Lecture 3 fp lecture notes engine2

Roger C. Montepio

Flywheel – absorb the violent thrust of power stroke and then release the energy back to the crankshaft

- provide additional power to the engine to run smoothly and helps overcome increased load

- Contributes uniform rotation of crankshaft during intervals when it is not receiving energy from piston

Lubrication system – provides a constant supply of oil to the engine

- to lubricate and cool the moving parts

Engine Accessory SystemREVIEW

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Fuel system – supplies the engine with the properly proportioned fuel and air mixture-regulates the amount of the mixture supplied to the engine to control engine speed and power output

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Ignition system – ignites the fuel and air mixture in the combustion chamber at the precise moment needed

Cooling system – removes the excess heat from the engine, generated by combustion


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Valve train/system

-Operates the valves (intake and exhaust valves)-Operates the valves in timed sequence-Valve construction (L-head and in-head type)

L-head constructionMechanisms consist of 1) Small gears on

crankshaft, 2)half time or cam gear, 3)cam, 4)tappet or short push rod

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Parts of valve system

-Raised piece on the camshaft called the camlobe

-function of valve spring closes the valve after it has been opened and to hold it tightly closed against its seat

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Timing gears or chain

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Valve in-head construction

-Valves are of the poppet or mushroom type-consist of flat head and stem-flat head has beveled edge called the face-beveled edge found in the cylinder block or head called the valve seat-seat angle usually 45˚, 30˚ angle is frequently used for intake valve

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Parts of engine valves head Lip/edge Face Shoulder Stem Lock groove

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When can we say that the Valve is correctly timed

if a valve starts to open and then closes at specified time wrt the crankshaft and piston positionValves action is gradual, that is , the valve is pushed slowly and it open and close.This sequence are determined by:1. Timing of crankshaft and camshaft gears2. Shape of the cam3. Tappet or rocker arm clearance

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Valve timing

Two revolution crankshaft = 4-stroke completes the cycle (Intake, Compression, Power, Exhaust)Timing gears are arranged to allow 2-revolution crankshaft for each revolution of the camshaft

Engine operate efficiently only if it is correctly timed

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Range of operation and cam shape

Range of operation – number of degrees through w/c the crank rotates from the point where the valve starts to open to the point where it is just completely closed

- 235 to 240 degrees- determined by:

1. camshaft shape (if angle of action and cam lobe height/lift are greater and longer – wide range of operation)

2. valve clearance (too much – decrease the range of operation)

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Valve clearance- space allowed between the end of the valve stem and

rocker arm (In-head type)- space allowed between the valve stem and the

tappet (L-head type)

Too much valve clearance would produce a very pronounce noise

Type Intake ExhaustAuto engine 0.006-0.012 inch 0.010-0.020 inchTractor engine 0.010-0.020 inch 0.012-0.030 inch

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What are the effects of incorrect valve timing?

- longer time of valve opening, would results to a generation of more power and operate efficiently

- short time (vice versa)- high-speed engine closes as much as 45˚ to

60˚ after BDC

Incorrect intake valve timing

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What are the effects of incorrect valve timing?

- earlier time of valve opening, results to a more satisfactory, it gives:1. more power, 2. run cooler, 3. uses less fuel, and 4. better cleaning of cylinder

- too late time - overheating- most engine open 45˚ before BDC

Incorrect exhaust valve timing

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Fuel Supply and Carburetion System

In gasoline engine, fuel is admitted into the cylinder of the engine by the carburetion process.

Carburetion process takes place in the carburetor

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Carburetors

Purpose of the carburetor is to produce a mixture of fuel and air on which the engine can operate

Supply definite proportion / metered to suit fuel requirements of the engine

Air-fuel ratio: 1:2 ratio when the engine is started1:9 ratio during cruising/traveling speed

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Carburetors

Idling speed- speed of the engine in which butterfly valve partially closed, only a limited amount of air is admitted and only idling jet operates to supply minimal amount of fuel

Must produce economical fuel consumption and smooth engine operation over a wide range of speeds

Requires complicated device rather than a simple mixing valve; price is very important!

