ice fuels basic - copy

FUELS

• Petro chemicals or hydro carbons (HC)• Gasoline/Petrol is a liquid obtained from crude

oil/mineral oil/rock oil--organic compound • It is a dark brown/black, foul smelling liquid• It undergoes no of refining processes in the refinery.

Usually fractional distillation• Hydrocarbons with more carbon atoms have higher

boiling point than the one with fewer carbon atoms.• HC with low boiling point are collected at the top of

the tower

FUELS

• Cracking is process of breaking large HC by thermal & catalytic cracking

• Reformation- why? To improve anti knock qualities of fuels

• Isomerisation- same no of molecular formula but different chemical structures

FRACTIONAL DISTILLATION

FUELSFRACTIONS BOILING RANGE NO OF CARBON

ATOMSUSES

PETROLEUM GAS BELOW 40 1-4 FUEL COOKING/HEATING

PETROL 40-75 5-10 CARS

NAPTHA 75-150 7-14 PLASTICS, DETERGENT/ FEED STOCK

KEROSENE/ PARAFIN

160-250 11-16 AIRCRAFTS, COOKING

DIESEL OIL 250-300 16-20 CI ENGINES

LUBRICATING OIL 300-350 20-35 WAXES / POLISH

BITUMEN/ ASPHALT

ABOVE 350 MORE THAN 70 PAVING ROAD

PROPERTIES OF FUELS

• Boiling & melting point increases as molecular size increases

• Density increases as molecular size increases• Viscosity increases with molecular size• Less flammable with increase in molecular size---

so ?• Fuel with less carbon atoms is more volatile &

heating value increases by proportion of hydrogen atoms.

• N2- 80 % , 02 -20 %

• H2 in HC forms H20 & O2 forms CO2

• But incomplete combustion may result in some HC going out to form CO & NOx

AIR/FUEL

• Volatility• Resistance to spark knock or detonation• Anti rust • Anti icers• Detergent-clean fuel/carburetor• Dye for colour

FUEL PROPERTIES

FUEL PROPERTIES

Natural Evaporation of Volatile Fuels

FUEL PROPERTIES

• Volatility : crank case dilution, vapour lock, starting issues

• Gum deposit: impurities due storage, clogs carburetor, carbon deposits

• Sulphur: corrosion, low ignition temp promoting knocks

FUEL PROPERTIES

• Flash point of a volatile material is the lowest temp at which it can vaporize to form an ignitable mixture in air.

• It requires an ignition source.• At flash point, the vapours cease to burn

when source of ignition is removed• SI engine, A/F mixture is heated above its flash

point, then ignited by spark plug.

FUEL PROPERTIES

• Knock: Abnormal combustion after spark at the plug resulting in high pitch metallic rapping noise called pinging.

• Pre-ignition: Hot spots causing ignition before spark plug. Hot exhaust valve, spark plug or carbon deposits. Rumble to mild detonation/ dull thud.

• To avoid pre-ignition, low flash & higher auto ignition temp.

COMBUSTION

COMBUSTION

• If T&P of A/F mixture is raised high enough, it will self ignite without a spark plug.

• In SI engines auto/pre-ignition is not desirable. Spark plug ignites A/F mixture at proper time in cycle.

• Compression ratio generally <10:1 to avoid pre-ignition

ID= Ignition Delay

COMBUSTION• Mechanical factors to

control combustion• Quench area prevents last

part of A/F mixture to detonate. It occurs at end of compression stroke. Mixture squeezed to promote turbulence.

• Hemisphere shape has a central plug. Flame travels a short distance. No end pockets

Gasoline/Petrol

• It is a complicated mixture of hydrocarbons boiling between 50 and 2000 C, with chemical formulas between C6H14 and C12H26, but a good "average" compound is C8H18.

OCTANE NO

• Organo-manganese & alcohols are substitutes of Tetra-ethyl Lead (TEL)

• Knock occurs at WOT when engine is loaded/ going uphill

• Solution- o High octane (slow burning): Ignition timing advanceoMedium octane: Retard ignition or starting

combustion later in compression stroke.

