Abstract
This study investigated the effects of H2 and CH4 concentrations on the ignition delay time and laminar flame speed during the combustion of CH4/H2 and multicomponent syngas mixtures using a novel constructed reduced syngas chemical kinetics mechanism. The results were compared with experiments and GRI Mech 3.0 mechanism. It was found that mixture reactivity decreases and increases when higher concentrations of CH4 and H2 were used, respectively. With higher H2 concentration in the mixture, the formation of OH is faster, leading to higher laminar flame speed and shorter ignition delay time. CH4 and H2 concentrations were calculated at different pressures and equivalence ratios, showing that at high pressures CH4 is consumed slower, and, at different equivalence ratios CH4 reacts at different temperatures. In the presence of H2, CH4 was consumed faster. In the conducted two-stage sensitivity analysis, the first analysis showed that H2/CH4/CO mixture combustion is driven by H2-based reactions related to the consumption/formation of OH and CH4 recombination reactions are responsible for CH4 oxidation. The second analysis showed that similar CH4-based and H2 -based reactions were sensitive in both, methane- and hydrogen-rich H2/CH4 mixtures. The difference was observed for reactions CH2O + OH = HCO + H2O and CH4 + HO2 = CH3 + H2O2, which were found to be important for CH4-rich mixtures, while reactions OH + HO2 = H2O + O2 and HO2 + H = OH + OH were found to be important for H2-rich mixtures.
Highlights
Serious environmental problems, due to the harmful exhaust gas emissions produced by the combustion of fossil fuels, along with ongoing fluctuations in crude oil prices, have prompted researchers and engine manufacturers to search for new, environmentally friendly and sustainable fuels [1,2]
The mechanism proposed in Reference [19] was used for a different type of analysis as we focused on the investigation of the effects of CH4 and H2 concentration on ignition delay time and laminar flame speed and the analysis of the combustion chemistry
Experimental results for various CH4 /H2 as well as H2 /CO/CH4 syngas mixtures were collected from the literature and used for mechanism testing
Summary
Serious environmental problems, due to the harmful exhaust gas emissions produced by the combustion of fossil fuels, along with ongoing fluctuations in crude oil prices, have prompted researchers and engine manufacturers to search for new, environmentally friendly and sustainable fuels [1,2]. The hydrogen concentration in a syngas mixture can vary from 25% to 80% depending on the gasification process and the feedstock type used [4] This variation of the concentration of the different gases in the syngas has a direct effect on important combustion characteristics such as the laminar flame speed, the ignition delay time and the exhaust gas emissions and in general. The mechanism proposed in Reference [19] was used for a different type of analysis as we focused on the investigation of the effects of CH4 and H2 concentration on ignition delay time and laminar flame speed and the analysis of the combustion chemistry. In contrast to the other published studies, this paper has analysed a two-stage chemical kinetics with the specific focus on, the first, methane oxidation and the second, the comparison of the chemical interactions during the combustion of methane-rich H2 /CH4 and hydrogen-rich H2 /CH4 mixtures
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