During the study of soot formation in laminar jet flames
of methane
at elevated pressures in a high-pressure combustion chamber, we have
observed an anomalous occurrence at the chamber pressures of 6 MPa
and higher. At pressures between 6 and 9 MPa, after the laminar methane
jet flame had been stabilized on a co-flow circular nozzle-type burner,
one of the following occurrences was observed: (a) the jet flame is
completely extinguished without any external interference, and immediately
after, a liquid material started to flow out of the fuel nozzle, and
(b) the jet flame started flickering or changing its shape, and at
the same time, a liquid stream started trickling out of the nozzle.
This outflowing liquid influenced the jet flame by widening the flame
near its base and decreasing the visible flame height. In consideration
of the temperatures and the pressures involved, the liquid is believed
to be a mixture of methane and water formed by the water vapor in
the combustion products of the flame mixing with supercritical methane
inside the nozzle.