00 Astounding Customer Serviceburn, the liquid oil must be converted into a vapor. In today’s...

00 Astounding Customer Service

Introduction to OilburnersChapter 1

Chapter 1—Introduction to Oil Burners 1-3

IntroductionTo understand oilburners, we must

understand a bit about combustion. Com-bustion (burning) is the rapid combining ofoxygen and the elements in the fuel. Whenthe oxygen and the fuel combine, theycreate heat, light—and combustion gases.(We cover Combustion Theory in detail inChapter 7.) In order for something to burn,we need three things:

1. Oxygen from the air

2. A fuel that will easily combinewith the oxygen

3. Heat

Heating oil will not burn as a liquid. Toburn, the liquid oil must be converted intoa vapor. In today’s burners, this is done bybreaking the oil into tiny droplets (atomiz-ing it). Next, each droplet is heated until itturns into a vapor. Then, to accomplishclean combustion, the oilburner must mixthe oil vapor with the proper amount of air.The combined air and vapors are raised tothe temperature at which they will burn.Therefore, every oilburner must atomizethe oil, vaporize it, mix it with air, and heatthe mixture above its ignition point.

High pressure atomizingToday’s oilburners are called high-

pressure burners because they use a fuelpump to pressurize the oil to 100 poundsper square inch (PSI) or more. This pres-sure forces the oil through a nozzledesigned to break (atomize) the oil into the

small droplets that are vaporized andburned in suspension in the combustionarea. An electric spark, from electrodesinstalled close to the nozzle, supplies heatfor ignition. A fan supplies the air requiredfor combustion. Figure 1-1 shows how aburner operates, Figure 1-2 shows thecombustion process.

Figure 1-1:Oilburneroperation

Figure 1-2:Simplified schematicof the combustionprocess

Chapter 1Intro to Oil Burners

BurnerHousing

FuelLine

Air Turbulator(Spinner)

AirFan

Combustion Air AdjustableAir Damper

Combustion Air

Atmomization

Combustion Air

Fuel Storage

Recirculation

Recirculation

Spark

1-4 Introduction to Oil Burners

Figure 1-3:Flame retentionburners

Although the high-pressure burner hasbeen the mainstay of the industry almostfrom the beginning of the modernoilburner era, it has gone through manymodifications. An advantage of oil is thatparts are largely interchangeable, and thusit has been possible to keep many burnersoperating for years. In fact, some burnersmade in the 1930s are still operating in thefield because of interchangeable parts.

Flame retentionoilburners

In the 1960s, the current design foroilburners was introduced, which is calledthe flame retention burner. As the nameimplies, the flame is held very close to theface of the combustion head. The flame issmaller and more compact than with olderburners. This design’s primary characteris-

tics are its head or end-cone, highmotor operating speeds (typically

3450 RPM) and high combus-tion air static pressures.Figure 1-3 shows pictures ofmodern flame retentionburners.

area back toward it. This recirculation iswhat pulls the fire back toward the head,creating the flame retention effect. Theflame stabilizes near the burner head, hencethe name flame retention. The air swirlingis achieved with airflow shaping heads andturbulators and by running the burnermotor and fan at high speed.

The flame retention head produces moreair swirl and combustion air recirculationflow, which improves fuel-air mixing. Thispermits operation with less excess air andwith lower smoke levels. Cleaner and morestable combustion is produced and systemefficiency is typically 5 to 15 percent

The flame retention head provides amodified airflow pattern for radicallyimproved air-oil mixing. The basic idea isto produce a strongly swirling air patternthat recirculates combustion products formore complete mixing of fuel and air. Thisis called recirculation.

As the air rushes out of the end of theburner, it sucks air from the combustion


Air Pattern—Non-Flame Retention Burner

Air Pattern—Flame Retention Burner

RecirculationArea0-25 Velocity

Nozzle

Nozzle


higher than with older burners. SeeFigures 1-4 and 1-5.

Flame retention heads produce hotterflames because less excess combustionair is used than with non-flame retentionhead oilburners. Therefore, the combus-tion chamber construction materials andgeneral condition must be checkedcarefully whenever a high efficiency oil-burner is installed or serviced.

Construction of the high-pressureatomizing flame retention oilburners

The high-pressure retention headburners are precision-built and con-structed for durability and long service.Every high-pressure burner consists of a

Non-flame Retention Flame Retention(Turbulator or Choke) Head Burners

Percent CO2 7-9 11-13Percent Excess Combustion Air 50-100 20-30Bacharach Smoke Number 1-3 0-1Percent Flue Heat Loss (on cycle) 30 10-20

Figure 1-5:Difference in flamebetween a non-flame retentionburner and a flameretention burner

Figure 1-4:Comparisonof burnerperformance

motor, fan (C), fuel unit (A), ignitiontransformer or igniter (E), nozzle assembly(B & D), and a housing to which all ofthese parts are attached, as illustrated inFigure 1-6 on following page.

