We are aware that in early future the world will suffer from the shortage of conventional fuels. Pollution from these conventional fuels is causing the global warming, ozone depletion this makes it essential to search the renewable, pollution free alternative fuel. Hydrogen seems to be most promising alternative fuel.
Hydrogen when burns produce clean energy. Hydrogen can be produce easily. Hydrogen is lightest fuel and richest in energy per unit mass (120 700 kJ/kg). Petrol vapor creeps along the ground while Hydrogen goes up in the air so it is relatively safe. Hydrogen can be stored as compressed gas, liquid or by chemical bonding (i.e. Metal Hydride). Some alloys stores Hydrogen at a higher density than pure Hydrogen even higher than the liquid Hydrogen.
Hydrogen, like petrol, diesel and natural gas, burns well in internal combustion engines. However, in Reciprocating engine during the suction stroke if the Hydrogen is expose to the red-hot particle or spark plug and pre-ignition takes place then it can burst entire fuel tank.
Solution to these problems is to use the Hydrogen in the Wankel rotary engine, which has advantages like high power to weight ratio, extended power stroke, and lesser moving parts. Rotor directly opens and closes ports, so correct timing of intake and exhaust is maintain even at high speed with flat torque curve. Vibration is very low because perfect balancing is possible. Cooler combustion means fewer oxides of nitrogen. Separation of combustion region from intake region is good for Hydrogen fuel.
Mazda began a two years trial period for its experimental low-pollution Hydrogen rotary engine vehicle in 1995. The Cappella Cargo van model vehicle will burn a Hydrogen fuel and will not emit carbon dioxide. Mazda lent the vehicle to the Hirohata Steel Mill for use as their company van and drove it for at least 20,000 kilometers on public roads. Hydrogen was stored as metal hydride.
Generating the Hydrogen:
Hydrogen from water: - The most common way of splitting water is by electrolysis, though it can also be done using a thermochemical reaction or simply by heating.
Hydrogen from hydrocarbons: - The cheapest way of making Hydrogen at present is by reforming it from natural gas. Most of the Hydrogen in use today is made by this method. In order to split the Hydrogen from the carbon in the natural gas (mainly Methane, CH4) a process called “steam reformation” is used.
Storing the Hydrogen : - Since Hydrogen is one of the lightest elements and has very small molecules, it can escape from tanks and pipes more easily than conventional fuels. However, if it is to be used as a fuel for transport or power generation then there must be ways of storing it cost-effectively. Storing Hydrogen can be done in three main ways, compressed form, in Liquid form and by chemical bonding (i.e. Metal Hydride).
A gram of Hydrogen gas occupies about 11 liters (2.9 gallons) of space at atmospheric pressure, so for convenience the gas must be intensely pressurized to several hundred atmospheres and stored in a pressure vessel. In liquid form, Hydrogen can only be stored under cryogenic temperatures. These options are not practical for everyday use. The solution to these difficulties is storage of Hydrogen in hydride form. This method uses an alloy that can absorb and hold large amounts of Hydrogen by bonding with Hydrogen and forming hydrides.
Hydrogen in Internal Combustion engines
Drawbacks of conventional Reciprocating engine: High weight to power ratio, More vibrations, Low efficiency due to reciprocating parts and valve mechanism, As Hydrogen is highly flammable, so in case of reciprocating engine Pre-ignition is major problem, Backfiring chances incase of Hydrogen as a fuel are more.
In Reciprocating engine during the suction stroke if the Hydrogen comes in contact with the red hot particle or spark plug and if pre-ignition takes place then it can cause the fire in fuel line and burst entire fuel tank
It can be concluded from this seminar that Hydrogen is the best preferred alternative for conventional fuel in every aspect. By using Hydrogen we can develop economical and efficient vehicle and industrial plants.
Use of Hydrogen in the rotary i.e. Wankel engine is inherently backfire preventing and can function through a wide operating range at excess air ratio λ = 1. It was experimentally proved that the pre-mixed Hydrogen Rotary engine achieved and O/P power up to 63 % of gasoline specifications, while the Hydrogen Reciprocating engine with pre-mixed mixture method marked only 50 % of gasoline specifications. Further, in case of Rotary engine, the induction-cycle-injection could be implemented easily with an achievement of an output power of 75 % of gasoline specifications.
When operated around excess air ratio λ = 2~3 in the partial load range, it was proved that a high thermal efficiency together with clean exhaust gas was attainable.
One of the greatest advantages of Hydrogen as an alternative fuel is that it is they are renewable and environmental friendly.