EFFECT OF TETRA ETHYL LEAD ON OCTANE NUMBER

OCTANE NUMBER (ON)

To find the ON of an SI engine fuel, the following test procedure is used:•A specially designed test engine is run at specified conditions using the fuel being tested.•Compression ratio is adjusted until a standard level of knock is experienced.•The test fuel is then replaced with a mixture of the two standard fuels.

OCTANE NUMBER (ON)

• The intake system of the engine is designed such that the blend of the two standard fuels can be varied to any percent from all iso-octane to all n-heptane.

• The blend of fuels is varied until the same knock characteristics are observed as with the test fuel.

OCTANE NUMBER (ON)

• The percent of iso-octane in the fuel blend is the ON given to the test fuel. For instance, a fuel that has the same knock characteristics as a blend of 87% iso-octane and 13% n-heptane would have an ON of 87.

ISOOCTANE (C8H18)

• Also written as: iso-octane• Also called : 2,2,4-Trimethylpentane • It is an organic liquid compound with the

formula (CH3)3CCH2CH(CH3)2.

• It is one of several isomers of octane. • It is an important component of gasoline,

frequently used in relatively large proportions to increase the knock resistance of the fuel.

DIESEL FUEL

• Has a high compression ratio of 16:1 to 22:1• Heat of compression ignites fuel as it sprays

into the engine cylinder. It does not require an ignition source.

• Volatility: less than petrol but it also has higher heating value (Long chain).

• Viscosity: Slightly more than petrol, otherwise it would not break into particles. Small particles burn fast.

DIESEL FUEL

• Immediately after injection, the fuel partially evaporates with a resulting chilling of the air in the immediate vicinity of each fuel particle.

• However, the extreme heat of compression rapidly heats the fuel particles to self ignition point and combustion begins. The fuel particles burn as they mix in the air.

DIESEL FUEL

• The smallest particles burn rapidly but larger ones take more time to ignite because heat has to reach them to bring them to self ignition.

• Combustion is slower and pressure rise is small (constant).

• A good CI engine has short ignition lag.• Ignition lag affects starting, warm up, and

produces smoke.

DIESEL FUEL

DIESEL FUEL• Knock: Time of injection and actual burning. If

lag increases, amount of fuel accumulated is more, abnormal amount of energy is released, excessive pressure rise with audible knock.

• Sulphur Content of Diesel: Excessive Sulphur causes cylinder wear/breaking down of lubricating oil.

OCTANE & CETANE NOs

Definition Cetane Number (CN)

• The cetane number is the percentage by volume of cetane in the mixture that has the same performance as the fuel being tested.

• It is a measure of a fuel's ignition delay, the time period between the start of injection and the first identifiable pressure increase during combustion of the fuel.

• In a particular diesel engine, higher cetane fuels will have shorter ignition delay periods than lower cetane fuels.


• Cetane numbers are only used for the relatively light distillate diesel oils.

• The higher the cetane number the more easily the fuel will burn in a compression setting (such as a diesel engine).

• The characteristic diesel "knock" occurs when the first portion of fuel that has been injected into the cylinder suddenly ignites after an initial delay.


• Once ignition occurs, all the remaining fuel burns smoothly as it leaves the injector nozzle.

• Minimizing this delay results in less unburned fuel in the cylinder at the beginning and less intense knock.

• Therefore higher-cetane fuel usually causes an engine to run more smoothly and quietly.

• This does not necessarily translate into greater efficiency, although it may, in certain engines.

CETANE NUMBER (CN)

• In the 1930's the Cooperative Fuel Research (CFR) committee sought a way of expressing the tendency of a diesel fuel to ignite quickly, and their work was taken up by the ASTM.

• A Hydrocarbon fuel that ignited very quickly, cetane (n-hexadecane) was arbitrarily given a rating of 100, and a Hydrocarbon that was very slow to ignite, called 1-methylnapthalene, was assigned a rating of zero.

• Values on this scale were named “cetane numbers.”

CETANE NUMBER (CN)

• A specially-designed engine with adjustable compression is used to determine a fuel’s cetane number. The fuel being tested is injected at 13° before top dead center.

• The engine’s compression ratio is then adjusted until the fuel ignites at top dead center.

