Non-flammable hydrogen gas composition for lighter-than-air vehicle and a method for optimizing the same

Abstract

The present invention relates to a non-flammable hydrogen gas composition consisting of a non-flammable mixture of hydrogen and C3-C4 hydrocarbon inhibitors. The C3-C4 hydrocarbon inhibitors are selected from hydrocarbons, for example, propane, propylene, n-butane, isobutylene, and the like. The present invention further provides a composition consisting of a mixture of saturated and unsaturated C3-C4 hydrocarbon inhibitors selected from the hydrocarbons, the hydrogen gas composition. Furthermore, the composition has the advantage of reducing hydrogen's flammability while simultaneously increasing its minimum ignition energy. The present invention provides a cost-effective, renewable, non- toxic, and non-corrosive composition for aerostats like zeppelins, airships, and balloons, ensuring operational safety during hydrogen storage and transport.

Description

[0001] “NON-FLAMMABLE HYDROGEN GAS COMPOSITION FOR

[0002] AEROSTATS AND A METHOD FOR OPTIMIZING THE SAME”

[0003] FIELD OF THE INVENTION

[0004] The present invention relates to a non-flammable gas composition; and more particularly to a non-flammable hydrogen gas composition for aerostats and a method for optimizing the said composition.

[0005] BACKGROUND OF THE INVENTION

[0006] It is well known in the prior art that an aerostat refers to any buoyant aircraft that remains aloft primarily through the use of buoyant gases, such as helium or hydrogen. The aerostats include balloons, airships, and other similar vehicles that rely on buoyancy for flight. Aerostats are used for a wide range of purposes, including transportation, reconnaissance, research, and recreational activities.

[0007] The aerostats and lighter than air (LTA) crafts fly through the skies using internal propulsion. In contrast to traditional aircraft, the lift generated by aerostats is not a consequence of their airborne motion. It originates from buoyancy instead. The principle of operation of these vehicles is a flexible, large envelope containing a gas or gas mixture with a density much lower than that of ordinary atmospheric air. By providing the necessary upward buoyant force, this gas filling enables the aerostat to maintain altitude without depending on the conventional aerodynamic lift produced by airspeed. The molecular weight of air, at standard conditions of 15 °C and 1 atm, is approximately 29 g / mol, resulting in a density of 1.225 kg / m3. In this environment, when an envelope is fdled with a gas of lower density than air, it experiences an upward buoyant force. The greater the disparity in density, the stronger the buoyant force generated. Numerous lighter-than-air gases, such as hydrogen, helium, ammonia, methane, superheated steam, and heated air, exhibit lower densities than that of air. In previous instances of related work, some of these gases, either individually or as mixtures, have been documented as suitable lift gases for aerostats.

[0008] Hydrogen stands as the lightest gas within the Earth's atmosphere, boasting a remarkably low density of 0.085 kg / m3at the standard conditions of 15°C and 1 atm. However, it is crucial to acknowledge that despite its favourable buoyancy properties, hydrogen comes with significant safety concerns. Hydrogen exhibits a broad flammability range, ranging from 4% to 74% by volume in the air, making it highly susceptible to accidental ignition. Additionally, its low minimum ignition energy, measuring a mere 0.019 mJ, further amplifies the risk associated with its use. Thus, hydrogen, although being the most suitable lift gas, has serious concerns relating to safety and storage as it ignites even on minor contact with atmospheric air.

[0009] Helium, the second-lightest gas in the atmosphere, follows hydrogen in terms of its low density. Yet, it is essential to note that helium is a non -renewable resource and cannot be generated through chemical reactions. Methane, another lighter-than-air gas, possesses a lift capability of 5.3 N / m3. However, it is classified as a flammable gas, which poses inherent safety risks. Ammonia, while being nonflammable, offers a lift of 4.9 N / m3. It is important to acknowledge that ammonia has its drawbacks, including toxicity, corrosiveness, and adverse environmental effects, making its use a matter of careful consideration.

[0010] The GB Patent 2356184A to Goodey Thomas John teaches steam as a lifting gas to fill the envelope of a lighter than air craft. The hot air is non-flammable, nontoxic and non-corrosive option. The LTA craft includes a boiler to provide variable quantity of steam to generate upper thrust. However, manufacturing of hot air at higher altitudes is practically not feasible and cost intensive.

