I.C. ENGINES
LECTURE NO: 11
(21 Apr 2014)
Air Required to Burn Fuel
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1 kg of H requires 8 kg O
1 kg of C requires 2.66kg O
1 kg of S requires 1kg O
1 kg of O is contained in 4.35kg air
Problem No 1
• A certain petrol consists of 84 % C and 16 % H
by mass. What mass of air is required for
complete combustion?
Problem No 1
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Data
Carbon
=
84 % C by mass
Hydrogen
=
16 % H by mass.
To Find
Mass of air is required for complete combustion?
Solution
O required to burn 1 kg of C = 2.66 kg
O required to burn 0.84 kg of C = 0.88 x 2.66 kg
Problem No 1
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Solution
O required to burn 1 kg of H = 8 kg
O required to burn 0.16 kg of H = 0.16 x 8 kg
Therefore
O required = (0.84 x 2.66)kg + ( 0.16 x 8)kg
Therefore
• Air required = (0.84 x 2.66)kg + ( 0.16 x 8)kg x 4.35 kg
• 15 .268 kg
Problem No 2
• A fuel oil contains, by mass, 87 % C, 11 % H, 1
% S and 1 % O. What mass of air is required
for complete combustion?
Problem No 2
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Data
Carbon
=
87 % C by mass
Hydrogen
=
11 % H by mass
Sulphur
=
1 % S by mass
Oxygen
=
1 % O by mass
To Find
Mass of air is required for complete combustion?
Solution
O required to burn 1 kg of C = 2.66 kg
O required to burn 0.87 kg of C = 0.87 x 2.66 kg
Problem No 2
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Solution
O required to burn 1 kg of H = 8 kg
O required to burn 0.11 kg of H = 0.11 x 8 kg
O required to burn 1 kg of S = 1 kg
O required to burn 0.11 kg of S = 0.11 x 1 kg
Fuel oil supplies 0.01 kg of O /kg of fuel
Actual mass of O required = 3.204 kg - 0.01kg
= 3.194 kg
• Mass of Air required = 3.194 x 4.35 kg
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= 13.894 kg
• Air fuel ratio by mass is 13.894 to 1
Problem No 3
• What is mass of air is required to burn
complete 1 kg of benzole C6 H6 ?
Problem No 3
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Data
Benzole C6 H6
To Find
Mass of air is required for complete combustion?
Solution
Molecular mass of Benzole C6 H6
(12 x 6) + ( 1 x 6) = 72 + 6 = 78
% of C by mass = (72/ 78) x 100 = 92
% of H by mass = (6/ 78) x 100 = 8
Problem No 3
• O required C = 0.92 x 2.66 = 2.45 kg
• O required H = 0.08 x 8 kg = 0.64
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Total = 3.09 kg
• Air required = 3.09 x 4.35 kg
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= 13.4 kg
• Air fuel ratio by mass is 13.4 to 1
Problem No 4
• What is mass of air is required to burn
complete 1 kg of ethyl alcohol C2 H6O ?
Problem No 4
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Data
ethyl alcohol C2 H6O
To Find
Mass of air is required for complete combustion?
Solution
Molecular mass of ethyl alcohol H2 C6O
( 12 x 2) + (1 x 6) + ( 16 x 1) = 46
% of C by mass = (24/ 46) x 100 = 52
% of H by mass = (6/ 46) x 100 = 13
% of O by mass = (16/ 46) x 100 = 35
Problem No 4
• Total = 2.423 kg
• The fuel supplies 0.35 kg of O per kg of fuel
• = 2.423 - 0.35 = 2.073 kg
• Air required = 2.073 x 4.073 kg
= 9 kg
• Air fuel ratio by mass is 9 to 1
LUBRICATION SYSTEM
LUBRICATION SYSTEM
• Lubrication is the introduction of a substance,
called a lubricant (e.g. oil to create an oil film,
between two moving contact surfaces, to reduce
friction.
• This reduction of friction greatly reduces the
wear of the surfaces and thus lengthens their
service life.
• It also reduces the energy required for the
movement.
• Lubrication is important in all moving parts of the
vehicle but the engine has the greatest need.
LUBRICATION SYSTEM
• Under a microscope, even the smoothest
engine components have a surface that looks
very rough.
• If these surfaces made contact they would rub
together, overheat and destroy themselves.
• To prevent this happening, engines have a
lubrication system that pumps or drips a
constant supply of oil on all the moving metal
components.
LUBRICATION SYSTEM
OTHER FUNCTIONS
• Although the BASIC FUNCTION of a lubricant is to
reduce friction and wear.
• It carries off generated heat
• It helps to form a gas-tight seal between piston rings
and cylinders.
• It also carries away harmful combustion waste
products.
• Lubrication helps to control corrosion by coating parts
with a protective film.
• A detergent added to the lubricant helps to removes
sludge deposits.
LUBRICATION SYSTEM
The Lubrication System (Reasons for)
• To separate the moving
parts of the engine, to
prevent excessive wear and
heat build up caused by
friction, without this, the
engine components would
get so hot, they could start
to melt and stick to
together (seized engine)
• To protect the engine
components from acids
formed from the burning of
the fuel.
