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8/20/2019 mesin bahan bakar bensin

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Content1.1 Introduction and Intent.1.2 Acknowledgements.1.3 Abbreviations.3. What Advantage will I gain from reading this FAQ

!.1 Where does crude oil come from.!.2 When will we run out of crude oil!.3 What is the histor" of gasoline!.! What are the h"drocarbons in gasoline!.!.1 #aturated h"drocarbons $ aka %araffins& alkanes '!.!.2 (nsaturated )"drocarbons!.* What are o+"genates!., Wh" were alk"l lead com%ounds added!.- Wh" not use other organometallic com%ounds!. What do the refining %rocesses do!./ What energ" is released when gasoline is burned

!.10 What are the gasoline s%ecifications!.10.1 a%our ressure and istillation Classes.!.10.2 a%our 4ock rotection Classes!.10.3 Antiknock Inde+ $ aka $5678967':2& ;um% 6ctane; '!.10.! 4ead Content!.10.* Co%%er stri% corrosion!.10., 9a+imum #ulfur content!.10.- 9a+imum #olvent Washed


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*.1! What are ;gross %olluters;,.1 Who invented 6ctane 5atings,.2 Wh" do we need 6ctane 5atings,.3 What fuel %ro%ert" does the 6ctane 5ating measure,.! Wh" are two ratings used to obtain the %um% rating

,.* What does the 9otor 6ctane rating measure,., What does the 5esearch 6ctane rating measure,.- Wh" is the difference called ;sensitivit";,. What sort of engine is used to rate fuels,./ )ow is the 6ctane rating determined,.10 What is the 6ctane istribution of the fuel,.11 What is a ;delta 5esearch 6ctane number;,.12 )ow do other fuel %ro%erties affect octane,.13 Can higher octane fuels give me more %ower,.1! oes low octane fuel increase engine wear,.1* Can I mi+ different octane fuel grades

,.1, What ha%%ens if I use the wrong octane fuel,.1- Can I tune the engine to use another octane fuel,.1 )ow can I increase the fuel octane,.1/ Are aviation gasoline octane numbers com%arable,.20 Can mothballs increase octane-.1 What is the 6ctane 7umber 5e?uirement of a ehicle-.2 What is the effect of Com%ression ratio-.3 What is the effect of changing the air@fuel ratio-.! What is the effect of changing the ignition timing-.* What is the effect of engine management s"stems-., What is the effect of tem%erature and load-.- What is the effect of engine s%eed.-. What is the effect of engine de%osits-./ What is the 5oad 6ctane 7umber of a Fuel-.11 What is the effect of altitude-.12 What is the effect of humidit".-.13 What does water inection achieve..1 What causes an em%t" fuel tank.2 Is knock the onl" abnormal combustion %roblem.3 Can I %revent carburetter icing.! #hould I store fuel to avoid the o+"genate season.* Can I im%rove fuel econom" b" using ?ualit" gasolines., What is ;stale; fuel& and should I use it.- )ow can I remove water in the fuel tank. Can I used unleaded on older vehicles./ )ow serious is valve seat recession on older vehicles/.1 o fuel additives work/.2 Can a ?ualit" fuel hel% a sick engine/.3 What are the advantages of alcohols and ethers/.! Wh" are C7< and 4< considered ;cleaner; fuels.

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/vehicles/gasoline-faq/6-9-How-is-the-Octane-rating-determined.htmlhttp://stason.org/TULARC/vehicles/gasoline-faq/6-10-What-is-the-Octane-Distribution-of-the-fuel.htmlhttp://stason.org/TULARC/vehicles/gasoline-faq/6-11-What-is-a-delta-Research-Octane-number.htmlhttp://stason.org/TULARC/vehicles/gasoline-faq/6-12-How-do-other-fuel-properties-affect-octane.htmlhttp://stason.org/TULARC/vehicles/gasoline-faq/6-13-Can-higher-octane-fuels-give-me-more-power.htmlhttp://stason.org/TULARC/vehicles/gasoline-faq/6-14-Does-low-octane-fuel-increase-engine-wear.htmlhttp://stason.org/TULARC/vehicles/gasoline-faq/6-15-Can-I-mix-different-octane-fuel-grades.htmlhttp://stason.org/TULARC/vehicles/gasoline-faq/6-16-What-happens-if-I-use-the-wrong-octane-fuel.htmlhttp://stason.org/TULARC/vehicles/gasoline-faq/6-17-Can-I-tune-the-engine-to-use-another-octane-fuel.htmlhttp://stason.org/TULARC/vehicles/gasoline-faq/6-18-How-can-I-increase-the-fuel-octane.htmlhttp://stason.org/TULARC/vehicles/gasoline-faq/6-19-Are-aviation-gasoline-octane-numbers-comparable.htmlhttp://stason.org/TULARC/vehicles/gasoline-faq/6-20-Can-mothballs-increase-octane.htmlhttp://stason.org/TULARC/vehicles/gasoline-faq/7-1-What-is-the-Octane-Number-Requirement-of-a-Vehicle.htmlhttp://stason.org/TULARC/vehicles/gasoline-faq/7-2-What-is-the-effect-of-Compression-ratio.htmlhttp://stason.org/TULARC/vehicles/gasoline-faq/7-3-What-is-the-effect-of-changing-the-air-fuel-ratio.htmlhttp://stason.org/TULARC/vehicles/gasoline-faq/7-4-What-is-the-effect-of-changing-the-ignition-timing.htmlhttp://stason.org/TULARC/vehicles/gasoline-faq/7-5-What-is-the-effect-of-engine-management-systems.htmlhttp://stason.org/TULARC/vehicles/gasoline-faq/7-6-What-is-the-effect-of-temperature-and-load.htmlhttp://stason.org/TULARC/vehicles/gasoline-faq/7-7-What-is-the-effect-of-engine-speed.htmlhttp://stason.org/TULARC/vehicles/gasoline-faq/7-8-What-is-the-effect-of-engine-deposits.htmlhttp://stason.org/TULARC/vehicles/gasoline-faq/7-9-What-is-the-Road-Octane-Number-of-a-Fuel.htmlhttp://stason.org/TULARC/vehicles/gasoline-faq/7-11-What-is-the-effect-of-altitude.htmlhttp://stason.org/TULARC/vehicles/gasoline-faq/7-12-What-is-the-effect-of-humidity.htmlhttp://stason.org/TULARC/vehicles/gasoline-faq/7-13-What-does-water-injection-achieve.htmlhttp://stason.org/TULARC/vehicles/gasoline-faq/8-1-What-causes-an-empty-fuel-tank.htmlhttp://stason.org/TULARC/vehicles/gasoline-faq/8-2-Is-knock-the-only-abnormal-combustion-problem.htmlhttp://stason.org/TULARC/vehicles/gasoline-faq/8-3-Can-I-prevent-carburetter-icing.htmlhttp://stason.org/TULARC/vehicles/gasoline-faq/8-4-Should-I-store-fuel-to-avoid-the-oxygenate-season.htmlhttp://stason.org/TULARC/vehicles/gasoline-faq/8-5-Can-I-improve-fuel-economy-by-using-quality-gasolines.htmlhttp://stason.org/TULARC/vehicles/gasoline-faq/8-6-What-is-stale-fuel-and-should-I-use-it.htmlhttp://stason.org/TULARC/vehicles/gasoline-faq/8-7-How-can-I-remove-water-in-the-fuel-tank.htmlhttp://stason.org/TULARC/vehicles/gasoline-faq/9-1-Do-fuel-additives-work.htmlhttp://stason.org/TULARC/vehicles/gasoline-faq/9-3-What-are-the-advantages-of-alcohols-and-ethers.htmlhttp://stason.org/TULARC/vehicles/gasoline-faq/9-4-Why-are-CNG-and-LPG-considered-cleaner-fuels.html


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/.* Wh" are h"drogen@%owered cars not available/., What are ;fuel cells; /.- What is a ;h"brid; vehicle/..1 Ammonia $7)3'/..2 Water

/..3 ro%"lene 6+ide/..! 7itromethane/./.1 7itrous 6+ide/./.2 9embrane =nrichment of Air 10.1 >he m"th of >ri%tane10.2 From )onda Civic to Formula 1 winner.11.1 Books and 5esearch a%ers11.2 #uggested Further 5eading

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%.% &ntro#uction an# &ntent.

>he intent of this FAQ is to %rovide some basic information on gasolines and other fuelsfor s%ark ignition engines used in automobiles. >he to+icit" and environmental reasonsfor recent and %lanned future changes to gasoline are discussed& along with recent and

%ro%osed changes in com%osition of gasoline. >his FAQ is intended to hel% readerschoose the most a%%ro%riate fuel for vehicles& assist with the diagnosis of fuel@related %roblems& and to understand the significance of most gasoline %ro%erties listed in fuels%ecifications. I make no a%ologies for the fairl" heav" em%hasis on chemistr" it is theonl" sensible wa" to describe the o+idation of h"drocarbon fuels to %roduce energ"&water& and carbon dio+ide.

%.' Ac(no)le#gements.

>hanks go to all the %osters in sci.energ" and rec.autos.tech who s%end valuable timeres%onding to ?uestions. I would also like to acknowledge the considerable effort of

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*. +hat A#vantage )ill & gain !rom rea#ing this ,A-

>his FAQ is intended to %rovide a fairl" technical descri%tion of what gasoline contains&how it is s%ecified& and how the %ro%erties affect the %erformance of "our vehicle. >heregulations governing gasoline have changed& and are continuing to change. >hese

changes have made much of the traditional lore about gasoline obsolete. 9otorists ma"wish to understand a little more about gasoline to ensure the" obtain the best value& andthe most a%%ro%riate fuel for their vehicle. >here is no %oint in %rematurel" destro"ing"our second most e+%ensive %urchase b" using unsuitable fuel& ust as there is no %oint inwasting hard@earned mone" on higher octane fuel that "our automobile can not utiliHe. 7ote that this FAQ does not discuss the relative advantages of s%ecific brands ofgasolines& it is onl" intended to discuss the generic %ro%erties of gasolines.


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.% +here #oes cru#e oil come !rom.

