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 H-2-O-2 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 H-2-O-2 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. (C) 2020 The Authors. Published by Elsevier Inc. on behalf of The Combustion Institute.

Automated summary

The study investigated the ignition and combustion properties of a stoichiometric CH2F2/C2HF5/air mixture. Experimental and computational results showed two separate reaction zones in the mixture with a 50:50 blending ratio, and two heat release rate peaks were observed for different mixing ratios. The second heat release rate peak corresponded to CO oxidation and was larger for CH2F2, while the first peak shifted with increasing C2HF5 mass fraction.