48
Liquid Fuels Liquid Fuels

Liquid Fuels

Embed Size (px)

DESCRIPTION

Liquid Fuels. Example. What is the air/fuel ratio and the exhaust products when ethanol is used as an engine fuel?. Solution. Calculate the Stoichiometric Air ? Calculate the theoretical CO2 content in flue gases ?. Heating Value Estimates for Petroleum Fuels. - PowerPoint PPT Presentation

Citation preview

Page 1: Liquid Fuels

Liquid FuelsLiquid Fuels

Page 2: Liquid Fuels

ExampleExample

What is the air/fuel ratio and the What is the air/fuel ratio and the exhaust products when ethanol is exhaust products when ethanol is used as an engine fuel? used as an engine fuel?

Page 3: Liquid Fuels

SolutionSolution

95.81/)866.6087.2(/

174.1913.1866.6866.6087.21

)18(3)44(2)28(28.11)28(28.11)32(3)46(1

3228.1128.113 2222262

FA

OHCONNOOHC

Page 4: Liquid Fuels

Calculate the Stoichiometric Air ?Calculate the theoretical CO2 content in flue gases ? ?

Page 5: Liquid Fuels

Heating Value Estimates for Heating Value Estimates for Petroleum FuelsPetroleum Fuels

Heating values are estimated from the API Heating values are estimated from the API gravity,gravity,

where Hwhere Hgg is the gross (high) heating value is the gross (high) heating value and Hand Hnn is the net (low) heating value. is the net (low) heating value.

)/(000,107190.0

)/(1093860,42

kgkJHH

kgkJAPIH

gn

g

Page 6: Liquid Fuels

66

Density

• Ratio of the fuel’s mass to its volume at 15 oC,

• kg/m3

• Useful for determining fuel quantity and quality

Properties of Liquid Fuels

Page 7: Liquid Fuels

77

Liquid Fuels

Specific gravity• Ratio of weight of oil volume to weight of same water volume at a given temperature

• Specific gravity of water is 1

• Hydrometer used to measure

0.88-0.980.89-0.950.85-0.87Specific Gravity

LSHS (Low SulphurHeavy Stock)

Furnace oilLDO(Light Diesel Oil)

Fuel oil type

Table Specific gravity of various fuel oils

Page 8: Liquid Fuels

88

Liquid Fuels

Viscosity• Measure of fuel’s internal resistance to flow

• Most important characteristic for storage and use

• Decreases as temperature increases

Flash point• Lowest temperature at which a fuel can be heated so that the vapour gives off flashes when an open flame is passes over it

• Flash point of furnace oil: 66oC

Page 9: Liquid Fuels

Typical UnitsTypical Units

Centipoise (cP) was the popular unit of Centipoise (cP) was the popular unit of dynamic viscosity.dynamic viscosity.

Centistoke (cSt) was the popular unit of Centistoke (cSt) was the popular unit of kinematic viscosity.kinematic viscosity.

smPacP 11

smmcSt /11 2

Page 10: Liquid Fuels

Reporting of ViscosityReporting of Viscosity

Kinematic viscosity (Kinematic viscosity () is reported as,) is reported as,

where where is absolute (or dynamic) is absolute (or dynamic) viscosity, and viscosity, and is the fluid mass density. is the fluid mass density.

Page 11: Liquid Fuels

Table SAE Motor Oil Table SAE Motor Oil ClassificationClassification

Page 12: Liquid Fuels

Cloud and Pour PointsCloud and Pour Points Cloud point is the temperature at which Cloud point is the temperature at which

crystals begin to form in the fuel.crystals begin to form in the fuel. Pour point is the temperature at which the Pour point is the temperature at which the

fuel ceases to flow. fuel ceases to flow. Indication of Indication of temperature at which fuel can be pumpedtemperature at which fuel can be pumped

Cloud point are typically 5 to 8 C higher Cloud point are typically 5 to 8 C higher than pour point,than pour point,

Not an issue for gasoline.Not an issue for gasoline. Values are important for diesel.Values are important for diesel.

Page 13: Liquid Fuels

Fundamental DefinitionsFundamental Definitions

Calorific valueCalorific value Amount of heat librated by the combustion of Amount of heat librated by the combustion of

unit quantity of fuel. kcal/ kg , kcal / m3unit quantity of fuel. kcal/ kg , kcal / m3 Gross Calorific Value (G.C.V) or HCVGross Calorific Value (G.C.V) or HCV

heating value measurement in which the heating value measurement in which the product water vapour is allowed to condenseproduct water vapour is allowed to condense

Net Calorific Value (N.C.V) or LCVNet Calorific Value (N.C.V) or LCV heating value in which the water remains a heating value in which the water remains a

vapor and does not yield its heat of vaporizationvapor and does not yield its heat of vaporization

