Halderman J.D., Linder J. Automotive Fuel and Emissions Control Systems

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GASOLINE 81

chapter

GASOLINE

OBJECTIVES: After studying Chapter 5 , the reader should be able to: • Describe how the proper grade of gasoline affects

engine performance. • List gasoline purchasing hints. • Discuss how volatility affects driveability. • Explain how oxygenated

fuels can reduce CO exhaust emissions. • Discuss safety precautions when working with gasoline.

KEY TERMS: Air-fuel ratio 85 • Antiknock index (AKI) 86 • American Society for Testing and Materials ( ASTM ) 83

• British thermal unit (BTU) 84 • Catalytic cracking 82 • Cracking 82 • Detonation 85 • Distillation 81 • Distillation curve 83

• Driveability index (DI) 88 • E10 88 • Ethanol 88 • Fungible 82 • Gasoline 81 • Hydrocracking 82 • Octane rating 85

• Oxygenated fuels 88 • Petroleum 81 • Ping 85

• Reformulated gasoline (RFG) 89 • Reid vapor pressure (RVP) 83

• Spark knock 85 • Stoichiometric 85 • Tetraethyl lead (TEL) 86 •

Vapor lock 83 • Volatility 83 • World Wide Fuel

Charter(WWFC ) 91

GASOLINE

DEFINITION Gasoline is a term used to describe a com-

plex mixture of various hydrocarbons refined from crude petro-

leum oil for use as a fuel in engines. Gasoline and air burns in

the cylinder of the engine and produces heat and pressure,

which is converted to rotary motion inside the engine and even-

tually powers the drive wheels of a vehicle. When combustion

occurs, carbon dioxide and water are produced if the process

is perfect and all of the air and all of the fuel are consumed in

the process.

CHEMICAL COMPOSITION Gasoline is a combination of

hydrocarbon molecules that have between five and 12 carbon

atoms. The names of these various hydrocarbons are based on

the number of carbon atoms and include:



Methane —one carbon atom



Ethane —two carbon atoms



Propane —three carbon atoms



Butane —four carbon atoms



Pentane —five carbon atoms



Hexane —six carbon atoms



Heptane —seven carbon atoms (Used to test octane

rating—has an octane rating of zero)



Octane —eight carbon atoms (A type of octane is used as

a basis for antiknock rating)

REFINING

TYPES OF CRUDE OIL Refining is a complex combination

of interdependent processing units that can separate crude

oil into useful products such as gasoline and diesel fuel. As

it comes out of the ground, petroleum (meaning “rock oil”)

crude can be as thin and light colored as apple cider or as thick

and black as melted tar. A barrel of crude oil is 42 gallons, not

55 gallons as commonly used for industrial barrels. Typical

terms used to describe the type of crude oil include:



Thin crude oil has a high American Petroleum Institute

(API) gravity, and therefore, is called high-gravity crude.



Thick crude oil is called low-gravity crude. High-

gravity-type crude contains more natural gasoline and

its lower sulfur and nitrogen content makes it easier to

refine.



Low-sulfur crude oil is also known as “sweet” crude.



High-sulfur crude oil is also known as “sour” crude.

DISTILLATION In the late 1800s, crude was separated into

different products by boiling in a process called distillation.

Distillation works because crude oil is composed of hydrocar-

bons with a broad range of boiling points.

In a distillation column, the vapor of the lowest-boiling hy-

drocarbons, propane and butane, rises to the top. The straight-

run gasoline (also called naphtha), kerosene, and diesel fuel cuts

are drawn off at successively lower positions in the column.

82 CHAPTER 5



Isomerization



Hydrotreating



Desulfurization



SEE FIGURE 5–1 .

SHIPPING The gasoline is transported to regional storage

facilities by railway tank car or by pipeline. In the pipeline

method, all gasoline from many refiners is often sent through

the same pipeline and can become mixed. All gasoline is said

to be fungible, meaning that it is capable of being interchanged

because each grade is created to specification so there is no

reason to keep the different gasoline brands separated except

for grade. Regular grade, mid-grade, and premium grades are

separated in the pipeline and the additives are added at the

regional storage facilities and then shipped by truck to indi-

vidual gas stations.

