Abstract:
Objective To address the challenges of poor low-temperature cold-start performance and low flame propagation rates associated with ethanol fuel, this study investigates the effects of ethanol blending on the laminar combustion characteristics of hydrogen-methane-air mixtures.
Method The laminar burning velocities (LBVs) of ethanol-hydrogen-methane-air mixtures were experimentally measured at atmospheric pressure and an initial temperature of 370 K using the spherically expanding flame method. The experiments covered various ethanol volume fractions (20%, 50%, 80% in the fuel blend) and equivalence ratios (0.7～1.4). Numerical simulations were conducted using the Chemkin-Pro software coupled with a chemical kinetic model. To isolate the chemical effect of H2, a virtual species, FH2, was introduced into a modified mechanism. Furthermore, a global reaction path analysis was performed to identify the main decomposition pathways of the fuel mixture and the sources of H2 generation.
Result The results show that increasing the H2 mole fraction in the fuel blend significantly enhances the LBV, with the peak value occurring at an equivalence ratio of 1.2. Conversely, increasing the ethanol proportion lowers the peak LBV and shifts it towards richer equivalence ratios. The modified mechanism, incorporating the virtual species FH2, successfully quantified the contribution of H2's chemical effect to the enhancement of LBV. The main decomposition pathway for ethanol was identified as C2H5OH→CH3CHO→CH3→CH2O→CO→CO2. Sensitivity analysis revealed that the presence of H2 primarily accelerates the combustion process by promoting the generation of key free radicals through reactions R1 (H+O2=O+OH) and R2 (O+H2=H+OH).
Conclusion This research clarifies the synergistic optimization pathways of ethanol blending on the combustion dynamics of H2/CH4 fuels. The findings provide new insights for the design of clean fuels and the development of efficient combustion control strategies for engines.
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