The quality of the fuel any engine uses is important to its proper operation and long life. If the fuel is not right for the air temperature or if the tendency of the fuel to evaporate is incorrect, severe driveability problems can result. An engine burns about 15 pounds of air for every pound of gasoline.
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. Thin crude oil has a high American Petroleum Institute ( API ) gravity, and is called high-gravity crude; thick oil is called low-gravity crude. High-gravity-type crude contains more natural gasoline; lower sulfur & nitrogen content makes it easier to refine.
Continued NOTE: Low-sulfur crude oil is also known as “sweet” crude and high-sulfur crude oil is also known as “sour” crude. Processes Refining is a complex combination of interdependent processing units starting with distillation .
Distillation In the 1800s, crude was separated by boiling.ude is composed of hydrocarbons with a wide range of molecular weights, and broad range of boiling points. Each product was assigned a temperature range and product was obtained by condensing vapor that boiled off in this range at atmospheric pressure (atmospheric distillation). Earliest were simple pot stills consisting of a container where crude was heated and a condenser to condense the vapor. Distillation later became a continuous process with a pump to provide crude flow, a furnace to heat the crude, and a distillation column. In a distillation column, vapor of propane and butane rises to the top. Straight-run gasoline (called naphtha), kerosene, and diesel fuel cuts are drawn off successively lower in the column. Continued
Cracking Hydrocarbons with higher boiling points can be cracked into lower-boiling hydrocarbons by subjecting them to very high temperatures. Called thermal cracking, it was used to increase gasoline production starting in 1913. Eventually heat was supplemented by a catalyst, transforming thermal cracking into catalytic cracking . A catalyst speeds up a chemical reaction without undergoing permanent chemical change itself. Catalytic cracking 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. More commonly it is used to produce diesel fuel rather than gasoline.
Figure 52–1 The crude oil refining process showing most of the major steps and processes.
Shipping Gasoline is transported to regional storage facilities by tank railway car or by pipeline. All gasoline is said to be miscible, meaning that it is capable of being mixed. Each grade is created to specification. There is no reason to keep different gasoline brands separated except for grade. Regular grade, midgrade, and premium grades are separated in the pipeline, additives are added at regional storage facilities. The gasoline is shipped by truck to individual gas stations.
Gasoline is a term used to describe a complex mixture of various hydrocarbons refined from crude petroleum oil for use as a fuel in engines. Most gasoline is “blended” to meet the needs of the local climates and altitudes.
To use this container, the nozzle release lever is held against the side of the fuel opening, allows air to enter the container and fuel to flow. The flow of fuel stops automatically when the tank is full, eliminating any spillage.
When researching for ways to reduce hydrocarbon emissions in California, it was discovered that leakage from small gasoline containers used to refill small lawn mowers and other power equipment was a major source of unburned gasoline entering the atmosphere. As a result of this discovery, a new design for a gas can (container) was developed that is kept closed by a spring and uses O-rings to seal the opening. What is a California Gas Can? Figure51 –2 A gas can that meets the California Resources Board (CARB) approval uses a spring-loaded sealed nozzle that eliminates gasoline spillage and leaks into the atmosphere.
Volatility describes how easily gasoline evaporates (forms vapor). The definition assumes vapors will remain in the fuel tank or fuel line and cause a certain pressure based on temperature of the fuel. Winter Blend Reid vapor pressure ( RVP ) is 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. Cold temperatures reduce normal vaporization of gasoline; winter-blended gasoline is specially formulated to vaporize at lower temperatures for proper starting and driveability at low ambient temperatures.
Summer Blend At warm ambient temperatures, gasoline vaporizes easily. 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. The American Society for Testing and Materials ( ASTM ) standards for summer-blend gasoline allow volatility of up to 10.5 pounds per square inch (PSI) RVP. According to ASTM standards, the maximum RVP should be 15 psi for winter-blend gasoline.