CRACKING Cracking is the process where hydrocarbons

with higher boiling points could be broken down (cracked) into

lower-boiling hydrocarbons by treating them to very high tem-

peratures. This process, called thermal cracking , was used to

increase gasoline production starting in 1913.

Instead of high heat, today cracking is performed using a

catalyst and is called catalytic cracking. A catalyst is a material

that speeds up or otherwise facilitates a chemical reaction without

undergoing a permanent chemical change itself. Catalytic crack-

ing produces gasoline of higher quality than thermal cracking.

Hydrocracking is similar to catalytic cracking in that it

uses a catalyst, but the catalyst is in a hydrogen atmosphere.

Hydrocracking can break down hydrocarbons that are resistant

to catalytic cracking alone, and it is used to produce diesel fuel

rather than gasoline.

Other types of refining processes include:



Reforming



Alkylation

LIGHT PETROLEUM

GAS TREATING

SULFUR

RECOVERY

FUEL GAS FOR

REFINERY USE

PROPANE

BENZENE

p-XYLENE

MOTOR

GASOLINE

AVIATION

GASOLINE

JET

DIESEL

AROMATICS

CHEMICAL AND

GASOLINE REFORMING

NAPTHA

HYDROTREATING

JET

HYDROTREATING

DIESEL

HYDROTREATING

GAS OIL

HYDROCRACKING

CATALYTIC

CRACKING

GAS OIL

HYDROTREATING

RESIDUE

PROCESSING

DISTILLATION

COLUMN

ALKYLATION

BUNKER

(SHIP FUEL)

PETROLEUM

COKE

FIGURE 5–1 The crude oil refining process showing most of the major steps and processes.

GASOLINE 83

DRIVEABILITY INDEX A distillation curve shows how

much of a gasoline evaporates at what temperature range. To

predict cold-weather driveability, an index was created called

the driveability index, also called the distillation index , and

abbreviated DI .

The DI was developed using the temperature for the evap-

orated percentage of 10% (labeled T10), 50% (labeled T50), and

90% (labeled T90). The formula for DI is:

DI ⫽ 1.5 ⫻ T10 ⫹ 3 ⫻ T50 ⫹ T90

The total DI is a temperature and usually ranges from

1,000°F to 1,200°F. The lower values of DI generally result in

good cold-start and warm-up performance. A high DI number

is less volatile than a low DI number.

NOTE: Most premium-grade gasoline has a higher

(worse) DI than regular-grade or midgrade gasoline,

which could cause poor cold-weather driveability. Ve-

hicles designed to operate on premium-grade gasoline

are programmed to handle the higher DI, but engines

designed to operate on regular-grade gasoline may not

be able to provide acceptable cold-weather driveability.

VOLATILITY-RELATED PROBLEMS At higher tempera-

tures, liquid gasoline can easily vaporize, which can cause vapor

lock. Vapor lock is a lean condition caused by vaporized fuel in

the fuel system. This vaporized fuel takes up space normally

occupied by liquid fuel. Bubbles that form in the fuel cause vapor

lock, preventing proper operation of the fuel-injection system.

Heat causes some fuel to evaporate, thereby causing bub-

bles. Sharp bends cause the fuel to be restricted at the bend.

When the fuel flows past the bend, the fuel can expand to fill the

space after the bend. This expansion drops the pressure, and

FIGURE 5–2 A gasoline testing kit, including an insulated

container where water at 100°F is used to heat a container

holding a small sample of gasoline. The reading on the pres-

sure gauge is the Reid vapor pressure (RVP).

VOLATILITY

DEFINITION OF VOLATILITY Volatility describes how

easily the gasoline evaporates (forms a vapor). The definition

of volatility assumes that the vapors will remain in the fuel tank

or fuel line and will cause a certain pressure based on the tem-

perature of the fuel.

REID VAPOR PRESSURE (RVP) Reid vapor pressure

(RVP) is the pressure of the vapor above the fuel when the fuel is

at 100°F (38°C). Increased vapor pressure permits the engine to

start in cold weather. Gasoline without air will not burn. Gasoline

must be vaporized (mixed with air) to burn in an engine.



