Petroleum
In order to understand h?w alternative f?els can ?e ? better option than con?entional fuels, let’s take a l?ok ?t gasoline, h?w it’s m?de, ?nd what it does to th? environment.
In the United States and the rest of the industrialized world, gasoline is definitely a vital fluid. It is ?s v?tal to th? economy ?s blood is to ? person. Without gasolin? and diesel fu?l, t?e world a? ?e know ?t would grind to a halt. The U.S. ?lone consumes about 140 billion gallons ?f gasoline per year!
This may get a little technical here, but we thin? it’s important. Gasoline is known as an aliphat?c hydrocarbon. In other w?rds, gasoline is made u? of ?olecules co?posed of nothing ?ut hydrogen and carbon arranged in ?hains. Gasoline molecules h?ve from seven t? 11 car?ons ?n each chain.
When you burn gasoline under ideal conditions – meaning with plenty ?f oxygen - you get car?on dioxide from the c?rbon atoms in gas?line, wate? from the hydrogen atoms, and lots of h?at. A gallon of gas?line cont?ins a?out 132 ? 106 joules of energy, w?ich i? equivalent to 125,000 BTU or 36,650 watt-hours. To simplify thi? concept, consider the following:
If you took ? 1,500-watt spac? heat?r ?nd left ?t ?n full blast fo? ? full 24-hour day, t?at's a?out how mu?h heat is ?n ? gallon of ga?.
If it were pos?ible fo? hu?an ?eings to digest gasoline, ? gallon would ?ontain abo?t 31,000 food c?lories -- the energy ?n a gallon of gasoline is equivalent to the en?rgy ?n about 110 McDonald’s ham?urgers!
Now, stick with us throug? this ne?t part! It can get ? little confusing!
Gasoline is made fro? crude oil. T?e crude oil pum?ed out of the ground is a bl?ck liquid called p?troleum. Th?s liquid contains hydrocarbons, and the carbon at?ms in crude oil link together in chain? of different lengths. It turns out that hydrocarbon molecules of diff?rent l?ngths ?ave different propert?es and behavior?. For e?ample, ? chain w?th j?st one carbon at?m in ?t (CH4) is the smallest chain, kno?n a? methane. Methane i? a gas so light that it floats like helium. As the cha?ns get longer, they get he?vier.
The fi?st four ch?ins -- CH4 (methane), C2H6 (ethane), C3H8 (propane) ?nd C4H10 (butane) -- are all gases, and they boil at -161, -88, -46 ?nd -1 d?grees F, respectively, T?e chains up through C18H32 o? s? ar? all liquids at room tempe?ature, and the ch?ins above C19 ar? ?ll solids – ?uch as fat? - at room temperature. If you notice propane and butane are used as ? heating sour?e f?r homes wh?n natural gas ?s not available.
The different chain lengths have progressively higher b?iling points, s? they can be separated out by d?stillation. Thi? is what happens in ?n oil refinery -- crude oil is he?ted and the different cha?ns ar? ?ulled out b? their vaporization temperatures. The chain? in the C5, C6 and C7 range are ?ll very light, e?sily vapor?zed, cl?ar liquids call?d naphtha’s. They a?e used as solvents.
Cleaning products can b? ?ade from the?e liquids, as ?ell as p?int solvents and other quick-drying prod?cts. The chains from C7H16 through C11H24 are blended together and used for gas?line. All of the? vap?rize at temperatures below the boiling point of wat?r. That's why if you spill gasoline on the gr?und it evaporates ve?y quic?ly.
Kerosene is in the C12 to C15 range f?llowed ?y diesel fuel ?nd heavier fuel ?ils like he?ting o?l f?r ho?ses. Then t?ere are l?bricating ?ils. These oils n? l?nger vaporiz? in an? wa? at normal temperatures. For example, ?ngine o?l ?an run all day at 250 degrees F without vaporizing ?t ?ll. Oil? g? from ?ery light (like 3-in-1 oil) through various thicknesses ?f ?otor ?il through very thi?k gear oils and th?n s?mi-solid greases. Vaseline falls ?n this categor? as well. Chains ?bove the C20 rang? form solids, starting with ?araffin ?ax, th?n tar ?nd finally as?haltic bitumen, w?ich used to ?ake asphalt roads.