Purpose of Lubrication System
•Lubricate
Reduces Friction by creating a thin film(Clearance)
between moving parts (Bearings and journals)
Purpose of Lubrication System
•Seals
The oil helps form a gastight
seal between piston rings
and cylinder walls
(Reduces Blow-By)
Internal oil leak (blow-by) will
result in BLUE SMOKE at the
tale pipe.
Purpose of Lubrication System
•Cleans
As it circulates through the engine, the oil picks up metal
particles and carbon, and brings them back down to the pan.
Purpose of Lubrication System
•Cools
Picks up heat when moving through the engine and then
drops into the cooler oil pan, giving up some of this heat.
Purpose of Lubrication System
•Absorbs shock
When heavy loads are imposed on the bearings, the oil
helps to cushion the load.
•Absorbs Contaminants
The additives in oil helps in absorbing the contaminants
that enter the lubrication system.
VISCOSITY
Viscosity is a measure of oil’s resistance to flow.
•A low viscosity oil is thin and flows easily
•A high viscosity oil is thick and flows slowly.
•As oil heats up it becomes more
viscous (Becomes thin)
VISCOSITY
•If the oil is too thin(has very low viscosity) it will be forced
out from between the moving parts, resulting in rapid wear.
•If the oil is too thick(has very high viscosity) it will flow very
slowly to engine parts, especially when the engine and the oil
are cold, resulting in rapid wear.
Viscosity Index is the measure of how much the viscosity of
an oil changes with temperature. (20 W)
Viscosity number is set by SAE (Society of Automotive
Engineers)
VISCOSITY
•Single viscosity oils SAE 5W, SAE 10W (Winter) and
SAE 20, SAE30 … (Summer)
•Multiple viscosity oils SAE 10W-30.
This means that the oil is same as SAE 10W when cold
and SAE30 when hot.
The higher the number the higher the viscosity(thickness) of oil.
Properties of oil
•Corrosion and Rust Inhibitor: Displaces water from
metal surfaces, to prevent corrosion.
•Foaming Resistance: Rotating crankshaft tends to cause
bubbles (Foam) in the oil and bubbles in oil will reduce the
effectiveness of oil to lubricate.
•Synthetic Oils: Made by chemical process and do not
necessarily come from petroleum.
Service Rating of Oil
SA, SB, SC, SD,…..SJ
SA and SB oils are not recommended for use in today’s
Automobile engines.
A.P.I. Ratings
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SA Straight mineral oil no additives.
SB 1930’s motor oil with some detergent.
SC 1950’s oil more additives.
SD 1960’s enter multi-viscosity oils.
SE 1970’s emission controls make heat is problem.
SF 1980’s improves fuel economy.
SG Late 1980’s wider viscosity ranges.
SH 1990’s great stuff.
SJ Late 1990’s
SL 2000’s
SM Current
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Motor Oil Characteristics
•Oil Viscosity/SAE
•Ease which oil flows
•S.A.E Rating (Society of Automotive
Engineers)
•Service Rating/API
•Oil Quality
•A.P.I. (American Petroleum Institute)
•Other Fluids & Lubricants
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Oil Viscosity Chart
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Parts
Oil Pumps Driven by camshaft, crankshaft (Rarely
rebuild by an auto technician)
•Rotor Pump(Two star shaped rotors
pumps the oil)
•Gear oil Pump
Parts
Oil Pan
Stores the oil and helps in cooling the oil
Pan gasket splits if over tightened.
Parts
Pressure Relief Valve to prevent the buildup of high
Pressure (Causes the oil filter to bulge, but not a common
problem).
Good oil pressure is
40-60 psi
Parts
Oil Pressure Indicator
•Light or a Gauge
The light turns on or gauge reads low when
the pressure drops below 10psi.
•Good oil pressure is 40-60 psi.
Common causes of low oil pressure are:
•Low oil level
•Worn out pump
Low oil pressure Safety system will shuts down the car by
cutting the ignition System(Spark).
Parts
Oil Filter filters the oil
Some particles are too small for the filter Element(paper
in the filter ) to trap.
Parts
Oil Galleries
Deliver the oil to top
end and returning it
To the oil pan.
Parts
Positive Crankcase ventilation Valve
•Pollution prevention
•Blow-by back into the intake
•Prevent sludge in the engine.
Parts
Oil Pressure sending unit electrically sends the
signal to the Light or Gauge mounted on the dash.
If the wires get shorted the light will come on or
the gauge will read high.
OIL CHANGE
•Every 5000Km
•3 months
Ignoring regular oil change intervals will shorten
engine life and performance.
Selecting Motor Oil
• Pick proper viscosity as
recommended by
manufacturer.
• Pick proper service
rating as recommended
by the manufacturer.
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Automatic Transmission Fluid
(ATF)
• Has red color to
identify it from motor
oil.
• Several kinds:
• Dexron/Mercon
• Type FA
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Gear Lube
• Used in manual
transmissions and
differentials on rear
drive cars.
• Heavy viscosity 90W.
• Looks like motor oil but
smells real bad!
