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Understanding Today’s Diesel Fuel
National Biodiesel Board Technician Outreach Program
Objectives
Understand the new face of diesel fuels What are today’s diesel fuel quality
standards How are these standards set? How do these fuel standards affect the
diesel engine operation? - performance - emissions - fuel economy
Emissions Regulations in the driver’s seat
The Clean Air Act of 1970 gave EPA broad authority to regulate motor vehicle pollution, and the Agency's emission control policies have become progressively more stringent since the early 1970's.
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Diesel Emission Reductions
What is Diesel Fuel
Various Petroleum Components:
Paraffins Isoparaffins Napthenes Olefins Aromatic Hydrocarbons
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 hydro-treating process to remove sulfur.
Typical Refinery Products
Solid Petroleum Coke
1000 + 540 + Asphalt
650 - 1200 340 - 650 Residual Oil
650 - 1000 340 - 540 Lube Oils
350 - 650 180 - 340 #2 Diesel, Furnace Oil
340 - 515 170 - 270 Kerosene, Jet Fuel, #1 Diesel
80 - 40030 - 200Gasoline
-40 - 31 -40 - 0 LPG
Product Boiling RangeDeg. F
Boiling RangeDeg. C
From: Schmidt, G.K. and Forster, E.J., “Modern Refining for Today’s Fuels and Lubricants,” SAE Paper 861176, 1986.
Grades of Diesel Fuel 1-D ( S15) 1-D ( S500) 1-D (S5000) 2-D ( S15) 2-D ( S500) 2-D (S5000) 4-D
S15, S500, & S5000 relate to sulfur content
Off-road versus On-road use
Varied in density and viscosity
ASTM Specifications for Diesel Fuel - ASTM D 975
Grade Grade Grade Grade Grade Property LS #1 LS #2 No. 1-D No. 2-D No. 4-D Flash point ° , C min 38 52 38 52 55
, Water and sediment % , .vol max 0.05 0.05 0.05 0.05 0.50
., Distillation temp° , 90%C .Min -- 282 -- 282 -- .Max 288 338 288 338 --
, Kinematic Viscosity mm2/ 40s at °C .Min 1.3 1.9 1.3 1.9 5.5 Ma .x 2.4 4.1 2.4 4.1 24.0
,Ramsbottom carbon residue 10%, % , .on mass max 0.15 0.35 0.15 0.35 -- , % , .Ash mass max 0.01 0.01 0.01 0.01 0.10
, % , Sulfur mass max 0.05 0.05 0.50 0.50 2.00 , Copper strip corrosion
3 50Max hours at°C . 3No . 3No . 3No . 3No -- , .Cetane Number min 40 40 40 40 30
One of the following :Properties must be met (1) cetane index 40 40 -- -- -- (2) , Aromaticity % , vol max 35 35 -- -- --
Diesel Fuel Specification ASTM D 975 Flashpoint Water and
Sediment Distillation Kinematic Viscosity Ramsbottom
Carbon Residue Ash
Sulfur Copper Strip
Corrosion Cetane Number Cetane Index Aromaticity Cloud Point
Cetane Number
Measures the readiness of a fuel to auto-ignite. High cetane means the fuel will ignite quickly at
the conditions in the engine (does not mean the fuel is highly flammable or explosive).
Most fuels have cetane numbers between 40 and 60.
ASTM D 975 requires a minimum cetane number of 40
Premium Diesel fuel typically has a cetane of 47 ASTM methods are ASTM D-613 (ISO 5165) and D-
6890
Cetane
Cetane engine shown above from petroleum testing facility Ignition Delay: the period that occurs between the start of
fuel injection and the start of combustion; the higher the cetane number, the shorter the ignition delay and the better the quality of combustion.
Low Cetane Impact
Poor Ignition QualityLong ignition delay
Abnormal CombustionPossible High Combustion
PressureIncreased Engine stressExcessive Engine Knock
Smoke on Cold start
Cetane Index Cetane index is used
as a substitute for the cetane number.
The cetane index is calculated based on the fuel's density and boiling range.
Two methods used ASTM D-976 or D-4737.
Cetane improvers that may be added are not accounted for in the index
Boiling Point and Volatility Diesel fuel volatility
needs vary for engine load, size, & speed
Buses & trucks benefit from more volatile fuel
ASTM D975 sets a min-max range
Defines the upper and lower limits for 90% distilled point. No. 1 diesel: no lower limit, upper = 288
C No. 2 diesel: lower limit = 282 C, upper
= 338 C.
282C - 338C
90% Distillation Temperature Volatility or Boiling Point is controlled by the Distillation
specifcaition or T90 Primarily used to separate diesel fuels into different grades. Limits the amount of wax allowed in No. 1 If distillation temperatures are too low, then the
fuel may have difficulty meeting the flashpoint requirement.
If distillation temperatures are too high, then there is an increased tendency of the fuel to deposit on the cylinder wall, where it can be swept down past the rings and into the lube oil.
Viscosity Low viscosity = power
loss, component wear due to injector leaking or injection pump leak-down
Low viscosity = poor lubrication ability
High viscosity = Poor fuel dispersion, ie improper injector spray pattern
High viscosity = high pump resistance and early pump failure
Critical property for fuel injection system performance
Measured with ASTM D 445. #1 diesel fuel = 1.3 – 2.4 mm2/s #2 diesel fuel = 1.9 – 4.1 mm2/s
Carbon Residue Measure of a diesel fuel’s tendency to form
engine deposit Tests basically involve heating a sample of fuel to
a temperature where the fuel will pyrolyze (decompose without oxygen), leaving a carbon-rich deposit (about 500°C)
Test is frequently done on the 10% residue of fuel distillation.