>he generall"@acce%ted origin of crude oil is from %lant life u% to 3 billion "ears ago& but %redominantl" from 100 to ,00 million "ears ago 1J. ;ead vegetarian dino dinner; ismore correct than ;dead dinos;. >he molecular structure of the h"drocarbons and other

com%ounds %resent in fossil fuels can be linked to the leaf wa+es and other %lantmolecules of marine and terrestrial %lants believed to e+ist during that era. >here arevarious biogenic marker chemicals $ such as iso%renoids from ter%enes& %or%h"rins andaromatics from natural %igments& %ristane and %h"tane from the h"drol"sis ofchloro%h"ll& and normal alkanes from wa+es '& whose siHe and sha%e can not be e+%lained b" known geological %rocesses 2J. >he %resence of o%tical activit" and the carbonisoto%ic ratios also indicate a biological origin 3J. >here is another h"%othesis thatsuggests crude oil is derived from methane from the earthKs interior. >he current main %ro%onent of this abiotic theor" is >homas he %rimar" c"cle $ turnover of [email protected] + 10L12 tonnes of organiccarbon ' has a half@life of da"s to decades& whereas the large secondar" c"cle $ turnover,.! + 10L1* tonnes of organic carbon ' has a half@life of several million "ears !J. 9uchof this organic carbon is too dilute or inaccessible for current technolog" to recover&however the estimates re%resent centuries to millenia of fossil fuels& even with continued

consum%tion at current or increased rates *J.

>he concern about ;running out of oil; arises from misunderstanding the significance of a %etroleum industr" measure called the 5eserves:roduction ratio $5:'. >his monitors the %roduction and e+%loration interactions. >he 5: is based on the conce%t of ;%roved;reserves of fossil fuels. roved reserves are those ?uantities of fossil fuels that geologicaland engineering information indicate with reasonable certaint" can be recovered in thefuture from known reservoirs under e+isting economic and o%erating conditions. >he5eserves:roduction ratio is the %roved reserves ?uantit" divided b" the %roduction in thelast "ear& and the result will be the length of time that those remaining %roved reserveswould last if %roduction were to continue at the current level ,J. It is im%ortant to notethe economic and technolog" com%onent of the definitions& as the %rice of oil increases$ or new technolog" becomes available '& marginal fields become ;%roved reserves;. Weare unlikel" to ;run out; of oil& as more fields become economic. 7ote that investment ine+%loration is also linked to the 5: ratio& and the world crude oil 5: ratio t"%icall"moves between 20@!0 "ears& however s%ecific national incentives to discover oil cane+tend that range u%ward.

Concerned %eo%le often refer to the ; )ubbert curves; that %redict fossil fuel discover"


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rates would %eak and decline ra%idl". 9. Ding )ubbert calculated in 1/2 that theultimate resource base of the lower ! states of the (#A was 1,38@2 billion barrels of oil&and the ultimate %roduction of natural gas to be 2!.,8@0. trillion cubic metres& withsome additional ?ualifiers. As %roduction and %roved resources were 1!- billion barrelsof oil and 22.* trillion cubic metres of gas& )ubbert was im%l"ing that volumes "et to be

develo%ed could onl" be 1,@!/ billion barrels of oil and 2.1@!.* trillion cubic metres.>echnolog" has confounded those %redictions for natural gas ,aJ.

>he (# he 1//* B #tatistical 5eview of World=nerg" %rovides the following data ,&-J.

Crude Oil Proved Reserves R/P

Ratio

Middle East 89.4 billion tonnes

93.4 year

USA 3.8

9.8 years

USA - 99! US"S data #.9

33.# years

$otal %orld 3&.343.# years

Coal Proved Reserves R/P

Ratio

USA '4#.!( billion tonnes '4&

years

$otal %orld )#43.8(4 '3!

years

*atural "as Proved Reserves R/P

RatioUSA 4.( trillion +ubi+ ,etres

8.( years

USA - 99! US"S data 9.

&.# years

$otal %orld 4.#

((.4 years.


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6ne billion E 1 + 10L/. 6ne trillion E 1 + 10L12.6ne barrel of Arabian 4ight crude oil E 0.1*/- m3 and 0.13, tonnes.

If the crude oil %rice e+ceeds N30:bbl then alternative fuels ma" become

com%etitive& and at N*0@,0:bbl coal@derived li?uid fuels are economic& asare man" biomass@derived fuels and other energ" sources J.

.* +hat is the history o! gasoline

In the late 1/th Centur" the most suitable fuels for the automobile were coal tar distillatesand the lighter fractions from the distillation of crude oil. uring the earl" 20th Centur"the oil com%anies were %roducing gasoline as a sim%le distillate from %etroleum& but theautomotive engines were ra%idl" being im%roved and re?uired a more suitable fuel.uring the 1/10s& laws %rohibited the storage of gasolines on residential %ro%erties& soCharles F. Dettering $ "es @ he of ignition s"stem fame ' modified an IC engine to run on

kerosine. )owever the kerosine@fuelled engine would ;knock; and crack the c"linderhead and %istons. )e assigned >homas 9idgle" Or. to confirm that the cause wasfrom the kerosine dro%lets va%orising on combustion as the" %resumed. 9idgle"demonstrated that the knock was caused b" a ra%id rise in %ressure after ignition& notduring %reignition as believed /J. >his then lead to the long search for antiknock agents&culminating in tetra eth"l lead 10J. >"%ical mid@1/20s gasolines were !0 @ ,0 6ctane11J.

Because sulfur in gasoline inhibited the octane@enhancing effect of the alk"l lead& thesulfur content of the thermall"@cracked refiner" streams for gasolines was restricted. B"the 1/30s& the %etroleum industr" had determined that the larger h"drocarbon molecules

$kerosine' had maor adverse effects on the octane of gasoline& and were develo%ingconsistent s%ecifications for desired %ro%erties. B" the 1/!0s catal"tic cracking wasintroduced& and gasoline com%ositions became fairl" consistent between brands duringthe various seasons.

>he 1/*0s saw the start of the increase of the com%ression ratio& re?uiring higher octanefuels. 6ctane ratings& lead levels& and va%our %ressure increased& whereas sulfur contentand olefins decreased. #ome new refining %rocesses $ such as h"drocracking '&s%ecificall" designed to %rovide h"drocarbons com%onents with good lead res%onse andoctane& were introduced. 9inor im%rovements were made to gasoline formulations toim%rove "ields and octane until the 1/-0s @ when unleaded fuels were introduced to %rotect the e+haust catal"sts that were also being introduced for environmental reasons.From 1/-0 until 1//0 gasolines were slowl" changed as lead was %hased out& lead levels %lummetted& octanes initiall" decreased& and then remained 2@* numbers lower& va%our %ressures continued to increase& and sulfur and olefins remained constant& whilearomatics increased. In 1//0& the (# Clean Air Act started forcing maor com%ositionalchanges on gasoline& resulting in %lummeting va%our %ressure and increaing o+"genatelevels. >hese changes will continue into the 21st Centur"& because gasoline use in #Iengines is a maor %ollution source. Com%rehensive descri%tions of the changes to


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gasolines this centur" have been %rovided b" 4.9.he move to unleaded fuels continues worldwide& however several countries haveincreased the aromatics content $ u% to *0M ' to re%lace the alk"l lead octane enhancers.>hese highl" aromatic gasolines can result in in damage to elastomers and increased

levels of to+ic aromatic emissions if used without e+haust catal"sts.

. +hat are the hy#rocarbons in gasoline

)"drocarbons $ )Cs ' are an" molecules that ust contain h"drogen and carbon& both ofwhich are fuel molecules that can be burnt $ o+idised 'to form water $ )26 ' or carbondio+ide $ C62 '. If the combustion is not com%lete& carbon mono+ide $ C6 ' ma" beformed. As C6 can be burnt to %roduce C62& it is also a fuel.

>he wa" the h"drogen and carbons hold hands determines which h"drocarbon famil"the" belong to. If the" onl" hold one hand the" are called ;saturated h"drocarbons;

because the" can not absorb additional h"drogen. If the carbons hold two hands the" arecalled ;unsaturated h"drocarbons; because the" can be converted into ;saturatedh"drocarbons; b" the addition of h"drogen to the double bond. )"drogens are omittedfrom the following& but if "ou remember C E ! hands& ) E 1 hand& and 6 E 2 hands&"ou can draw the full structures of most )Cs.

he boiling range is narrowing as the initial boiling %oint is increasing& and the final boiling %oint is decreasing& both changes are for environmental reasons. etailed descri%tions ofstructures can be found in an" chemical or %etroleum te+t discussing gasolines 1!J.

..% 0aturate# hy#rocarbons 1 a(a para!!ins2 al(anes 3

@ stable& the maor com%onent of leaded gasolines.@ tend to burn in air with a clean flame.@ octane ratings de%end on branching and number of carbon atoms.

alkanesnormal E continuous chain of carbons $ Cn )2n82 '@ low octane ratings& decreasing with carbon chain length.

nor,al etane C-C-C-C-C-C-C C&(

iso E branched chain of carbons $ Cn )2n82 '@ higher octane ratings& increasing with carbon chain branching.

iso o+tane 0 C C

1 a2a ')')4-tri,etylentane

C-C-C-C-C

C88


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C

c"clic E circle of carbons $ Cn )2n '$ aka 7a%hthenes '

@ high octane ratings.

+y+loe5ane 0 C

/ 6

C C

C('

C C

6 /

C

..' Unsaturate# Hy#rocarbons

@ (nstable& are the remaining com%onent of gasoline.@ >end to burn in air with a smok" flame.

Alkenes $ aka olefins& have carbonEcarbon double bonds '@ >hese are unstable& and are usuall" limited to a few M.@ tend to be reactive and to+ic& but have desirable octane ratings.

C

C!#

'-,etyl-'-butene C-C0C-C

Alk"nes $ aka acet"lenes& have carbon@carbon tri%le bonds '@ >hese are even more unstable& are onl" %resent intrace amounts& and onl" in some %oorl"@refined gasolines.

A+etylene C0C

C''

Arenes $ aka aromatics '@ (sed to be u% to !0M& graduall" being reduced to P20M in the (#.@ tend to be more to+ic& but have desirable octane ratings.@ #ome countries are increasing the aromatic content $ u% to *0M in somesu%er unleaded fuels ' to re%lace the alk"l lead octane enhancers.