[0011] The US Patent Application 2023117737A1 to Miftakhov Valery teaches a mixture of helium and hydrogen as a lift gas for lighter than air craft. The lift gas has a lift of 10.4 N / m3that is slightly higher than the lift obtained by using neat helium. Although helium is inert and safe during handling and operation, it is not stored in the form of any compound. The drawback with the use of helium includes cost, non-renewability, and rapid exhaustibility.

[0012] Accordingly, there is a need of a non-flammable gas composition for aerostats that overcomes the shortcomings of the gases available in the prior art for aerostats; and provide a feasible composition that is safe for storage and transportation, without compromise in the lift performance.

[0013] SUMMARY OF THE INVENTION:

[0014] The present invention discloses a non-flammable hydrogen gas composition consisting of a non-flammable mixture of hydrogen and C3-C4 hydrocarbon inhibitors. The present invention further describes a method of optimising the hydrogen gas composition. The non-flammable hydrogen gas composition specifically includes C3-C4 hydrocarbon inhibitors that are selected from hydrocarbons, for example, propane, propylene, n-butane, isobutylene, and the like. The present invention further describes a composition that includes a mixture of C3-C4 saturated hydrocarbon inhibitors and C3-C4 unsaturated hydrocarbon inhibitors, wherein the C3-C4 saturated hydrocarbon inhibitors are selected from propane and butane and the C3-C4 unsaturated hydrocarbon inhibitors are selected from propylene and isobutylene. Thus, the mixture of C3-C4 saturated hydrocarbon inhibitor and C3-C4 unsaturated hydrocarbon inhibitor is selected from ‘propane and propylene’, ‘propane and isobutylene’, ‘butane and propylene’, or ‘butane and isobutylene’.

[0015] The present invention also describes a method 100 for optimizing the hydrogen gas composition. This method includes various steps. In a first step of introduction and mixing of hydrogen gas and air 105, hydrogen gas and air are introduced at a temperature of 298 K into an evacuated reactor at a pressure of up to 1 bar and uniformly mixed before a process of ignition. After the ignition, a spherical flame front starts to develop, leading to combustion. In a second step of preliminary introduction C3-C4 hydrocarbon inhibitor 110, the C3-C4 hydrocarbon inhibitor is gradually introduced into the hydrogen air mixture in different batches, starting at 0.5%.

[0016] The next step, i.e., a third step of, flame speed determination 115 includes determination of the flame speed by the temporal evolution of the flame front. With the increase in inhibitor content in the above mixture, the flame speed first increases and then decreases, and ultimately there is no ignition at all afterwards. Further, in a fourth step of secondary introduction of a C3-C4 hydrocarbon inhibitor 120, C3- C4 hydrocarbon inhibitor is further introduced with an increment of 0.5%. This step is repeated until a total suppression of the flame speed is achieved. When no flame front is detected even with the gradual increment of ignition energy, the said concentration of C3-C4 hydrocarbon inhibitor is considered the optimum concentration along with hydrogen as the lift gas composition for aerostats.

[0017] The present invention discloses a safe, non-flammable, and lightweight lifting medium for aerostats such as zeppelins, blimp airships, and tethered or unguided balloons, while also ensuring operational safety during the safe storage and transport of hydrogen. Advantageously, the hydrogen gas composition for aerostats is non-flammable even after supplying higher ignition energy and safe as it doesn’t undergo any accidental ignition during the operations.

[0018] BRIEF DESCRIPTION OF DRAWINGS

[0019] The objectives and advantages of the present invention will become apparent from the following description read in accordance with the accompanying drawings wherein

[0020] FIG. la shows the effect of propane on the flame speed of the hydrogen-air mixture in accordance with a preferred embodiment of the present invention; FIG. lb shows the effect of propylene on the flame speed of the hydrogen-air mixture in accordance with a preferred embodiment of the present invention;

[0021] FIG. 1c shows the effect of butane on the flame speed of the hydrogen-air mixture in accordance with a preferred embodiment of the present invention;

[0022] FIG. Id shows the effect of isobutylene on the flame speed of the hydrogen-air mixture in accordance with a preferred embodiment of the present invention;

[0023] FIG. 2 shows the flammability limit of hydrogen-inhibitor mixture in accordance with a preferred embodiment of the present invention;

[0024] FIG. 3a shows the net composition of a mixture of propane and propylene inhibitors for optimizing non-flammable hydrogen (17.5% hydrogen in air) in accordance with a preferred embodiment of the present invention;

