Biodiesel
Fuel standards
100% biodiesel according to the common international standard for biodiesel EN 14214 is available at several fuel stations.
In Germany, the requirements for biodiesels are fixed in a DIN standard. There are standards for three different varieties of biodiesel, which are made of different oils:
- RME (rapeseed methyl ester, according to DIN E 51606)
- PME (vegetable methyl ester, purely vegetable products, according to DIN E 51606)
- FME (fat methyl ester, vegetable and animal products, according to DIN V 51606)
Characteristics
Biodiesel (FAME fatty acid ethyl ester) is consisting of different esters having a smaller boiling range , may have a slightly higher density (0.88 kg/l) and a lower heating value (89%) compared diesel. Cetane number and viscosity may be higher, the stochiometric air demand is lower (13.8 instead of 15), lubricity is higher compared to ultra low sulphur diesel but problems may occur at higher fuel temperatures with common rail injection pumps.
Most important the cold filter plugging point as most relevant figure (following the cloud and pour point) may be much higher compared to diesel which results in limits using pure biodiesel (FAME) in very cold climates. The absolute value depends on the feedstock.
The oxygen content reduces low soot emission caused by a very complete combustion, low sulphur content reduces the emission of particels.
The water hazard class is lower and 98% may be biodegradable within 3 weeks. As solvent there are problems with natural or butyl rubber an some (white) paints. Although most modern engines and fuel systems are prepared to use biodiesel, but only some models allow B100 usage.
Operational issues
Caused by the dilution potential of biodiesel for the motor oil, it should be chosen carefully according to manufacturers' recommendations and checked regularily. The suggested intervals for replacement of oil and filters should be observed carefully.
Check the motor oil level regularly -In case the oil level rises, replace the oil prematurely.
In addition to the items listed above, the stress on the engine has effects on oil dilution. In fact, oil dilution is at its maximum at low workloads of the engine.
When switching to biodiesel, deposits from earlier diesel fuels may be mobilised- so check fuel filters especially if you experience an engine power reduction.
Soaked rags should be stored in a fire safe area or dried individually to avoid spontaneous fire.
More Info
Biodiesel Industry Factsheets
EPA Fact Sheet
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Sunfuel/Synfuel
Sunfuel/Synfuel may be produced from gasified biomass or biogas via Fischer Tropsch Synthesis.
GTL is a very narrowly defined fuel with low impurities,lacking sulphur and aromatic compounds. The Cetane figure is higher (>70 to 90). The boiling range differs depending on the feedstock. Bio-GTL (gas to liquid) has a lower boiling range compared to diesel.
The low aromomatic content decreases swelling of elastomeres.
GTL-fuel is biodegradable under aquatic and aerobic conditions.
A low amount of additive is needed to ensure sufficient lubricity.
Because of the higher H/C ration the density is smaller (0.75 kg/l) but the heating value higher (47.1 MJ/kg) compared to diesel.
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Bio-Ethanol
Sources
Bio Ethanol may be produced from different feedstocks and no international standards have been set up.
Properties
The biggest difference to gasoline/petrol is the the oxygen content.
Pure Ethanol is a flammable, colorless liquid which looks like water.
The heating value per litre is 27% lower compared to gasoline/petrol (26.74 MJ/kg 11,500 BTI/lb). The fuel mileage in practice is 5% to 12% lower(Handbook for Handling, Storing and Dispensing E85). This also relates to the higher densitiy which is at the upper level of gasoline/petrol. And the stochiometric air/fuel ration is smaller (9) compared with gasoline/petrol (14.7) reducing the energy demand for air intake and compression.
Ethanol fuel shall contain 99.8% ethanol at minimum, 0.3 % water maximum, acetaldehyde 0.0025% max, acetic acid 0.0025% max..
Ignition improver, MTBE, Isobutanol and corrosion inhibitor may be added more....
Ethanol is not as toxic and corrosive as Methanol, it contains in its pure form no carcinogenic compounds, but is used only with a certain gasoline/petrol amount inheriting the carcinogenic characteristics.