HHV = LHV + (HHV = LHV + (mmwaterwater /m /mfuelfuel)ʎ)ʎwaterwater

Page 14: Liquid Fuels

1414

Liquid Fuels

Calorific value• Heat or energy produced

• Gross calorific value (GCV): vapour is fully condensed

• Net calorific value (NCV): water is not fully condensed

Fuel Oil Gross Calorific Value (kCal/kg)Kerosene 11,100Diesel Oil 10,800Furnace Oil 10,500

Page 15: Liquid Fuels

1515

Liquid Fuels

Sulphur content• Depends on source of crude oil and less on the refining process

• Furnace oil: 2-4 % sulphur

• Sulphuric acid causes corrosion

Ash content• Inorganic material in fuel

• Typically 0.03 - 0.07%

• Corrosion of burner tips and damage to materials /equipments at high temperatures

Page 16: Liquid Fuels

1616

Liquid Fuels

Carbon residue• Tendency of oil to deposit a carbonaceous solid residue on a hot surface

• Residual oil: >1% carbon residue

Water content• Normally low in furnace oil supplied (<1% at refinery)

• Free or emulsified form

• Can damage furnace surface and impact flame

Page 17: Liquid Fuels

Four stroke cycle theory

Intake strokePiston moving downIntake valve openExhaust valve closed

Page 18: Liquid Fuels

Four stroke cycle theory

Compression strokePiston moving upIntake valve closedExhaust valve closed

Page 19: Liquid Fuels

Four stroke cycle theory

Power strokePiston moving downIntake valve closedExhaust valve closed

Page 20: Liquid Fuels

Four stroke cycle theory

Exhaust strokePiston moving upIntake valve closedExhaust valve open

Page 21: Liquid Fuels

Engine measurements

Bore • Diameter of cylinder

Stroke• Distance between TDC & BDC

Page 22: Liquid Fuels

Engine measurements

Displacement per cylinder• r² S

Displacement for the engine• Disp per cylinder times the Number of cylinders

Page 23: Liquid Fuels

Engine measurements

Compression ratioD + CV

CV

To calculate clearance volume D . CR-1

Page 24: Liquid Fuels

Abnormal Combustion in SI Engine

Knock is the term used to describe a pinging noise emitted from a SI engineundergoing abnormal combustion.

The noise is generated by shock waves produced in the cylinder when unburned gas autoignites.

Page 25: Liquid Fuels

Knock in SI engines.Knock in SI engines.

Page 26: Liquid Fuels

Octane RatingsOctane Ratings

Octane is a measure of gasoline’s Octane is a measure of gasoline’s resistance to “knock.”resistance to “knock.”

““Knock” is the uncontrolled release Knock” is the uncontrolled release of energy when combustion initiates of energy when combustion initiates somewhere other than the spark somewhere other than the spark plug.plug.

Symptoms of engine “knock” include Symptoms of engine “knock” include an audible “knocking” or “pining” an audible “knocking” or “pining” sound under acceleration. sound under acceleration.

Page 27: Liquid Fuels

How to Reduce Engine How to Reduce Engine KnockKnock

Use gasoline with higher octane Use gasoline with higher octane ratings – these ratings are ratings – these ratings are associated with gasoline that has associated with gasoline that has few straight chain carbons have few straight chain carbons have longer ignition delay times. longer ignition delay times.

Page 28: Liquid Fuels

Octane Rating MeasurementOctane Rating Measurement

Procedure developed by the Procedure developed by the Cooperative Fuels Research Cooperative Fuels Research Committee (CFR).Committee (CFR).

The committee proposed a single The committee proposed a single cylinder SI engine to measure octane cylinder SI engine to measure octane – the CFR engine has an adjustable – the CFR engine has an adjustable compression ratio.compression ratio.

Engine is driven at a constant speed Engine is driven at a constant speed with an electric motor. with an electric motor.

Page 29: Liquid Fuels

Octane Rating MeasurementOctane Rating Measurement Octane ratings are obtained by Octane ratings are obtained by

comparing fuel in question to iso-comparing fuel in question to iso-octane (Octane Rating of 100) and octane (Octane Rating of 100) and heptane (Octane Rating of 0).heptane (Octane Rating of 0).

CR is adjusted until “knocking” is CR is adjusted until “knocking” is detected with fuel being tested.detected with fuel being tested.

Blends of iso-octane and heptane are Blends of iso-octane and heptane are tested until the same level of knock is tested until the same level of knock is obtained.obtained.

Octane rating is % of iso-octane in Octane rating is % of iso-octane in test blend. test blend.

Page 30: Liquid Fuels

Fuel Knock Scale

To provide a standard measure of a fuel’s ability to resist knock, a scale has been devised by which fuels are assigned an octane number ON.

