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Operational expertise Commercial vehicle directory

Fuel storage (technical)
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Natural Gas

CNG (Compressed Natural Gas)

CNG-powered vehicles use natural gas stored in cylinders at pressures of 2,000 to 3,500 pounds per square inch (which equals 138-241 bar or 13.8-24.1 MPa) . Compressed natural gas is used in light-duty passenger vehicles and pickup trucks, medium-duty delivery trucks, and in transit and school buses.

The filling apparatus using LNG more...

Refueling NGV more...

LNG (Liquefied Natural Gas)

Natural gas turns into a liquid for easy storage or transport by extreme cooling to minus 263.2 degrees Fahrenheit (-164 degrees Celsius). LNG is almost pure methane and, because it is a liquid, has an energy storage density much closer to gasoline than CNG. The requirements of keeping the liquid very cold, along with its volatility, make its applications more limited for transportation purposes. It is typically used in heavy-duty applications such as transit buses, heavy-duty long-haul semi-trucks or train locomotives.

NG as vehicle fuel by NGV more...




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Sunfuel/Synfuel

GTL Gas to liquid fuel is a synthetic fuel which has similar characteristics to diesel. No Reduced aromatic content increases biodegradibility. Corrosivity is nearly absent source.


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Biodiesel

Biodiesel is hygroscopic (i.e. has a great affinity for water), thus storage tank condensation should be considered. Biodiesel also degrades when stored over a long time. Temeperatures have to be kept above the gel point, which varies with different types of sources. best suited are peanut, safflower, crambe but alos sunflower more..

There are similar recommendations as with diesel - biodiesel should be used within six months. Longer shelf lives depend on the fuel composition and the use or storage enhancing additives.

When planning storage containements account for additional space since the specific density of 37 MJ/kg and 0.88 kg/l gives only 32.6 MJ/l whereas fossil fuel may have 36 MJ/l (42.5 MJ/kg and 0.85 kg/l)

Wiki about biodiesel


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Bio Ethanol

Ethanol may not be confounded with Methanol. Earlier problems with Methanol do not apply.
Light metals (aluminium, magnesium) corrosion from anhydrous methanol may be avoided by addition of either 0.5% water to pure methanol, or corrosion inhibitors to methanol-gasoline blends.
more...
Methanol proof equipment may be used with Ethanol. Nozzles should be of nickel-plated alloys, other parts may be out of galvanized black iron, bronze or stainless steel. Aluminium and zinc-plated steel has to be avoided.
Seals should be teflon based or equal.

When storing ethanol, affinity for water and separation is to be considered.
  • Fresh fuel is less likely to be contaminated with moisture.
  • Full fuel tanks avoid condensing especially during cold weather
Thus avoid storing/shelving for more than three months.

Tanks previously filled with gasoline/petrol have to be cleaned before being filled with ethanol because alcohol will place the sludge into suspension and will lead to serious problems when fuelling vehicles.

A 1-micron in-line filter is recommended for fuel ethanol dispensing.

Every 1-2 months electric conductivity and particulate content should be checked. Hydrocarbon content and reid vapour pressure should be checked frequently.

Wiki Alcohol Fuel





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Electric charging

The charging process is either of the inductiove or the conductive type. Charging from the electric grid is most efficient - intermediate storage in batteries is not.
Charging stations have to take into consideration vandalism and forgetting to plug out before starzing the engine and driving away.

Sacramento municipality info about charging station more..

The on board energy storage may be short, medium and long term using ultracapacitators, NI-Mh batteries with high self discharge or batteries with separate electrolyte storage (so called flow batteries) with no self discharge.


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Hydrogen

Gaseous Hydrogen
The most commonly used and simplest method is to store hydrogen in its natural form as a gas. Storage of gaseous hydrogen is primarily limited by volume considerations as a result of hydrogen's low density, as even at high-pressure very large volumes are required resulting in high material costs. Today gaseous hydrogen is stored in prodominaly in steel cylinders at a pressure of 150-200 bar and at an ambient temperature of approximately 298K. The most common conventional steel gaseous cylinders contain a volume of 40 litres and a pressure of 150 bar and in the last decade significant progress has been made in a move towards lightweight cylinders using chrome-molybdenum steel. Frequently the individual cylinders are clustered together to be filled and released through just one valve and the cylinders are interconnected through high-pressure tubing, a grouping of cylinders also allows for financial savings.

