basic diesel fuel and analysis

7/31/2019 Basic Diesel Fuel and Analysis

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Basic Diesel Fuel

and Fuel Analysis

Mark Mathys

Butler Machinery Company

Caterpillar and Cat Are Trademarks of Caterpillar Inc

1998 Mark Mathys & Butler Machinery Company


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Overview

Fuel System Types

Fuel Classification

Fuel Properties and Tests

Contamination

Diesel Additives Fuel Testing


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Fuel System Types

Direct Injection (DI)

Fuel injected directly in combustion chamber

Mixing achieved by using a multi-hole nozzleand or by causing the intake air to swirl

High injection pressures (2,000-30,000 psi)required for fine atomization

Generally uses less fuel than PC engine

More sensitive to fuel quality


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Direct Injection


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Fuel System Types

Precombustion Chamber (PC)

Fuel injected into a precombustion chamberMixing is achieved by spraying fuel into theturbulent air (generally a single-hole nozzle)

Low injection pressures (1,500-5,000 psi)

Less sensitive to the degree of fuel atomization

Less sensitive to fuel quality

Lower fuel economy


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Precombustion Chamber


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Fuel Selection

Classification Fuel Properties


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Classification No. 1-D

Volatile fuels from kerosene to theintermediate distillates

Use in high-speed engines involving frequentand wide variations in speeds and loads

For use in low ambient temperatures

Was designed to meet for Detroit Diesel Series71 engines in city bus service


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Distillate gas oils of lower volatility

For use in high speed engines involving highloads and uniform speeds not requiring thehigher volatility or other properties of grade 1-D

Used by most automotive and truck-type dieselengines


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The more viscous distillates and blends of

distillates with residual fuel oils For use in low- and medium-speed services

involving sustained loads and constant speeds

Used by large stationary power generation andmarine engines


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No. 1-D No. 2-D No. 4-D

Gravity API 39-45 31-37 14-23Flash Point F 102-130 150-240 155-260

Viscosity (cSt) 1.3-1.7 2.8-4.1 5.5-24.0

Sulfur % 0.05-0.5 0.03-0.45 0.24-1.5

Cetane No. 45-48 45-48 32-36

BTU/lb 19,700 19,500 18,800BTU/gal 134,000 138,000 148,000

Typical Diesel Fuel Properties


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Properties and Tests

Cetane NumberIgnition quality measure - affects cold starting,

smoke, and combustion Sulfur Content

Affects wear, deposits, and particulateemissions

API GravityRelated to heat content, affecting power and

economy


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Heating Value

Affects power output and fuel economy

Volatility

Affects ease of starting and smoke

Flash Point

Related to volatility and fire hazard in handling


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Viscosity

Affects injector lubrication and atomization

Cloud Point

Affects low-temperature operation

Water & Sediment

Affects life of fuel filters, pump, and injectors


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Carbon Residue

Measures residue in fuel, can influence

combustion

Ash

Measures deposit-forming inorganic residues

Corrosion

Measures possible corrosive attack on metal

parts


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Cetane Number

Ignition quality measure

Affects: cold starting, warm-up, combustion

roughness, acceleration, and exhaust smoke density Cetane number is based on the ignition characteristics

of two hydrocarbons:

Cetane - short delay period and ignites readily (100)

Alphamethylnaphthalene (AMN) - long delay period andpoor ignition quality (0)

It is the percentage by volume of normal cetane in ablend with AMN


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Cetane Number

High cetane number indicates good ignition quality(short delay period)

Low cetane number indicates poor ignition quality(long delay period)

PC engines require a minimum cetane # of 35

DI engines require a minimum cetane # of 40 Cetane improver additive can improve ignition quality

and reduce white smoke during start up


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Sulfur Content

Affects wear, deposits, and particulate emissions

Depends on the crude oil source and refining stepsit undergoes

Sulfur oxides (SO2 and SO3) are produced duringcombustion of fuel. SO3 combines with water in

the exhaust to form sulfuric acid (H2SO4)

Sulfuric acid causes corrosive wear andcontributes to engine deposits


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Sulfur Damage


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API Gravity

Related to heat content, affects power andeconomy

It is an arbitrary index of the weight of ameasured volume of fuel and is related tospecific gravity and density

The scale is inverse to specific gravity

Lighter fuels have higher API numbers

Heavier fuels have lower API numbers


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API Gravity

For most Cat engines an API reading of 35 isoptimum

Lighter fuels, like kerosene, read about 44 API

Lighter fuels will not produce rated HP

Heavier fuels (below 30 API) create combustionchamber deposits which cause abnormal wear

Blending is the only way to correct fuel densityproblems


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Heating Value

Affects power output and fuel economy

The heat of combustion (BTU per pound orgallon) is a measure of the amount of energyavailable to produce work

In general, a fuel with a higher volumetricheating value (BTU per gallon) will producemore power or provide better fuel economy


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Volatility

Affects ease of starting and smoke

Less volatile fuels (higher boiling points)normally have a higher heating value

Starting and warm-up are better with higherfront-end volatility (lower D 86 10% distillation

temperatures) Deposit formation, wear, and exhaust smoke are

worse with higher D 86 90% and end pointtemperatures


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Flash Point

Related to volatility and fire hazard in handling

It is the temperature at which fuel vapors can beignited when exposed to a flame

Affected by the type of fuel and the air/fuel ratio

It is important for safety reasons, not for engineoperating characteristics

The minimum flash point for most diesel fuels is

about 100F (38C)