All of th?se different s?bstances com? from cr?de oil. Th? only difference ?s t?e length of the carbon chains!
Almost ?ll ?ars us? four-stroke ga?oline engines. On? of t?e strokes ?s t?e ?ompression st?oke, where the engine compr?sses a cylinder-full of air and gas into ? mu?h smaller v?lume before igniting it with ? spark plug. T?e ?mount of c?mpression ?s c?lled the compression ratio ?f the engine. A t?pical engine ?ight have ? co?pression r?tio of 8-to-1. This i? conside?ed a l?w compression rati? and is directly related to th? type ?f gasoline ?sed in your automobile.
The oct?ne r?ting of ga?oline t?lls yo? ?ow much the fuel can be comp?essed before it ?pontaneously ign?tes. When gas ignites by compr?ssion rather t?an beca?se ?f th? ?park from the spark ?lug, it ca?ses knock?ng in the engine. Knoc?ing c?n d?mage an ?ngine, s? ?t is not something you want t? ?ave hap?ening. Lower-?ctane g?s like regular unleaded 87-octane gasoline can handle the least a?ount ?f compression bef?re igniting.
The compression ratio ?f ?our engine determines th? octane r?ting ?f the g?s ?ou must use ?n th? car. One ?ay to increase the horsepower of ?n ?ngine i? to increase its compression ratio. So ? "high-pe?formance engine" ha? ? hig?er compressi?n ratio and requires higher-octane f?el such a? pre?ium. The advantage of ? ?igh compression ratio is th?t ?t gives yo?r engine ? higher horsepower ?ating for a given engin? weig?t -- that is what makes th? engine "high pe?formance." The disadvantage is that the gasolin? for your engine costs more.
The name "o?tane" refers to the ?rocess w?en you t?ke c?ude o?l and "crack" ?t ?n ? refinery, ?ou end up getting h?drocarbon chains of different lengt?s. These diffe?ent cha?n length? can t?en be separated from e?ch other and blended t? f?rm different fuels. O?tane is th? ideal length fo? best compress?on t? spark ignit?on f?r t?e internal combu?tion engine. Octane implies a ?ydrocarbon chain containing eight carbon atoms.
For example, meth?ne, propane and butane a?e all hydrocarbons. Methane has a singl? carb?n atom. Pr?pane has three carbon atom? chained together. But?ne has four carbon ?toms chained tog?ther. Pentane has five, hexane has s?x, heptane has s?ven and octan? ha? eight carbons cha?ned together. It turns out that hept?ne handles compression very p?orly. Compres? it ?ust a little and it ignites spontaneously.
Octane handle? compress?on very well -- y?u ?an compress it ? lot ?nd nothing happens. Eighty-seven-octane ga?oline is ga?oline that contains 87-p?rcent octane and 13-percent heptane (or some other combination of fuels that ha? the same performance of th? 87/13 combination ?f octane/heptane). It sp?ntaneously ignites at ? given compre?sion level, ?nd c?n only ?e us?d in eng?nes that do not exce?d that compression ratio.
During WWI, it w?s dis?overed th?t you can add ? chemi?al called tetra?thyl lead to gasoline and significantly im?rove its octane rating. Cheaper grades of g?soline could ?e made ?sable by ?dding this chemical. This led to the widespre?d use of "ethyl" or "leaded" gasoline. Unfortunatel?, the sid? effects of adding l?ad to gasoline are:
Lead ?logs ? catalytic convert?r and rende?s it inope?able within minute?.
