58870 - Laminar Flame Speed Measurements of Hydrogen/natural Gas Mixtures for Gas Turbine Applications 

With increasing concern about environmental protection and shortage of fossil fuel, the major research areas in the combustion are about reduction of exhausts emission and alternative fuel.  Natural gas is one of the promising alternative fuels from crude oil for engines or turbine. Because of slow flame speed of natural gas and poor lean burn ability, engine power will be decreased in lean burn region. Due to this disadvantage of natural gas, natural gas engines are usually operated at stoichiometric condition.  To overcome the disadvantage of natural gas, blended hydrogen is used in engine. The lower flammability limit of the natural gas will be extended when mixed with hydrogen. Extending lean region helps to reduce NO_x and mixing hydrogen reduce greenhouse gases (CO and CO₂). The low exhaust emission level is extra economic benefit because an engine does not need exhaust emission controller such as catalyst. In this study, we focused our investigation on natural gas and hydrogen mixture. Measurements of properties such as ignition delay time and laminar burning velocity (LBV) are necessary for these fuels in order to understand their performance and applicability in turbine. One key combustion metric is the LBV in air over a range of equivalence ratios. LBV is dependent on reactive mixture composition, temperature, and pressure.  LBV is useful as it: (i) gives a measure of combustion efficiency and heat release rate; (ii) enables validation of chemical kinetic mechanisms; (iii) and gives turbine design engineers a metric for the expected time required to burn the fuel charge. However, studies available for the mixture of natural gas and hydrogen are not sufficient to understand its combustion phenomena. While there exist studies for natural gas and hydrogen under atmospheric condition, there are only few studies on combustion characteristics at high pressures in the literature. Here we present measurements of laminar burning velocities of natural gas/hydrogen up to an initial pressure of 10 atm and initial temperature of 300 K. Equivalence ratio was varied in a wide range to examine the effects on laminar burning velocity. The results presented are also compared with the performance of detailed kinetic models as part of their validation process.  The kinetic model is used to explore the source of the differences in the observed laminar burning velocities of the fuels.