[0025] FIG. 3b shows the net composition of a mixture of butane and propylene inhibitors for optimizing non-flammable hydrogen (17.5% hydrogen in air) in accordance with a preferred embodiment of the present invention;

[0026] FIG. 3c shows the net composition of a mixture of propane and isobutylene inhibitors for optimizing non-flammable hydrogen (17.5% hydrogen in air) in accordance with a preferred embodiment of the present invention;

[0027] FIG. 3d shows the net composition of a mixture of butane and isobutylene inhibitors for optimizing non-flammable hydrogen (17.5% hydrogen in air) in accordance with a preferred embodiment of the present invention; and FIG. 4 shows the flammability limit of hydrogen - inhibitor mixtures in accordance with the present invention.

[0028] DETAILED DESCRIPTION OF THE INVENTION

[0029] The present invention describes a non-flammable hydrogen gas composition that provides essential upward buoyant force to aerostats to stay aloft.

[0030] The invention described herein is explained using specific exemplary details for better understanding. However, the invention disclosed can be worked on by a person skilled in the art without the use of these specific details.

[0031] References in the specification to "one embodiment" or "an embodiment" means that particular feature, structure, characteristic, or function described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment.

[0032] References in the specification to “preferred embodiment” means that a particular feature, structure, characteristic, or function described in detail thereby omitting known constructions and functions for clear description of the present invention.

[0033] The foregoing description of specific embodiments of the present invention has been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. As used herein, ‘lift gas’ refers to gas having density lower than the density of atmospheric air, resulting in said lifting gas to have property to rise above the atmospheric air.

[0034] The present invention discloses a non-flammable hydrogen gas composition as a lift gas composition for aerostats consisting of a non-flammable mixture of hydrogen and C3-C4 hydrocarbon inhibitors. The present invention also teaches a method for optimization of the said lifting gas composition.

[0035] In accordance with the preferred embodiment, the non-flammable hydrogen gas composition of the present invention includes hydrogen gas and hydrocarbon inhibitors. Accordingly, the non-flammable hydrogen gas composition specifically includes

[0036] 1) hydrogen gas 90 - 95 vol%; and

[0037] 2) a C3-C4 hydrocarbon inhibitor 5 - 10 vol%.

[0038] In this preferred embodiment, the C3-C4 hydrocarbon inhibitors are selected from hydrocarbons, for example propane, propylene, n-butane, isobutylene and the like. It is noted, however, that the interaction of C3-C4 hydrocarbon inhibitor with active radicals of hydrogen result in the formation of inactive alkyl intermediates, leading to chain termination and the cessation of flame propagation.

[0039] In accordance with another embodiment, the hydrogen gas composition includes:

[0040] 1) hydrogen gas 90 - 95 vol%; and 2) a mixture of C3-C4 saturated hydrocarbon inhibitor and C3-C4 unsaturated hydrocarbon inhibitor 5 - 10 vol%.

[0041] In accordance with this embodiment, the C3-C4 saturated hydrocarbon inhibitors are selected from propane and butane; and the C3-C4 unsaturated hydrocarbon inhibitors are selected from propylene and isobutylene. Thus, the mixture of C3-C4 saturated hydrocarbon inhibitor and C3-C4 unsaturated hydrocarbon inhibitor is selected from ‘propane and propylene’, ‘propane and isobutylene’, ‘butane and propylene’, or ‘butane and isobutylene’.

[0042] Now, a method 100 for optimizing the hydrogen gas composition in accordance with the present invention is described. This method includes various steps.

[0043] The first step 105 is introduction and mixing of hydrogen gas and air. In this step, hydrogen gas and air are introduced at a temperature of 298 K into an evacuated reactor at a pressure up to 1 bar and uniformly mixed before a process of ignition. After the ignition, a spherical flame front starts to develop leading to combustion.

[0044] The second step 110 is preliminary introduction of C3-C4 hydrocarbon inhibitor. In this step, initially the selected C3-C4 hydrocarbon inhibitor is gradually introduced in the hydrogen air mixture in different batches starting from 0.5%.

[0045] The third step 115 is flame speed determination. In this step, the flame speed is determined with temporal evolution of the flame front. The flame speed is an important parameter to understand the effect of inhibitors on the combustion. With the increase of the inhibitor content in the above mixture, the flame speed first increases, and then decreases, and ultimately there is no ignition at all afterwards.