12/91

C C

// 6 // 6

C C C-C C

7enene $oluene

C C C C

66 / 66 /

C C

C(( C&8

ol"nuclear Aromatics $ aka 7As or A)s '@ >hese are high boiling& and are onl" %resent in small amounts in gasoline.>he" contain benHene rings oined together. >he sim%lest& and least to+ic&is 7a%hthalene& which is onl" %resent in trace amounts in traditionalgasolines& and even lower levels are found in reformulated gasolines.>he larger multi@ringed 7As are highl" to+ic& and are not %resent ingasoline.

C C

// 6 / 66

C C C

*atalene

C#8

C C C

66 / 6 //

C C

.4 +hat are o$ygenates

6+"genates are ust %reused h"drocarbons G@'. >he" contain o+"gen& which can not %rovide energ"& but their structure %rovides a reasonable antiknock value& thus the" aregood substitutes for aromatics& and the" ma" also reduce the smog@forming tendencies ofthe e+haust gases 1*J. 9ost o+"genates used in gasolines are either alcohols $ C+@6@) '

or ethers $C+@6@C"'& and contain 1 to , carbons. Alcohols have been used in gasolinessince the 1/30s& and 9>B= was first used in commercial gasolines in Ital" in 1/-3& andwas first used in the (# b" A5C6 in 1/-/. >he relative advantages of aromatics ando+"genates as environmentall"@friendl" and low to+icit" octane@enhancers are still beingresearched.


13/91

Etanol C-C-O-

C'!O

C

Metyl tertiary butyl eter C-C-O-C

C49OC3

1a2a tertiary butyl ,etyl eter

C

>he" can be %roduced from fossil fuels eg methanol $9e6)'& meth"l tertiar" but"l ether$9>B='& tertiar" am"l meth"l ether $>A9='& or from biomass& eg ethanol$=t6)'& eth"ltertiar" but"l ether $=>B=''. 9>B= is %roduced b" reacting methanol $ from naturalgas ' with isobut"lene in the li?uid %hase over an acidic ion@e+change resin catal"st at100C. >he isobut"lene was initiall" from refiner" catal"tic crackers or %etrochemicalolefin %lants& but these da"s larger %lants %roduce it from butanes. 9>B= %roduction hasincreased at the rate of 10 to 20M %er "ear& and the s%ot market %rice in Oune 1//3 wasaround N2-0:tonne 1*J. >he ;ether; starting fluids for vehicles are usuall" dieth"l ether$li?uid' or dimeth"l ether $aerosol'. 7ote that ; %etroleum ethers ; are volatile alkaneh"drocarbon fractions& the" are not a C+@6@C" com%ound.

6+"genates are added to gasolines to reduce the reactivit" of emissions& but the" are onl"effective if the h"drocarbon fractions are carefull" modified to utilise the octane andvolatilit" %ro%erties of the o+"genates. If the h"drocarbon fraction is not correctl"modified& o+"genates can increase the undesirable smog@forming and to+ic emissions.6+"genates do not necessaril" reduce all e+haust to+ins& nor are the" intended to.

6+"genates have significantl" different %h"sical %ro%erties to h"drocarbons& and thelevels that can be added to gasolines are controlled b" the 1/-- Clean Air Actamendments in the (#& with the laws %rohibiting the increase or introduction of a fuel orfuel additive that is not substantiall" similar to an" fuel or fuel additive used to certif"1/-* or subse?uent "ears vehicles. Waivers can granted if the %roduct does not cause orcontribute to emission device failures& and if the =A does not s%ecificall" decline thea%%lication after 10 da"s& it is taken as granted. In 1/- the =A granted 10M b" volumeof ethanol a waiver& and have subse?uentl" issued waivers for P10 volM ethanol $1/2'&- volM tertiar" but"l alcohol $1/-/'& *.* volM 1G1 9e6):>BA $1/-/'& 3.* massMo+"gen derived from 1G1 9e6):>BA E /.* volM of the alcohols $1/1'& 3.- massMo+"gen derived from methanol and cosolvents E * volM ma+ 9e6) and 2.* volM mincosolvent @ with some cosolvents re?uiring additional corrosion inhibitor $1/*&1/'&

-.0 volM 9>B= $1/-/'& and 1*.0 volM 9>B= $1/'. 6nl" the ethanol waiver wase+em%ted from the re?uirement to still meet A#>9 volatilit" re?uirements 1,J.

In 1/1 the =A ruled that fuels could contain ali%hatic alcohols $ e+ce%t 9e6) ' and:orethers at concentrations until the o+"gen content is 2.0 massM. It also %ermitted *.* volMof 1G1 9e6):>BA. In 1//1 the ma+imum o+"gen content was increased to 2.- massM.>o ensure sufficient gasoline base was available for ethanol blending& the =A also ruled that gasoline containing u% to


14/91

2 volM of 9>B= could subse?uentl" be blended with 10 volM of ethanol 1,J.

Initiall"& the o+"genates were added to h"drocarbon fractions that were slightl"@modifiedunleaded gasoline fractions& and these were known as ;o+"genated; gasolines. In 1//*&the h"drocarbon fraction was significantl" modified& and these gasolines are called

;reformulated gasolines; $ 5F


15/91

economic additives that could be added to gasoline or kerosine to %revent knock& as itwas a%%arent that engine develo%ment was being hindered. >he kerosine for home fuelssoon became a secondar" issue& as the magnitude of the automotive knock %roblemincreased throughout the 1/10s& and so more resources were %oured into the ?uest for aneffective ;antiknock;. A higher octane aviation gasoline was re?uired urgentl" once the

(# entered WWI& and almost ever" %ossible chemical $ including melted butter ' wastested for antiknock abilit" 2!J.

6riginall"& iodine was the best antiknock available& but was not a %ractical gasolineadditive& and was used as the benchmark. In 1/1/ aniline was found to have su%eriorantiknock abilit" to iodine& but also was not a %ractical additive& however aniline becamethe benchmark antiknock& and various com%ounds were com%ared to it. >he discover" oftetra eth"l lead& and the scavengers re?uired to remove it from the engine were made b"teams lead b" >homas 9idgle" Or. in 1/22 /&10&2!J. >he" tried selenium o+"chloridewhich was an e+cellent antiknock& however it reacted with iron and ;dissolved; theengine. 9idgle" was able to %redict that other organometallics would work& and slowl"

focused on organoleads. >he" then had to remove the lead& which would otherwiseaccumulate and coat the engine and e+haust s"stem with lead. >he" discovered anddevelo%ed the halogenated lead scavengers that are still used in leaded fuels. >hescavengers& $ eth"lene dibromide and eth"lene dichloride '& function b" %rovidinghalogen atoms that react with the lead to form volatile lead halide salts that can esca%eout the e+haust. >he ?uantit" of scavengers added to the alk"l lead concentrate iscalculated according to the amount of lead %resent. If sufficient scavenger is addedto theoreticall" react with all the lead %resent& the amount is called one ;theor";.>"%icall"& 1.0 to 1.* theories are used& but aviation gasolines must onl" use one theor".>his ensures there is no e+cess bromine that could react with the engine.

>he alk"l leads ra%idl" became the most cost@effective method of enhancing octane. >heintroduction was not universall" acclaimed& as the to+icit" of >=4 soon became a%%arent&and several eminent %ublic health officials cam%aigned against the wides%readintroduction of alk"l leads 2*J. >heir cause was assisted b" some maor disasters at >=4manufacturing %lants& and although these incidents were mainl" attributable to a failureof management and:or staff to follow instructions& the" resulted in a %rotracted dis%ute inthe chemical and %ublic health literature that even involved 9idgle" 2*&2,J. We should be careful retros%ectivel" a%%l"ing udgement to the 1/20s& as the increased octane ofleaded gasoline %rovided maor gains in engine efficienc" and lower gasoline %rices.

>he develo%ment of the alk"l leads $ tetra meth"l lead& tetra eth"l lead ' and the to+ichalogenated scavengers meant that %etroleum refiners could then configure refineries to %roduce h"drocarbon streams that would increase octane with small ?uantities of alk"llead. If "ou kee% adding alk"l lead com%ounds& the lead res%onse of the gasolinedecreases& and so there are economic limits to how much lead should be added.

(% until the late 1/,0s& alk"l leads were added to gasolines in increasing concentrationsto obtain octane. >he limit was 1.1!g b:l& which is well above the diminishing returns %art of the lead res%onse curve for most refiner" streams& thus it is unlikel" that much


16/91

fuel was ever made at that level. I believe 1.0* was about the ma+imum& and articlessuggest that 1/-0 100 567 %remiums were about 0.-@0. g b:l and /! 567 regulars0.,@0.- g b:l& which matches %ublished lead res%onse data 2-&2J eg.

or Catalyti+ Re:or,ate Strai;t Run

*ata.

he most famous of these is meth"lc"clo%entadien"lmanganese tricarbon"l $99>'& which was used in the (#A until banned b" the =Afrom 2- 6ct 1/- 30J& but is a%%roved for use in Canada and Australia. 5ecentl" the

=A ban was overturned& and 99> can be used u% to 0.031g9n:(#


17/91

6ther com%ounds that enhance octane have been suggested& but usuall" have significant %roblems such as to+icit"& cost& increased engine wear etc..=+am%les includedic"clo%entadien"l iron and nickel carbon"l. B= feed.

#ome other countries are removing the alk"l lead com%ounds for health reasons& and


18/91

re%lacing them with aromatics and o+"genates. If the vehicle fleet does not have e+haustcatal"sts& the emissions of some to+ic aromatic h"drocarbons can increase. If ma+imumenvironmental and health gains are to be achieved& the removal of lead from gasolineshould be accom%anied b" the immediate introduction of e+haust catal"sts andso%histicated engine management s"stems&

.7 +hat energy is release# )hen gasoline is burne#

It is im%ortant to note that the theoretical energ" content of gasoline when burned in air isonl" related to the h"drogen and carbon contents. >he energ" is released when theh"drogen and carbon are o+idised $burnt'& to form water and carbon dio+ide. 6ctanerating is not fundamentall" related to the energ" content& and the actual h"drocarbon ando+"genate com%onents used in the gasoline will determine both the energ" release andthe antiknock rating.