SEE

FIGURE 5–2.

SEASONAL BLENDING Cold temperatures reduce the

normal vaporization of gasoline; therefore, winter-blended gas-

oline is specially formulated to vaporize at lower temperatures

for proper starting and driveability at low ambient temperatures.

The American Society for Testing and Materials (ASTM)

standards for winter-blend gasoline allow volatility of up to

15pounds per square inch (PSI) RVP.

At warm ambient temperatures, gasoline vaporizes easily.

However, the fuel system (fuel pump, carburetor, fuel-injector

nozzles, etc.) is designed to operate with liquid gasoline. The

volatility of summer-grade gasoline should be about 7.0 PSI

RVP. According to ASTM standards, the maximum RVP should

be 10.5 PSI for summer-blend gasoline.

DISTILLATION CURVE Besides Reid vapor pressure,

another method of classifying gasoline volatility is the distilla-

tion curve . A curve on a graph is created by plotting the tem-

perature at which the various percentage of the fuel evaporates.

A typical distillation curve is shown in



FIGURE 5–3.

Why Do I Get Lower Gas Mileage in the Winter?

Several factors cause the engine to use more fuel in

the winter than in the summer, including:

• Gasoline that is blended for use in cold climates is

designed for ease of starting and contains fewer

heavy molecules, which contribute to fuel econ-

omy. The heat content of winter gasoline is lower

than summer-blended gasoline.

• In cold temperatures, all lubricants are stiff, causing

more resistance. These lubricants include the en-

gine oil, as well as the transmission and differential

gear lubricants.

• Heat from the engine is radiated into the outside air

more rapidly when the temperature is cold, resulting

in longer run time until the engine has reached

normal operating temperature.

• Road conditions, such as ice and snow, can cause

tire slippage or additional drag on the vehicle.

FREQUENTLY ASKED QUESTION

84 CHAPTER 5

the fuel. In a gasoline engine, a spark starts the combustion

process, which takes about 3 ms (0.003 sec) to be completed

inside the cylinder of an engine. The chemical reaction that

takes place can be summarized as follows: hydrogen (H) plus

carbon (C) plus oxygen (O

) plus nitrogen (N) plus spark equals

heat plus water (H

O) plus carbon monoxide (CO) (if incomplete

combustion) plus carbon dioxide (CO

) plus hydrocarbons (HC)

plus oxides of nitrogen (NO

) plus many other chemicals. In an

equation format it looks like this:

H ⫹ C ⫹ O

⫹ N ⫹ Spark ⫽ Heat ⫹ CO

⫹ HC ⫹ NO

HEAT ENERGY The heat produced by the combustion pro-

cess is measured in British thermal units (BTUs). One BTU is

the amount of heat required to raise one pound of water one

Fahrenheit degree. The metric unit of heat is the calorie (cal).

One calorie is the amount of heat required to raise the tempera-

ture of one gram (g) of water one Celsius degree:

Gasoline —About 130,000 BTUs per gallon

AIR-FUEL RATIOS Fuel burns best when the intake sys-

tem turns it into a fine spray and mixes it with air before sending

it into the cylinders. In fuel-injected engines, the fuel becomes

bubbles form in the fuel lines. When the fuel is full of bubbles, the

engine is not being supplied with enough fuel and the engine runs

lean. A lean engine will stumble during acceleration, will run rough,

and may stall. Warm weather and alcohol-blended fuels both tend

to increase vapor lock and engine performance problems.

If winter-blend gasoline (or high-RVP fuel) is used in an en-

gine during warm weather, the following problems may occur:

1. Rough idle

2. Stalling

3. Hesitation on acceleration

4. Surging

TAIL

END

FRONT

END

MIDRANGE

TEMPERATURE

EASY COLD

STARTING

EVAP

RATED

0 20

60 80 100

100

200

300

400

WARM-UP AND COOL

WEATHER DRIVEABILITY

SHORT TRIP ECONOMY

DILUTION OF ENGINE OIL

CRANKCASE DEPOSITS

SPARK PLUG FOULING

COMBUSTION CHAMBER DEPOSITS

RESIDUE (LESS THAN 2.7)

FIGURE 5–3 A typical distillation curve. Heavier molecules evaporate at higher temperatures and contain more heat energy for

power, whereas the lighter molecules evaporate easier for starting.