The octane number determines whether or not a fuel will knock in a given engine under given operating conditions.

By definition, normal heptane (n-C7H16) has an octane value of zero andisooctane (C8H18) has a value of 100.

The higher the octane number, the higher the resistance to knock.

Blends of these two hydrocarbons define the knock resistance of intermediate octane numbers: e.g., a blend of 10% n-heptane and 90% isooctane has an octane number of 90.

A fuel’s octane number is determined by measuring what blend of these two hydrocarbons matches the test fuel’s knock resistance.

Page 31: Liquid Fuels

Octane Number Measurement

Two methods have been developed to measure ON using a standardizedsingle-cylinder engine developed under the auspices of the Cooperative Fuel Research (CFR) Committee in 1931.

The CFR engine is 4-stroke with 3.25” bore and 4.5” stroke, compression ratio can be varied from 3 to 30.

Research Motor

Inlet temperature (oC) 52 149Speed (rpm) 600 900Spark advance (oBTC) 13 19-26 (varies with r)Coolant temperature (oC) 100Inlet pressure (atm) 1.0Humidity (kg water/kg dry air) 0.0036 - 0.0072

Note: In 1931 iso-octane was the most knock resistant HC, now there are fuels that are more knock resistant than isooctane.

Page 32: Liquid Fuels

Testing procedure:• Run the CFR engine on the test fuel at both research and motor conditions.• Slowly increase the compression ratio until a standard amount of knock occurs as measured by a magnetostriction knock detector.• At that compression ratio run the engines on blends of n-heptane and isooctane.• ON is the % by volume of octane in the blend that produces the stand. knock

The antiknock index which is displayed at the fuel pump is the average of the research and motor octane numbers:

Octane Number Measurement

2

MONRONindexAntiknock

Note the motor octane number is always lower because it uses more severeoperating conditions: higher inlet temperature and more spark advance.

The automobile manufacturer will specify the minimum fuel ON that will resist knock throughout the engine’s operating speed and load range.

Page 33: Liquid Fuels

Fig. CFR EngineFig. CFR Engine

Page 34: Liquid Fuels

Octane RatingsOctane Ratings

CFR developed initial method (Motor Octane CFR developed initial method (Motor Octane Number – MON).Number – MON).

ASTM developed a new method (Research ASTM developed a new method (Research Octane Number – RON).Octane Number – RON).

RON octane ratings are 8 points low than MON RON octane ratings are 8 points low than MON for most gasoline.for most gasoline.

Most retailers report the Anti-Knock Index Most retailers report the Anti-Knock Index which is an average of MON and RON.which is an average of MON and RON.

Octane ratings of fuel are adjusted for Octane ratings of fuel are adjusted for elevation – lower atmospheric pressure elevation – lower atmospheric pressure reduces the tendency for engine knock to reduces the tendency for engine knock to occur. occur.

Page 35: Liquid Fuels

Cetane RatingsCetane Ratings

Cetane rating are an indication of the Cetane rating are an indication of the fuel’s anti-knock resistance for CI fuel’s anti-knock resistance for CI engines.engines.

Fuels with high cetane ratings are Fuels with high cetane ratings are created by increasing the proportion created by increasing the proportion of long chain molecules, thereby of long chain molecules, thereby reducing the ignition delay.reducing the ignition delay.

Fuels with high Octane Rating have Fuels with high Octane Rating have low cetane ratings!low cetane ratings!

Page 36: Liquid Fuels

Cetane RatingsCetane Ratings

CFR cetane rating process is similar to CFR cetane rating process is similar to the Octane process with a couple of the Octane process with a couple of differences:differences: Cetane and Alpha methyl naphthalene Cetane and Alpha methyl naphthalene

are the reference fuels.are the reference fuels. Cetane is given a cetane number of 100. Cetane is given a cetane number of 100.

Alpha methyl naphthalene has cetane Alpha methyl naphthalene has cetane rating of zerorating of zero

Hyptamethylnonane has a cetane rating Hyptamethylnonane has a cetane rating of 15. of 15.

Page 37: Liquid Fuels

Effect of Cetane RatingEffect of Cetane Rating If cetane rating is too low, the ignition If cetane rating is too low, the ignition

delay results in hard starting (combustion delay results in hard starting (combustion after piston is moving downward) and after piston is moving downward) and characteristic ”white smoke.”characteristic ”white smoke.”

High cetane ratings start the combustion High cetane ratings start the combustion process to soon, and some of the fuel is process to soon, and some of the fuel is not volatized and does not burn.not volatized and does not burn.

““Black smoke” in heavily loaded engines Black smoke” in heavily loaded engines is a symptom of high cetane ratings.is a symptom of high cetane ratings.

