed constant-volume propane combustion

The effects of pressure, temperature and equivalence ratio on soot formation in premixed propane-oxygen-inert gas combustion have been investigated over wide ranges of pressure (0.1 to 6 MPa), temperature (1200 to 2100 K) and equivalence ratio (1.5 to 2.7) in a specially designed disk-type constant-volume combustion chamber. To observe the soot formation under high pressure, premixtures are simultaneously ignited by eight spark plugs located on the circumference of chamber at 45 degree intervals. The eight converging flames compress the end gases to a high pressure. The soot volume fraction in the chamber center during the final stage of combustion at the highest pressure is measured by the in situ laser extinction technique and the burnt gas temperature during the same period by the two-color pyrometry method. The pressure and temperature during soot formation are varied by changing the initial charge pressure and by changing the volume fraction of inert gas in the premixture, respectively. It is found that the soot yield is dependent on the pressure, temperature and equivalence ratio, and the soot yield increases under the following conditions; (1) decreasing temperature and increasing equivalence ratio at constant pressure, (2) increasing pressure and decreasing temperature at constant equivalence ratio, (3) increasing equivalence ratio at constant temperature and pressure.