CHEMICAL REACTIONS The combustion process involves

the chemical combination of oxygen (O

) from the air (about

21% of the atmosphere) with the hydrogen and carbon from

GASOLINE COMBUSTION

PROCESS

GASOLINE 85

a spray and mixes with the air in the intake manifold. There is

a direct relationship between engine airflow and fuel require-

ments; this is called the air-fuel ratio.

The air-fuel ratio is the proportion by weight of air and gaso-

line that the injection system mixes as needed for engine com-

bustion. The mixtures, with which an engine can operate without

stalling, range from 8 to 1 to 18.5 to 1.

 SEE FIGURE 5–4.

These ratios are usually stated by weight, such as:



8 parts of air by weight combined with 1 part of gasoline

by weight (8:1), which is the richest mixture that an

engine can tolerate and still fire reliably.



18.5 parts of air mixed with 1 part of gasoline (18.5:1),

which is the leanest practical ratio. Richer or leaner air-fuel

ratios cause the engine to misfire badly or not run at all.

STOICHIOMETRIC AIR-FUEL RATIO The ideal mixture

or ratio at which all of the fuel combines with all of the oxygen

in the air and burns completely is called the stoichiometric

ratio, a chemically perfect combination. In theory, this ratio for

gasoline is an air-fuel mixture of 14.7 to 1.

 SEE FIGURE 5–5.

In reality, the exact ratio at which perfect mixture and com-

bustion occurs depends on the molecular structure of gasoline,

which can vary. The stoichiometric ratio is a compromise between

maximum power and maximum economy.

STALL –

MIXTURE

TOO LEAN

STALL –

MIXTURE

TOO RICH

8.0:1

18.5:1

RUNNING

RANGE

BEST

MIXTURE

14.7:1

FIGURE 5–4 An engine will not run if the air-fuel mixture is

either too rich or too lean.

CONVERSION EFFICIENCY (%)

AIR–FUEL (A–F) RATIO

LEAN A–F

MIXTURE

RICH A–F

MIXTURE

THREE-WAY

CATALYST

OPERATING

RANGE

100

13:1

14:1 14.7:1

15:1

16:1

FIGURE 5–5 With a three-way catalytic converter, emission

control is most efficient with an air-fuel ratio between 14.65 to

1 and 14.75 to 1.

COMPRESSION

IGNITION COMBUSTION COMBUSTION

COMPLETED

COMBUSTION

CONTINUED

FIGURE 5–6 Normal combustion is a smooth, controlled burning of the air-fuel mixture.

The octane rating of gasoline is the measure of its antiknock

properties. Engine knock (also called detonation, spark knock,

or ping ) is a metallic noise an engine makes, usually during ac-

celeration, resulting from abnormal or uncontrolled combustion

inside the cylinder.

Normal combustion occurs smoothly and progresses

across the combustion chamber from the point of ignition.

 SEE FIGURE 5–6.

Normal flame-front combustion travels between 45 and

90 mph (72 and 145 km/h). The speed of the flame front

NORMAL AND

ABNORMAL COMBUSTION

86 CHAPTER 5

Except in high-altitude areas, the grades and octane

ratings are as follows:

depends on the air-fuel ratio, combustion chamber design

( determining amount of turbulence), and temperature.

During periods of spark knock (detonation), the combus-

tion speed increases by up to 10 times to near the speed of

sound. The increased combustion speed also causes increased

temperatures and pressures, which can damage pistons, gas-

kets, and cylinder heads.

 SEE FIGURE 5–7.

One of the first additives used in gasoline was tetraethyl lead

(TEL). TEL was added to gasoline in the early 1920s to reduce the

tendency to knock. It was often called ethyl or high-test gasoline.

FIGURE 5–8 A pump showing regular with a pump octane

of 87, plus rated at 89, and premium rated at 93. These rat-

ings can vary with brand as well as in different parts of the

country.

