CO ₂ and H ₂ effects on lean limits and combustion characteristics of ethanol flame

High efficiency can be achieved by running the IC engines under lean conditions. Besides, ethanol known as a renewable fuel is used in combustion engines due to its low carbon emission compared to liquid hydrocarbon fuels. However, the carbon emission from ethanol combustion is still an environmental issue, and the lean flammability limits are also not wider compared to zero-carbon fuel. Besides, the EGR impact on the lean limits of ethanol is still unclear. Currently, the effects of CO₂ and H₂ on the lean limits and burning characteristics of ethanol flame were studied by using the spherical combustion chamber and Arrhenius model at 373-473 K and 100 kPa. The hydrodynamic and thermal instabilities were induced under the addition of H₂ while CO₂ impeded diffusional-thermal and hydrodynamic instability. The lean limits of ethanol increased from λ = 2.1 to λ = 2.6, λ = 3.2, λ = 4.3, and λ = 6.8 at 30%, 50%, 70%, and 90% H₂ addition in ethanol/air mixture, respectively. In contrast, CO₂ is inflammable gas, which decreased the lean limits of ethanol from λ = 2.1 to λ = 1.9, λ = 1.6, and λ = 1.2 under 5%, 10% and 15% enrichment, respectively. CH₃CHO, CH₄, CH₂O, O₂CHO, CH₃ and CO species were found correlated to the hydrogen-ethanol and CO₂-ethanol flames. Hydrogen significantly increased the combustion process thru CH₄ and O₂CHO species, whereas the flame propagation deteriorated by a decrement in peak molar fractions of CH₃CHO, CH₄, CH₂O, CH₃ and CO species thru CO₂ dilution.