>wo im%ortant reactions areG@

C 8 62 E C62) 8 62 E )26>he mass or volume of air re?uired to %rovide sufficient o+"gen to achieve this com%letecombustion is the ;stoichiometric; mass or volume of air.Insufficient air E ;rich;& ande+cess air E ;lean;& and the stoichiometric mass of air is related to the carbonGh"drogenratio of the fuel. >he %rocedures for calculation of stoichiometric air@fuel ratios are full"documented in an #A= standard 3*J.

Atomic masses used areG@ )"drogen E 1.00-/!& Carbon E 12.011&6+"gen E 1*.//!& 7itrogen E 1!.00,-& and #ulfur E 32.0,,.

>he com%osition of sea level air $ 1/-, data& hence low C62 value ' is


19/91

thus 1.000 kg of C-)1, re?uires 3.*13 kg of 62 E 1*.1-/ kg of air.

>he chemical stoichiometric combustion of h"drocarbons with o+"gen can be written asG@C+)" 8 $+ 8 $":!''62 @T +C62 8 $":2')26

6ften& for sim%licit"& the remainder of air is assumed to be nitrogen& which can be addedto the e?uation when e+haust com%ositions are re?uired. As a general rule& ma+imum %ower is achieved at slightl" rich& whereas ma+imum fuel econom" is achieved at slightl"lean.

>he energ" content of the gasoline is measured b" burning all the fuel inside a bombcalorimeter and measuring the tem%erature increase. >he energ" available de%ends onwhat ha%%ens to the water %roduced from the combustion of the h"drogen. If the waterremains as a gas& then it cannot release the heat of va%orisation& thus %roducing the 7ettCalorific alue. If the water were condensed back to the original fuel tem%erature& thenhe calorific values are fairl" constant for families of )Cs& which is not sur%rising& giventheir fairl" consistent carbonGh"drogen ratios. For li?uid $ l ' or gaseous $ g ' fuelconverted to gaseous %roducts @ e+ce%t for the 2@meth"lbutene@2& where onl" gaseous isre%orted. R E Blending 6ctane 7umber as re%orted b" AI roect !* using ,0 octane base fuel& and the numbers in brackets are Blending 6ctane 7umbers currentl" used formodern fuels.>"%ical )eats of Combustion are 3,JG@

uel State eat o: Co,bustion Resear+ Motor

M=/2; O+tane O+tane

n-etane l 44.!9' # #

; 44.9!!i-o+tane l 44.3&4 ## ##

; 44.(8'

toluene l 4#.!!4 '4> 1 '> 194

; 4#.9(&

'-,etylbutene-' 44.&'# &(> 13 4> 18

Because all the data is available& the calorific value of fuels can be estimated ?uiteaccuratel" from h"drocarbon fuel %ro%erties such as the densit"& sulfur content& andaniline %oint $ which indicates the aromatics content '.

It should be noted that because o+"genates contain o+"gen that can not %rovide energ"&

the" will have significantl" lower energ" contents. >he" are added to %rovide octane& notenerg". For an engine that can be o%timised for o+"genates& more fuel is re?uired toobtain the same %ower& but the" can burn slightl" more efficientl"& thus the %ower ratio isnot identical to the energ" content ratio. >he" also re?uire more energ" to va%orise.


20/91

Ener;y Content eat o: ?aorisation O5y;en Content

*ett M=/2; M=/2; @t

Metanol 9.9! .!4 49.9

Etanol '(.(8 #.93 34.&

M$7E 3!.8 #.3'' 8.'

E$7E 3(.'9 #.3# !.&

$AME 3(.'8 #.3'3 !.&

"asoline 4' - 44 #.'9& #.#

>"%ical values for commercial fuels in megaoules:kilogram are 3-JG@

"ross *ett

ydro;en 4.9 '#.#

Carbon to Carbon ,ono5ide #.' -

Carbon to Carbon dio5ide 3'.8 -

Sul:ur to sul:ur dio5ide 9.( -

*atural "as !3. 48.#

"%ical %ro%erties areG@


21/91

.%8.% 9apour ressure an# ;istillation Classes.

, different classes according to location and:or season. As gasoline is distilled& thetem%eratures at which various fractions are eva%orated are calculated. #%ecificationsdefine the tem%eratures at which various %ercentages of the fuel are eva%orated.

istillation limits include ma+imum tem%eratures that 10M is eva%orated $*0@-0C'& *0Mis eva%orated $110@121C'& /0M is eva%orated $1*@1/0C'& and the final boiling %oint$22*C'. A minimum tem%erature for *0M eva%orated $--C'& and a ma+imum amount of5esidue $2M' after distillation. a%our %ressure limits for each class $ *!& ,2& ,/& -/& /3&103 ka ' are also s%ecified. 7ote that the =A has issued a waiver that does not re?uiregasoline with /@10M ethanol to meet the re?uired s%ecifications between 1st 9a" @ 1*#e%tember.

.%8.' 9apour Loc( rotection Classes

* classes for va%our lock %rotection& according to location and:or season. >he limit for

each class is a ma+imum a%our@4i?uid ratio of 20 at one of the s%ecified testingtem%eratures of !1& !-& *1& *,& ,0C.

.%8.* Anti(noc( &n#e$ 1 a(a 1R?heresults do not correlate well with actual engine de%osits caused b" fuel va%orisation !0J.


22/91

.%8. ?inimum his ensures the fuel remains chemicall" stable& and does not form additional gumsduring %eriods in distribution s"stems& which can be u% to 3@, months. >he sam%le isheated with o+"gen inside a %ressure vessel& and the dela" until significant o+"gen u%take

is measured.

.%8.7 +ater Tolerance

)ighest tem%erature that causes %hase se%aration of o+"genated fuels. >he limits var"according to location and month. For Alaska @ 7orth of ,2 latitude& it changes from @!1Cin ec@Oan to /C in Oul"& but remains 10C all "ear in )awaii. Because %hos%horusadversel" affects e+haust catal"sts& the =A limits %hos%horus in all gasolines to 0.0013g:4.

As well as the above& there are various restrictions introduced b" the Clean Air Act and

state bodies such as CaliforniaKs Air 5esources Board $CA5B' that often have morestringent limits for the above %ro%erties& as well as additional limits. 9ore detaileddescri%tions of the com%le+ regulations can be found elsewhere 1,&!1&!2J @ IKve ustincluded some of the maor changes& as some %ro%erties are determined b" levels of %ermitted emissions& eg the to+ics reduction re?uired for fuel that has the ma+imum %ermitted benHene $1.0M'& means total aromatics are limited to around 2-M. >here have been some changes in earl" 1//, to the im%lementation timetable& and the followingtimetable has not "et been changed.

>he Clean Air Act also s%ecifies some regions that e+ceed air ?ualit" standards have touse reformulated gasolines $5F


23/91

a %er gallon basis& more details are available elsewhere& including the details of the baseline fuel com%ositions to be used for testing 1,&!1&!2&!3&!3aJ.

99# Clean Air A+t CAR7

Si,le Co,le5 Pase '

hat level was increased to

.%% +hat are the e!!ects o! the speci!ie# !uel properties

9olatility

>his affects eva%orative emissions and driveabilit"& it is the %ro%ert" that must changewith location and season. Fuel for mid@summer AriHona would be difficult to use in mid@winter Alaska. >he (# is divided into Hones& according to altitude and seasonaltem%eratures& and the fuel volatilit" is adusted accordingl". Incorrect fuel ma" result indifficult starting in cold weather& carburetter icing& va%our lock in hot weather& andcrankcase oil dilution. olatilit" is controlled b" distillation and va%our %ressures%ecifications. >he higher boiling fractions of the gasoline have significant effects on the

emission levels of undesirable h"drocarbons and aldeh"des& and a reduction of !0C in thefinal boiling %oint will reduce the levels of benHene& butadiene& formaldeh"de andacetaldeh"de b" 2*M& and will reduce )C emissions b" 20M !!J.

Combustion Characteristics

As gasolines contain mainl" h"drocarbons& the onl" significant variable between differentgrades is the octane rating of the fuel& as most other %ro%erties are similar. 6ctane is


24/91

discussed in detail in #ection ,. >here are onl" slight differences in combustiontem%eratures $ most are around 2000C in isobaric adiabatic combustion !*J'. 7ote thatthe actual tem%erature in the combustion chamber is also determined b" other factors&such as load and engine design. >he addition of o+"genates changes the %re@flamereaction %athwa"s& and also reduces the energ" content of the fuel. >he levels of o+"gen

in the fuel is regulated according to regional air ?ualit" standards.

0tability

9otor gasolines ma" be stored u% to si+ months& conse?uentl" the" must not form gumswhich ma" %reci%itate. 5eactions of the unsaturated )Cs ma" %roduce gums $ thesereactions can be catal"sed b" metals such as co%%er '& so antio+idants and metaldeactivators are added. =+istent he co%%er stri% test measures active sulfur&whereas the sulfur content re%orts the total sulfur %resent.

9anufacturers man" also add additional tests& such as filterabilit"& to ensure nodistribution %roblems are encountered.

.%' Are bran#s #i!!erent

es. >he above s%ecifications are intended to ensure minimal ?ualit" standards aremaintained& however as well as the fuel h"drocarbons& the manufacturers add their owns%ecial ingredients to %rovide additional benefits. A ?ualit" gasoline additive %ackagewould includeG@R octane@enhancing additives $ im%rove octane ratings 'R anti@o+idants $ inhibit gum formation& im%rove stabilit" 'R metal deactivators $ inhibit gum formation& im%rove stabilit" 'R de%osit modifiers $ reduce de%osits& s%ark@%lug fouling and %reignition 'R surfactants $ %revent icing& im%rove va%orisation& inhibit de%osits& reduce 76+emissions 'R freeHing %oint de%ressants $ %revent icing 'R corrosion inhibitors $ %revent gasoline corroding storage tanks 'R d"es $ %roduct colour for safet" or regulator" %ur%oses '.


