Nitrogen dilution is a common procedure for ensuring safety in used of the flammable gas like hydrogen enriched natural gas which has higher burning velocity. The objective of this study is to determine the flammability limits of hydrogen enriched natural gas to the combustion and to determine the correlation of nitrogen dilution towards the hydrogen enriched natural gas. The experiment was performed in a 20L closed vessel of explosion unit. The mixtures were ignited by using spark permanent wire that place at the centre of the vessel. The pressure-time variation data during the explosion of the natural gas/hydrogen/air mixture after nitrogen is added in a vessel was recorded. Since the explosion vessel does not allow direct visual observation of the flame, the explosion vessel uses an indirect measurement of the flame propagation which is the explosion pressure. The explosion pressure data is use to determine the flammability limits of hydrogen enriched natural gas. In this study, the result shows that the flammability limits of natural gas/hydrogen/air mixture are changed after nitrogen is added into the mixture. When 7 % volume of nitrogen is added into the natural gas/ hydrogen/ air mixture, the upper flammability limit is changed from 16 % to 14 % volume of natural gas. Then, nitrogen diluted from 7 % volume up to 9 % volume of nitrogen reduces the upper flammability limit of hydrogen enriched natural gas from 14 % to 11 % of natural gas by volume. So, the range of the flammability limits also reduced when the volume of nitrogen is increased.

Hydrogen- enriched natural gas has been widely used in all over the world for application in gas turbine and internal combustion engine. The theory behind this concept is the addition of hydrogen in natural gas can extend the lean operation limit, improve the lean burn ability, and decrease the emission of NOx, CO and unburned hydrocarbon. The aims of this study are to determine the effect of vacuum pressures on the flammability limits of hydrogen enrichment in natural gas. In this experiment, methane is use to replace the natural gas. The experiments were performed in a 20 L closed explosion vessel. The mixtures were ignited by using spark permanent wire that placed at the centre of the vessel. The explosion pressure data is used to determine the flammability limits, when the low pressure is used in the explosion, the explosion limit will become wide. In this study, the result shows the flammability limits of methane is from 5 % volume to 15 % volume of methane and have revealed that the addition of hydrogen in methane /air mixture will reduce the lower flammability limit initially at 5 % volume to 1 % volume of methane at 0.98 bar. As the conclusion, we can come out that explosion of methane at lower pressure with addition of hydrogen has proven benefit of widen the flammability limit of methane, improving the combustion stability, reduce the emission of NOx, CO and unburned hydrocarbon and decreasing the spark timing. Hence, the cold start phenomenon that usually occurs at the initial stage of combustion could be overcome by adding hydrogen at low pressure.

The use of hydrogenated fuels shows considerable promise for applications in gas turbines and internal combustion engines. The aims of this study are to determine the flammability limits of natural gas/ air and to investigate the effect on flammability limit of natural gas/ air enriched up to 60% hydrogen of fuel by volume at atmospheric pressure and ambient temperature. The experiments were performed in a 20 L closed explosion vessel. The mixtures were ignited by using spark permanent wire that placed at the centre of the vessel. The pressure-time variations during explosions of natural gas/air mixtures in explosion vessel were recorded. The explosion pressure data is used to determine the flammability limit which flame propagation is considered occurred if explosion pressure greater than 0.1 bar. In this study, the result shows the flammability limits is from 6 vol% to 15 vol% of natural gas and have revealed that the addition of hydrogen in natural gas extends the lower flammability limit initially 6 vol% to 2 vol% of methane.

Flammability limit is a most significant property of substances to ensure safety of chemical processes and fuel application. Although there are numerous flammability literature data available for pure substances, for fuel mixtures these are not always available. Especially, for fuel mixture storage, operation, and transportation, inert gas inerting and blanketing have been widely applied in chemical process industries while the related date are even more scarce. Lower and upper flammability limits of hydrocarbon mixtures in air with and without additional nitrogen were measured in this research. Typically, the fuel mixture lower flammability limit almost keeps constant at different contents of added nitrogen. The fuel mixture upper flammability limit approximately linearly varies with the added nitrogen except mixtures containing ethylene. The minimum added nitrogen concentration at which lower flammability limit and upper flammability limit merge together is the minimum inerting concentration for nitrogen, roughly falling into the range of 45 plus/minus 10 vol % for all the tested hydrocarbon mixtures. Numerical analysis of inert gas dilution effect on lower flammability limit and upper flammability limit was conducted by introducing the parameter of inert gas dilution coefficient. Fuel mixture flammability limit can be quantitatively characterized using inert gas dilution coefficient plus the original Le Chatelier's law or modified Le Chatelier's law. An extended application of calculated adiabatic flame temperature modeling was proposed to predict fuel mixture flammability limits at different inert gas loading. The modeling lower flammability limit results can represent experimental data well except the flammability nose zone close to minimum inerting concentration. Le Chatelier's law is a well-recognized mixing rule for fuel mixture flammability limit estimation. Its application, unfortunately, is limited to lower flammability limit for accurate purpose. Here, firstly a detailed derivation was conducted on lower flammability limit to shed a light on the inherent principle residing in this rule, and then its application was evaluated at non-ambient conditions, as well as fuel mixture diluted with inert gases and varied oxygen concentrations. Results showed that this law can be extended to all these conditions.