Volatility Problems At higher temperatures, liquid gasoline can easily vaporize and cause vapor lock , a lean condition caused by vaporized fuel in the fuel system. Vapor lock is caused by bubbles in the fuel, preventing proper operation of the fuel-injection system. Bubbles in the fuel can be caused by heat or by sharp bends in the fuel system. Heat causes some fuel to evaporate, 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 bubbles form in the fuel lines. When fuel is full of bubbles, the engine is not being supplied with enough fuel. A lean engine will stumble during acceleration, will run rough, and may stall. Warm weather and alcohol-blended fuels tend to increase vapor lock and performance problems.
If winter-blend gasoline (or high-RVP fuel) is used in an engine during warm weather, the following problems may occur:
Figure 52–3 A gasoline testing kit. Included is an insulated container where water at 100°F is used to heat a container holding a small sample of gasoline. The reading on the pressure gauge is the Reid vapor pressure (RVP).
Gasoline that is blended for use in cold climates is designed for ease of starting and contains fewer heavy molecules, which contribute to fuel economy. 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 engine 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.
Several factors cause the engine to use more fuel in the winter : Why Do I Get Lower Gas Mileage in the Winter?
Octane rating of gasoline is the measure of antiknock properties. Engine knock (called detonation , spark knock , or ping ) is a metallic noise an engine makes, usually during acceleration, from abnormal or uncontrolled combustion in the cylinder.
Continued Figure 52–5 Normal combustion is a smooth, controlled burning of the air–fuel mixture. Normal combustion occurs smoothly and progresses across the combustion chamber from the point of ignition.
Figure 52–6 Detonation is a secondary ignition of the air–fuel mixture. It is also called spark knock or pinging.
Normal flame-front combustion travels between 45 and 90 mph (72 and 145 km/h). Speed of the flame front depends on air–fuel ratio, combustion chamber design, and temperature.
During periods of spark knock (detonation), combustion speed increases by up to 10 times, causing increased temperatures and pressures, which can damage pistons, gaskets, and cylinder heads.
Some experts recommend that diesel fuel additive be used to kill bacteria and fungi growth that occurs in fuels when moisture is present. To kill algae and stop bacterial growth, use from 0.25 to 0.50 fl oz of additive in each 20 gallons. While algae growth is usually associated with diesel fuel when water collects at the bottom of the tank, gasoline tanks can still be a source of algae, especially when vehicles are stored for long periods of time, usually over 90 days.
Problems can occur with stale gasoline from which the lighter parts of the gasoline have evaporated. Stale gas usually results in a no-start situation. If stale gas is suspected, sniff it. If it smells rancid, replace with fresh. The Sniff Test NOTE: If storing a vehicle, boat, or lawn mower over the winter, put some gasoline stabilizer into the gasoline to reduce the evaporation and separation that can occur during storage. Gasoline stabilizer is frequently available at lawn mower repair shops or marinas.
One of the first additives used in gasoline was tetraethyl lead ( TEL ). TEL was added in the early 1920s to reduce the tendency to knock. It was often called ethyl or high-test gasoline. The antiknock standard or basis of comparison was the knock-resistant hydrocarbon isooctane, chemically called trimethylpentane ( C 8 H 18 ), also known as 2-2-4 trimethylpentane . If a gasoline tested had the same antiknock characteristics as isooctane, it was rated as 100-octane gasoline. If only 85% of the antiknock properties, it was rated as 85 octane. Octane rating is only a comparison test.
Two methods used to rate gasoline for antiknock properties (octane rating) are the research method and the motor method . Each uses a 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. 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 for the fuel in the previous example, the rating posted would be: The pump octane is called the antiknock index ( AKI ).
The posted octane rating on gasoline pumps is the rating achieved by the average of the research and the motor methods.
See the chart on Page 592 of your textbook. Figure 52–7 A fuel pump showing regular (87 octane), plus (88.5 octane), and premium (90 octane). These ratings can vary with brand as well as in different parts of the country, especially in high-altitude areas where the ratings are lower as shown here.
Due to the various grades and additives used in commercial 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. What Grade of Gasoline Does the EPA Use When Testing Engines?