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Chassis Grease
• Conventional type of
petroleum grease.
• Grease steering and
suspension parts.
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Other Types of Grease
• Lithium grease or white
lube.
• Used on mis. parts.
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Other Lubricants
• WD-40 is a light oil
with graphite.
• Liquid wrench is a
penetrating oil for dry
and rusted bolts.
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Non Petroleum Lubricants
• Silicone spray is for
rubber and plastic
parts. Doesn’t work well
on metal.
• Brake cleaner is like dry
cleaning fluid. Cleans
off grease and
evaporates in seconds.
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Other Useful Fluids
• Carburetor choke and
throttle body cleaner.
Contains toluene.
• Starting fluid. Contains
ether.
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Oil Changes
• Oil Change
frequency:
• Every 25 -30
hours.
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Oil Contamination
• Blow-by gases add raw
gasoline and water to the
oil causing deterioration.
• Excessive heat can cause
thermal breakdown.
• Excessive cranking can
dilute oil with gasoline.
• Cooling gasket leaks will
ruin oil causing sludge.
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Things That Make Oil Deteriorate
Faster
• Short distance driving.
(which is most trips)
• Extensive idling.
• Cold weather operation.
• Trailer towing.
• Excessive heavy loads
• Dirty and dusty
conditions.
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Proper Oil Disposal
• Waste motor oil is a
controlled waste.
• Be sure to properly
dispose of.
• Oil filters too!
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ENGINE PERFORMANCE
PARAMETERS
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Indicated Thermal Efficiency
Brake Thermal Efficiency
Mechanical Efficiency
Volumetric Efficiency
Relative Efficiency
Mean Effective Pressure
Mean Piston Speed
Specific Power Output
Specific Fuel Consumption
ENGINE PERFORMANCE
PARAMETERS
• Inlet Value Mach Index
• Fuel Air Ratio
• Calorific Value of the Fuel
INDICATED THERMAL EFFICIENCY
• Indicated thermal efficiency is the ratio of
energy in the indicated power ip, to the input
fuel energy in appropriate units
ηith =
ip [kJ/s]
energy in fuel per second [kJ/s]
ηith =
ip [kJ/s]
mass of fuel/s x calorfic value of fuel
BRAKE THERMAL EFFICIENCY
• Brake thermal efficiency is the ratio of energy
in the brake power bp, to the input fuel
energy in appropriate units
ηbth =
bp [kJ/s]
energy in fuel per second [kJ/s]
ηith =
ip [kJ/s]
mass of fuel/s x calorfic value of fuel
MECHANICAL EFFICIENCY
• Mechanical efficiency is the ratio of bp
(delivered power) to indicated power ( power
provided to the piston)
ηm = bp [kJ/s] =
bp
ip [kJ/s] bp+fp
fp = ip - bp
VOLUMETRIC EFFICIENCY
• Volumetric efficiency is the ratio actual
volume flow rate of air into the intake system
to the rate at which the volume is displaced by
the system
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ηv = ma / ρa
V disp N/2
ρa = Inlet density
SI = 80 to 85 %
CI = 85 to 90 %
RELATIVE EFFICIENCY OR EFFICIENCY RATIO
• Relative efficiency is the ratio thermal
efficiency of actual cycle to ideal cycle
.
ηrel = Actual Thermal Efficiency
Air Standard Efficiency
MEAN EFFECTIVE PRESSURE
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Ip
pim
L
A
N
n
K
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ip =
pim LAnK
60 x 1000
= Indicated power [kW]
= Indicated mean effective pressure [N/m2 ]
= Length of the stock [m]
= Area of the piston [m2]
= Speed in revolutions per minute [rpm]
= Number of stock N/2 & N
= Number of cylinder
bp = pbm LAnK
60 x 1000
MEAN PISTON SPEED
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Sp = 2LN
L
N
= Length of the stock [m]
= Crank Speed in revolutions per minute
[rpm]
SPECIFIC POWER OUTPUT
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Ps = bp/A
= constant x pbm x Sp
SPECIFIC FUEL CONSUMPTION
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• sfc = Fuel Consumption per unit Time
Power
PROBLEMS
PROBLEM NO 1
• The Cubic capacity of a four stroke over
square spark ignition engine is 245 cc. The
pver square ratio is 1.1. The clearance volume
is 27.2 cc. Calculate:Bore
Stroke
Compression Ration
SOLUTION
• Vs =
(π/4) d2 L
• L =
d/1.1
• Compression Ratio r
=
Vs + Vc
Vc
PROBLEM NO 2
• The Mechanical effencicy of a single cylinder
four stroke engine is 80 %. The frictional
power is esitmated to be 25 kW. Calculate:Ip
bp
SOLUTION
• ηm =
bp/ip
• fp =
ip - bp
PROBLEM NO 3
• A 42.5 kW has a mechanical efficency of 85%.
Find the ip and fp. If the frictional power is
assumede to be constant with load, What will
be mechanical efficiency at 60 % of the load?
SOLUTION
• ηm =
bp / ip
• fp =
ip – bp
• ηm =
bp / (bp + fp)