COMPRESSION SPARK IGNITION COMBUSTION DETONATION COMBUSTION

CONTINUED

FIGURE 5–7 Detonation is a secondary ignition of the air-fuel mixture. It is also called spark knock or pinging.

OCTANE RATING

The antiknock standard or basis of comparison is the knock-

resistant hydrocarbon isooctane, chemically called trimethylpen-

tane (C

), also known as 2-2-4 trimethylpentane. If a gasoline

tested had the exact same antiknock characteristics as isooc-

tane, it was rated as 100-octane gasoline. If the gasoline tested

had only 85% of the antiknock properties of isooctane, it was

rated as 85 octane. Remember, octane rating is only a compari-

son test.

The two basic methods used to rate gasoline for antiknock

properties (octane rating) are the research method and the mo-

tor method . Each uses a model of the special cooperative fuel

research (CFR) single-cylinder engine. The research method and

the motor method vary as to temperature of air, spark advance,

and other parameters. The research method typically results in

readings that are 6 to 10 points higher than those of the motor

method. For example, a fuel with a research octane number (RON)

of 93 might have a motor octane number (MON) of 85.

The octane rating posted on pumps in the United States is

the average of the two methods and is referred to as (R  M) 2,

meaning that, for the fuel used in the previous example, the rating

posted on the pumps would be

RON 1 MON

93 1 85

5 89

The pump octane is called the antiknock index (AKI).

GASOLINE GRADES AND OCTANE NUMBER The posted

octane rating on gasoline pumps is the rating achieved by the aver-

age of the research and the motor methods.



SEE FIGURE 5–8.

Grades Octane rating

Regular 87

Midgrade (also called Plus) 89

Premium 91 or higher

What Grade of Gasoline Does the EPA Use

When Testing Engines?

Due to the various grades and additives used in com-

mercial fuel, the government (EPA) uses a liquid called

indolene. Indolene has a research octane number of

96.5 and a motor method octane rating of 88, which

results in an R  M  2 rating of 92.25.

FREQUENTLY ASKED QUESTION

GASOLINE 87

A secondary reason for the lowered octane requirement of

engines running at higher altitudes is the normal enrichment of

the air-fuel ratio and lower engine vacuum with the decreased

air density. Some problems, therefore, may occur when driving

out of high-altitude areas into lower-altitude areas where the

octane rating must be higher. Most computerized engine con-

trol systems can compensate for changes in altitude and modify

air-fuel ratio and ignition timing for best operation.

Because the combustion burn rate slows at high altitude,

the ignition (spark) timing can be advanced to improve power.

The amount of timing advance can be about 1 degree per 1,000 ft

over 5,000 ft. Therefore, if driving at 8,000 ft of altitude, the ignition

timing can be advanced 3 degrees.

High altitude also allows fuel to evaporate more easily. The

volatility of fuel should be reduced at higher altitudes to prevent

vapor from forming in sections of the fuel system, which can

cause driveability and stalling problems. The extra heat gener-

ated in climbing to higher altitudes plus the lower atmospheric

pressure at higher altitudes combine to cause vapor lock prob-

lems as the vehicle goes to higher altitudes.

FIGURE 5–9 The posted octane rating in most high-altitude

areas shows regular at 85 instead of the usual 87.

Horsepower and Fuel Flow

To produce 1 hp, the engine must be supplied with

0.50 lb of fuel per hour (lb/hr). Fuel injectors are rated in

pounds per hour. For example, a V-8 engine equipped

with 25 lb/hr fuel injectors could produce 50 hp per cyl-

inder (per injector) or 400 hp. Even if the cylinder head

or block is modified to produce more horsepower, the

limiting factor may be the injector flow rate.

The following are flow rates and resulting

horsepower for a V-8 engine:

30 lb/hr: 60 hp per cylinder or 480 hp

35 lb/hr: 70 hp per cylinder or 560 hp

40 lb/hr: 80 hp per cylinder or 640 hp

Of course, injector flow rate is only one of many

variables that affect power output. Installing larger in-

jectors without other major engine modification could

decrease engine output and drastically increase ex-

haust emissions.