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 cylinder (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. Following are flow rates and horsepower for a V-8: Horsepower and Fuel Flow Of course, injector flow rate is only one of many variables that affect power output. Installing larger injectors without other major engine modification could decrease engine output and drastically increase exhaust emissions.
The service tech slid into the driver’s seat and turned the ignition key. When the engine started, the tech depressed the accelerator slightly and the engine continued to run without any apparent problem. The car owner had never depressed the accelerator pedal and had never had any previous engine trouble. The tech suspected winter-grade (high-RVP) gasoline was the problem. The owner replied the present tank of fuel had been purchased during the last week in February.
On a warm day in March, a customer walked into an automotive repair shop and asked for help. The owner complained that the engine would start, then immediately stall. The engine would again start, and then stall during another attempt. The Stalling Honda The tech explained that the uncommonly warm weather caused the fuel to vaporize in the fuel rail. Enough condensed fuel was available to start the engine, but the fuel injectors were designed to handle liquid fuel—not vapor—so the engine stalled. The technician was probably lucky because by the third start enough of the remaining vapor had been drawn into the engine that all that remained was liquid gasoline.
Propane and butane, which are volatile by-products of the refinery process, are also often added to gasoline as octane improvers. The increase in volatility caused by the added propane and butane often leads to hot-weather driveability problems.
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 commonly 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.
Yes. It is usually possible to use regular-grade or midgrade (plus) gasoline in most newer vehicles without 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 detonation 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 that some scan tools will show the “estimated octane rating” of the fuel being used, which is based on knock sensor activity. Can Regular-Grade Gasoline Be Used If Premium Is the Recommended Grade? - Part 1
Can Regular-Grade Gasoline Be Used If Premium Is the Recommended Grade? - Part 2 As a result of this spark timing retardation, 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. It may take several tanks of premium gasoline to restore normal fuel economy. For best overall performance, use the grade of gasoline recommended by the vehicle manufacturer.
Oxygenated fuels contain oxygen in the fuel molecule itself. Examples 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 areas to reduce carbon monoxide (CO) emissions. The extra oxygen in the fuel itself is used to convert harmful CO into carbon dioxide (CO 2 ) and helps ensure that there is enough oxygen to convert all the CO into CO 2 during the combustion process in the engine or catalytic converter
Methyl Tertiary Butyl Ether ( MTBE ) Manufactured by means of the chemical reaction of methanol and isobutylene. Does not increase volatility of fuel; not as sensitive to water as other alcohols. Tertiary-Amyl Methyl Ether Tertiary-amyl methyl ether (TAME ) An oxygenate added to gasoline; flammable; can form explosive mixtures with air. Slightly soluble in water, very soluble in ethers and alcohol. TAME is an ether, which contains an oxygen atom bonded to two carbon atoms. Ethyl Tertiary Butyl Ether ETBE Derived from ethanol. Use of ETBE is the cause of much of the odor from the exhaust of vehicles using reformulated gasoline.
Ethanol Ethyl alcohol is drinkable alcohol, made from grain. Adding 10% ethanol (ethyl alcohol or grain alcohol) increases the (R + M)/2 octane rating by three points.
Figure 52–8 This fuel tank indicates that the gasoline is blended with 10% ethanol (ethyl alcohol) and can be used in any gasoline vehicle. E-85 contains 85% ethanol and can only be used in vehicles specifically designed to use it. Alcohol also raises volatility of the fuel about 0.5 PSI. Most manufacturers permit up to 10% ethanol if driveability problems are not experienced. Oxygen content of a 10% blend of ethanol in gasoline, called E - 10 , is 3.5% oxygen by weight. Continued
Methanol Made from wood (wood alcohol), natural gas, or coal. Methyl alcohol ( Methanol ) is poisonous if ingested and more harmful to materials in the fuel system.