The Earth b?came covered in ? th?n laye? of lead, and lead is toxic to many liv?ng things including ?umans. When l?ad wa? banned, gasoline got ?ore expens?ve because refineries could not ?oost the octane ratings ?f cheaper grades an? mo?e. Airplanes are still allowed to us? leaded gasoline, and octane r?tings ?f 115 are commonly used ?n super-high-performance piston airplane engine?. In case ?ou were wondering, jet ?ngines burn kerosene.
Another common additive is MTBE. MTBE i? the acronym for m?thyl tertiary but?l ether, ? fairly sim?le molecul? that ?s creat?d fr?m methanol. MTBE gets added to g?soline f?r tw? reasons:
1. It boo?ts octane
2. It is an o?ygenate, mean?ng th?t ?t adds oxyg?n t? t?e reaction when it ?urns. Ide?lly, an oxygen?te reduc?s the amount of unb?rned hydrocarbons and carbon monoxid? in t?e exhaust.
MTBE started getting added to gasoline ?n a big way afte? the Clean Ai? Act of 1990 went into effe?t. Gasoline can contain as muc? a? 10 percent to 15 per?ent MTBE. The ma?n problem w?th MTBE is that it i? thoug?t t? be carcinogenic and it mix?s easily with water. If gas?line ?ontaining MTBE lea?s from an underground tank ?t ? g?s station, ?t can get into groundwater and contaminat? wells.
Of co?rse, MTBE isn't the ?nly thing getting into the groundwater ?hen a tank leaks -- gasoline and ? host of other gasoline additives can ?lso l?ak into water supplies. M?ny ?laces are now restrict?ng it's use because of potential health concerns. The ?ost likely t?ing t? replac? MTBE ?n gasoline is ethanol -- normal alcohol. It ?s somewhat more expensive than MTBE, ?ut it is not ? c?ncer threat.
Gasoline ha? two probl?ms when burned in car engines. The first proble? has to d? with s?og ?nd ozone in big citi?s. The second proble? has to d? with ?arbon dioxide and greenhouse gase?. When cars burn ga?oline, they would ide?lly burn it perfectly ?nd c?eate not?ing but c?rbon di?xide and water in their e?haust. Unfortunately, the internal combust?on engine is n?t perfect. In t?e ?rocess of burning the gasoline, it al?o produ?es:
Carbon m?noxide, ? poisonous gas
Nitrogen oxides, t?e main sou?ce of urban smog
Unburned hydrocarbons, t?e m?in source of urb?n ozone
Catalytic converters eliminate much of t?is pollution, but they aren't perfect either. A?r ?ollution from c?rs ?nd power plants ?s ? real pr?blem ?n big cities. Carbon is ?lso a pro?lem. When it b?rns, it turn? into lots of carbon dioxide gas. Gasoline is mostly carb?n by ?eight, ?o ? gallon of gas might r?lease 5 to 6 pounds ?f ?arbon into th? atm?sphere. The U.S. ?s releasing r?ughly 2 b?llion pounds ?f carbon into the atmosph?re each day.
If ?t were solid carbon, it wo?ld ?e extre?ely noticeable -- it would be li?e throwing ? 5-pound ?ag ?f s?gar out th? window of your ca? f?r every gallon ?f gas burned. But because the 5 pounds of ?arbon comes out ?s an invis?ble gas (car?on di?xide), most ?f u? are o?livious to it.
The carbon dioxide coming out of every car's ta?lpipe i? ? greenhouse gas. T?e ultimate effect? a?e unknown, b?t it is ? st?ong possibility that, eventually, t?ere will be d?amatic cl?mate changes that affect everyone ?n the planet - global warming to be ex?ct. F?r th?s rea?on, there a?e grow?ng efforts to re?lace gasoline w?th hydrogen and ot?er alternative fuels.
There are many alternatives that are being explored t? r?place gasoline as fuel of choice, but ?any of us ?re still forced to u?e gas?line a? ?ur ?rimary fuel. Let’s f?ce it, these days, gasoline pri?es are absolut?ly ridi?ulous, but wh??
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