I.C. ENGINES

I.C. ENGINES

LECTURE NO: 11(21 Apr 2014)

Air Required to Burn Fuel

• 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• 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• 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• 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• 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• = 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• 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• Total = 3.09 kg• Air required = 3.09 x 4.35 kg• = 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• 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 SYSTEMOTHER 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

•LubricateReduces Friction by creating a thin film(Clearance) between moving parts (Bearings and journals)


•Seals

The oil helps form a gastight seal between piston rings and cylinder walls (Reduces Blow-By)

Internal oil leak (blow-by) willresult in BLUE SMOKE at thetale pipe.


•CleansAs it circulates through the engine, the oil picks up metalparticles and carbon, and brings them back down to the pan.


•CoolsPicks up heat when moving through the engine and thendrops into the cooler oil pan, giving up some of this heat.


•Absorbs shock

When heavy loads are imposed on the bearings, the oilhelps to cushion the load.

•Absorbs Contaminants The additives in oil helps in absorbing the contaminantsthat 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.

31

A.P.I. Ratings• 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

32

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

33

Oil Viscosity Chart

PartsOil 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 PanStores the oil and helps in cooling the oilPan 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.

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).

•Good oil pressure is 40-60 psi.

Parts

Oil Filter filters the oilSome 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 orthe gauge will read high.

OIL CHANGE

•Every 5000Km

•3 months

Ignoring regular oil change intervals will shorten engine life and performance.

43

Selecting Motor Oil

• Pick proper viscosity as recommended by manufacturer.

• Pick proper service rating as recommended by the manufacturer.

44

Automatic Transmission Fluid(ATF)

• Has red color to identify it from motor oil.

• Several kinds:• Dexron/Mercon• Type FA

45

Gear Lube

• Used in manual transmissions and differentials on rear drive cars.

• Heavy viscosity 90W.• Looks like motor oil but smells real bad!

46

Chassis Grease

• Conventional type of petroleum grease.

• Grease steering and suspension parts.

47

Other Types of Grease• Lithium grease or white

lube.• Used on mis. parts.

48

Other Lubricants

• WD-40 is a light oil with graphite.

• Liquid wrench is a penetrating oil for dry and rusted bolts.

49

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.

50

Other Useful Fluids

• Carburetor choke and throttle body cleaner. Contains toluene.

• Starting fluid. Contains ether.

51

Oil Changes

• Oil Change frequency:

• Every 25 -30 hours.

52

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.

53

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.

54

Proper Oil Disposal

• Waste motor oil is a controlled waste.

• Be sure to properly dispose of.

• Oil filters too!

ENGINE PERFORMANCE PARAMETERS

• 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

. ηv = ma / ρa

V disp N/2ρa = 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• ip = pim LAnK

60 x 1000Ip = Indicated power [kW]pim = Indicated mean effective pressure [N/m2 ]L = Length of the stock [m]A = Area of the piston [m2]N = Speed in revolutions per minute [rpm]n = Number of stock N/2 & NK = Number of cylinder• bp = pbm LAnK

60 x 1000

MEAN PISTON SPEED

• Sp = 2LN

L = Length of the stock [m]N = Crank Speed in revolutions per minute

[rpm]

SPECIFIC POWER OUTPUT

• Ps = bp/A = constant x pbm x Sp

SPECIFIC FUEL CONSUMPTION

• • 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:-

BoreStrokeCompression 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:-

Ipbp

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)

I.C. ENGINES

Documents