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Venturi (nozzle)

• Use force of atmospheric pressure and artificially created low pressure area to mix fuel and air

• Use a venturi nozzle to lower air pressure in carburetor to create suction to “pull” fuel into air

Venturi (nozzle)

P+1/2 V2 = ConstantBernoulli Principle:

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Venturi-type Carburetor

Ref. Obert

Constant level is maintained in bowl -as float moves down, valve stem moves down, allowing more fuel into bowl, float moves up and closes valve

Valve StemFuel Inlet

Float

Metering Orifice

Throttle Plate

Air/Fuel Mixture To Engine

Choke Plate

Fuel Nozzle

Inlet Air

Bowl

Atomized Fuel

Venturi

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Flo-Jet Carburetor

• Fuel tank is above carburetor

• Fuel is fed directly to carburetor by gravity

• Vent connected to float (fuel chamber or cup) …..Why the vent?

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Flo-Jet Carburetor

Fuel from tank

Air flow

Air-fuelmixture

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Pulsa-Jet Carburetor

• Incorporates a diaphragm type fuel pump and a constant level fuel chamber

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Pulsa-Jet Carburetor Operation

Intake stroke of piston creates a vacuum in carburetor elbow

Pulls cap A and pump diaphragm B inward and compresses spring

Vacuum thus created on “cover side” of diaphragm pulls fuel up suction pipe S into intake valve D

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When engine intake stroke is complete, spring C pushes plunger A outward

Gasoline in pocket above diaphragm to close inlet valve D and open discharge valve E

Fuel is then pumped into fuel cup F

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Venturi in carburetor is connected to intake pipe I which draws gasoline from fuel cup F

Process is repeated on the next stroke, keeping the fuel cup full

Since fuel cup level is constant, engine gets constant air-fuel ratio

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Fuel Injection in CI Engines

Fuel injection is a critical process in CI enginesInjection pump use to deliver individual fuel injections via high strength lines to injectors.

Classed of injection of fuels into the engine cylinder1. directly 2. indirectly

Basic objectives - to atomize and inject the fuel- provide right quantity at right time

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Modern Fuel Injection System

Electronic injection systemElectronic control unit controls the timing and duration of injections by opening solenoid valvesInjection timing and duration can be customized to meet various objectives, including maximizing power or fuel economy or minimizing exhaust emissions

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Fuel injection system components

Gravity feed injection pump of a diesel engineDay-tankStop cork/fuel valveFuel linePrimary and secondary Fuel filterCam followerTransfer pump, Injection pump and injector unitHigh pressure fuel lineNozzle

INJECTOR UNIT- fuel injector and meterer at the same time

NOZZLE - atomizer

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Injection pump and unit injector

Injection pumpConsidered as the heart of diesel engineDelivers the needed amount of fuel at proper time and formOperates at high hydraulic pressure at ranges from 70 to 700 kg/cm2

Basic parts:1. Plunger2. Barrel It operates very much alike that of the syringe

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Methods of controlling the amount of fuel

Depends upon the length of plunger strokeDepends on the manner of bypassing the excess fuel from the barrel

The variation of the plunger stroke and by-passing of fuel from the barrel is acted on by the GOVERNOR

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Governing system

GOVERNOR a device that controls the speed of the engineVaries the air or fuel supply requirement of the engine

Types of governorHydraulic /pneumatic controlledMechanically controlled

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GOVERNOR

Three physical principles involved in which the governors will workCreating vacuum – pneumatic controlled governorCreating hydraulic pressure – hydraulic controlled governorCreating centrifugal force – mechanical controlled governor

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Mechanical Governor

Works alike the principle of the slingConsists of flyweights, sleeve, yoke, and return spring

The mechanical governor drive gear engages with the engine camshaft. The drive gear turns the entire governor assembly. The flyweights move outward from the drive shaft axis as the governor assembly turns. There is then a chain of movements to the sleeve, yoke, control rack and finally with the plunger w/c is a part of the injection pump that controls the amount of fuel for the engine.