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Viscosity

Affects injector lubrication and atomization

Low viscosity fuels may not provide sufficientlubrication in close-fit pumps and injectors

Can cause abnormal wear, loss of power & smoke

Influences the size of the fuel droplets High viscosity increases wear of fuel pump and

gear train due to high injection pressures


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Effect of Viscosity


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Cloud Point

Affects low-temperature operation

Cloud Point is the temperature where a cloud orhaze appears in the fuel

Happens when the temperature falls below themelting point of the wax in the fuel

CP must be below the lowest outside operatingtemperature to prevent filter plugging

Use a fuel heater or blended fuel, additives arenot recommended


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Water & Sediment

Affects life of fuel filters, pump, and injectors

Water introduced during shipment or ascondensation during storage

Cause damage, especially to fuel lubricated pumps

Water separators are critical to fuel systems

Sediment (rust, scale, dirt,weld slag, etc.)

Removed by settling, straining/filtration, orcentrifuging


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Sediment


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Water & Sediment

Eliminate water by draining the fuel tank regularly

Obtain fuel from reliable sources

Water separators should be used

Sediment should not exceed 0.05% to the engine

Primary and secondary filtering is usually required


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Nozzle Orifice Wear


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Carbon Residue

Measures residue in fuel, can influencecombustion

Carbon rich fuels are harder to burn

Leads to the formation of soot and carbondeposits

Hot spots on liners, burned oil film, scuffing,stuck rings, turbocharger and engine depositsare the results


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Carbon Residue


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Ash

Deposit-forming inorganic residues

Consists of metal and other contaminants that

cannot be burned

Cause localized overheating of metal surfacessuch as the exhaust valve seat

Causes abrasive wear of cylinder and fuelsystem components, and the turbocharger

Avoid use of unproven additives, use filtersand settling tanks to remove solids


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Ash Deposits


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Corrosion

Hydrogen Sulfide

Fuel Sulfur

Copper Strip Corrosion


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Hydrogen Sulfide

H2S is a poisonous gas present in somecrude oils and residual fuels

Forms sulfuric acid when combined withwater vapor in the cylinder

Corrosive to metals, particularly valve

guides, rings, and liners If above 0.05% coolant temp must be kept

above 190F to prevent condensation


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Fuel Sulfur

Naturally occurring element in all crude oils

Heavy fuels have a higher sulfur content Sulfur can be reduced or eliminated during the

refining process

Sulfur over 0.5% can greatly reduce engine life Know your fuel sulfur level


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Fuel Sulfur

Keep operating temperature above 175F toreduce condensation

Select an oil with TBN 20 times the sulfur level

Follow standard oil change intervals unlessSOS indicates differently

Maintain crankcase breather system to preventTBN depleting condensation


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Bacteria and Fungi


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Microbial Contamination

Plug filters with a greenish-black or brown slime

Frequently strong odor Some produce corrosive acid byproducts

Prevent growth by keeping fuel system dry

Treat with biocides when a reoccurring problem Tanks and lines must be cleaned to reduce filter

plugging


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Microbe Test


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Stability

Sulfur and Nitrogen present in diesel fuel makeit more prone to oxidative attack in storage,

and thermal degradation in use, than gasoline Gums and Resins are the result of oxidation

and cause rapid filter plugging

Commercial fuels usually contain additives tohelp prevent oxidative breakdown

Storage time should be less than one year


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Smoke and Particulates

White/Blue SmokeUsually the result of too low a temperature in

the combustion chamberBlue component is excess lubricating oil in thecombustion chamber

Black SmokeProduced at or near full load

Excess fuel or not enough air


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Diesel Additives

Contaminant Control

Biocides - prevent bacterial growth

Demulsifiers - separate water from fuelCorrosion Inhibitor- protect against rust and corrosion

FuelStabilityOxidation Inhibitors - protect against breakdown

Metal Deactivators - chelate trace metals

Dispersants - disperse residues and preventagglomerations


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Diesel Additives

Engine Performance

Detergents - prevent deposit buildup and extend

injector life. Increase filter life by keeping the filtersclean

Cetane Improvers - raise cetane number

Lubricity - replaces natural lubricants

Fuel Handling

Anti-foam - reduces foaming when pumping fuel

Anti-Static - lowers risk of static induced explosion


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Fuel System Maintenance

Clean around filter housing before removing filter

Lubricate and clean the new filter gasket with

clean fuel

NEVER pour fuel into the new filter element

Always bleed the fuel system to remove air after

changing the filter

Fill the fuel tank at the end of the day to preventcondensation of water


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Drain Water and sediment from the fuel tank at thestart of each day or after the tanks has been filledand allowed to stand for 10-15 minutes

Install and maintain a water separator before theprimary fuel filter

Clean and change filter at the recommended

interval

Inspect new filters for debris or metal filings,especially the threads of spin-on filters


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Drain storage tanks every week

Use genuine Caterpillar fuel filters. There are

great differences in fuel filters

Properly store new filters to prevent dust anddirt entry

Cut apart used filters to examine contaminantsand compare brands of filters


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Fuel Testing at Butler

API Gravity*

Bacteria and Fungi*

Microscope Exam*

Flash Point

Sulfur content

Water and Sediment

Distillation

Cold Temperature Tests

* performed on site


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Problems With Testing

Hard to get a representative sample

Tests are expensive - often cost more fortest than it does to correct problem

Not practical to test a sample to find out

whats in it

Must test for specific things


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Fuel Quality is Not Visually Apparent

basic diesel fuel and analysis

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