TECH TIP

As the altitude increases, atmospheric pressure drops. The air

is less dense because a pound of air takes more volume. The

octane rating of fuel does not need to be as high because

the engine cannot take in as much air. This process will reduce

the combustion (compression) pressures inside the engine. In

mountainous areas, gasoline (R  M)  2 octane ratings are

two or more numbers lower than normal (according to the SAE,

about one octane number lower per 1,000 ft or 300 m in altitude).



SEE FIGURE 5–9.

HIGH-ALTITUDE OCTANE

REQUIREMENTS

GASOLINE ADDITIVES

DYE Dye is usually added to gasoline at the distributor to

help identify the grade and/or brand of fuel. In many countries,

fuels are required to be colored using a fuel-soluble dye. In the

United States and Canada, diesel fuel used for off-road use and

not taxed is required to be dyed red for identification. Gasoline

sold for off-road use in Canada is dyed purple.

OCTANE IMPROVER ADDITIVES When gasoline com-

panies, under federal EPA regulations, removed tetraethyl lead

from gasoline, other methods were developed to help main-

tain the antiknock properties of gasoline. Octane improvers

(enhancers) can be grouped into three broad categories:

1. Aromatic hydrocarbons (hydrocarbons containing the

benzene ring) such as xylene and toluene

2. Alcohols such as ethanol (ethyl alcohol), methanol (methyl

alcohol), and tertiary butyl alcohol (TBA)

3. Metallic compounds such as methylcyclopentadienyl man-

ganese tricarbonyl (MMT)

NOTE: MMT has been proven to be harmful to catalytic

converters and can cause spark plug fouling. However,

MMT is currently one of the active ingredients com-

monly found in octane improvers available to the public

and in some gasoline sold in Canada. If an octane boost

additive has been used that contains MMT, the spark

plug porcelain will be rust colored around the tip.

Propane and butane, which are volatile by-products of the

refinery process, are also often added to gasoline as octane im-

provers. The increase in volatility caused by the added propane

and butane often leads to hot-weather driveability problems.

88 CHAPTER 5

OXYGENATED FUEL ADDITIVES Oxygenated fuels

contain oxygen in the molecule of the fuel itself. Examples

of oxygenated fuels include methanol, ethanol, methyl tertiary

butyl ether (MTBE), tertiary-amyl methyl ether (TAME), and ethyl

tertiary butyl ether (ETBE).

Oxygenated fuels are commonly used in high-altitude ar-

eas to reduce carbon monoxide (CO) emissions. The extra oxy-

gen in the fuel itself is used to convert harmful CO into carbon

dioxide (CO

). The extra oxygen in the fuel helps ensure that

there is enough oxygen to convert all CO into CO

during the

combustion process in the engine or catalytic converter.

METHYL TERTIARY BUTYL ETHER (MTBE). MTBE is manufactured

by means of the chemical reaction of methanol and isobutylene.

Unlike methanol, MTBE does not increase the volatility of the

fuel and is not as sensitive to water as are other alcohols. The

maximum allowable volume level, according to the EPA, is 15%

but is currently being phased out because of health concerns,

as well as MTBE contamination of drinking water if spilled from

storage tanks.

TERTIARY-AMYL METHYL ETHER. Tertiary-amyl methyl ether

(TAME) contains an oxygen atom bonded to two carbon atoms

and is added to gasoline to provide oxygen to the fuel. It is

FIGURE 5–10 This refueling pump indicates that the gasoline

is blended with 10% ethanol (ethyl alcohol) and can be used

in any gasoline vehicle. E85 contains 85% ethanol and can be

used only in vehicles specifically designed to use it.

Can Regular-Grade Gasoline Be Used If

Premium Is the Recommended Grade?

Maybe. It is usually possible to use regular-grade or

midgrade (plus) gasoline in most newer vehicles with-

out danger of damage to the engine. Most vehicles

built since the 1990s are equipped with at least one

knock sensor. If a lower octane gasoline than specified

is used, the engine ignition timing setting will usually

cause the engine to spark knock, also called detona-

tion or ping. This spark knock is detected by the knock

sensor(s), which sends a signal to the computer. The

computer then retards the ignition timing until the

spark knock stops.