MotorThe electric motor drives the fan and the

fuel pump. The motor is manufactured inone of two designs, either a split phase typeor permanent split capacitor (PSC) typemotor. The motor is mounted to the housingof the burner by means of a two, three, orfour bolt flange. Removing these boltsallows easy removal of the motor and accessto the fan, which is attached to the motorshaft. In the event of motor failure, be sure


Non-Flame Retention Combustion Flame Retention Combustion

Target Wall

Combustion ChamberAir Vanes

Non-Flame RetentionCombustion Head Rear View Cast Iron

Combustion Chamber(Optional)

Combustion Air

Nozzle

CircumferentialSlots

Radial Vanes

Flame RetentionCombustion Head Rear View Stainless Steel

Combustion Air

Nozzle


Figure 1-6:Components of aflame retentionburner

Electrode Clamp

Electrode Spacer

NozzleAdapter

ElectrodeClamp Screw

Spider Spacer Ass’y.

Electrode Ass’y.

Nozzle LineBulkhead Ass’y.

Static PlateKnurled Nut



can cause a vibration and put an extra strainon the motor bearings. Any fan wheel thatdoes not slip off the motor shaft withoutneeding to be pried off with a screwdrivermust be removed with a wheel puller.

When replacing the burner fan, one mustpay strict attention to the rotation asindicated by the beveled blades. Also,remember that the burner manufacturer hasprovided the proper fan for the properamount of combustion air needed. Alwaysreplace it with one that has the samedimensions.

Fuel pumpThe fuel pump, also referred to as the

fuel unit, is driven by the motor. The pumpshaft is attached to the motor shaft by theburner coupling. The pump consists ofthree basic parts:

1. Strainer—to remove any foreignmatter from the oil before it enters thepump gears.

2. Pump—to lift the oil from the tankand deliver it to the regulating valve.

3. Regulating valve—to build up andmaintain the proper operating pressure foratomizing the oil. (See Chapter 4 for moredetails on Fuel Units.)

Ignition transformeror solid state igniter

The ignition transformer or solid-stateigniter (on new burners) provides a “stepup” from the line voltage of 120 volts toover 10,000 volts. The high voltage sparkproduced by these components jumpsacross the gap between the electrode tips.This spark provides the heat necessary tovaporize the atomized oil from the nozzleand achieve ignition. (See Chapter 9 formore information on Ignition Systems.)

to replace the motor with a new motor of thesame rotation, frame size, and revolutionsper minute (RPM). Figure 1-7 shows a motor,fan and coupling. The coupling attaches tothe motor shaft on one end and the pumpshaft on the other, taking power from themotor and transferring it to the pump.(Motors and couplings are covered inChapter 10.)

Multiblade fanand air shutter

A fan wheel within the burner housing isdriven directly by the motor shaft, andprovides the necessary air to supportcombustion. An adjustable air shutter onthe burner housing controls the volume ofair handled by the fan.

The oilburner fan, or blower wheel as itis often called, supplies the combustion airfor the flame. See Figure 1-8. They are ofthe squirrel cage type with beveled bladesthat must be kept free of dirt and lint. The

slightest amount of dirt willreduce the blade bevel and

reduce the amount of airdelivered. They areprecision balanced andevery effort must bemade to preventbending the wheel at itshub.

A blower wheel with abent or broken blade willbe out of balance. This

Figure 1-8: Oil-burner fan orblower wheel

Figure 1-7:Motor, fanand coupling



Figure 1-9:Adjustable headburner

The nozzle assemblyThe nozzle assembly also known as the

“drawer” assembly, or firing assembly,consists of the oil feed pipe (called thenozzle line), the nozzle, nozzle adapter,electrodes, transformer connections, and onsome burners, a flame retention ring. Theentire assembly is located in the air tube ofthe burner. An opening at the rear, top orside of the burner housing permits accessto and removal of the nozzle assembly.

Combustion headsThe combustion head (also referred to as

the turbulator, fire ring, retention ring, andend cone) creates a specific pattern of air atthe end of the air tube. The air is directedin such a way as to force oxygen into the

oil spray so the oil can burn. In order to doso, the combustion head must have theright amount of air delivered to it down theair tube from the fan, and the fuel pumpand nozzle must deliver the right amount offuel at the proper pressure.

Elements neededfor combustion

As we have discussed, the three elementswe need for combustion are oil, air, andspark. If we examine these three elementsone at a time we will see that:

• The amount of oil is based on theflow rate in gallons per hour (GPH) thatyou wish to burn. The size of the nozzleorifice (in GPH) and the pressure setting ofthe fuel unit determine the flow rate.

• The spark is the ignition source forthe fuel oil. With new advanced

control systems, the spark is onlyon for a short period of time(usually 25 seconds maxi-mum) at the beginning of therunning cycle of the burner.Once flame is established, theheat from the flame keepscombustion going. Continuingto have the spark on afterignition is accomplished willonly detract from the perfor-mance of the burner.