25/91

uring the 1/0s significant %roblems with de%osits accumulating on intake valvesurfaces occurred as new fuel inection s"stems were introduced. >hese intake valvede%osits $I' were different than the inector de%osits& in %art because the valve canreach 300C. =ngine design changes that %revent de%osits usuall" consist of ensuring thevalve is flushed with li?uid gasoline& and %rovision of ade?uate valve rotation. e+aco to modif" some of their claims *1J. 9ost su%%liers of ?ualit" gasolineswill formulate similar additives into their %roducts& and chea%er %roduct lines are lesslikel" to have such additives added. As different brands of gasoline use different additivesand o+"genates& it is %robable that im%ortant fuel %arameters& such as octane distribution&are slightl" different& even though the %um% octane ratings are the same.

#o& if "ou know "our car is well@tuned& and in good condition& but the driveabilit" is %athetic on the correct octane& tr" another brand. 5emember that the com%osition willchange with the season& so if "ou lose driveabilit"& tr" "et another brand. As variousClean Air Act changes are introduced over the ne+t few "ears& gasoline will continue tochange.

.%* +hat is a typical composition

>here seems to be a %erce%tion that all gasolines of one octane grade are chemicall"similar& and thus general rules can be %romulgated about ;energ" content ;& ;flames%eed;& ;combustion tem%erature; etc. etc.. 7othing is further from the truth. >he behaviour of manufactured gasolines in octane rating engines can be %redicted& using %revious octane ratings of s%ecial blends intended to determine how a %articular refiner"stream res%onds to an octane@enhancing additive. 5efiners can design and reconfigurerefineries to efficientl" %roduce a wide range of gasolines feedstocks& de%ending onmarket and regulator" re?uirements. >here is a worldwide trend to move to unleadedgasolines& followed b" the introduction of e+haust catal"sts and so%histicated enginemanagement s"stems.

It is im%ortant to note that ;o+"genated gasolines; have a h"drocarbon fraction that is nottoo different to traditional gasolines& but that the h"drocarbon fraction of ;reformulated


26/91

gasolines; $ which also contain o+"genates ' are significantl" different to traditionalgasolines.

>he last 10 "ears of various com%ositional changes to gasolines for environmental andhealth reasons have resulted in fuels that do not follow historical rules& and the

regulations ma%%ed out for the ne+t decade also ensure the com%osition will remain in astate of flu+. >he reformulated gasoline s%ecifications& es%eciall" the 1:Oan:1//Com%le+ model& will %robabl" introduce maor reductions in the distillation range& aswell as changing the various limits on com%osition and emissions.

IKm not going to list all *008 )Cs in gasolines& but the following are re%resentative of thevarious classes t"%icall" %resent in a gasoline. >he numbers after each chemical areG@5esearch Blending 6ctane G 9otor Blending 6ctane G Boiling oint $C'G ensit" $g:ml U1*C' G 9inimum Autoignition >em%erature $C'. It is im%ortant to realise that theBlending 6ctanes are derived from a 20M mi+ of the )C with a ,0G!0 iCGnC- $ ,06ctane 7umber ' base fuel& and the e+tra%olation of this 20M to 100M. >hese numbers

result from AI roect !*& and are readil" available. As modern refiner" streamshave higher base octanes& these Blending 6ctanes are higher than those t"%icall" used inmodern refineries. For e+am%le& modern Blending 6ctane ratings can be much lower$ toluene E 111567 and /!967& 2@meth"l@2@butene E 113567 and 1967 '& butdetailed com%ilations are difficult to obtain.

>he techni?ue for obtaining Blending 6ctanes is different from rating the %ure fuel&which often re?uires adustment of the test engine conditions outside the acce%table limitsof the rating methods. he (# is reducingthe levels of aromatics to 2*M or lower for environmental and human health reasons.

#ome countries are increasing the level of aromatics to *0M or higher in su%er unleadedgrades& usuall" to avoid refiner" reconfiguration costs or the introduction of o+"genatesas the" %hase out the to+ic lead octane enhancers. An u%%er limit is usuall" %laced on theamount of benHene %ermitted& as it is known human carcinogen.

! n-ara::ins RO* MO* 7P d A$

n-butane 3 F 4 F -#.!F ;as F 3

n-entane (' F (( F 3! F #.('( F '(#

n-e5ane 9 F '' F (9 F #.(!9 F ''!

n-etane 1#F# by de:inition # F # F 98 F #.(84 F ''!

n-o+tane -8 F -( F '( F #. F ''#

1 you @ould not @ant to ave te :ollo@in; al2anes in ;asoline)

so you @ould never blend 2erosine @it ;asoline


27/91

n-de+ane -4 F -38 F &4 F #.&3# F '#

n-dode+ane -88 F -9# F '( F #.&!# F '#4

n-tetrade+ane -9# F -99 F '!3 F #.&(3 F '##

3# iso-ara::ins

'-,etylroane '' F '# F -' F ;as F 4(#

'-,etylbutane ## F #4 F '8 F #.('# F 4'#

'-,etylentane 8' F &8 F (' F #.(!3 F 3#(

3-,etylentane 8( F 8# F (4 F #.((4 F -

'-,etyle5ane 4# F 4' F 9# F #.(&9 F

3-,etyle5ane !( F !& F 9 F #.(8& F

')'-di,etylentane 89 F 93 F &9 F #.(&4 F

')')3-tri,etylbutane ' F ' F 8 F #.(9# F 4'#

')')4-tri,etylentane ## F ## F 98 F #.(9' F 4!

1 ##F## by de:inition

' +y+loara::ins

+y+loentane 4 F 4 F !# F #.&! F 38#

,etyl+y+loentane #& F 99 F &' F #.&49 F

+y+loe5ane # F 9& F 8 F #.&&9 F '4!

,etyl+y+loe5ane #4 F 84 F # F #.& F '!#

3! aro,ati+s

benene 98 F 9 F 8# F #.8&4 F !(# toluene '4 F ' F F #.8(& F 48#

etyl benene '4 F #& F 3( F #.8(& F 43#

,eta-5ylene (' F '4 F 38 F #.8(8 F 4(3

ara-5ylene !! F '( F 38 F #.8(( F !3#

orto-5ylene '( F #' F 44 F #.8 F !3#

3-etyltoluene (' F 38 F !8 F #.8(! F

)3)!-tri,etylbenene F 3( F (3 F #.8(4 F

)')4-tri,etylbenene 48 F '4 F (8 F #.889 F

8 ole:ins

'-entene !4 F 38 F 3& F #.(49 F

'-,etylbutene-' &( F 4# F 3( F #.((' F

'-,etylentene-' !9 F 48 F (& F #.(9# F

+y+loentene & F '( F 44 F #.&&4 F

1 te :ollo@in; ole:ins are not resent in si;ni:i+ant a,ounts

in ;asoline) but ave so,e o: te i;est blendin; o+tanes

-,etyl+y+loentene 84 F 4( F &! F #.&8# F

)3 +y+loentadiene '8 F 49 F 4' F #.8#! F

di+y+loentadiene ''9 F (& F F .#& F


28/91

>here are some other %ro%erties of o+"genates that have to be considered when the" aregoing to be used as fuels& %articularl" their abilit" to form ver" volatile aHeotro%es thatcause the fuelKs va%our %ressure to increase& the chemical nature of the emissions& andtheir tendenc" to se%arate into a se%arate water@o+"genate %hase when water is %resent.>he reformulated gasolines address these %roblems more successfull" than the originalo+"genated gasolines.

Before "ou rush out to make a highl" aromatic or olefinic gasoline to %roduce a highoctane fuel& remember the" have other adverse %ro%erties& eg the aromatics attackelastomers& ma" generate smoke& and result in increased emissions of to+ic benHene. >heolefins are unstable $ besides smelling foul ' and form gums. >he art of correctl"formulating a gasoline that does not cause engines to knock a%art& does not cause va%ourlock in summer @ but is eas" to start in winter& does not form gums and de%osits& burnscleanl" without soot or residues& and does not dissolve or %oison the car catal"st orowner& is based on knowledge of the gasoline com%osition.

.% &s gasoline to$ic or carcinogenic

>here are several known to+ins in gasoline& some of which are confirmed humancarcinogens. >he most famous of these to+ins are lead and benHene& and both areregulated. >he other aromatics and some to+ic olefins are also controlled. 4ead alk"lsalso re?uire eth"lene dibromide and:or eth"lene dichloride scavengers to be added to thegasoline& both of which are sus%ected human carcinogens. In 1//3 an International#"m%osium on the )ealth =ffects of heo+"genates are also being evaluated for carcinogenicit"& and even ethanol and =>B= ma" be carcinogens. >he introduction of o+"genated gasoline to Alaska and some other areasof the (#A resulted in a range of com%laints. 5ecent research has been unable to identif"additional to+icit"& but has detected increased levels of offensive smell *!J. It should benoted that the o+"genated gasolines were not initiall" intended to reduce the to+icit" ofemissions. >he reformulated gasolines will %roduce different emissions& and s%ecificto+ins must initiall" be reduced b" 1*M all "ear.

>he removal of alk"l lead com%ounds certainl" reduces the to+icit" of e+haust gasemissions when used on engines with modern engine management s"stems and 3@wa"e+haust catal"sts. If unleaded gasolines are not accom%anied b" the introduction ofcatal"sts& some other to+ic emissions ma" increase. =ngines without catal"sts will %roduce increased levels of to+ic carbon"ls such as formaldeh"de and acrolein whenusing o+"genated fuels& and increased levels of to+ic benHene when using highl"aromatic fuels.

>here is little doubt that gasoline is full of to+ic chemicals& and should therefore betreated with res%ect. )owever the biggest danger remains the flammabilit"& and therelative haHards should alwa"s be ke%t in %ers%ective. >he maor to+ic risk from


29/91

gasolines comes from breathing the tail%i%e& eva%orative& and refuelling emissions& ratherthan occasional skin contact from s%ills. Breathing va%ours and skin contact shouldalwa"s be minimised.

