Hydrogen gas
-Clean burning fuel and has the highest energy content per unit mass of any chemical fuels which can reduce the dependency on hydrocarbon based fuels
Production of Hydrogen
Most common method of producing hydrogen involves splitting water (H2O) into its component parts of hydrogen (H2) and oxygen (O). There are different methods to produce hydrogen-
i. Steam reformation or partial oxidation of hydrocarbons such as natural gas, naphtha or crude oil. It converts methane into hydrogen and carbon monoxide by reaction with steam over a nickel catalyst.
ii. Coal gasification- Hydrogen made from coal can probably be justified as a fuel for special applications where the unique characteristics of hydrogen can be put to advantage such as its weight or its non-polluting characteristics.
iii. Electrolysis- it uses electrical current to split water into hydrogen at the cathode (+) and oxygen at anode (-).
iv. Thermo chemical method- it utilizes heat to achieve the chemical splitting of water to its elements without the need for intermediate electricity generation and without the need to use the extremity high temperature of 2500 °C or more.
v. Photo-electrolysis- it uses sunlight and catalysts to split water. In this method, a current is generated by exposing on or both electrodes to sunlight. Hydrogen and oxygen gases are liberated at the 2 electrodes by the decomposition of water. A catalyst may be included to facilitate the electrode process.
vi. Biological and photo-biological water splitting use sunlight and biological organisms to split water.
vii. Thermal water splitting uses a very high temperature (approximately 1000 °C) to split water.
viii. Biomass gasification uses selected microbes to break down a variety of biomass feed stocks into hydrogen.
Utilization of hydrogen gas
Hydrogen can be utilized for the following purpose:
i. Residential use- hydrogen can be used in domestic cooking (stoves), radiant space heaters, electricity for lighting and for operating domestic appliances (e.g. refrigerator) which could be generated by means of fuel cells, with hydrogen gas at one electrode and air at other.
ii. Industrial use- hydrogen can be used as a fuel or a chemical reducing (i.e. oxygen removal) agent. It can also be used instead of coal or coal derived gases, to reduce oxide ores (iron ore) to the material (iron).
iii. Air craft application- The earliest application of liquid hydrogen fuel is expected to be in a jet air craft. Cold liquid hydrogen can be used directly or indirectly to cool the engine and the air frame surfaces of a high speed air craft.
iv. Electric power generation- It comprises the production of electricity by using hydrogen in fuel cell system. Hydrogen could also be used as a means for storing and distributing electrical energy. The objective of developing fuel cell power stations is to centralized and local generation of electricity.
v. As an alternative transport fuel- Hydrogen is tried as an alternative fuel in internal combustion engine. The stoichiometric hydrogen air mixture burns seven times as fast as the corresponding gasoline air mixture which is a great advantage in internal combustion engines, leading to higher engine speeds and greater thermal efficiency. Hydrogen fuel used in IC engines is in automobiles, buses, trucks and farm machinery.
Methods of using Hydrogen as a fuel in CI engines
i. A mixture of fuel gas and air, with an approximately constant fuel to air ratio is introduced into the cylinder intake manifold. The engine power is controlled by varying the quantity of mixture entering the cylinder by means of throttle valve. It is not safe because the mixture is formed in the manifold.
ii. The hydrogen is injected directly into the engine cylinder through a valve under pressure and air is inducted through another intake valve. This method is safer one, since hydrogen and air are supplied separately; an explosive mixture is occurred inside the cylinder only. The engine power output is controlled by varying the pressure of hydrogen gas from about 14 atm at low power to 70 atm at high power.
iii. During the intake stroke, the hydrogen gas at normal or moderate pressure is drawn through the throttle valve into the engine cylinder whereas unthrottled air is drawn in through the intake port. The variation of engine power can be achieved with adjustment of hydrogen inlet throttle. The changes in fuel proportion as well as power is developed due to supply of un throttle air and power variation is possible because of the wide composition range over which hydrogen-air mixture can be ignited.
Advantages of using Hydrogen fuelled engine
i. It provides high efficiency because it utilizes a higher proportion of the energy in the fuel.
ii. The amount of carbon monoxide and hydrocarbons in the exhaust is very small since they are originating only from the cylinder lubricating oil.
iii. It can be easily available because it is produced by electrolysis of water.
iv. Fuel leakage to environment is not pollutant.
Disadvantages of using Hydrogen fuelled engine
i. Due to high heat release the combustion temperature may be high and also a level of nitrogen oxide is high. It can be reduced by reducing the combustion temperature by injecting water vapor into the cylinder from the exhaust.
ii. It requires heavy, bulky fuel storage both in vehicle and at the service station.
iii. Difficulty in refueling and possibility of detonation.
iv. Poor engine volumetric efficiency- gaseous fuel will displace some of inlet air and poor volumetric efficiency will result.
v. Fuel cost would be high at present day technology.
 |
| Hydrogen gas |
ConversionConversion EmoticonEmoticon