The hydrocarbon CO2 mixture is identified as the most advantageous working medium in the medium-high temperature Organic Rankine cycle (ORC). However, the flammable zones of hydrocarbon CO2 mixtures at atmospheric condition are rare. In order to measure the flammability limits of mixture, an experimental setup based on the ASTM E681-09 has been built completely. In the design of the experiment, an innovative tactic about gas distribution is proposed to improve the precision. The flammable zones of five mixtures were measured carefully at 30 degrees C in this paper. But in reality, ORC system operates within the temperature range from 87 to 300 degrees C. Meanwhile the flammability zones of mixtures at higher temperature are not available in the existing literatures. To solve this problem, a modified critical flame temperature model is modified to estimate the flammable zones of mixtures at different temperatures. The modified model presents a higher prediction precision with average relative difference of 1.24% at LFL. Thus, it is easier to estimate the flammable zones of mixtures at different temperatures with the modified model. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.