FACULTY OF ENGINEERING, SCIENCE AND THE BUILT ENVIRONMENT
We have been asked to present an essay on a topic related to sustainability, renewable technologies or environmental design. We have decided to base this essay on liquid Hydrogen as a renewable source applied to a certain type of engine.
The use of Hydrogen as a form of fuel started back in the 1800s, by a Swiss inventor Francois Isaac de Rivaz, and all the way through the past century up to today, manufacturers have tried to implement this system as an alternative to the conventional internal combustion engine that uses fossil fuels.
Throughout this report, we will elaborate the general principles behind the use of Hydrogen, its benefits and drawbacks and we will give a personal statement on where we stand on the matter.
1. The Liquid Hydrogen H2:
Liquid Hydrogen can be defined as the liquid form of Hydrogen (H2). To obtain liquid hydrogen, the natural Hydrogen has to be cooled to a temperature around -250/-253°C and once in its liquid state, it has to be stored in pressurized and thermally insulated containers.
2. Principles behind the use of H2:
The principle behind the use of Hydrogen as fuel for engines was to offer an alternative to the combustion engine that is highly pollutant. Both have been developed around the same time but up to the last century, with the rise of carbon emissions, green gases, global warming issues; governments and manufacturers alike are starting to look for less damaging sources of energy.
In a Hydrogen engine, the combustion of Hydrogen produces water as its only product. The reaction is written as the following: 2H2+O2?2H2O
But in reality the combustion of Hydrogen results in the production of water and oxides of Nitrogen. The equation becomes: H2+O2+N2?H2O+N2+NOx
Because of problems related to global warming, Liquid Hydrogen would be the perfect replacement. If properly fitted, those types of engines would provide, according to experts and experiments, about 20% more efficiency that the current ones we are using, but with a 70 to 80% less on carbon dioxide emissions which is fantastic for the environment.
As we speak, car manufacturers such as Honda, BMW, Ford... are working towards developing engines or systems capable of using Hydrogen as fuel.
It can also be implemented to other means of transportation such as Rockets, Airplanes, Motorcycles...
In the following lines, we'll try to elaborate on those possibilities.
3. EXAMPLES OF POSSIBLE SECTORS OF USE:
3.1- USE IN AUTOMOBILES:
As stated earlier on, many car manufacturers are as we speak, developing and testing ways to implement Liquid Hydrogen into their engines.
For example the 2007 BMW Hydrogen 7 (limited edition) is an alternate version of the 7series BMW powered by a system called dual-fuel Internal Combustion in short, Hydrogen can be used as an alternate fuel in the same combustion engine;
Or the 2006 F250 super Chief which was labelled the next generation of pickup trucks. It uses what Ford presented as a V10 tri-Flex engine, an engine that was at the same time compatible with Hydrogen, gasoline and ethanol;
In automobiles Hydrogen gives the following advantages over conventional fuels: No carbon emissions, improved efficiency, fuel economy (a small amount is required to operate the engine). However it also comes with numerous and significant problems such as the high inflammable property of Liquid Hydrogen (very dangerous to use in crowed area), or the fact that because Hydrogen liquid does not exist naturally, it has to be obtain from reactions using other components and can only stored in special containers thus posing a storage problem. They also cost more to manufacture (about 10 times) than conventional cars.
3.2- USE IN ROCKET AND SPACE SHUTTLE:
This is the area where Hydrogen liquid is commonly used. It is known that Hydrogen gives the highest effective exhaust velocity (in astronautics is defined as the ratio of the speed at which the fuel is burned divided by the amount of time it takes for the fuel to be burned to give the rocket the same thrust) as well as keeping most of its properties even at high altitudes. The process is to first cool the nozzle and other parts before mixed them with the oxidizer, liquid oxygen is commonly used, and burned to produce water and traces of ozone O3 and an element called hydrogen peroxide. Basically what it means is that the engine of the rocket combust the Hydrogen in a confined space creating pressurized gas. When that gas is released, it is released with high velocity lifting the rocket off the ground. Since the combustion of Hydrogen produces vapours of water, this type of propulsion system is categorized as harmless to the environment.
3.3- USE IN AIRPLANES:
Researches into adapting Hydrogen powered engines to planes started back in the 1950s but it was not until back in 1998 that a US based company called AeroVironment completed the first successful testing of an airplane fully powered by Hydrogen. The liquid Hydrogen was stored on board and was combined to oxygen extracted from the air. Electrical power was then produced to power the propellers.
Hydrogen in airplanes can be burned in the jet's engine or be used to create electricity to power a propeller. Kerosene or Kerosene based fuels are the ones commonly used for aircraft. They are less pollutant that gasoline based ones but still have high CO2 emissions. So as an alternative, Hydrogen can be used. Not only it has a higher energy density per unit mass but it also has a lower energy density per unit volume. It is stored in carbon fibre tanks that are very light and appropriate for element kept at high pressure. Liquid Hydrogen however is highly volatile; in conventional aircraft the fuel is stored in the wings. In Hydrogen aircraft, the Hydrogen is stored in the fuselage but because it is so difficult to store (high pressure and low temperature) an alternative to high pressure tanks needs to be developed. As of now, the only possibility for storing would be cryogenic tank.
e.g.: A310 Airbus 2 Cryoplane" concept aircraft
If Liquid Hydrogen was available in its natural form, it would provide fewer CO2 emissions than current plane's engines. So there are obstacles in implementing the system to modern day aviation. Not only Hydrogen engines are expensive to build but the storage requires special arrangements that are also very costly. Added to that, the product of the combustion of Hydrogen is water in vapour form; in high altitudes it contributes to greenhouses effect. So using Hydrogen as an aircraft fuel would require planes to fly at lower altitude which in some cases is not such a adequate solution.
4. INCONVENIENTS OF ITS USEAGE:
So Hydrogen could in theory be a source of energy for the next generation of means of transportation. In principle there is an unlimited supply of it in the form of water (H2O). The ideal prospect would be to extract that hydrogen and put it to use. If that issue can somehow be resolve, we could be in for a renewable source of energy as abundant as light itself, it could be some sort of closed cycle water-Hydrogen-water.
But today's technology has its limitations. First of all Liquid Hydrogen as we said before does not exist as a natural element (source) but is first produced then stored. The use for the next generation of vehicles and means of transportation would require renewable energies. Liquid Hydrogen requires special thermally insulated containers and requires special handling.
Even with thermally insulated containers it is difficult to keep it at the low temperatures it requires and because of its chemical properties will gradually leak away. Added to that, liquid Hydrogen is very volatile which can be an explosion hazard.
The biggest issue of all is the time frame for solving technical as well as economical challenges to implement the wide-scale use of Liquid Hydrogen as a power source. Critics think that because of all its drawbacks, the use of Hydrogen vehicles may never be entirely available. Although they have a strong case in reducing the use of fossil fuels vehicles, thus reducing carbon emissions, they do not pose a plausible solution or alternative compare to solar energy or wind energy for example. Some say that Hydrogen vehicles are probably not worthy in this difficult financial time (with fragile economies surrounding us). Even though in the running of the engines themselves, the principles would be unchanged, swapping your local gasoline for Hydrogen would be more costly not only for the manufacturer but for us consumers too.
There are still researches as to how to adapt Hydrogen to engines, with promising experiments showing that in the next half century, technology would have advanced sufficiently to implement the system into cars and buses at least.
Implementing Hydrogen to an engine is a very complicated process however. First of all it does not exist naturally on Earth and with the current technology is made from methane or other fossil fuels.