[0046] The fourth step 120 is secondary introduction of inhibitor. In this step, the C3-C4 hydrocarbon inhibitor is further introduced with an increment of 0.5%. This step is repeated till a total suppression of the flame speed is achieved. When no flame front is detected even with the gradual increment of ignition energy; the said concentration of C3-C4 hydrocarbon inhibitor is considered as the optimum concentration along with hydrogen as the lift gas composition for aerostats.

[0047] The method of optimization of the hydrogen gas composition of the present invention is conducted in a stainless-steel spherical chamber supported by a pair of horizontal side arm rotors for uniform gas mixing. The chamber is equipped with a pair of electrodes to provide the external ignition and a pair of glass windows, placed opposite to visualize the flame through Schlieren mirrors using a high-speed camera.

[0048] In accordance with the present invention, the combustion of the hydrogen is the kinetic process of the self-acceleration of chemical reactions augmented by a release of energy in the form of heat and light. The phenomenon of the substantial self-heating of a reaction mixture and the rapid growth of active intermediate products takes place through a series of elementary chemical reactions following a branched-chain mechanism.

[0049] After the ignition, the key role in hydrogen combustion is played by the following reactions involved in the flame propagation:

[0050] H2+ O2 = H + HO2* (1) H + 02= OH* + O (2)

[0051] O + OH* = O2+ H (3)

[0052] OH* + H2= H2O + H (4)

[0053] O + H2= OH* + H (5)

[0054] In the present invention during the hydrogen combustion reactions, the generation and recombination of H, O, and OH* atoms / radicals advantageously produce the chain branching. Further the flame propagates because of such elementary reactions. A flame continues to propagate when the heat generated in the reaction zone raises the temperature of the nearby unbumt mixture to a level sufficient to ignite the chain reactions.

[0055] Advantageously, the inhibitors present in the adjacent fresh layer of the mixture disrupt the chain branching by trapping free radicals, leading to the cessation of flame propagation. Also, the inhibitors absorb a significant amount of heat generated during chemical reactions, preventing the sustenance of the combustion process any further. Accordingly, the interactions between the inhibitor and active radicals of the hydrogen result in the formation of inactive alkyl intermediates, leading to chain termination.

[0056] The extent of suppression of hydrogen combustion depends on the inhibitor content in the unbumt mixture. A higher content of inhibitors leads to an increased number of inhibitory reactions, resulting in a faster reaction rate compared to the propagating reactions.

[0057] After analysing the optimum inhibitor concentration, the lifting force of the hydrogen and C3-C4 hydrocarbon inhibitor mixture is required to be carried out. The C3-C4 hydrocarbon inhibitors not only suppress the flammability of hydrogen but also enhance the minimum ignition energy. So, utilizing hydrogen and C3-C4 hydrocarbon inhibitors as lift gas would not ignite even after encountering any ignition source while under accidental exposure to air. Now FIG.2 describes the detailed flammability diagram indicating that any mixture falling under the curve (i.e., left of the curve) is the flammable zone, while the outside (right) of the curve is a non-flammable zone. Therefore, the hydrogeninhibitor system under the non-flammable zone is suitable as a lift gas for aerostats.

[0058] Table 1 summarizes the overall molecular weight and density of hydrogen gas compositions and their corresponding lift performance. The hydrogenisobutylene system is the most effective among other systems due to its special molecular structure. The presence of o-7t* conjugation in the molecule increases the reactivity of the H atoms located in the a-position. Therefore, the activation energy of H + iCTHx = iC4H9 is almost insignificant, resulting in a high reaction rate. Such an effect is not observed in other systems. Table 1 : Overall molecular weight and density of hydrogen gas compositions, and their corresponding lift performances

[0059] Furthermore, the lifting performance can be determined as the product of the density difference between air and lift gas and the acceleration due to gravity. Thus, the lower the density of the lift gas, the higher the lifting force. From Table 1, it is observed that the effective molecular weight of the hydrogen-inhibitor system lies between 4 and 6 g / mol, i.e., slightly higher than helium. Also, the overall density of hydrogen-inhibitor systems is 2.5-3 times higher than hydrogen, 1.2-1.5 times higher than helium. Considering the drawbacks of pure hydrogen and helium, this approach is safer as well as economically feasible.

[0060] Table 2 summarizes the overall molecular weight and density of the hydrogen gas compositions, and the corresponding lift performance of inhibitors individually and in combination with saturated and unsaturated hydrocarbon inhibitors for optimising non-flammable hydrogen.

