Laminar burning velocity and flammability limits in biogas: A literature review

A detailed literature review of laminar burning velocity and flammability limits of biogas mixtures combustion is presented. Biogas alone and in mixtures with other fuels is particularly significant because of its capability of application as fuels for internal combustion engines (ICES). Therefore, a strict determination of the fundamental combustion characteristics required for their application in ICEs is crucial. Producing energy from biogas has the additional advantage of preventing its release into the atmosphere, where it results into significant air pollution. CH4 and CO2 are the main compounds of biogas, such as landfill, agricultural and sewage gas, after the removal of the trace amounts of organic compounds. For the same equivalence ratio, the presence of CO2 in the fuel feed results in substantial reduction of the laminar flame speed and flammability limits. Several research projects have shown that the decrease in the laminar flame speed of a fuel mixture containing dilution components is caused by the increase in specific heat capacity and the decrease in heat release, flame temperature and thermal diffusivity. The most promising strategies to increase the laminar burning velocity and the flammability limits of biogas are revised and discussed. The thermodynamic conditions under which these properties are determined are analyzed and the work still required for a comprehensive laminar burning velocity and flammability limits determination, at typical ICEs thermodynamic conditions, is addressed. The article provides a brief review of pollutant emissions of ICEs running on biogas and the current and future technological solutions to meet the increasing strict regulation. (C) 2016 Elsevier Ltd. All rights reserved.