Flame temperature theory-based model for evaluation of the flammable zones of hydrocarbon-air-CO2 mixtures

Nitrogen dilution effect on the flammability limits for hydrocarbons

The knowledge of flammability limits is essential in the prevention of fire/explosion when handling combustible gases and vapors. In this study, the lower flammability limits (LFLs) of hydrogen–air, methane–air, ethane–air, n-butane–air, and ethylene–air were measured in a closed cylindrical vessel (inner diameter 10.22 cm, length 100 cm) with upward flame propagation, at room temperature (20 °C) and initial pressure of 1.0, 0.7, 0.5, 0.3, and 0.1 atm. The LFL of hydrogen initially decreased with pressure from 1.0 to 0.3 atm, and then the LFL increased with the further decrease of pressure. In contrast, the LFLs of the hydrocarbons increased when the pressure decreased from 1.0 to 0.1 atm, except for methane for which the LFL did not change with pressure. The adiabatic flame temperatures (AFTs) at the obtained LFL concentrations of hydrogen and the hydrocarbons were also calculated at subatmospheric pressure conditions. The behaviors of the AFTs of hydrogen and the hydrocarbons were similar to those of the LFLs under the influence of low pressures. On average, at initial pressures from 1.0 to 0.1 atm and LFL concentration, the AFT of hydrogen was 730 K, of the alkanes was 1900 K, and of ethylene was 1800 K. On the basis of the LFLs and AFTs, the risk/hazard associated with fire/explosion of hydrogen and the hydrocarbons at subatmospheric pressures was also discussed.

Carbon dioxide dilution effect on flammability limits for hydrocarbons

Predicting both lower and upper flammability limits for fuel mixtures from molecular structures with same descriptors

Dependence of flammability limits of a combustible particle cloud on particle diameter distribution

In the present study, a novel model is proposed to evaluate the lower flammability limit (LFL) of alkane diluted with CO2. The LFL model is based on flame phenomenon simulation (FS-LFL). The model consists of combustion, turbulence, and igniter models, which are used to characterise the combustion based on the chemical kinetics and CFD, which is not feasible with traditional methods. The flame simulation phenomenon was validated by contrast with experiment and same criterion of flammability limit in the experiment was adopted. The FS-LFL model was used to predict the LFLs of a propane-CO2 mixture and propane at various temperatures. The model performance was analysed by comparing the results with experimental data and predictions obtained from existing methods. The AARDs between the predicted and experimentally determined LFLs of the propane-CO2 mixture are 0.34%, 1.19%, and 1.35% at 30°C, 50°C, and 70°C, respectively. The model also has a good predictive power with respect to the LFLs of propane at initial temperatures ranging from 30°C-300°C, with an AARD of 2.10%. When the dilution of CO2 is 90%, the model yields a better result due to the utilisation of the chemical kinetics mechanism. This result is instructive for the use of this method in the prediction of upper flammability limits.

Effect of low temperature on the flammability limits of methane/nitrogen mixtures

A new model based on adiabatic flame temperature for evaluation of the upper flammable limit of alkane-air-CO2 mixtures

Experimental study of flammability limits of methane/air mixtures at low temperatures and elevated pressures

Flammability limit behavior of methane with the addition of gaseous fuel at various relative humidities

An experimental study of flammability limits of LPG/air mixtures ☆

Study on the lower flammability limit of H2/CO in O2/H2O environment

The boiling point, flashpoint, and flammability limit are key parameters to evaluate the combustion behavior of flammable liquids. In this study, the boiling point (TB), the flashpoint (TF), and the lower flammable limit (LFL) of two multiple-component fuels (diesel and Jet A) and two single-component fuels (n-hexanol and n-decane) were measured at low pressures ranging from 35 to 101 kPa. The dependences of TB, TF, and LFL on pressure have been theoretically derived to explain the experimental measurements. In addition to the observation that both boiling point and flashpoint decrease with decreasing pressure, the measurements also revealed that the open-cup and closed-cup flashpoints decrease at different rates. The lower flammability limit, on the other hand, was shown to increase with the decreasing of pressure. The measurements of the lower flammability limit versus pressure were well correlated with different theoretical formulas proposed in the literature and the current study. The relationships among TB, TF, and LFL at low pressure are also discussed and verified against the measurements.

The objective of this experiment is to determine the flammability limits of hydrogen, oxygen, and helium mixtures in confined spaces. The test apparatus is designed to simulate the volume around the shaft that connects the turbine and turbo-pump of a liquid rocket engine. The flammability limits were determined for hydrogen and oxygen mixtures and then helium was added to the mixture. Tests were conducted for gap sizes of 0.2, 0.1, and 0.025 inches. Tests were performed at standard atmospheric conditions and the mixture was premixed and quiescent. The flammability limits are reported as a function of gap size and diluent concentration. Without the helium diluent, the lower flammability limit (LFL) ranged from 6% to 13% and the upper flammability limit (UFL) ranged from 88% to 93%. When helium was added to the mixture the LFL increased by approximately 3% volume of hydrogen for all helium concentrations and gap sizes. The UFL shows a large decrease with helium, which is primarily due to replacing the excess hydrogen with helium.

Experimental and theoretical study on the influence of temperature and humidity on the flammability limits of ethylene (R1150)