[0061] The suppression of the hydrogen-air mixture is improved by the inhibitors of saturated and unsaturated hydrocarbons (HCs). Since the unsaturated HC molecule has a double bond, the active H radical abstraction's activation energy is significantly lower (6.5 kJ / mol), enabling the consumption of such active radicals at greater reaction rates. Saturated hydrocarbons cease the propagation of flames by permitting the environment's oxygen to become consumed (CsHg+ ^ b+iC H? and iC3H7+O2=C3H6+HO2). From C3-C4 hydrocarbons, four combinations of mixtures were carefully selected so that there are saturated and unsaturated hydrocarbons in each mixture. The experiments to determine the optimal inhibitor contents were carried out at 17.5 % hydrogen in air, j ust below the LEL ( 18.3 %) . Among the other systems, propane + isobutylene and butane + isobutylene hydrocarbon mixtures were found to be the most efficient.

[0062] Table 2: Overall molecular weight and density of the hydrogen gas compositions, and their corresponding lift performances Furthermore, the combination compositions of C3-C4 hydrocarbon inhibitors have advantages over the individual ones. Less inhibitor contents are required to optimize the non-flammable mixture; the effect of this is eventually reflected in the lift performance. Moreover, in the premixed conditions of a hydrogen-inhibitor system, unsaturated hydrocarbons rapidly scavenge the active radicals, whereas saturated hydrocarbons capture even the trace amount of oxygen (if present) and form passive molecules, which is advantageous from a safety perspective.

[0063] EXAMPLES:

[0064] Only a few examples and implementations are disclosed wherein the mechanical implements under consideration were transformed by using the method of the present invention to enhance the mechanical properties and service life of the implements. It is understood that one or more variations, modifications, and enhancements to the described examples and implementations and other implementations can be made based on what is disclosed.

[0065] Examples are set forth herein below and are illustrative of different types of reactions and reaction conditions that can be utilized in practicing the disclosure. It will be apparent, however, that the disclosure can be practiced with other types of reactions and reaction conditions than those used in the examples, in accordance with the disclosure above and as pointed out hereinafter.

[0066] Example 1: Optimisation of the hydrogen gas composition for hydrogen gas 90 - 95 vol % and a propane inhibitor 5 - 10 vol%.

[0067] Referring to FIG. la, FIG. 2 and Table 1, the optimisation of the composition consisting of hydrogen and propane; and its effect on the flame speed of the hydrogen-air mixture is described. Initially, hydrogen and air were introduced into the reactor followed by propane inhibitor and uniformly mixed before the ignition. After the ignition, the spherical flame front started to develop leading to combustion. Next, propane was introduced gradually in different batches, starting from 0.5% with a further increment of 0.5% till the total suppression was achieved. Further, the flame speed was determined as 49.4, 96, 22.5 and 4.5 cm / s at 0, 2, 4 and 6% of propane respectively in the mixture. Finally, with 8% propane in the hydrogen-air mixture, no flame front was detected even with the gradual increment of ignition energy. Accordingly, 8% propane was considered the optimum concentration with hydrogen as lift gas for the aerostat. The said optimum concentration provided a net lift 9.8 N / m3to aerostat. Advantageously, the propane inhibitor not only suppresses the flammability of hydrogen but also enhance the minimum ignition energy.

[0068] Now referring to FIG. 2, the curve 2a shows the non-flammable zone for the said combination gas of hydrogen gas and propane inhibitor. The flammable zone is indicated by left side of curve 2a. The non-flammable zone is to the right side i.e., outside of the curve 2a. The hydrogen-inhibitor system under the nonflammable zone is suitable as a lift gas for the aerostat. The overall density of the hydrogen-propane system was found to be 0.228 kg / m3with a lifting performance of 9.8 N / m3and a 12.8% lift loss with respect to pure hydrogen.

[0069] Example 2: Optimisation of the hydrogen gas composition for hydrogen gas 90 - 95 vol % and a propylene inhibitor 5 - 10 vol%.