NOTE: Some scan tools will show the

“estimated octane rating” of the fuel being

used, which is based on knock sensor activity.

As a result of this spark timing retardation, the

engine torque is reduced. While this reduction in

power is seldom noticed, it will reduce fuel economy,

often by 4 to 5 miles per gallon. If premium gasoline is

then used, the PCM will gradually permit the engine to

operate at the more advanced ignition timing setting.

Therefore, it may take several tanks of premium gaso-

line to restore normal fuel economy. For best overall

performance, use the grade of gasoline

recommended by the vehicle manufacturer.

FREQUENTLY ASKED QUESTION

slightly soluble in water, very soluble in ethers and alcohol, and

soluble in most organic solvents including hydrocarbons.

ETHYL TERTIARY BUTYL ETHER. ETBE is derived from ethanol.

The maximum allowable volume level is 17.2%. The use of ETBE

is the cause of much of the odor from the exhaust of vehicles

using reformulated gasoline.

ETHANOL. Ethanol, also called ethyl alcohol is drinkable alco-

hol and is usually made from grain. Adding 10% ethanol (ethyl

alcohol or grain alcohol) increases the (R  M)  2 octane

rating by three points. The alcohol added to the base gasoline,

however, also raises the volatility of the fuel about 0.5 PSI. Most

automobile manufacturers permit up to 10% ethanol if drive-

ability problems are not experienced.

The oxygen content of a 10% blend of ethanol in gasoline,

called E10 , is 3.5% oxygen by weight.



SEE FIGURE 5–10.

Keeping the fuel tank full reduces the amount of air and

moisture in the tank.



SEE FIGURE 5–11 .

What Is Meant by “Phase Separation?”

All alcohols absorb water, and the alcohol–water

mixture can separate from the gasoline and sink to

the bottom of the fuel tank. This process is called

phase separation . To help avoid engine performance

problems, try to keep at least a quarter tank of fuel at

all times, especially during seasons when there is a

wide temperature span between daytime highs and

nighttime lows. These conditions can cause moisture

to accumulate in the fuel tank as a result of condensa-

tion of the moisture in the air.

FREQUENTLY ASKED QUESTION

GASOLINE 89

FIGURE 5–11 A container with gasoline containing alcohol.

Notice the separation line where the alcohol–water mixture

separated from the gasoline and sank to the bottom.

GAS & ETHANOL

FIGURE 5–12 In-line blending is the most accurate method

for blending ethanol with gasoline because computers are

used to calculate the correct ratio.

ETHANOL

GAS

FIGURE 5–13 Sequential blending uses a computer to

calculate the correct ratio as well as the prescribed order in

which the products are loaded.

ETHANOL

GAS

FIGURE 5–14 Splash blending occurs when the ethanol is

added to a tanker with gasoline and is mixed as the truck

travels to the retail outlet.

GASOLINE BLENDING

Gasoline additives, such as ethanol and dyes, are usually added

to the fuel at the distributor. Adding ethanol to gasoline is a way

to add oxygen to the fuel itself. Gasoline containing an addition

that has oxygen is called oxygenated fuel . There are three ba-

sic methods used to blend ethanol with gasoline to create E10

(10% ethanol, 90% gasoline):

1. In-line blending. Gasoline and ethanol are mixed in a stor-

age tank or in the tank of a transport truck while it is being

filled. Because the quantities of each can be accurately

measured, this method is most likely to produce a well-

mixed blend of ethanol and gasoline.



SEE FIGURE 5–12 .

2. Sequential blending. This method is usually performed

at the wholesale terminal and involves adding a measured

amount of ethanol to a tank truck followed by a measured

amount of gasoline.



SEE FIGURE 5–13 .

3. Splash blending. Splash blending can be done at the

retail outlet or distributor and involves separate purchases

of ethanol and gasoline. In a typical case, a distributor can

purchase gasoline, and then drive to another supplier and

purchase ethanol. The ethanol is then added (splashed)

into the tank of gasoline. This method is the least-accurate

method of blending and can result in ethanol concentration

for E10 that should be 10% to range from 5% to over 20%

in some cases.



