# I.C. ENGINES LECTURE NO: 11 (21 Apr 2014).

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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 = 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 = x 8 kg Therefore O required = (0.84 x 2.66)kg + ( 0.16 x 8)kg Air required = (0.84 x 2.66)kg + ( 0.16 x 8)kg x 4.35 kg 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 = 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 = x 8 kg O required to burn 1 kg of S = 1 kg O required to burn 0.11 kg of S = x 1 kg Fuel oil supplies 0.01 kg of O /kg of fuel Actual mass of O required = kg kg = kg Mass of Air required = x 4.35 kg = kg Air fuel ratio by mass is 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) = = 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 = x 8 kg = 0.64 Total = 3.09 kg Air required = 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 = kg The fuel supplies 0.35 kg of O per kg of fuel = = kg Air required = x 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 SA Straight mineral oil no additives.
SB ’s motor oil with some detergent. SC ’s oil more additives. SD ’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 ’s great stuff. SJ Late 1990’s SL 2000’s SM Current

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

Oil Viscosity Chart

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 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.

Automatic Transmission Fluid (ATF)
Has red color to identify it from motor oil. Several kinds: Dexron/Mercon Type FA

Gear Lube Used in manual transmissions and differentials on rear drive cars. Heavy viscosity 90W. Looks like motor oil but smells real bad!

Chassis Grease Conventional type of petroleum grease.
Grease steering and suspension parts.

Other Types of Grease Lithium grease or white lube.
Used on mis. parts.

Other Lubricants WD-40 is a light oil with graphite.
Liquid wrench is a penetrating oil for dry and rusted bolts.

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.

Other Useful Fluids Carburetor choke and throttle body cleaner. Contains toluene. Starting fluid. Contains ether.

Oil Changes Oil Change frequency: Every hours.

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.

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.

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/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
ip = pim LAnK 60 x 1000 Ip = 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 & N K = Number of cylinder bp = pbm LAnK

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

Important definitions
Brake Power [B.P]: It is the power developed by the engine at the output shaft. Where, N = Speed of the crank shaft in rpm. T =Torque applied on the brake drum due to load “W”, (N-m) R = Radius of the brake drum (m) T = W x R kg-m = 9.81 x W x R N-m

Frictional Power [F.P]: It is the difference between the indicated power and the brake power.
F.P = [I.P – B.P] kW , Mechanical Efficiency [ηmech ]: It is the ratio of the brake power and the indicated power.

Indicated Power [I.P]: It is the power developed inside the IC engine cylinder
Where, n = No. of working cycles/ min. n = N/2, for 4 stroke engine = N, for 2 stroke engine L = Stroke length (m), D = Bore diameter (m) Pm = Indicated mean effective pressure (N/m2) A = Area of the cylinder, ,

Brake thermal Efficiency [ηbth ]: It is the ratio of
the brake power to the heat supplied by the fuel. Indicated thermal Efficiency [ηith ]: It is the ratio of the indicated power to the heat supplied by the fuel. Where, mf = mass of the fuel supplied (kg/hr) CV = Calorific Value of the fuel (kJ/kg)

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)