Ethanol vapor is heavier than air. Ethanol will mix with water, only higher amounts tend to separate, thus condensing in tanks should be avoided.
The octane number is 98-100.
Ethanol flame are less bright than gasoline/petrol but easily visible in daylight. At low temperatures (0°C 32°F) E85 vapor is more flammable than gasoline but at normal temperatures E85 is less flammable because of the higher autoignition temperature of 454°C 850°F. Ignition may occur between 3% to 19% fuel vapor in air which is elevated compared to gasoline/petrol with 1% to 8%.
Ethanol is not an electric insolator like gasoline/petrol.
The reid vapor pressure is much lower compared to gasoline (0.15 bar 15 kPa 2.3 psi).
Starting with 80% Ethanol the vapor pressure at 37.8°C is 38-58 kPa.
Commercial fuel blends
E85 is specified in the US more...
In any case Ethanol has to be denatured in order to avoid consuming by humans. This gives E95, if 5% gasoline/petrol is added.
With the Ethanol part of the blend, no additives used for gasoline/petrol are necessary.
compounds shall be limited (ASTM D5798-99):
- Lead <2.6 mg/l
- Phosphorus < 0.3 mg/l
- Water < 1%
- Methanol <0.5%
- Higher alipatic alcohols C3-C8 < 2%
- Acidity as acetic acid < 50 mg/kg
- Inorganic chloride < 1 mg/kg
- Total chlorine as chlorides < 2 mg/kg
- Gum unwashed < 20 mg/100ml
- Gum solvent washed < 5 mg/100ml
- Copper < 0.07 mg/100ml
Consequences of Ethanol usage
The car fuel filter should be changed after the first few tankfuls of ethanol after having been operated with other fuels. After this, the ethanol will maintain a clean system.
Cold weather starting is poor compared to gasoline/petrol. Therefore winter blend contain up to 30% gasoline.
Because Ethanol conducts electricity aluminium parts shall be avoided.
Other materials degrading when in contact with Ethanol include natural rubber, polyurethane, cork gasket material, leather, polyvinyl chloride (PVC), polyamides, methyl-methacrylate plastics and certain thermo and thermoset plastics.
More Info
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Compressed Hydrogen
Hydrogen is an odorless and colorless (even when burning) gas, with a boiling point of -252.77°C.
Its density of 0.0899 grams/liter make it lighter than the
surrounding air.Hydrogen has the highest energy to weight ratio of all
fuels. The lower heating value is 119,972 kJ/kg.
1 Kg of hydrogen contains the same amount of
energy as 2.1 Kg of natural gas or 2.8 Kg of gasoline.
Hydrogen has the lowest energy to volume ratio of
common fuels. Hydrogen possesses 2.36 kWh/liter as a
liquid, natural gas contains 5.8 kWh/liter and gasoline
contains 8.76 kWh/liter.
The inflamability range in air is very wide from 4 to 75%. The ignition energy is only 0.02 mJ.
The ever cited Hindenburg desaster occured because of the painting which had similar charcheristics to rocket fuel and was charged electrostatically igniting the hydrogen. The Hydrogen burned in one minute but the diesel fuel burned for a longer time causing most of the deaths.
Course materials on hydrogen safety more...
Database with hydrogen related incidents
Compressed Natural Gas
Characteristics
CNG is a non toxic GAS liquid at -259 °F -162 °C which ignites at 1350°F 732°C. The octance number is 120. It may be inflamed having a share of 5.3 to 15% in air.
Methane has only 42.4% of the density of air and thus is ligther and may disappear in case of leackages. The lower heating value is 50,020 kJ/kg. Ignition energy is 0.29 mJ.
