The conditions which I want to know are: -
1. Pressure
2. Temperature
3. Internal Energy of a mixture @ the time of combustion.
4. A function through which we can find different temperature and pressure conditions at which combustion would start.
The temperature of the mixture should be higher than that of the self ignition temperature of hydrogen which is higher than the self ignition temperature of hydrocarbon fuels.
Hydrogen is often burned with air rather than oxygen
The stoichiometric air/fuel ratio for hydrogen is 34:1. At this air/fuel ratio, hydrogen will displace 29% of the combustion chamber leaving only 71% for the air.
I assume we're not talking about a liquid hydrogen rocket engine which has major problems of its own. In my understanding, the ratio of H2 to O2 is fairly critical. On the other hand I am not keen to try the experiment of mixing them in a laboratory in various rations and then trying to ignite them just to see what happens. You are supposed to be able to drop a lighted match into a full petrol tank of a car . . . but that's something else I would never actually try and do.
In order to start combustion, temperature is supposed to be higher than ignition temperature (it is about 500-550C at Pabs.=14.7 PSI) or an ignition source should be present. Generally, the higher is the pressure the ignition temperature is lower. Some info is given in Perry's chemical engineering handbook
Hydrogen is a unique flammable gas where it flammability limits are very broad, with a typical range from 4 to 76% by volume in air at 1 atm pressure and room temperatures. This range gets broader when hydrogen is burn in pure oxygen atmosphere (from 4 to 95%). Higher temperatures will enlarge this range and higher pressures will have opposite effects with less influence than the first. As mentioned before, typical auto-ignition temperatures are around 536 C (997 F).
In order to start combustion, the temperature of mixture is supposed to be higher than ignition temperature.
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