.%4 &s unlea#e# gasoline more to$ic than lea#e#

>he short answer is no. )owever that answer is not global& as some countries havere%laced the lead com%ound octane@im%rovers with aromatic or olefin octane@im%roverswithout introducing e+haust catal"sts. >he aromatics contents ma" increase to around!0M& with high octane unleaded fuels reaching *0M in countries where o+"genates arenot being used& and the %roducers have not reconfigured refineries to %roduce high octane %araffins. In general& aromatics are significantl" more to+ic than %araffins. =+haustcatal"sts have a limited o%erational life& and will be immediatel" %oisoned if misfuelledwith leaded fuel. Catal"st failure can result in higher levels of to+ic emissions if catal"stsor engine management s"stems are not re%laced or re%aired when defective. 9a+imum benefit of the switch to unleaded are obtained when the introduction of unleaded is

accom%anied b" the introduction of e+haust catal"sts and so%histicated enginemanagement s"stems.

(nfortunatel"& the manufacturers of alk"l lead com%ounds have embarked on aworldwide misinformation cam%aign in countries considering emulating the lead@free (#.>he use of lead %recludes the use of e+haust catal"sts& thus the emissions of aromatics areonl" slightl" diminished& as leaded fuels t"%icall" contain around 30@!0M aromatics.6ther to+ins and %ollutants that are usuall" reduced b" e+haust catal"sts will be emittedat significantl" higher levels if leaded fuels are used **J.

>he use of unleaded on modern vehicles with engine management s"stems and catal"sts

can reduce aromatic emissions to 10M of the level of vehicles without catal"sts **J.Alk"l lead additives can onl" substitute for some of the aromatics in gasoline&conse?uentl" the" do not eliminate aromatics& which will %roduce benHene emissions*,J. Alk"l lead additives also re?uire to+ic organohalogen scavengers& which also reactin the engine to form and emit other organohalogens& including highl" to+ic dio+in *-J.4eaded fuels emit lead& organohalogens& and much higher levels of regulated to+ins because the" %reclude the use of e+haust catal"sts. In the (#A the gasoline com%ositionis being changed to reduce fuel to+ins $ olefins& aromatics ' as well as emissions ofs%ecific to+ins.

.%5 &s re!ormulate# gasoline more to$ic than unlea#e#

>he evidence so far indicates that the com%onents of reformulated gasolines $ 5F


30/91

emission of 9>B= is increased about 10+ on cars without catal"sts and !+ on cars withcatal"sts **J.When all the emissions $ eva%orative and tail%i%e ' are considered& 5Fhere has been an e+tensive series of re%orts on the emissionsfrom 5Fhe maor ?uestion about 5Fhe (#=A also mandated their use to reduce %ollution& mainl" via the ;enleanment; effect onengines without so%histicated management s"stems& but also because of the ;aromaticssubstitution; effect. As vehicles with fuel inection and so%histicated engine managements"stems became %ervasive& reformulated gasolines could be introduced to further reduce %ollution. >he h"drocarbon com%onent of 5Fheeffect of the additional C62 on the global environment is not known& but the ?uantit" ofman@made emissions of fossil fuels must cause the s"stem to move to a new e?uilibrium.=ven if current research doubles the efficienc" of the IC engine@gasoline combination&and reduces )C& C6& 76+& #6+& 6Cs& %articulates& and carbon"ls& the amount ofcarbon dio+ide from the use of fossil fuels ma" still cause global warming.


31/91

9ore and more scientific evidence is accumulating that warming is occurring ,!&,*J.>he issue is whether it is natural& or induced b" human activities and and a large %anel ofscientific e+%erts continues to review scientific data and models. Interested reader shouldseek out the various %ublications of the Intergovernmental anel on Climate Change$ICC'. >here are international agreements to limit C62 emissions to 1//0 levels& a

target that will re?uire more efficient& lighter& or a%%ro%riatel"@siHed vehicles& @ if we areto maintain the current usage. 6ne o%tion is to use ;renewable; fuels in %lace of fossilfuels. Consider the amount of energ"@related C62 emissions for selected countries in1//0 ,,J.

CO' E,issions

1 tonnes/year/erson

USA '#.#

Canada (.4

Australia !.9

"er,any #.4

United in;do, 8.(

=aan &.&

*e@ Gealand &.(

>he number of new vehicles %rovides an indication of the magnitude of the %roblem.Although vehicle engines are becoming more efficient& the distance travelled isincreasing& resulting in a gradual increase of gasoline consum%tion. >he world %roductionof vehicles $in thousands' over the last few "ears was ,-J@

Cars

Re;ion 99# 99 99' 993 994

A:ri+a ''' '3 94 '# '#9

Asia-Pa+i:i+ ')#(4 ')' )8(9 )4(3 )#'#Central H Sout A,eri+a 8## 888 )!8 )!'3 )&'&

Eastern Euroe ')4(( 984 )&'( )83& )!4&

Middle East 3! '4 3## 39# '&4

*ort A,eri+a &)&(' &)'3# &)4 8)&' 8)((

%estern Euroe 3)(88 3)'8( 3)#9& )4 ')8!

$otal %orld 3&)#39 34)&39 3!)8! 34)&' 3()'89

>rucks $ including heav" trucks and buses '

Re;ion 99# 99 99' 993 994

A:ri+a 33 '3 #8 # (

Asia-Pa+i:i+ !)# !)#&4 !)& !)#!& !)4#&Central H Sout A,eri+a 3' 3'& 3! 43 4!&

Eastern Euroe 98# &&( &# (## '44

Middle East 3( '8 ## '8 &(

*ort A,eri+a 4)8! 4)!!4 !)3& ()#3& &)#4#

%estern Euroe )9'4 )88 )8(9 )&8 ')(

$otal %orld 3)33( ') 3)('& 4)#&3 !)4!&

>o fuel all o%erating vehicles& considerable ?uantities of gasoline


32/91


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>here was a further reason wh" alk"l lead com%ounds were subse?uentl" reduced& andthat was the growing recognition of the highl" to+ic nature of the emissions from aleaded@gasoline fuelled engine. 7ot onl" were to+ic lead emissions %roduced& but theadded to+ic lead scavengers $ eth"lene dibromide and eth"lene dichloride ' could reactwith h"drocarbons to %roduce highl" to+ic organohalogen emissions such as dio+in. =ven

if catal"sts were removed& or lead@tolerant catal"sts discovered& alk"l lead com%oundswould remain banned because of their to+icit" and to+ic emissions -0&-1J.

4. +hy are evaporative emissions a problem

As tail%i%e emissions are reduced due to im%roved e+haust emission control s"stems& theh"drocarbons %roduced b" eva%oration of the gasoline during distribution& vehiclerefuelling& and from the vehicle& become more and more significant. A recent =uro%eanstud" found that !0M of man@made volatile organic com%ounds came from vehicles -2J.9an" of the %roblem h"drocarbons are the aromatics and olefins that have relativel" highoctane values. An" sensible strateg" to reduce smog and to+ic emissions will also attack

eva%orative and tail%i%e emissions.

>he health risks to service station workers& who are continuousl" e+%osed to refuellingemissions remain a concern -3J. ehicles will soon be re?uired to tra% the refuellingemissions in larger carbon canisters& as well as the normal eva%orative emissions thatthe" alread" ca%ture. >his recent decision went in favour of the oil com%anies& who wereo%%osed b" the auto com%anies. >he automobile manufacturers felt the service stationshould tra% the emissions. >he activated carbon canisters adsorb organic va%ours& andthese are subse?uentl" desorbed from the canister and burnt in the engine during normalo%eration& once certain vehicle s%eeds and coolant tem%eratures are reached. A fewactivated carbons used in older vehicles do not function efficientl" with o+"genates& but

carbon cannister s"stems can reduce eva%orative emissions b" /*M from uncontrolledlevels.

4.4 +hy control tailpipe emissions

>ail%i%e emissions were res%onsible for the maorit" of %ollutants in the late 1/,0s afterthe crankcase emissions had been controlled. 6Hone levels in the 4os Angeles basinreached !*0@*00%%b in the earl" 1/-0s& well above the t"%ical background of 30@*0%%b-!J.

>uning a carburetted engine can onl" have a marginal effect on %ollutant levels& and therestill had to be some fre?uent& but long@term& assessment of the state of tuning. =+haustcatal"sts offered a %ost@engine solution that could ensure %ollutants were converted tomore benign com%ounds. As engine management s"stems and fuel inection s"stems havedevelo%ed& the volatilit" %ro%erties of the gasoline have been tuned to minimiseeva%orative emissions& and "et maintain low e+haust emissions.

>he design of the engine can have ver" significant effects on the t"%e and ?uantit" of %ollutants& eg unburned h"drocarbons in the e+haust originate mainl" from combustion


34/91

chamber crevices& such as the ga% between the %iston and c"linder wall& where thecombustion flame can not com%letel" use the )Cs. >he t"%e and amount of unburnth"drocarbon emissions are related to the fuel com%osition $volatilit"& olefins& aromatics&final boiling %oint'& as well as state of tune& engine condition& and condition of the enginelubricating oil -*J. articulate emissions& es%eciall" the siHe fraction smaller than ten

micrometres& are a serious health concern. >he current maor source is from com%ressionignition $ diesel ' engines& and the modern #I engine s"stem has no %roblem meetingregulator" re?uirements.

>he abilit" of reformulated gasolines to actuall" reduce smog has not "et been confirmed.>he com%osition changes will reduce some com%ounds& and increase others& making %redictions of environmental conse?uences e+tremel" difficult. lanned future changes&such as the CAA 1:1:1// Com%le+ model s%ecifications& that are based on several maor ongoing government:industr" gasoline and emission research %rogrammes& are morelikel" to %rovide unambiguous environmental im%rovements. 6ne of the maor %roblemsis the nature of the oHone@forming reactions& which re?uire several com%onents

$ 6C& 76+& ( ' to be %resent. ehicles can %roduce the first two& but the their ratio isim%ortant& and can be affected b" %roduction from other natural $ 6C E ter%enes fromconifers ' or manmade $ 76+ from %ower stations ' sources ,2&,3J. >he regulations fortail%i%e emissions will continue to become more stringent as countries tr" to minimiselocal %roblems $ smog& to+ins etc.' and global %roblems $ C62 '. 5eformulation does notalwa"s lower all emissions& as evidenced b" the following aldeh"des from an engine withan ada%tive learning management s"stem **J.