Limitation is 0.35 mass percent for No. 2 D Limitation is 0.15 mass percent for No. 1 D
Ramsbottom Carbon Residue There are many tests for carbon
residue: Ramsbottom (D 524) Conradson (D 189) Micro Method (D 4530)
Diesel fuel specification requires Ramsbottom
Carbon reside can vary with refinery processes
Sulfur Content Sulfur can impact engine wear and deposits due
varying levels Sulfur in diesel will now harm new emission
control devices of 2007 & newer vehicles Sulfur burns to sulfur dioxide and sulfur
trioxide, which can combine with water to form sulfuric acid.
Small droplets of sulfuric acid and other sulfates contribute to particulate emissions.
Sulfur is limited by the EPA for both on & off road diesel fuels: In 1993: Reduced from 5000 ppm to 500 ppmIn 2006: Reduced from 500 ppm to 15 ppm
Sulfur Testing ASTM D 129 was traditional method
but did not have sensitivity for new low sulfur fuels. (Bomb method)
ASTM D 2622, X-Ray Spectrometry, is more sensitive but may not be adequate for 15 ppm diesel fuels.
Flashpoint Measures the temperature at which the vapors
above the liquid can be ignited. Primarily used to determine whether a liquid is
flammable or combustible Flashpoint is important for safety and hazard
rating Both DOT and OSHA say that any liquid with a
flash point below 100F is flammable ASTM D 93 is most common test for diesel fuels. Can also be used to identify contamination from
other fuels. No. 1 = 38°C, No. 2 = 52°C
Flashpoint
Low temperature Operation Cloud point is the measurement of low
temperate operation It dictates the temperature at which fuel first
starts to crystallize and wax up when cooled Cloud point can predicate fuel filter clogging in
some fuel delivery systems, but not all Other Low temp tests include:CFPP: Cold Filter Plugging PointLTFT: Low Temperature Flow TestPour Point and Cold Soak Filtration Test
Cloud Point
No specific value is given in ASTM D975. Requirements vary depending on
geography. 10th percentile temperature map
corresponds to the minimum temperature that would be reached no more than 3 days out of 30 for the month.
ASTM D 975 contains similar maps for other low temperature months in the United States.
Ash Abrasive Solids Soluble metallic
soaps Originates from
inorganic fuel components
D 975 requires ash to be < 0.01%, by mass
Injector & Fuel pump wear
Piston and Ring wear
Solids = engine deposits
Copper Strip Corrosion Used to predict problems with copper, brass, or bronze
components in a fuel system A measure of corrosiveness Polished copper strip is placed in fuel for 3 hours at 50°C,
then cleaned with a solvent and inspected for tarnish or corrosion.
The strip is given a score between 1 and 4 with subdivisions indicated by letters, i.e. 2c means moderate tarnish with lavender coloring.
Diesel fuel is allowed to be No. 3, which allows all tarnish but no actual corrosion.
Water and Sediment
Measures free, not emulsified, water and insoluble particles.
Uses a centrifuge and cone-shaped or pear-shaped bottles.
Total volume of water and sediment must be < 0.05%.( 500 ppm)
Contamination issue in supply line
Engine impact: Filter plugging, fuel injection system wear, and corrosion, and opportunity for microbial growth
Lubricity Lubricity test methods are
continually improving and being evaluated
Most common tests available to test lubricity: SLBOCLE (scuffing load ball
on cylinder lubricity evaluator)• ASTM D 6078-99
HFRR (high frequency reciprocating rig)
• ASTM D 6079-99
D975 points to the HFRR test
Limitation is 520 micron max of wear at 60C
SLBOCLE SLBOCLE “ Scuffing Load Ball-On
Cylinder Lubricity Evaluator” Steel ball bearing on a steel
rotating-ring Immersed in the test fluid Weight is applied until a “scuff”
mark is seen on the rotating ring Tangential force recorded High Friction coefficient =
scuffing 3100 grams without scuffing
passes the SLBOCLE. (SWRI)
HFRR A steel ball Reciprocated (1mm) 200g load at 50 Hz
for 75 minutes 2 mL of Fuel Adjust to 25 °C or 60
°C (77 °F or 140 °F 60°C preferred
Ball contacts test disk (in fuel)
Specific Gravity & API Density
Density Specific gravity – ratio of the density of the fuel to
the density of water. #1 diesel = 0.81 #2 diesel = 0.840 – 0.855
API gravity – common in petroleum industry. API = 141.5/SG – 131.5
Can be one indicator of fuel economy, power, deposits, wear, and exhaust smoke
For example, a low API (or high density) has bore BTUs/gallon which could improve fuel economy
Energy Content Heating value of the
fuel Not specified by
ASTM Typically expressed
as BTUs/gallon Engine
Manufacturers Impact fuel ecomony
No. 2 D 130,000 BTUs/gallon
Gasoline 114,200 BTUs/gallon
Thermal & Oxidative Stability
Chemical degradation occurs with contact with oxygen for long periods or at high temperatures.
Oxidation of diesel fuel can form insolubles and peroxides
Peroxides increase deposits and gumming on fuel pumps and injection systems
Filter plugging will also occur
ASTM D975 now specifies a stability parameter
Diesel Fuel Additives
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Recent Changes in ASTM D975 Diesel Fuel specification
Acid Number Allowance of up to 5 % biodiesel
content Lubricity Stability
Resources for Diesel Fuel Properties
ASTM International EPA, Environmental Protection Agency Changes in Diesel Fuel USDA Biodiesel education• Internal Combustion Engine Fundamentals, John B.
Heywood, McGraw Hill, 1988 ISBN 0-07-100499-8• Automotive Fuels Reference Book, Keith Owen,
Trevor Coley SAE, 1995, ISBN 1-56091-589-7