Minimum cetane rating for CI engines is Minimum cetane rating for CI engines is 40 according to SAE.40 according to SAE.

Commercial fuels seldom exceed 50.Commercial fuels seldom exceed 50. Cetane rating should never exceed 60. Cetane rating should never exceed 60.

Page 38: Liquid Fuels

Cetane Ratings and CI Cetane Ratings and CI EnginesEngines

Octane rating is not a good way to predict Octane rating is not a good way to predict “knock” in CI engines.“knock” in CI engines.

Combustion in diesel engines consists of a Combustion in diesel engines consists of a two part delay – physical and chemical.two part delay – physical and chemical.

Physical - the fuel is injected and Physical - the fuel is injected and atomized.atomized.

Chemical - process proceeds with a pre-Chemical - process proceeds with a pre-flame chemical reaction, similar to that of flame chemical reaction, similar to that of SI engines. SI engines.

Page 39: Liquid Fuels

Altering Knock in CI EnginesAltering Knock in CI Engines

Ignition delay controls the relative Ignition delay controls the relative release of energy between the two release of energy between the two phases of combustion – a longer phases of combustion – a longer delay results in more energy delay results in more energy produced in the pre-mix phase.produced in the pre-mix phase.

Since “knock” occurs when more Since “knock” occurs when more energy is released at the start of energy is released at the start of combustion, it follows that “knock” is combustion, it follows that “knock” is reduced with short delay periods. reduced with short delay periods.

Page 40: Liquid Fuels

Fuel ViscosityFuel Viscosity

Viscosity is a measure of the flow Viscosity is a measure of the flow resistance of liquid.resistance of liquid.

Fuel viscosity must be high enough Fuel viscosity must be high enough to insure good lubrication of injection to insure good lubrication of injection pump mechanisms in CI engines.pump mechanisms in CI engines.

Fuel viscosity must be low enough to Fuel viscosity must be low enough to insure proper atomization at the time insure proper atomization at the time of injection. of injection.

Page 41: Liquid Fuels

Fuel Impurities - SulfurFuel Impurities - Sulfur

Sulfur oxides – can convert to acids Sulfur oxides – can convert to acids which corrode engine parts and which corrode engine parts and cause increased wear.cause increased wear.

Assessed by immersing copper strip Assessed by immersing copper strip in fuel for three hours, then in fuel for three hours, then comparing corrosion to standard comparing corrosion to standard strips.strips.

Page 42: Liquid Fuels

Fuel Impurities - AshFuel Impurities - Ash

Ash – small solid particles or water-Ash – small solid particles or water-soluble metals found fuels.soluble metals found fuels.

Defined as un-burned fuel residue Defined as un-burned fuel residue left behind.left behind.

Can cause accelerated wear of close-Can cause accelerated wear of close-fitting injection system parts.fitting injection system parts.

Page 43: Liquid Fuels

Fuel Impurities – Water and Fuel Impurities – Water and SedimentSediment

Moisture can condense in fuel Moisture can condense in fuel storage tanks, or seep in from storage tanks, or seep in from underground leaks.underground leaks.

Fuel should be bright and clear, and Fuel should be bright and clear, and visibly free of water and sediment.visibly free of water and sediment.

Page 44: Liquid Fuels

Fuel Impurities - GumFuel Impurities - Gum

Gum can form in gasoline, leaves Gum can form in gasoline, leaves behind deposits on carburetors. behind deposits on carburetors. Gum is dissolved by gasoline – more Gum is dissolved by gasoline – more prevalent in gasoline that is made by prevalent in gasoline that is made by cracking.cracking.

Antioxidants are now added to both Antioxidants are now added to both diesel and gasoline to extend storage diesel and gasoline to extend storage life without gum formation.life without gum formation.

Page 45: Liquid Fuels

Fuel AdditivesFuel Additives

Until 1970, gasoline contained TEL Until 1970, gasoline contained TEL (tetraethyl lead). TEL was used as an (tetraethyl lead). TEL was used as an octane booster.octane booster.

MTBE (methyl tertiary butyl ether) is MTBE (methyl tertiary butyl ether) is often substituted as an octane often substituted as an octane booster – could be phased booster – could be phased out/banned soon.out/banned soon.

Page 46: Liquid Fuels

Table 5.5: Gasoline Table 5.5: Gasoline additivesadditives

Page 47: Liquid Fuels

Fuel StorageFuel Storage

Fuels classified according to Fuels classified according to flammability – gasoline is more flammability – gasoline is more dangerous with a flash point of -dangerous with a flash point of -40 C.40 C.

Major concern with regard to Major concern with regard to environmental contaminationenvironmental contamination

Page 48: Liquid Fuels

Lubricating Oil AdditivesLubricating Oil Additives