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Lubrication system

The lubrication system

supplies a constant supply of oil to all moving parts constant supply of fresh oil is to minimize wear, flush

bearing surfaces clean remove the localized heat that develops between

moving parts as a result of friction oil that is supplied to the cylinder walls helps the

piston rings make a good seal to reduce blowby

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Ignition system

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Purpose of Lubrication

a. Oil as a Lubricant.

primary function of engine oil is to reduce friction between moving parts (lubricate)

Without lubrication??????????

Lubrication system

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Without lubricationaddition to wasting engine power, creates destructive heat and rapid wear of parts or

(melts)greater energy required to overcome that friction

Purpose of Lubrication

b. Oil as a Coolant. also serves to remove heat from the friction points

Lubrication system

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1) How Oil Lubricates

(a) oil is fed to the surface it forms a film, preventing the moving part from actually touching the surface

(b) As a part rotates, the film of oil acts as a series of rollers

It is important that sufficient clearance be allowed between the part and the bearing; otherwise the film might be too thin.

It also is important that the clearance not be too large between rotating parts and their bearings – cause bearing failure

Lubrication system

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How Oil Lubricates

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(2) Oil Contamination Lubrication

systemOil does not wear out, but it does become contaminatedHow oil becomes contaminated??????

foreign matter enters through the air intake,

will pass by the piston rings

enter the crankcase

CASE 1

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combined with foreign matter entering through the crankcase breather pipe mixes with the oil, forced into the bearings, Water will emulsify with the oil to form a thick sludge

crankcase

(2) Oil Contamination Lubrication

systemCASE 2 products of combustion is WATER,

condense in the crankcase

will seep by thepiston rings as steam

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How oil becomes contaminated??????

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Lubrication system(2) Oil Contamination

What happen when the oil, mixed with the contaminants? loses its lubricating qualitiesBecomes acidic

Engine oil must be changed periodically to prevent contaminated oil from allowing excessive wear and causing etching of bearings

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How to control engine contamination

a) Control engine temperature;

b) The use of oil filters

c) An adequate crankcase ventilation system

d) The use of air intake filters

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Oil Dilution Engine oil thins out when mixed with gasoline,

causing a dramatic drop in its lubricating qualities Some of the causes of oil dilution are the

following:

(a)Excessive use of a hand choke(b)defective ignition system(c)a malfunctioning thermostat, or an engine

that is operated for short durations only,

Lubrication system

Roger C. Montepio

American Petroleum Institute (API) Rating System.Lubrication

systemThe API system for rating oil classifies oil according to its

performance characteristics (quality). The higher rated oils contain additives that provide maximum protection against rust, corrosion, wear, oil oxidation, and thickening at high temperatures.

six oil classifications for gasoline engines (SA, SB, SC, SD, SE, and SF)four classifications for diesel engines (CA, CB, CC, and CD).

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API DesignationsLubrication

system(a)SA (Utility Gasoline Engines). Adequate for utility engines subjected to light loads, moderate

speeds, and clean conditions. SA-rated oils generally contain no additives.

(b) SB (Minimum Duty Gas Automotive)Adequate for automotive use under favorable conditions (light loads, low speeds, and moderate temperatures) with relatively short oil change intervals. SB-rated oils generally offer minimal protection to the engine against bearing friction, corrosion, and oil oxidation.

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system(c) SC. Meets all automotive manufacturers' requirements for vehicles manufactured from 1964 to 1967.

(d) SD. Meets all automotive manufacturers' requirements for vehicles manufactured from 1968 to 1970. SD oil offers additional protection over SC oils, necessary with the introduction of emission controls.

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(e) SE. Meets all automotive manufacturers‘ requirements for vehicles manufactured from 1971 to 1979.


system

(f) SF. Meets all automotive manufacturers' requirements for vehicles manufactured after 1980. SF oil is designed to meet the demands of the small, high-revving engines made necessary by the trend toward smaller vehicles. An SF oil can be used in all automotive vehicles.

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Viscosity and Viscosity Measurement.