[0070] Referring to FIG. lb, FIG. 2 and Table 1, the optimisation of the composition consisting of hydrogen and propylene; and its effect on the flame speed of the hydrogen-air mixture is described. Initially, hydrogen and air were introduced into the reactor followed by propylene and uniformly mixed before the ignition. After the ignition, the spherical flame front started to develop leading to combustion. Next, propylene was introduced gradually in different batches, starting from 0.5% with a further increment of 0.5% till the total suppression was achieved. Further, the flame speed was determined as 49.4, 102.4, 40.6, 8.3 and 3.2 cm / s at 0, 2, 4, 6 and 8% of propylene respectively in the mixture. With 10% propylene in the hydrogen-air mixture, no flame front was detected even with the gradual increment of ignition energy. Accordingly, 10% propylene was considered the optimum concentration with hydrogen as lift gas for the aerostat. The said optimum concentration provided a net lift 9.5 N / m3to aerostat. Advantageously, the propylene inhibitor not only suppresses the flammability of hydrogen but also enhances the minimum ignition energy.

[0071] Now referring to FIG. 2, curve 2b shows the non-flammable zone for the said combination gas of hydrogen gas and propylene inhibitor. The flammable zone is indicated by left side of curve 2b. The non-flammable zone is to the right side i.e., outside of the curve 2b. The hydrogen-inhibitor system under the nonflammable zone is suitable as a lift gas for the aerostat. The overall density of the hydrogen-propylene system was found to be 0.255 kg / m3with a lifting performance of 9.5 N / m3and a 15% lift loss with respect to pure hydrogen.

[0072] Example 3: Optimisation of the hydrogen gas composition for hydrogen gas 90 - 95 vol % and n-butane inhibitor 5 - 10 vol%.

[0073] Referring to FIG. 1c, FIG. 2 and Table 1, the optimisation of the composition consisting of hydrogen and n-butane; and its effect on the flame speed of the hydrogen-air mixture is described. Initially, hydrogen and air were introduced into the reactor followed by butane inhibitor and uniformly mixed before the ignition. After the ignition, the spherical flame front started to develop leading to combustion. Next, butane was introduced gradually in different batches, starting from 0.5% with a further increment of 0.5% till the total suppression was achieved. Further, the flame speed was obtained as 49.4, 85, 8.9 and 2.4 cm / s at 0, 2, 4 and 6% of butane respectively in the mixture. With 7% butane in the hydrogen-air mixture, no flame front was detected even with the gradual increment of ignition energy. Finally, 7% butane in the hydrogen-air mixture was considered the optimum concentration with hydrogen as lift gas for the aerostat. The said optimum concentration provided a net lift 9.54 N / m3to aerostat. Advantageously, the butane inhibitor not only suppresses the flammability of hydrogen but also enhances the minimum ignition energy.

[0074] Now referring to FIG. 2, the curve 2c shows the non-flammable zone for the said combination gas of hydrogen gas and n-butane inhibitor. The flammable zone is indicated by left side of curve 2c. The non-flammable zone is to the right side i.e., outside of the curve 2c. The hydrogen-inhibitor system under the nonflammable zone is suitable as a lift gas for the aerostat. The overall density of the hydrogen-butane system was found to be 0.25 kg / m3with a lifting performance of 9.54 N / m3and a 14.8% lift loss with respect to pure hydrogen.

[0075] Example 4: Optimisation of the hydrogen gas composition for hydrogen gas 90 - 95 vol % and an isobutylene inhibitor 5 - 10 vol%.

[0076] Referring to FIG. Id, FIG. 2 and Table 1, the optimisation of the composition consisting of hydrogen and isobutylene; and its effect on the flame speed of the hydrogen-air mixture is described. Initially, hydrogen and air were introduced into the reactor followed by isobutylene and uniformly mixed before the ignition. After the ignition, the spherical flame front started to develop leading to combustion. Next, isobutylene was introduced gradually in different batches, starting from 0.5% with a further increment of 0.5% till the total suppression was achieved. Further, the flame speed was obtained as 49.4, 84.8 and 10.05 cm / s at 0, 2 and 4% of isobutylene respectively in the mixture. Finally, with 5% isobutylene in the hydrogen-air mixture, no flame front was detected even with the gradual increment of ignition energy. Accordingly, 5% isobutylene was considered the optimum concentration with hydrogen as lift gas for the aerostat. The said optimum concentration provided a net lift 10.05 N / m3to aerostat. Advantageously, the isobutylene inhibitor not only suppresses the flammability of hydrogen but also enhances the minimum ignition energy.

