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

Fuel technology

Combustion technology

Aftertreatment technology

Fuel system technology

Better understanding of combustion

Alternate Fuels (Biodiesel)Low sulfur De-NOx

DOC

PM trap

Rate controlHigh pressure Multi-injection

EGR technology

Others

Control technology

Technology Pathway

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.

3 PROPANE METHANOL ETHANOL

8 ISO OCTANE (GASOLINE)

20 CETANE (DIESEL FUEL)

Benzene

Toluene Xylene

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

Low ash lubricating oils - NEW

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)

Enhanced Lubricity

Ultra-low Sulfur Diesel

0100200300400500600700800

0.0 1.0 2.0 3.0 4.0 5.0

Biodiesel Blend (%)

HFRR WSD (micron)

Equipment benefits Superior lubricity B2 has up to 66% more

lubricity than #2 Diesel EPA required sulfur

reduction in diesel No overdosing concerns

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