• The air is the key elementand the final adjustment of aburner. Air is introduced into theair tube by the fan through the airintake controlled by adjustableshutters or bands.

The flame retention headincorporates three basic air-directing

elements: the center opening forprimary air, the secondary slots, and the


tertiary opening. See Figure 1-9. Thecenter opening is the orifice in the center ofthe head that allows clearance for the oilspray and the electrode spark to passthrough the head without interference. Thesecondary slots are the slots that radiate outfrom the center opening towards theoutside of the head. The tertiary opening isa slot that is concentric to the centeropening and follows the circumference ofthe combustion head. All three openingsaffect the way air is delivered to the oilspray.

• The primary air is the air that exitsthrough the center opening hole in theflame retention ring where the oil from thenozzle is sprayed. Primary air has the leastdesirable effect on combustion. Air willalways take the path of least resistance, sothe larger the center opening, the more theair will tend to pass through this openingand push the flame out away from the faceof the head. This air travels in a forwardmotion only. The smaller the centeropening, the more air will be forced to seekits passageway through the other openingsin the combustion head. (Figure 1-9).

• The secondary air is the air that exitsthrough the slots cut into the flame reten-tion ring. The secondary slots are where themost important mixing of oil and airoccurs. The slot width regulates thevelocity of the air passing through the slot.This is where the air acquires a spinningaction. The air moves mostly in a rotarymotion with little forward movement.Narrow slots will cause the air to spin fasterand move forward less. This will cause thebest mixing of oil and air and create acompact, intense, and efficient flame.

The secondary slots also aid in keepingthe surface of the head clean and free ofcarbon. This air is turbulated by the flame

retention ring and it is this Secondary Airthat creates the flame retention effect. Byspinning this secondary air, the flame isactually pulled back toward the flameretention ring. (Figure 1-9).

• The tertiary air is the air that exitsaround the outside of the flame retentionring or through the tertiary slots. For cleanoil combustion, every droplet of atomizedoil MUST be completely blanketed with airin order to provide total combustion.

Tertiary Air ensures that any droplets ofatomized oil escaping the oil spray patternwill contact this air and burn. Creating anenvelope or curtain of air between the mainswirl area of the flame and the walls of thecombustion area or the chamber. The widthof the slots in the outside ring control theamount of tertiary air entering the combus-tion area. The larger the slots the moretertiary air and less secondary air, thus thesize of the slots affects the firing rate of theburner. (Figure 1-9).

Fixed and adjustable headsFlame retention heads fall into one of

two categories: fixed or adjustable (some-times called variable heads). The differencebetween them is the method by which theycontrol the tertiary opening and hence, thefiring rate of the burner.

The fixed head group’s tertiary openingis pre-set to a specific opening size for aspecific firing rate range. There are avariety of one-piece heads available withfixed tertiary slots sized according to thefiring rate for which it was designed. Tochange firing rates, you have to change thehead.

With an adjustable head burner, the headis designed to move against or away from aring, thus closing or opening the tertiary



slot according to the firing rate require-ments.

The adjustable head operation is basedon the relationship between what is calledthe “throttle ring” and the “flame retentionring.” The throttle ring is a ring at the endof the air tube that works in conjunctionwith the flame retention ring to create anair restriction and provide for the tertiaryair effect. The adjustable head group allowsthe technician to move the head forward orbackward in order to change the tertiaryopening to accommodate different firingrate requirements, allowing fine-tuning ofthe burner.

The fixed head is simple and easy to use;but remember that each head is only goodfor a specific range of firing rates. Whenyou are installing a new burner or changinga firing rate to optimize performance, youmust be sure you have installed the properhead for the specific firing rate. Thevariable head burner allows an infiniteability to fine-tune the burner for hard-to-fire applications.

With the wide variety of adjustmentspossible, you must be careful in picking thecorrect adjustments. Most variable headburners come with adjustment guides tohelp you set the head properly.

Static pressureStatic pressure is the means of produc-

ing and maintaining flow against resis-tance. Oilburners on the market todaycreate much higher static pressures thanunits made in the 1980s and earlier.

Some of these burners create such highstatic pressures that they can force theproducts of combustion through the heatexchanger and out of the building withoutthe use of a chimney or power venter. Seethe section on direct venting in the VentingChapter. (Chapter 6).

High static pressure burners have beendeveloped to accommodate the modern,flow resistive appliances (boilers, furnaces,and water heaters) and to assist with low orno draft conditions. A drop in staticpressure can cause problems that rangefrom delayed ignition, rumbles, andpulsation to the inability to adjust theburner for clean operation.

The fan in a high static pressure burnerstarts with enough pressure to effectivelypush the products of combustion throughthe appliance without interruption. Thehigher static pressure also acts like a shockabsorber or tightly wound spring to resistand absorb flame pulsations.

This is especially needed in mostmodern appliances, which are designedwith tighter, more efficient heat exchangerpassages and increased draft drop thatresults in great heat absorption by the heatexchanger, and thus, greater efficiency.



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