Significant amounts of hydrogen can also be stored within high-pressure storage tanks, that can be situated above ground or underground which is similar to the storage of natural gas. The construction material properties in above ground storage impose limitations on the quantity of gaseous hydrogen that can be stored and the hydrogen can be stored at an increased pressure in an underground pressure tank or underwater tank.

Liquid Hydrogen
Hydrogen stored in a liquid form is substantially more compressed than in gaseous form and superficially it appears an appealing means of energy storage but there are various contributory negative factors. Primarily that the liquidification requires a large expenditure of energy and secondly, through the use of insulation, liquid hydrogen must be continually kept at a low temperature (<20K). There are risks associated with this constant low temperature, due to the high expansion ratio of liquid hydrogen to gaseous hydrogen. If there was a warming of liquid hydrogen extremely high pressures could accumulate and result in damage or an explosion.

Liquid hydrogen must be stored in cryogenic tanks, which is a well-established technique. There are three ways that heat transfer occurs from the external air to the liquid hydrogen; conduction, convection and radiation. Heat transfer increases with external surface area therefore the majority of cryogenic tanks are spherical or cylindrical to minimise the surface area. Most liquid hydrogen storage tanks are also double walled tanks that are insulated with an evacuated layer of Perlite insulation.

HOW IS IT STORED?
LNG tanks are always of double-wall construction with extremely efficient insulation between the walls. Large tanks are low aspect ratio (height to width) and cylindrical in design with a domed roof. Storage pressures in these tanks are very low, less than 5 psig. Smaller quantities, 70,000 gallons and less, are stored in horizontal or vertical, vacuum-jacketed, pressure vessels. These tanks may be at pressures any where from less than 5 psig to over 250 psig. LNG must be maintained cold (at least below -117°F) to remain a liquid, independent of pressure.

LNG is stored as a "boiling cryogen," that is, it is a very cold liquid at its boiling point for the pressure. LNG will stay at near constant temperature if kept at constant pressure. This phenomenon is called "autorefrigeration". As long as the steam (LNG vapor boil off) is allowed to leave the tea kettle (tank), the temperature will remain constant.
If the vapor is not drawn off, then the pressure and temperature inside the vessel will rise. However, even at 100 psig, the LNG temperature will still be only about -200°F.

Metal Hydride
Another means of hydrogen storage is that of metal hydride storage, this method is a relatively new method, the advantage of the system is that hydrogen being stored as a metal at low pressure and that it stores more volume than compressed gaseous or liquid hydrogen. The basic principle is that certain metals alloys absorb hydrogen to form a metal hydride. The hydrogen is absorbed at a lower temperature and when the hydrogen gas is needed the gas is recaptured by lowering the pressure below, or raising the temperature of the metal hydride above the absorption process. The hydrating alloy is stored in stainless steel tubes and according to the Van't Hoff equation hydrogen reacts with the metal alloy granules in the tank at a specific temperature and pressure. The steel tubes are surrounded by a water jacket that facilitates heat exchange during absorption and desorption of hydrogen gas. The need for a compressor is eliminated in the hydride system as the hydriding and dehydriding reactions occur at specified temperature and pressure depending on the electrolyser specifications.

Nano tubes
Hydrogen may stored through chemisorption in single-walled carbon nanotubes (SWCN) at 5 wt. % storage capacity.
download

Other considerations

Hydrogen may be produced near refuelling stations using
  • methanol via steam reforming
  • water via electrolysis
The second possibility is to have hydrogen production near the power generation units (wind power, hydraulic energy)
Fast filling is no problem. Hydrogen is harmful to some steel grades making them brittle.
Solutions for Hydrogen Storage and Distribution (pdf)
Basics about storage


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Biogas

Biogas my be fed into the natural gas network. Byproducts however should be limited.
  • H2S is higly corrosive
  • H2O may condense and obstruct pipes when freezing.

When storing biogas in liquid form the byproducts may be removed easily while cooling down.

SCG report on Biogas as vehicle fuel for the conference in Steyr Austria more...


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Straight Vegetable Oil

SVO is not suited for longer storage. Depending on the type of oil several phenomena are occurring (for example oxidising).
This results in polymerising also building epoxy deposits in engines more...
wiki SVO



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DME Dimethyl ether

DME may be stored like LPG. It may solved in water. Fuel carrying pipes shall be cooled. DME is a good solvent, therefore material being in contact with DME have to be chosen accordingly.


 


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