SEE FIGURE 5–14 .

REFORMULATED GASOLINE

Reformulated gasoline (RFG) is manufactured to help reduce

emissions. The gasoline refiners reformulate gasoline by using

additives that contain at least 2% oxygen by weight and reduc-

ing the additive benzene to a maximum of 1% by volume. Two

other major changes done at the refineries are as follows:

1. Reduce light compounds. Refineries eliminate butane,

pentane, and propane, which have a low boiling point

and evaporate easily. These unburned hydrocarbons are

released into the atmosphere during refueling and through

the fuel tank vent system, contributing to smog formation.

Therefore, reducing the light compounds from gasoline

helps reduce evaporative emissions.

2. Reduce heavy compounds. Refineries eliminate heavy

compounds with high boiling points such as aromatics

and olefins. The purpose of this reduction is to reduce the

amount of unburned hydrocarbons that enter the catalytic

Is Water Heavier Than Gasoline?

Yes. Water weighs about 8.3 pounds per gallon,

whereas gasoline weighs about 6 pounds per gallon.

The density as measured by specific gravity includes:

Water  1.000 (the baseline for specific gravity)

Gasoline  0.730 to 0.760

This means that any water that gets into the fuel tank

will sink to the bottom.

FREQUENTLY ASKED QUESTION

90 CHAPTER 5

6. Take a reading near the bottom of the cylinder at the

boundary between the two liquids.

7. For percent of alcohol in gasoline, subtract 10 from the

reading.

For example,

The reading is 20 mL: 20  10  10% alcohol

If the increase in volume is 0.2% or less, it may be assumed

that the test gasoline contains no alcohol.



SEE FIGURE 5–15.

Alcohol content can also be checked using an electronic tester.

See the step-by-step sequence at the end of the chapter.

converter, which makes the converter more efficient, thereby

reducing emissions.

Because many of the heavy compounds are eliminated, a

drop in fuel economy of about 1 mpg has been reported in ar-

eas where reformulated gasoline is being used. Formaldehyde

is formed when RFG is burned, and the vehicle exhaust has a

unique smell when reformulated gasoline is used.

TESTING GASOLINE

FOR ALCOHOL CONTENT

Take the following steps when testing gasoline for alcohol

content:

Do not smoke or run the test around sources

of ignition!

WARNING

How Does Alcohol Content in the Gasoline

Affect Engine Operation?

In most cases, the use of gasoline containing 10%

or less of ethanol (ethyl alcohol) has little or no effect

on engine operation. However, because the addition

of 10% ethanol raises the volatility of the fuel slightly,

occasional rough idle or stalling may be noticed,

especially during warm weather. The rough idle and

stalling may also be noticeable after the engine is

started, driven, then stopped for a short time. Engine

heat can vaporize the alcohol-enhanced fuel causing

bubbles to form in the fuel system. These bubbles in

the fuel prevent the proper operation of the fuel injec-

tion system and result in a hesitation during accelera-

tion, rough idle, or in severe cases repeated stalling

until all the bubbles have been forced through the fuel

system, replaced by cooler fuel from the fuel tank.

FREQUENTLY ASKED QUESTION

1. Pour suspect gasoline into a graduated cylinder.

2. Carefully fill the graduated cylinder to the 90-mL mark.

3. Add 10 mL of water to the graduated cylinder by counting

the number of drops from an eyedropper.

4. Put the stopper in the cylinder and shake vigorously for

1minute. Relieve built-up pressure by occasionally remov-

ing the stopper. Alcohol dissolves in water and will drop to

the bottom of the cylinder.

5. Place the cylinder on a flat surface and let it stand for

2minutes.

COLLECT

90 ml of

GASOLINE

100

STEP 1 STEP 2 STEP 3

100

ADD

10 ml of

WATER

ALCOHOL

WILL ABSORB

THE WATER

100

FIGURE 5–15 Checking gaso-

line for alcohol involves using a

graduated cylinder and adding

water to check if the alcohol

absorbs the water.