Ranking Renewable and Fossil Fuels on Global Warming Potential Using Respiratory Quotient Concept

Abstract

Carbon dioxide (CO2) is one of the greenhouse gases which cause global warming. The amount of fossil fuels consumed to meet the demands in the areas of power and transportation is projected to increase in the upcoming years. Depending on carbon content, each power plant fuel has its own potential to produce carbon dioxide. Similarly, the humans consume food containing carbohydrates (CH), fat, and protein which emit CO2 due to metabolism. The biology literature uses respiratory quotient (RQ), defined as the ratio of CO2 moles exhausted per mole of O2 consumed within the body, to estimate CO2 loading in the blood stream and CO2 in nasal exhaust. Here, we apply that principle in the field of combustion to relate the RQ to CO2 emitted in tons per GJ of energy released when a fuel is combusted. The RQ value of a fuel can be determined either from fuel chemical formulae (from ultimate analyses for most liquid and solid fuels of known composition) or from exhaust gas analyses. RQ ranges from 0.5 for methane (CH4) to 1 for pure carbon. Based on the results obtained, the lesser the value of "RQ" of a fuel, the lower its global warming potential. This methodology can be further extended for an "online instantaneous measurement of CO2" in automobiles based on actual fuel use irrespective of fuel composition.