• Retaining this compression ratio, the engine is then run on various blends of cetane with 1-methylnapthalene, until a blend is found for which ignition occurs at top dead center.

Typical Values

• Generally, diesel engines operate well with a CN from 40 to 55.

• Higher speed diesel engines operate more effectively with higher cetane number fuels.

• In North America, most states adopt ASTM D975 as their diesel fuel standard and the minimum cetane number is set at 40, with typical values in the 42-45 range.

Typical values

• In Europe, diesel cetane numbers were set at a minimum of 38 in 1994 and 40 in 2000.

• The current standard for diesel sold in European Union, Iceland, Norway and Switzerland is set in EN 590, with a minimum cetane index of 46 and a minimum cetane number of 51.

• Premium diesel fuel can have a cetane number as high as 60.

• In Pakistan High Speed Diesel is about CN 45

Cetane Index• Because of need for special engines/test equipment,

often cetane number cannot be determined experimentally.

• Instead an estimate is made from the fuel’s specific gravity and the temperature at which half of a sample will boil away.

• Such an estimate is called cetane index, not cetane number.

• An improved method relies on the temperatures at which 10%, 50% and 90% of the sample boils away.

•

Diesel Petrol

Diesel Petrol

Uses:In diesel engines, heating systems

In petrol engines

Energy content: 38.6 MJ/litre 34.6 MJ/litre

Torque (for 10L engine): 1000 Nm @ 2000 rpm 300Nm @ 4000 rpm

Power (for 10L engine): 490Hp @ 3500 rpm 600Hp @ 5500 rpm

Power = torque*RPM: More torque at low speeds Runs at higher RPM

Auto-ignition temperature: 210°C 246°C

Diesel Petrol

CO2 emission:

More than petrol. Diesel fuel produces approximately 13% more CO2 gas per litre of fuel burned, compared to petrol engines.

Lower than diesel.

Viscosity:increases at lower temperatures

No change

US Consumption (2006): 50 Billion gallons 148 Billion gallons

High-Speed Diesel Fuel

• High-speed diesel fuel has a higher cetane number than fuel for low-speed, stationary engines.

• The cetane number of high-speed diesel fuel is typically around 50. Cetane numbers for diesel fuel range from 40 to 55.

• High-speed diesel fuel is also classified as 1D or 2D, indicating pour point and viscosity.


• 1D and 2D Fuels: Pour point refers to the minimum temperature at which the fuel will flow, while viscosity measures its resistance to flow. – A 1D fuel, which has a lower pour point and

less viscosity, works better in low temperatures.

– A 2D fuel, with a higher pour point and more viscosity, is more suitable under warmer conditions.


• More BTUs: 2D fuel maintains its lubricating qualities at high speeds. It also contains more BTUs (British Thermal Units, a measure of power), produces more power per gallon and reduces consumption.

• The fuel requirements for a specific diesel engine typically appear in the owner's car manual

AdditivesPremium diesels may or may not have higher cetane, depending on the supplier. Additives are often used to improve :-•CN •Lubricity•Detergents to clean the fuel injectors and minimize carbon deposits •Water dispersants•Other additives depending on geographical and seasonal needs.

Additives

• Additives. Alkyl nitrates (principally 2-ethylhexyl nitrate) and di-tert-butyl peroxide are used as additives to raise the cetane number.

• Alternative fuels. Biodiesel from vegetable oil sources have been recorded as having a cetane number range of 46 to 52, and animal-fat based biodiesels cetane numbers range from 56 to 60.

• Dimethyl ether is a potential diesel fuel as it has a high cetane rating (55-60) and can be produced as a biofuel.

Alkanes, Alkenes & Alkynes

• Alkanes, alkenes and alkynes are simple hydrocarbon chains with no functional groups. Alkanes are identified because the carbon chain has only single bonds.

• Common alkanes include • Methane (natural gas), • Propane (heating and cooking fuel), • Butane (lighter fluid) and • Octane (automobile fuel).

Isooctane’s Structural FormulaC8H18

Butane's Structural Formula C4H10

Benzene’s Structural Formula

C6H6

Structural Formulae of Benzene and Toluene

Naphthalene's Structural Formula

C10H8

ice fuels basic - copy

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