Measurement of laminar burning speed and flame instablity study of syngas/oxygen/helium premixed flame.

摘要

Synthesis gas also known as syngas, which is a mixture of hydrogen and carbon monoxide have been expected to play an important role in future energy demand. Research studies into understanding the knowledge of its fundamental thermo-physical properties, such as laminar burning speed, flame structure, etc. are extremely relevant in internal combustion engine, gas turbine combustor and power plant. The aim of this thesis is to measure laminar burning speed and study flame instability of syngas/oxygen/helium mixtures. Different methods of measurement of laminar burning speed have been discussed in this thesis. In present works, the experiments were conducted in a constant volume cylindrical chamber coupled with a Z-shaped Schlieren/shadowgraph system. Pressure rise data during the flame propagation was obtained through pressure transducers on the cylindrical chamber wall and was a primary input into the thermodynamic model used to measure the laminar burning speed. A high speed CMOS camera capable of taking pictures up to 40,000 frames per second can be used to determine the stability of the flames. A syngas with different hydrogen concentrations (5%, 10% and 25%) have been used in this experiment. The laminar burning speed and flame instability of spherically expanding flames of syngas with oxygen/helium have been studied over a wide range of equivalence ratios (0.6, 1, 2 and 3), initial mixture temperatures (298 K, 400 K and 480 K) and initial pressures (0.5 atm, 1 atm and 2 atm). Based on these initial conditions, laminar burning speed has been measured for temperatures ranging from 298 K to 650 K, pressures between 0.5 to 7.3 atmospheres and equivalence ratios ranging from 0.6 to 3.0. The flame instabilities have been observed during flame propagation and considered into hydrodynamic and diffusive-thermal effects. Helium increases the stability of flame, and it has larger heat capacity ratio (gamma=1.67) than nitrogen (gamma=1.40). Those are the reasons why helium was used instead of nitrogen to increase the range of laminar burning speed measurement that can be used for kinetic validation. Data shows that the laminar burning speed of oxygen/helium is also higher than oxygen/nitrogen from the results in this thesis.