Sustainable Energy Solutions: Straight Vegetable Oil

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Sustainable Energy SolutionsStraight Vegetable
Oil

• Physical Properties of Diesel Fuel

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How is diesel made?

• Petroleum coke is heated up to separate the
  complex mixture of hydrocarbons into usable
  products like diesel.
• Each petroleum derived product is distinguished
  by its boiling point.
• Diesel fuel undergoes a hydrotreating process to
  remove sulfur.

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Typical Refinery Products
From Schmidt, G.K. and Forster, E.J., Modern
Refining for Todays Fuels and Lubricants, SAE
Paper 861176, 1986.
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Diesel Properties Cold

• At low temperatures, diesel fuel (especially 2)
  can gel or crystallize and cause the engine to
  stop. A large amount of research has been done to
  estimate the lowest temperature at which a given
  fuel can be used. At least four different
  techniques are in common use
• Cloud Point (ASTM D2500) is the temperature at
  which a cloud of wax crystals first appears in a
  fuel sample that is cooled. B100 has a cloud
  point of 32 deg. F (2 diesel is 4 deg. F)
• Pour Point (ASTM D97) is the lowest temperature
  at which movement of the fuel sample can be
  determined when the sample container is tilted
  B100 has a pour point of 25 deg. F (2 diesel is
  -30 deg. F)
• Low Temperature Flow Test (LTFT) - (ASTM D4539)
  is designed to evaluate whether a fuel can be
  expected to pass through an engine fuel
  filtration system (at 17 microns)
• Cold Filter Plugging Point (CFPP) (ASTM D
  6371-99) is designed to evaluate whether a fuel
  can be expected to pass through an engine fuel
  filtration system (at 45 microns) B100 has a cold
  CFPP 22 deg. F (2 diesel is 1 deg. F)

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Winterizing Agents

• A.K.A. pour point depressants and anti-gelling
  additives
• When diesel fuel starts to solidify it forms
  microscopic crystals. If allowed to agglomerate,
  these crystals will grow large enough to plug
  fuel filters and lines.
• Anti-gelling additives can be used to disrupt the
  agglomeration process by inhibiting the crystals
  from combining and growing to a size large enough
  to plug filters.
• The additives are generally waxes that are used
  in small amounts. They surround the small
  crystals and provide a barrier to agglomeration.

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Diesel Properties Cetane

• One of the most important properties of a diesel
  fuel is its readiness to auto-ignite at the
  temperatures and pressures present in the
  cylinder when the fuel is injected.
• The cetane number is the standard measure of this
  property.
• Cetane (ASTM D613) is tested by adjusting the
  fuel/air ratio and the compression ratio in a
  single cylinder, indirect injection diesel engine
  to produce a standard ignition delay (the period
  between the start of fuel injection and the start
  of combustion). B100 has a minimum cetane number
  of 47
• Cetane improvers are fuel additives that are
  designed to readily decompose to give precursors
  to combustion and thus enhance the rate at which
  auto-ignition occurs.
• Typical compounds used are alkyl nitrates, ether
  nitrates, dinitrates of polyethylene glycols, and
  certain peroxides. Due to low cost and ease of
  handling, alkyl nitrates are the most widely used
  cetane improvers.

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Diesel Properties Density

• Specific gravity is the ratio of the mass of a
  volume of the fuel to the mass of the same volume
  of water. It is dependent on the temperature of
  both the fuel and the water. B100 has a specific
  gravity of 0.880 g/cm3 (between 0.860 and 0.900)
• The specific gravity of a substance is a
  comparison of its density to that of water.
  Imagine a gallon bottle filled with water, a
  second filled with feathers, a third filled with
  lead weights. There are equal volumes of material
  present, but the bottle with the feathers will
  weigh less than that containing water the bottle
  with lead weights will weigh the most.
• From the example above what has the highest
  specific gravity?

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Diesel Properties Viscosity

• Viscosity - (ASTM D445) is a measure of a fluids
  resistance to flow.
• The greater the viscosity, the less readily the
  liquid flows.
• The viscosity of petroleum oils is a strong
  function of temperature with the viscosity
  decreasing as the temperature increases.
• The ASTM test provides a measure of the time
  required for a volume of liquid to flow under
  gravity through a calibrated glass capillary
  tube. B100 has a kinematic viscosity of 1.9 - 6.0
  mm2/sec

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Diesel Properties Volatility

• Distillation Curve - (ASTM D86) The distillation
  curve is determined by relating the fraction of a
  fuel sample which is removing by heating a fuel
  sample to progressively higher temperatures.
  Typically, the curve is characterized by the
  initial point, the temperature at which the first
  drop of liquid leaves the condenser, the
  temperatures at each 10 of the liquid and the
  end point. B100 has a distillation temperature of
  360 deg. C
• Flash point (ASTM D93) is the lowest temperature
  at which a combustible mixture (gas) can be
  formed above the liquid fuel. Liquids and solids
  do not burn. Gasses burn. B100 has a minimum
  flash point of 130 deg. C (2 diesel is between
  50 and 80 deg. C)
• The flash point is determined by heating a sample
  of the fuel in a stirred container and passing a
  flame over the surface of the liquid. If the
  temperature is at or above the flash point, the
  vapor will ignite and an easily detectable flash
  can be observed.

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Diesel Properties Lubricity

• Lubricity - (ASTM D 6078-99 ASTM D 6079-99) The
  property of a fuel that causes a difference in
  friction. The lower the friction the higher the
  lubricity.
• Diesel acts as a lubricant for the precision
  parts in the injection system. While all diesel
  fuel injection systems depend on the fuel to act
  as a lubricant, rotary pump style injection
  systems seem to be the most sensitive to fuel
  lubricity.
• In 1993 the EPA mandated that the sulfur content
  of on-highway diesel fuel be lowered from 5000
  ppm to 500 ppm. Recent EPA regulations will
  further lower sulfur content to 15 ppm.
• There is disagreement about how sulfur reduction
  changes affects lubricity. Some suggest that
  sulfur itself provides lubricity, others suggest
  that nitrogen compounds or naphthenic
  hydrocarbons are responsible.
• The addition of small amounts of biodiesel (0.25
  to 2) to diesel fuel has a dramatic effect on
  the lubricity of that fuel. Pure biodiesel and
  high level blends have excellent lubricity.

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Material Compatibility

• Some metals have a catalytic effect on the
  biodiesel oxidation process. Contact with
  material such as copper, copper-containing alloys
  such as brass and bronze, lead, tin, and zinc
  should be avoided, particularly for long-term
  storage.
• Galvanized and copper pipe should not be used for
  biodiesel or diesel fuel.
• Aluminum, steel, and stainless steel are
  acceptable tank materials and stainless steel and
  black iron are commonly used for piping.

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Material Compatibility
Table from Biodiesel Handling and Use
Guidelines, K. Shaine Tyson, National Renewable
Energy Laboratory, NREL/TP-580-30004, September
2001.