Natural gas may consist of:
- Methane CH4 70-90%
- Ethane C2H6 0-20%
- Propane C3H8
- Butane C4H10
- Carbon Dioxide CO2 0-8%
- Oxygen O2 0-0.2%
- Nitrogen N2 0-5%
- Hydrogen sulphide H2S 0-5%
- Rare gases A, He, Ne, Xe trace
CNG quality may be expressed with the
- Wobbe Index
- Methane Number MN80 (Volume percent hydrogen atoms / carbon atoms)
OR
More detailed:
- C3or higher <=3%
- C6 or higher <=0.2%
OR
even more detailed:
- Hydrogen <=0.1%
- Carbon Monoxide <=0.1%
- Oxygen <=1%
- Intert gases (sum of CO2 and N2) 1.5-<=4.5%
- Sulfur <=16ppmv
- Water: the dewpoint shall be at least 5 K lower than the 99% winter design temperature
- Particulate Mater: no dust, sand, dirt,gums, oil injurious to the filling stations
- Odorant should be detectable at 20% of the lower limit of flammability
In Germany two CNG-grades ar offered depending on the sources for natural gas:
- H-gas 87 - 99,1 Vol.% CH4 and 10,0 - 11,1 kWh/m3 lower heating value
- L-gas 79,8 - 87 Vol.% CH4 and 8,2 - 8,9 kWh/m3 LHV
More Info
more in German...
EPA factsheet download
Methane (Biogas)
Methane is the major part of Natural Gas but gas from wood gasification or digesters may contain CO2, N2 and other unwanted gases, tar and metals.
Pure methane is odorless colorless, noncorrosive and nontoxic.
Wood gas
The quality gas to be as follows (Wood gas as engine fuel more...)
dust:
lower than 50 mg/m³ gas preferably 5 mg/m³ gas
tars:
lower than 500 mg/m³ gas
acids:
lower than 50 mg/m³ gas (measured as acetic acid).
Wood gas
Digester gas
Depending on the waste feedstock and the system design, biogas is typically 55 to 75 percent pure methane.
Land fill gas
The typical dry composition of the low-energy content gas from a landfill is 57 percent methane (natural gas), 42 percent carbon dioxide, 0.5 percent nitrogen, 0.2 percent hydrogen, and 0.2 percent oxygen. In addition, a significant number of other compounds are found in trace quantities. These include alkanes, aromatics, chlorocarbons, oxygenated compounds, other hydrocarbons and sulfur dioxide.
Liquefied Hydrogen
Because of the low densitiy of hydrogen liquifying at very low temperatures (-252.77° C at ambient pressure) allows transport of hydrogen. because of the low temperatures liquifying H2 requires substantial energy. The liquified hydrogen needs to be perfectly insulated because temeprature losses result in boiling and increasing pressure which has to be prevented by venting hydrogen to the ambient.
Mg hydrides are used to achieve a high hydrogen-storage capacity at ambient pressure in a reversible reaction but has high dehydriding temperature and slow adsorption kinetics.
Liquefied Natural Gas
Liquefied natural gas has to be stored at very low temperatures (depending on the pressure). Therefore the higher condensing fraction is eliminated and only methane is present (99% CH4 1% C2H6). This means that it is a very ideal fuel.
LNG FAQ Regards insulation losses there will be a blow off when stored over a longer period of time.
EPA LNG factsheet download
DME Dimethyl ether
DME is used under different names like methoxymethane, oxybismethane, methyl ether, wood ether. DME is a colourless gaseous ether with an light ethereal odour. Dimethyl ether gas is water soluble. Dimethyl ether is a renewable alternative to liquefied petroleum gas.
The cetane number of 55 is higher compared to fossil diesel.
It can be made from natural gas, coal, or biomass. DME is comparable to LPG when storing. In use an odorant and lubricating additive have to be used.
The high pressure fuel system in vehicles needs a purge tank.
Straight Vegetable Oils
Carbon residue is the main problem for the engine- In Elsbett engines up to 0.4% weight percent is allowed. Other standards state 0.05 w %. The carbon residue for non modified engines and high mileages should be as low as possible.
Gas content may be reduced so SVO is usable in high pressure injection systems.
More materials:
Comparision with Biodiesel and Diesel (in German)
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