$P-@ei;ted e,ission rates 1,;/,i

"asoline Re:or,ulated

or,aldeyde 4.8& 8.43

A+etaldeyde 3.#& 4.&

>he t"%e of e+haust catal"st and management s"stem can have significanteffects on the emissions **J.

$P-@ei;ted e,ission rates. 1,;/,i

$otal Aro,ati+s $otal Carbonyls

"asoline Re:or,ulated "asoline Re:or,ulated

*on+atalyst '9'.4! 4.8' &4.!# 98.&3

O5idation Catalyst (8.(# !#.&9 (&.#8 &(.94

3-@ay Catalyst 3'. 93.3& '3.93 '3.#&

Adative he latter four are combined as C Aromatics below **J.

Aro,ati+s $P-@ei;ted e,ission rates. 1,;/,i

7enene $oluene C8 Aro,ati+s

"as Re:or, "as Re:or, "as Re:or,

*on+atalyst !(.8 38.48 338.3( 34.4 4'!.84 38#.44

O5idation Cat. '&.!& '!.# !.## 44.3 !'.'& 4&.#&

3-@ay Catalyst 9.39 !.(9 3(.(' '(.4 4'.38 '9.#3


35/91

Adative here are several bodies res%onsible for establishing standards& and the" %romulgate testc"cles& anal"sis %rocedures& and the M of new vehicles that must com%l" each "ear. >hetest c"cles and %rocedures do change $ usuall" indicated b" an anomalous increase in thenumbers in the table '& and I have not listed the %ercentages of the vehicle fleet that arere?uired to com%l". >his table is onl" intended to conve" where we have been& and where

we are going. It does not cover an" regulation in detail @ readers are advised to refer tothe relevant regulations. Additional limits for other %ollutants& such as formaldeh"de$0.01*g:mi.' and %articulates $0.0g:mi'& are omitted. >he 1//! tests signal the federaltransition from *0&000 to 100&000 mile com%liance testing& and I have not listed thesubse?uent *0&000 mile limits 2&-,&--J.

Iear ederal Cali:ornia

Cs CO *O5 Eva Cs CO *O5 Eva

;/,i ;/,i ;/,i ;/test ;/,i ;/,i ;/,i ;/test

7e:ore re;s #.( 84.# 4. 4& #.( 84.# 4. 4&

add +ran2+ase J4. J4.

9(( (.3 !.# (.#

9(8 (.3 !.# (.#

9 4. 34.# 4. 34.# (9& 4. 34.# (1CC 4. 34.# 4.# (

9&' 3.# '8.# ' '.9 34.# 3.# '

9&3 3.# '8.# 3.# '.9 34.# 3.# '

9&4 3.# '8.# 3.# '.9 34.# '.# '

9&! .! !.# 3. ' #.9# 9.# '.# '

9&& .! !.# '.# ' #.4 9.# .! '

98# #.4 &.# '.# (1SED #.4 9.# .# '

98 #.4 3.4 .# ' #.39 &.# #.& '


36/91

993 #.4 3.4 .# ' #.'! 3.4 #.4 '

994 !#)### #.'( 3.4 #.3 ' $


37/91

'. E$7E) $AME

4.( ;asoline @itout o5y;enates

>he engine management s"stem ra%idl" switches the stoichiometr" between slightl" richand slightl" lean& e+ce%t under wide o%en throttle conditions when the s"stem runs o%enloo%. >he res%onse of the o+"gen sensor to com%osition changes is about 3 ms& and

closed loo% switching is t"%icall" 1@3 times a second& going between *0m $ lambda E1.0* $4ean'' to /00m $lambda E 0.// $ 5ich''. >he catal"st o+idises about 0M of the)2& C6& and )Cs& and reduces the 76+ -,J.

>"%ical reactions that occur in a modern 3@wa" catal"st areG@

'' J O' -K ''O

'CO J O' -K 'CO'

C5y J 15 J 1y/4O' -K 5CO' J 1y/''O

'CO J '*O -K *' J 'CO'

C5y J '15 J 1y/4*O -K 15 J 1y/4*' J 1y/''O J 5CO'

'' J '*O -K *' J ''O

CO J '# -K CO' J ' C5y J 5'O -K 5CO J 15 J 1y/''

>he use of e+haust catal"sts have resulted in reaction %athwa"s that can accidentall" beres%onsible for increased %ollution. An e+am%le is the CA5B@mandated reduction of fuelsulfur. A change from !*0%%m to *0%%m& which will reduce )C V C6 emissions b" 20M&was shown to increase formaldeh"de b" !*M& but testing in later model cars did note+hibit the same effect 32&*& */J. >his demonstrates that continuing changes to enginemanagement s"stems can also change the res%onse to fuel com%osition changes.

>he re?uirement that the e+haust catal"sts must now endure for 10 "ears or 100&000miles will also encourage automakers to %ush for lower levels of elements that affecte+haust catal"st %erformance& such as sulfur and %hos%horus& in both the gasoline andlubricant. 9odern catal"sts are unable to reduce the relativel" high levels of 76+ that are %roduced during lean o%eration down to a%%roved levels& thus %reventing the a%%licationof lean@burn engine technolog". 5ecentl" 9aHda has announced the" have develo%ed a;lean burn; catal"st& which ma" enable automakers to move the fuel combustion towardsthe lean side& and different gasoline %ro%erties ma" be re?uired to o%timise thecombustion and reduce %ollution 1J. 9aHda claim that fuel efficienc" is im%roved b" *@M& while meeting all emission regulations& and some Oa%anese manufacturers haveevaluated lean@burn catal"sts in limited numbers of 1//* %roduction models.

Catal"sts also inhibit the selection of gasoline octane@im%roving and cleanliness additives$ such as 99> and %hos%horus@containing additives ' that ma" result in refractor"com%ounds known to %h"sicall" coat the catal"st& reducing available catal"st and thusincreasing %ollution.


38/91

4.6 +hy are @col# start@ emissions so important

>he catal"st re?uires heat to reach the tem%erature $ T300@3*0C ' where it functions most

efficientl"& and the dela" until it reaches o%erating tem%erature can %roduce moreh"drocarbons than would be %roduced during the remainder of man" t"%ical urban shorttri%s. It has been estimated that -0@0M of the non@methane )Cs that esca%e conversion b" the catal"sts are emitted during the first two minutes after a cold start. As e+haustemissions have been reduced& the significance of the eva%orative emissions increases.#everal engineering techni?ues are being develo%ed& including the Ford =+haust here are several maor %roects intending to furtherreduce emissions from automobiles& mainl" focusing on vehicle mass and engine fuelefficienc"& but gasoline s%ecifications and alternative fuels are also being investigated. Itma" be that changes to IC engines and gasolines will enable the IC engine to continuewell into the 21st centur" as the %rime motive force for %ersonal trans%ortation --&*J.>here have also been calls to use market forces to reduce %ollution from automobiles,J& however most such suggestions $ increased gasoline ta+es& congestion tolls& andemission@based registration fees ' are currentl" considered %oliticall" unacce%table. >heissue of how to target the s%ecific ;gross %olluters; is being considered& and is describedin #ection *.1!.

4.7 +hy are only some gasoline compoun#s restricte#

>he less volatile h"drocarbons in gasoline are not released in significant ?uantities duringnormal use& and the more volatile alkanes are considerabl" less to+ic than man" otherchemicals encountered dail". >he newer gasoline additives also have %otentiall"


39/91

undesirable %ro%erties before the" are even combusted. 9ost h"drocarbons are ver"insoluble in water& with the lower aromatics being the most soluble& however the additionof o+"gen to h"drocarbons significantl" increases the mutual solubilit" with water.

Co,ound in %ater %ater in Co,ound

,ass/,ass L C ,ass/,ass L C

nor,al de+ane #.#####!' '! #.##&' '!iso-o+tane #.###'4 '! #.##!! '#

nor,al e5ane #.##'! '! #.# '#

+y+loe5ane #.##!! '! #.## '#

-e5ene #.##(9& '! #.#4&& 3#

toluene #.#!! '! #.#334 '!

benene #.&9 '! #.#(3! '!

,etanol +o,lete '! +o,lete '!

etanol +o,lete '! +o,lete '!

M$7E 4.8 '# .4 '#

$AME - #.( '#

>he concentrations and ratios of benHene& toluene& eth"l benHene& and +"lenes $ B>=S 'in water are often used to monitor groundwater contamination from gasoline storagetanks or %i%elines. >he o+"genates and other new additives ma" increase the e+tent ofwater and soil %ollution b" acting as co@solvents for )Cs.

arious government bodies $ =A& 6#)A& 7I6#) ' are charged with ensuring %eo%le arenot e+%osed to unacce%table chemical haHards& and maintain ongoing research into theto+icit" of li?uid gasoline contact& water and soil %ollution& eva%orative emissions& andtail%i%e emissions -J. As to+icit" is found& the ?uantities in gasoline of the s%ecificchemical $ benHene '& or famil" of chemicals $ alk"l leads& aromatics& olefins ' areregulated.

>he recent dramatic changes caused b" the need to reduce alk"l leads& halogens& olefins&and aromatics has resulted in whole new families of com%ounds $ ethers& alcohols ' beingintroduced into fuels without %rior detailed to+icit" studies being com%leted. If adverseresults a%%ear& these com%ounds are also likel" to be regulated to %rotect %eo%le and theenvironment.

Also& as the chemistr" of emissions is unravelled& the chemical %recursors to to+ictail%i%e emissions $ such as higher aromatics that %roduce benHene emissions ' are alsocontrolled& even if the" are not themselves to+ic.

4.%8 +hat #oes @rene)able@ !uel or o$ygenate mean

>he general definition of ;renewable; is that the carbon originates from recent biomass&and thus does not contribute to the increased C62 emissions. A trul" ;long@term; viewcould claim that fossil fuels are ;renewable; on a 100 million "ear timescale G@'. >herewas a maor battle between the ethanol:=>B= lobb" $ agricultural& corn growing '& andthe methanol:9>B= lobb" $ oil com%an"& %etrochemical ' over an =A mandatedemanding that a s%ecific %ercentage of the o+"genates in gasoline are %roduced from


40/91

;renewable; sources J. 6n 2 A%ril 1//* a Federal a%%eals court %ermanentl" voidedthe =A ruling re?uiring ;renewable; o+"genates& thus fossil@fuel derived o+"genatessuch as 9>B= are acce%table o+"genates /J.

