수소/공기/희석제 혼합기의 자연점화 특성

Abstract

Hydrogen has been considered as clean energy comparing with fossil fuel and the use of hydrogen in social daily life and economic industry activities will be expected to a huge increase. For hydrogen society, the main systems is fuel cell, which have been actively applied to hydrogen cars and small-scale power generation, and the related facilities is a hydrogen stations for fueling and storage. The by-product gas produced in various chemical processes is also important source of hydrogen gas and should be treated appropriately. However the use of hydrogen energy is limited now because of hydrogen production and safety. The burning velocity of hydrogen mixture is about 7 times faster than hydrocarbon fuels and hydrogen has wide flammability and small minimum ignition energy. Therefore there is a high risk of fire and explosion in all areas of hydrogen manufacturing, transportation, storage, and use. In this study, the auto-ignition characteristics was investigated numerically for diluted hydrogen mixtures. Auto-ignition temperature was determined on well-stirred reactor as the most important property representing fire and explosion risk in hydrogen combustion. When nitrogen and carbon dioxide were diluted at hydrogen/air mixture, the ignition delay time was increased with increasing dilution ratio on both cases but the ignition of CO2 dilution was more delayed than N2 dilution. It was also confirmed that the lower the initial ignition temperature, the greater the ignition delay time at 950K or higher temperature. Overall autoignition characteristics such as the concentrations of participating species and ignition delay time were mainly affected by initial temperature of the mixture. The critical temperature at which the chain-branching rate becomes of the same order as the chain-breaking rate is defined as crossover temperature and redefined to the temperature at which the total production rate of hydrogen radical is zero. Crossover temperature of CO2 diluted hydrogen mixture is higher than that of N2 dilution. The water vapor addition results in the higher crossover temperature due to high Chaperon efficiency of H2O.