Fire Safety Evaluation of High-Pressure Ammonia Storage Systems

Ammonia combustion is a promising energy source as a carbon free fuel without greenhouse gas emissions. However, since the auto-ignition temperature is 651 degrees Celsius and the range of flammability limit is not wide compared to other fuels, fundamental studies on ammonia fires have rarely been conducted so far. Therefore, this study aims to numerically estimate fire spread characteristics when ammonia fuel in a high-pressure state leaks to the outside, especially focusing on the flammability limit according to oxygen concentration. Three kinds of reaction mechanism for numerical analysis were adopted to compare the flame structure, flammability limit, and combustion characteristics. Plank-mean absorption coefficients of nitrogen species were taken for the radiation model, in addition to the optically thin model. The effect of radiation heat loss could be identified from the maximum flame temperature trend at a low strain rate. It was confirmed that the pyrolysis of ammonia in the preheated zone results in hydrogen production, and the generated hydrogen contributes to heat release rate in the flame zone. It is found that the contribution of hydrogen would be an important role in the flammability limit of ammonia combustion. Finally, Karlovitz and Peclet numbers showed well the extinction behaviors of ammonia combustion as a result of LOC (Limit Oxygen Concentration) analysis as a function of global strain rate.

IGNITION BEHAVIOR OF SUPERCRITICAL LIQUID FUEL IN COMBUSTION SYSTEM

In systems that involve super-critical liquid fuel combustion, the temperature of the propellants is in the sub-critical state when they are injected into the combustion chamber. However, during the process of combustion, the system experiences a shift in its state of thermodynamics from subcritical to supercritical. The present study predicts the ignition behavior for super-critical liquid fuel combustion through the techniques of computational fluid dynamics (CFD). Simulations are carried out for a single shear coaxial injector’s test case of the combustion chamber. For super-critical combustion, the present research uses kerosene as a fuel and gaseous oxygen as the oxidizer. Simulations are carried out at a steady state for various values of rich flammability limit (RFL). The real gas model, Soave-Redlich-Kwong (SRK) is used for performing simulations in the present study. On the other hand, for the various values of rich flammability limit (RFL), transient simulations are carried out for ideal gas. It has been observed that the simulations performed for steady-state closely approximate the experimental data in comparison to transient simulations. It is also observed that the inherent stability issues involved in transient simulations emphasize the use of an ideal gas model for its computation.

Experimental Study on the Effect of Nano Additives γAl2O3 and Equivalence Ratio to Bunsen Flame Characteristic of Biodiesel from Nyamplung (Calophyllum Inophyllum)

Nano γAl2O3 has been one of the nanometal oxides that has improved the characteristics of biodiesel. The effect of γAl2O3 nanoparticles addition on premixed flame combustion is investigated with an experiment on the laminar flame speed of Calophyllum inophyllum methyl ester 30% and 70% petrodiesel mixtures, at atmospheric pressure and preheated temperature T = 473K. The γAl2O3 nanoparticles added to CIME30 biodiesel were 0ppm, 100ppm, 200ppm, and 300ppm. Experiments were carried out on a bunsen burner. The equivalent ratio of the mixture between ϕ = 0.67 to 1.17. Experiments revealed that the addition of nanoparticles to CIME30 biodiesel expands the flammability limit and increases the laminar flame speed. CIME30 without nanoparticles, flame stable between ϕ = 0,76 -1,17. CIME30 with nanoparticles, flame stable between ϕ = 0,67 -1,17. Combustion of CIME30 required a lot of air. The highest laminar flame speed occurred at the equivalent ratio ϕ = 0.83. The highest laminar flame speed of CIME30 0, 100, 200, and 300 ppm were 30.77, 34.50, 35.90, 38.45 cm/s respectively. The higher the nano γAl2O3 concentration the higher the laminar flame speed. This occurs due to the catalytic effect of γAl2O3 on biodiesel and its mixtures.