Lubrication system

viscosity of an oil refers to its resistance to flow

When oil is hot, it will flow more rapidly than when it is cold In cold weather, oil should be thin (low viscosity)

to permit easy flow In hot weather, oil should be heavy (high

viscosity) to permit it to retain its film strength

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Viscosity Measurement

Lubrication system

Oils are graded according to their viscosity by a series of Society of Automotive Engineers (SAE) numbers. The viscosity of the oil will increase progressively with the SAE number.

SAE 5 oil would be very light (low viscosity) SAE 90 oil would be very heavy (high viscosity) oil used in gasoline engines generally ranges from SAE 5 (arctic use/colder region) to SAE 60 (desert use).

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Lubrication system

The viscosity number of the oil is determined by heating the oil to a predetermined temperature and allowing it to flow through a precisely sized orifice while measuring the rate of flow. The faster an oil flows, the lower the viscosityThe testing device is called a viscosimeter. Any oil that meets SAE low temperature requirements will be followed by the letter W. An example would be SAE 10W.

Viscosity Measurement

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Multiweight Oilsare manufactured to be used in most climates

because they meet the requirements of a light oil in cold temperatures and a heavy oil in hot temperatures

viscosity rating will contain two numbers An example of this would be 10W-30 An oil with a viscosity rating of 10W-30 would be as thin

as a 10W-weight oil at 0° F (-17.7° C) and as thick as a 30-weight oil at 210° F (99° C).

Lubrication system

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Detergent OilsOil contain additives that help keep the engine clean by

preventing the formation of sludge and gumAll SE and SF oils are detergent oils

Lubrication system

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Oil Pumps

Lubrication system

mounted either inside or outside of the crankcase,depending on the design of the engine They are usually mounted so that they can be driven by a worm or spiral gear directly from the camshaftOil pumps generally are of: the gear the rotor type.

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Lubrication systemOil Pumps

Rotor Type Oil Pump The rotor oil pump makes use of an inner rotor with lobes that match similarly shaped depressions in the outer rotor

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Gear Type Oil Pump Gear-type oil pumps have a primary

gear that is driven by an external member, and which drives a companion gear

Oil Pumps

Lubrication system

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Oil Strainer and Pickup

Lubrication system

Strainer/ screen is usually a fine mesh bronze screen, located inthe oil sump on the end of the oil pickup tubeThe oil pickup tube is then threaded directly into the pump inlet or may attach to the pump by a bolted flange

A fixed-type strainer, like the one described, is located so that a constant supply of oil will be assured

The pickup is designed to float on top of the oil, thus preventing sediment from being drawn into the oiling system.

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Lubrication systemOil Strainer and Pickup figure

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Oil Filters.

Lubrication system

removes most of the impurities that have been picked up by the oil as it is circulated through the engine The filter is mounted outside the engine and is designed to be readily replaceableTwo basic filter element configurations: the cartridge-type the sealed cam-type

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Oil Filters.

Lubrication system

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Lubrication systemOil Filters.

(a) cartridge-type filter element fits into a permanent metal container The element is changed easily by removing the cover from

the container when this typeof filter is used

(b) sealed cam-type filter element is completely self-contained,consisting of an integral metal container and filter element.

This type of filter is screwed onto its base and is removed by spinning it off

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Filter Medium Materials

Lubrication system

most popular automotive filter mediums1. Cotton waste 2. resin-treated paper

They are held in place by sandwiching them between two perforated metal sheets

3. layers of metal that are thinly spaced apart for heavy-duty applications

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Filter Medium Materials

Lubrication system

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Filter System Configurations.

Lubrication system

Two-filter system configurationsthe full-flow system bypass system. Operation

(a)full-flow system the most popular in current automotive design All oil in a full-flow system is circulated through the filter before

it reaches the engine It incorporate a bypass valve in the oil filter to allow the oil topass through the element in the event it becomes clogged. This will prevent the oil supply from being cut off to the engine.

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(a)full-flow system


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(b) bypass system

diverts only a small quantity of the oil each time it is circulated and returns it directly to the oil pan after it is filtered.


