Burning behaviour of selected biogas and syngas mixtures

Experimental evaluation of the combustion characteristics of carbon-neutral, biomass-derived fuels has been carried out. Since these fuels are meant as likely replacement for CH4, a comparison was drawn with methane in the same operating conditions. Tests were performed in the high-pressure, constant-volume DHARMA reactor at Istituto Motori - CNR. The laminar burning parameters were evaluated analyzing spherical expanding flames. The flame growth was recorded by means of high-speed, high-resolution shadowgraph; image processing and stretch analysis allowed to infer the laminar burning velocity and the Markstein length for each test case. Results are presented for the combustion in air of CH4-CO2 (55-45 % vol.), H2-CO (5-95 % vol.) and a wood gasification product. All the tests were performed at 0.6 MPa and 301 K. The equivalence ratio ranged between 1.0 and the lower flammable limit. The unstretched laminar burning velocity and the Markstein length are reported for each fuel as a function of the equivalence ratio.