Effects of blending ratios on the reactivities of CH₂F₂/C₂HF₅ refrigerant blends

The R410A refrigerant (a blend of CH₂F₂ and C₂HF₅ with a mass ratio of 50:50) has been extensively used because of its small impact on the environment. We investigated the effects of the CH₂F₂-to-C₂HF₅ blending ratio in a stoichiometric CH₂F₂/C₂HF₅/air mixture on the ignition and combustion properties using a microflow-reactor with a controlled temperature profile. Experiments with weak flames showed two separated reaction zones of CH₂F₂ and blend of CH₂F₂ and C₂HF₅ (50:50), while a single reaction zone was observed for C₂HF₅. This was computationally reproduced using the Linteris mechanism. According to computations for different CH₂F₂-to-C₂HF₅ ratios with steps of 10 wt%, two heat release rate (HRR) peaks were observed under all conditions. The first HRR peak at the lower temperature and second HRR peak at the higher temperature corresponded to the consumption of refrigerant and CO oxidation, respectively. The second HRR peak was larger than the first peak for CH₂F₂. The second HRR peak shifted to a higher temperature and decreased with the increase in C₂HF₅ mass fraction up to 50 wt%, because the OH production by the H₂–O₂ reaction decreased owing to the increased HF production in the low-temperature zone. At C₂HF₅ mass fractions larger than 50 wt%, the first HRR peak became dominant because CO oxidation did not occur. The first HRR peak shifted to a lower temperature with the increase in C₂HF₅ mass fraction in the range of 60 to 100 wt% because the reactions contributing to the production of OH from H₂O increased in the low-temperature zone, instead of the H₂–O₂ reaction. A large change in HRR was observed at an F/H ratio in the refrigerant blend of 1.8, owing to the change in OH production reactions. The tendency of the reactivities of the refrigerants is useful to prevent unwanted ignition.