[0077] Now referring to FIG. 2, the curve 2d shows the non-flammable zone for the said combination gas of hydrogen gas and isobutylene inhibitor. The flammable zone is indicated by left side of curve 2d. The non-flammable zone is to the right side i.e., outside of the curve 2d. The hydrogen-inhibitor system under the nonflammable zone is suitable as a lift gas for the aerostat. The overall density of the hydrogen-isobutylene system was found to be 0.2 kg / m3with a lifting performance of 10.05 N / m3and a 10.3% lift loss with respect to pure hydrogen.

[0078] Example 5: Optimisation of the hydrogen gas composition for hydrogen gas 90 - 95 vol % and the mixture of propane and propylene inhibitor 5 - 10 vol%. Referring to FIG. 3a and Table 2, the optimisation of the composition consisting of hydrogen and inhibitors; and its effect on the non-flammability of hydrogen-air mixture is described. Initially, hydrogen and air were introduced into the reactor followed by propane and propylene and uniformly mixed before the ignition. After the ignition, the spherical flame front started to develop leading to combustion. Next, both propane and propylene were introduced gradually in different batches, starting from 0.5% with a further increment of 0.5% till the total suppression was achieved.

[0079] Now referring to FIG. 3a and FIG. 4, non-flammable mixtures were obtained at different propane-to-propylene ratios, however, 3.5% propane to 4% propylene was considered the optimum concentration with hydrogen as lift gas for the aerostat, as it provided a maximum lifting force compared to other synergistic compositions as well as individual inhibitors. The overall density of the hydrogeninhibitor system was found to be 0.215 kg / m3with a lifting performance of 9.91 N / m3and an 11.54% lift loss with respect to pure hydrogen.

[0080] Example 6: Optimisation of the hydrogen gas composition for hydrogen gas 90 - 95 vol % and the mixture of butane and propylene inhibitor 5 - 10 vol%.

[0081] Referring to FIG. 3b and Table 2, the optimisation of the composition consisting of hydrogen and inhibitors; and its effect on the non-flammability of hydrogen-air mixture is described. Initially, hydrogen and air were introduced into the reactor followed by butane and propylene and uniformly mixed before the ignition. After the ignition, the spherical flame front started to develop leading to combustion. Next, both butane and propylene were introduced gradually in different batches, starting from 0.5% with a further increment of 0.5% till the total suppression was achieved.

[0082] Now referring to FIG. 3b and FIG.4, non-flammable mixtures were obtained at different butane-to-propylene ratios, however, 3.5% butane to 3% propylene was considered the optimum concentration with hydrogen as lift gas for the aerostat, as it provided a maximum lifting force compared to other synergistic compositions as well as individual inhibitors. The overall density of the hydrogen -inhibitor system was found to be 0.219 kg / m3with a lifting performance of 9.87N / m3and an 11.88% lift loss with respect to pure hydrogen.

[0083] Example 7: Optimisation of the hydrogen gas composition for hydrogen gas 90 - 95 vol % and the mixture of propane and isobutylene inhibitor 5 - 10 vol%.

[0084] Referring to FIG. 3c and Table 2, the optimisation of the composition consisting of hydrogen and inhibitors; and its effect on the non-flammability of hydrogen-air mixture is described. Initially, hydrogen and air were introduced into the reactor followed by propane and isobutylene and uniformly mixed before the ignition. After the ignition, the spherical flame front started to develop leading to combustion. Next, both propane and isobutylene were introduced gradually in different batches, starting from 0.5% with a further increment of 0.5% till the total suppression was achieved.

[0085] Now referring to FIG. 3c and FIG.4, non-flammable mixtures were obtained at different propane-to-isobutylene ratios, however, 0.5% propane to 4.5% isobutylene was considered the optimum concentration with hydrogen as lift gas for the aerostat, as it provided a maximum lifting force compared to other synergistic compositions as well as individual inhibitors. The overall density of the hydrogen-inhibitor system was found to be 0.197 kg / m3with a lifting performance of 10.09 N / m3and a 9.95% lift loss with respect to pure hydrogen.

[0086] Example 8: Optimisation of the hydrogen gas composition for hydrogen gas 90 - 95 vol % and the mixture of butane and isobutylene inhibitor 5 - 10 vol%.

[0087] Referring to FIG. 3d and Table 2, the optimisation of the composition consisting of hydrogen and inhibitors; and its effect on the non-flammability of hydrogen-air mixture is described. Initially, hydrogen and air were introduced into the reactor followed by butane and isobutylene and uniformly mixed before the ignition. After the ignition, the spherical flame front started to develop leading to combustion. Next, both butane and isobutylene were introduced gradually in different batches, starting from 0.5% with a further increment of 0.5% till the total suppression was achieved.