Lubrication system

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Lubrication system

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Oil Coolers.

Lubrication system

be able to dissipate more heat from their oil than normal airflow can accomplishOil Temperature Regulator

used to prevent the oil temperature from rising too high in hot weather, and to assist in raising the temperature during cold starts in winter weather

The regulator makes use of the liquid in the cooling system

provides a more positive means of controlling oil temperature than does cooling by radiation of heat from the oil pan wells.

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Lubrication systemOil Temperature Regulator

made up of a core and a housingThe core through which the oil circulates is of cellular or bellows construction, built to expose as much oil as possible to the coolant that circulates through the housingattached to the engine so that the oil will flow through the regulator after passing through the pump

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Oil Cooler consist of a radiator through which air is circulated by movement of the vehicle, or by a cooling fan Oil from the engine is circulated through this radiator and back to the sump or supply tank

Lubrication system

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Lubrication system

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Oil Level Indicator The oil level indicator is usually of

a bayonet type consists of a small rod, known as

a dipstick, that extends through a tube into the crankcase

It is marked to show when the crankcase is full or, if it is low, how much oil is needed

Lubrication system

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Lubrication system

Pressure Regulator

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Pressure RegulatorThe oil pump will produce pressures in great excess

to those necessaryThis excess pressure, if uncontrolled, would cause

excess oil consumption due to flooded cylinder walls and leakage through oil seals

spring-loaded regulator valve is installed in the lubrication system to control pump pressure

Lubrication system

Roger C. Montepio

Lubrication systemTypes of Lubrication Systems

a. Splash System no longer used in automotive

engines, it is used in small equipment

engines Operation

dippers on the connecting rods enter oil in the crankcase with each crankshaft revolution, thus splashing the oil.

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b.Combination Splash and Force Feed System oil is delivered to some parts by means of splash and to other parts through oil passages, under pressure from a pump in the crankcaseThe main and the camshaft bearings are usually the items that are force fed while the connecting rods are fitted with dippers that supply oil to the rest of the engine by splash

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c. Force Feed Lubrication System more complete

pressurization of lubrication

oil is forced by the oil pump from the crankcase to the main bearings and the camshaft bearing

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all of the bearings are lubricated by oil under pressureincludes main bearings, rod bearings, camshaft bearings, and the complete valveprovides lubrication under pressure to the pistons

d.Full Force Feed Lubrication System

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Cooling systemCooling medium

(1)Liquid is the most popular coolant in automotive use cooling system provides the most positive cooling best for maintaining uneven engine temperature

(2) Air most practical for small vehicles and equipment because no radiator or hoses are requireddo not run at even temperatures and require extensive use of aluminum to dissipate heat.

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Cooling systemother sources of heat dissipation for the engine in addition to the cooling system

(1) The exhaust system dissipates as such, if not more, heat than the cooling system, although that is not its purpose

(2) The engine oil, removes heat from the engine and dissipates it to the air from the sump

(3) The fuel provides some engine cooling through vaporization

(4) A measurable amount of heat is dissipated to the air through radiation from the engine.

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Types of cooling systemCooling system

Air Cooling system Use air as a cooling medium Cooling effect is produced by means of fins or projections

on the walls of the cylinder

Common examples of air-cooled engine airplaneMotorcycleLawn mower, garden tractorSmall and medium diesel tractor

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Cooling systemTypes of cooling system

Advantages Lighter in weightSimpler in constructionMore convenient and less troubleNo danger of freezing in cold weather

Disadvantage Difficult to maintain proper cooling under all

conditions impossible to fully control cylinder temperatureUsually run a little hotter than water cooled engine

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Liquid Cooling system Use liquid as a cooling medium use in all types of engine

AdvantagesPlentiful and available anywhereabsorbs heat wellCirculates freely at all temperature between freezing to

boilingNo danger

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Liquid Cooling Systems

Lecture 3 fp lecture notes engine2

Engineering

Transcript of Lecture 3 fp lecture notes engine2