(nfortunatel"& ;renewable; ethanol is not cost com%etitive when crude oil is N1:bbl& so a

federal subsid" $ N0.*!:(# enn.':(# he ;reactivit";


41/91


42/91

a%%lies for the )C emitters@ which ma" not be the same vehicles /1@102J. 20M of the C6 emitters are res%onsiblefor 0M of the C6 emissions& conse?uentl" modif"ing gasoline com%osition is onl" oneas%ect of %ollution reduction. >he new additives can hel% maintain engine condition& butthe" can not com%ensate for out@of@tune& worn& or tam%ered@with engines. >here has

recentl" been some un%ublished studies that demonstrate that the current generation ofremote sensing s"stems can not %rovide sufficient discrimination of gross %olluterswithout also %roducing false %ositives for some acce%tion vehicles @ more work isre?uired& and in some states IV9 emissions testing using d"namometers is beingintroduced to identif" gross %olluters.

>he most famous of the remote sensing s"stems is the F=A> $ Fuel =fficienc"Automobile >est ' team from the (niversit" of enver //J. >his team is %robabl" theworld leader in remote sensing of auto emissions to identif" grossl" %olluting vehicles.>he s"stem measures C6:C62 ratio& and the )C:C62 ratio in the e+haust of vehicles

%assing through an infra@red light beam crossing the road 2*cm above the surface. >hes"stem also includes a video s"stem that records the licence %late& date& time& calculatede+haust C6& C62& and )C. >he s"stem is effective for traffic lanes u% to 1 metreswide& however rain& snow& and water s%ra" can cause scattering of the beam.5eferencesignals monitor such effects and& if %ossible& com%ensate. >he s"stem has beencom%rehensivel" validated& including using vehicles with on@board emissions monitoringinstruments.

>he" can monitor u% to 1000 vehicles an hour and& as an e+am%le&the" were invited torovo& (tah to monitor vehicles& and gross %olluters would be offered free re%airs 100J.>he" monitored over 10&000 vehicles and mailed 11! letters to owners of vehicles newer

than 1/,* that had demonstrated high C6 levels. >he" received *2 res%onses and re%airsstarted in ec. 1//1& and continued to 9ar 1//2.

$e entire ,onitored :leet at Provo 1Uta durin; %inter 99F99'

Model year "ra,s CO/;allon *u,ber o:

1Median value 1,ean value ?ei+les

9' 4# 8# '4&

9 !! '''

9# &! 4(&

89 8# !'

88 8! (!

8& 9# 439

8( ## 3## !(3

8! '# !&!

84 '! '#(

83 4! &9

8' (39

8 '3# ('

8# ''# !## !!

&9 3!# ((&

&8 4'# !84

&& 43# 43#

&( & 3&


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&! &(# 9!# (3

Pre &! 9'# #(# 8&8

As observed elsewhere& over half the C6 was emitted b" about 10M of the vehicles. If the!- worst %olluting vehicles were removed& that achieves more than removing the 2&*00lowest emitting vehicles from the total tested fleet.

#urve"s of vehicle %o%ulations have demonstrated that emissions s"stems had been tam%ered with on over !0M of the gross %olluters& and an additional 20M haddefective emission control e?ui%ment 101J. 7o matter what changes are made togasoline& if owners ;tune; their engines for %ower& then the maorit" of such ;tuned;vehicle will become gross %olluters. rofessional re%airs to gross %olluters usuall"im%roves fuel consum%tion& resulting in a low cost to owners $ N32:%a:>on C6 "ear '.>he removal of C6 in the rovo e+am%le above was costed at N200:>on C6& com%ared toIns%ection and 9aintenance %rograms $N-0:>on C6 '& and o+"genates $ N103!@N12,!:>on C6 in Colorado 1//1@2 '& and (76CA4s vehicle scra%%ing %rogramme$ N102*:>on of all %ollutants '.

>hus& identif"ing and re%airing or removing gross %olluters can be far more cost@effectivethan %la"ing around with reformulated gasolines and o+"genates. A recent stud" hasconfirmed that gross %olluters are not alwa"s older vehicles& and that vehicles have beenscra%%ed that %assed the 1//3 new vehicle emission standards 102J. >he stud" alsoconfirmed that if estimated costs and benefits of various emission reduction strategieswere a%%lied to the tested fleet& the identification and re%air techni?ues are the mostcost@effective means of reducing )C and C6. It should be noted that some strategies$ such as the use of o+"genates to re%lace aromatics and alk"l lead com%ounds ' haveother environmental benefits.

A+tion ?ei+les Esti,ated redu+tion redu+tion

A::e+ted Cost er

billion

1,illions 1billion C CO C CO

Re:or,ulated uels '# .! &

&.3

S+ra re-98# vei+les 3.' '.' 33 4' ! 9

S+ra re-988 vei+les 4.( & 44 (& '.(

3.9

Reair @orst '# o: vei+les 4 #.88 !# ( !&

(9

Reair @orst 4# o: vei+les 8 .&( (8 83 39

4&


44/91

5.% +ho invente# he engineers had blamed the ;knock; on the batter" ignition s"stem that was added tocars along with the electric self@starter. >he engine develo%ers knew that the" couldim%rove %ower and efficienc" if knock could be overcome.

Dettering assigned >homas 9idgle"& Or. to the task of finding the e+act cause of knock2!J. >he" used a obbie@9cInnes manogra%h to demonstrate that the knock did notarise from %reignition& as was commonl" su%%osed& but arose from a violent %ressure riseRafterR ignition. >he manogra%h was not suitable for further research& so 9idgle" andBo"d develo%ed a high@s%eed camera to see what was ha%%ening. >he" also develo%ed a;bouncing %in; indicator that measured the amount of knock /J. 5icardo had develo%edan alternative conce%t of )(CF $ )ighest (seful Com%ression 5atio ' using a variable@

com%ression engine. )is numbers were not absolute& as there were man" variables& suchas ignition timing& cleanliness& s%ark %lug %osition& engine tem%erature. etc.

In 1/2- oda" we call it ; iso@octane ;or 2&2&!@trimeth"l %entane. >he octane had a high antiknock value& and he suggestedusing the ratio of the two as a reference fuel number. )e demonstrated that all thecommerciall"@ available gasolines could be bracketed between ,0G!0 and !0G,0 %arts b"volume he%taneGiso@octane.

>he reason for using normal he%tane and iso@octane was because the" both have similarvolatilit" %ro%erties& s%ecificall" boiling %oint& thus the var"ing ratios 0G100 to 100G0should not e+hibit large differences in volatilit" that could affect the rating test.

eat o:

Meltin; Point 7oilin; Point Density ?aorisation

C C ;/,l M=/2;

nor,al etane -9#.& 98.4 #.(84 #.3(! L '!C

iso o+tane -#&.4! 99.3 #.(99 #.3#8 L '!C

)aving decided on standard reference fuels& a whole range of engines and test conditionsa%%eared& but toda" the most common are the 5esearch 6ctane 7umber $ 567 '& and the9otor 6ctane 7umber $ 967 '.

5.' +hy #o )e nee# o obtain the ma+imum energ" from the gasoline& the com%ressed fuel@air mi+ture insidethe combustion chamber needs to burn evenl"& %ro%agating out from the s%ark %lug until


45/91

all the fuel is consumed. >his would deliver an o%timum %ower stroke. In real life& aseries of %re@flame reactions will occur in the unburnt ;end gases; in the combustionchamber before the flame front arrives. If these reactions form molecules or s%ecies thatcan autoignite before the flame front arrives& knock will occur 21&22J.

#im%l" %ut& the octane rating of the fuel reflects the abilit" of the unburnt end gases toresist s%ontaneous autoignition under the engine test conditions used. If autoignitionoccurs& it results in an e+tremel" ra%id %ressure rise& as both the desired s%ark@initiatedflame front& and the undesired autoignited end gas flames are e+%anding. >he combined %ressure %eak arrives slightl" ahead of the normal o%erating %ressure %eak& leadingto a loss of %ower and eventual overheating. >he end gas %ressure waves aresu%erim%osed on the main %ressure wave& leading to a sawtooth %attern of %ressureoscillations that create the ;knocking; sound.

>he combination of intense %ressure waves and overheating can induce %iston failure in afew minutes. Dnock and %reignition are both favoured b" high tem%eratures& so one ma"

lead to the other. (nder high@s%eed conditions knock can lead to %reignition& which thenaccelerates engine destruction 2-&2J.

5.* +hat !uel property #oes the he fuel %ro%ert" the octane ratings measure is the abilit" of the unburnt end gases tos%ontaneousl" ignite under the s%ecified test conditions.Within the chemical structure ofthe fuel is the abilit" to withstand %re@flame conditions without decom%osing into s%eciesthat will autoignite before the flame@front arrives. ifferent reaction mechanisms&occurring atvarious stages of the %re@flame com%ression stroke& are res%onsible for theundesirable& easil"@autoignitable& end gases.

uring the o+idation of a h"drocarbon fuel& the h"drogen atoms are removed one at atime from the molecule b" reactions with small radical s%ecies $such as 6) and )62'&and 6 and ) atoms. >he strength of carbon@h"drogen bonds de%ends on what the carbonis connected to. #traight chain )Cs such as normal he%tane have secondar" C@) bondsthat are significantl" weaker than the %rimar" C@) bonds %resent in branched chain )Cslike iso@octane 21&22J.

>he octane rating of h"drocarbons is determined b" the structure of the molecule& withlong& straight h"drocarbon chains %roducing large amounts of easil"@autoignitable %re@flame decom%osition s%ecies& while branched and aromatic h"drocarbons are moreresistant. >his also e+%lains wh" the octane ratings of %araffins consistentl" decrease withcarbon number. In real life& the unburnt ;end gases; ahead of the flame front encountertem%eratures u% to about -00C due to com%ression and radiant and conductive heating&and commence a series of %re@flame reactions. >hese reactions occur at different thermalstages& with the initial stage $ below !00C ' commencing with the addition of molecularo+"gen to alk"l radicals& followed b" the interna

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