Basic Electronics for diploma students as per technical education Kerala Syll...
Ice fuels basic
1. 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
2. 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
5. FUELS
FRACTIONS BOILING RANGE NO OF CARBON
ATOMS
USES
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
6.
7. 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.
14. 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.
15. 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.
19. 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
20. 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
21. 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.
22. 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 advance
o Medium octane: Retard ignition or starting
combustion later in compression stroke.
24. 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.
25. 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.
26. 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.
27. 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.
28. 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.
29. 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.
30. 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.
32. 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.
34. 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.
35. Definition Cetane Number (CN)
• 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.
36. Definition Cetane Number (CN)
• 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.
37. 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.”
38. 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-methyl-
napthalene, until a blend is found for which ignition
occurs at top dead center.
39. 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.
40. 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
41. 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.
•
42. 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
43. 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
44. 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.
45. High-Speed Diesel Fuel
• 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.
46. High-Speed Diesel Fuel
• 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
47. Additives
Premium 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.
48. 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.
49. 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).