[0088] Now referring to FIG. 3d and FIG.4, non-flammable mixtures were obtained at different butane-to-isobutylene ratios, however, 0.5% butane to 4.5% isobutylene was considered the optimum concentration with hydrogen as lift gas for the aerostat, as it provided a maximum lifting force compared to other synergistic compositions as well as individual inhibitors. The overall density of the hydrogen-inhibitor system was found to be 0. 199 kg / m3with a lifting performance of 10.06 N / m3and a 10.2% lift loss with respect to pure hydrogen.

[0089] The present invention discloses a safe, non-flammable and lightweight lifting medium for aerostats. Advantageously, the hydrogen gas composition for aerostats is non-flammable even after supplying higher ignition energy. From a safety perspective, the mixture is safer as it doesn’t undergo any accidental ignition during the operations. Further, the present invention enables excellent lifting performance to the aerostats with minimal lift loss. The composition of the present invention is cheap, renewable, non-corrosive and non-toxic composition for aerostats. As all the inhibitors are renewable and are synthesized through biofuels, it is economical and easily available in the market. Additionally, the present invention discloses composition for aerostats, to reduce venting of the lifting medium during operation.

[0090] The effective molecular weight and density of hydrogen and inhibitor systems are quite low, that provides excellent lift performance. Also, the deployment of the lift gas into the envelope can be easily executed in the field, with diminished possibilities of venting during operation. The hydrogen gas composition can be deployed in aerostats such as lighter than air (LTA) crafts, zeppelins, blimp airships, and tethered or unguided balloons.

[0091] Further, as hydrogen is the preferred fuel due to wide range of flammability, low minimum ignition energy, and rapid burning velocity; the safe storage and transportation of hydrogen is crucial for its operational safety. The hydrogen gas composition of the present composition prevents hydrogen-air explosions, enabling the safe storage and transport of hydrogen.

[0092] The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, to thereby enable others, skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated.

[0093] It is understood that various omission and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the scope of the present invention.

Claims

Claims1. A non-flammable hydrogen gas composition for aerostats comprising: a. hydrogen gas 90 - 95 vol%; and b. a C3 - C4 hydrocarbon inhibitor 5 - 10 vol%.

2. The non-flammable hydrogen gas composition for aerostats as claimed in claim1, wherein the C3 - C4 hydrocarbon inhibitors being selected from the hydrocarbons propane, propylene, n-butane, and isobutylene.

3. The non-flammable hydrogen gas composition for aerostats as claimed in claim 1, wherein the C3 - C4 hydrocarbon inhibitor being selected from a mixture of saturated and unsaturated C3-C4 hydrocarbon inhibitors.

4. The non-flammable hydrogen gas composition for aerostats as claimed in claim3, wherein the mixture of C3 - C4 saturated and unsaturated hydrocarbon inhibitors being selected from ‘propane and propylene’, ‘butane and propylene’, ‘propane and isobutylene’, or ‘butane and isobutylene’.

5. The non-flammable hydrogen gas composition for aerostats as claimed in claim1, wherein a method 100 for optimizing the non-flammable hydrogen gas composition including:a. a first step 105 of introduction and mixing of hydrogen gas and air, wherein hydrogen gas and air being introducing at 298 K into an evacuated reactor up to 1 bar and being uniformly mixed before the ignition; followed by a spherical flame front being developed, leading to combustion after the ignition; b. a second step 110 of preliminary introduction C3-C4 hydrocarbon inhibitor, wherein initially the C3-C4 hydrocarbon inhibitor being gradually introduced to the hydrogen air mixture in different batches starting from 0.5%; c. a third step 115 of flame speed determination, wherein the flame speed being determined with the temporal evolution of the flame front, by increasing of inhibitor content in the mixture obtained; and d. a fourth step 120 of secondary introduction, wherein the C3-C4 hydrocarbon inhibitor being further introduced with an increment of 0.5%, and the step being repeated till a total suppression of flame speed being achieved; and when no flame front being detected after the gradual increment of ignition energy, the said concentration of the C3-C4 hydrocarbon inhibitor being considered as the optimum concentration along with hydrogen as lift gas composition for aerostats.

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