Tends to separate when combined with gasoline unless used with a co-solvent. A co-solvent is another substance (usually another alcohol) soluble in both methanol and gasoline, used to reduce the tendency of the liquids to separate. Methanol can damage fuel system parts. It is corrosive to lead, aluminum, magnesium, and some plastics and rubber. It can also cause rubber products (elastomers) to swell and soften. Methanol contains oxygen, and gasoline containing 5% methanol would have an oxygen content of 2.5% by weight
These conditions can cause moisture to accumulate in the fuel tank as a result of condensation of the moisture in the air. Keeping the fuel tank full reduces the amount of air and moisture in the tank.
CAUTION: 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. Figure 52–9 A container with gasoline containing alcohol. Notice the separation line where the alcohol–water mixture separated from the gasoline and sank to the bottom.
Use of alcohol can result in clogging of fuel filters with dirt and other debris cleaned from the fuel tank, pump, and lines.
Alcohol raises the volatility of fuel about 0.5 PSI; this can cause hot-weather driveability problems.
Alcohol reduces the heat content of the resulting fuel mixture (it has about one-half of the energy content of gasoline); 60,000 to 75,000 British thermal units ( BTUs ) per gallon for alcohol vs. about 130,000 BTUs per gallon for gasoline.
Alcohol absorbs water and then separates from the gasoline, especially as temperature drops. Separated alcohol and water on the tank bottom can cause hard starting during cold weather. Alcohol does not vaporize easily at low temperatures.
Yes! Water weighs about 7 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 any water that gets into the fuel tank will sink to the bottom. Is Water Heavier Than Gas?
Take the following steps when testing gasoline for alcohol:
Pour suspect gasoline into a small clean beaker or glass container.
Carefully fill the graduated cylinder to the 10-mL mark.
Add 2 mL of water to the graduated cylinder by counting the number of drops from an eyedropper. (Before performing the test, the eyedropper must be calibrated to determine how many drops equal 2.0 mL.)
Put the stopper in the cylinder and shake vigorously for 1 minute. Relieve built-up pressure by occasionally removing the stopper. Alcohol dissolves in water and will drop to the bottom of the cylinder.
Place cylinder on a flat surface and let stand for 2 minutes.
Take a reading near the bottom of the cylinder at the boundary between the two liquids.
For percent of alcohol in gasoline, subtract 2 from the reading and multiply by 10. For example,
Reading: 3.1 mL : 3.1 2 = 1.1 × 10 = 11% alcohol Reading: 2.0 mL : 2 2 = 0 × 10 = 0% alcohol If the increase in volume is 0.2% or less, it may be assumed that the test gasoline contains no alcohol. Alcohol content can also be checked using an electronic tester. See the photo sequence at the end of the chapter.
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 injection system and result in a hesitation during acceleration, 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. How Does Alcohol Content in the Gasoline Affect Engine Operation?
Internal combustion engines burn an organic fuel to produce power. Organic refers to a product (gasoline) from a source that originally was alive. Crude oil originally came from living plants and animals. All products of petroleum are considered organic fuels and are composed primarily of hydrogen ( H ) and carbon ( C ). C ombustion involves chemical combination of oxygen ( O 2 ) from the air with hydrogen and carbon from fuel. In a gasoline engine, a spark starts combustion, 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:
Continued hydrogen ( H ) plus carbon ( C ) plus oxygen ( O 2 ) plus nitrogen ( N ) plus spark equals heat plus water ( H 2 O ) plus carbon monoxide ( CO ) (if incomplete combustion) plus carbon dioxide ( CO 2 ) plus hydrocarbons ( HC ) plus oxides of nitrogen ( NO X ) plus many other chemicals .
Fuel burns best when the intake system turns it into a fine spray and mixes it with air before sending it to the cylinders. There is a direct relationship between engine airflow and fuel requirements; this is called the air - fuel ratio . The air–fuel ratio is the proportion by weight of air and gasoline that the injection system mixes as needed for engine combustion. The mixtures, with which an engine can operate without stalling, range from 8 to 1 to 18.5 to 1. These ratios are usually stated by weight.
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.
Figure 52–11 With a three-way catalytic converter, emission control is most efficient with an air–fuel ratio between 14.65:1 and 14.75:1. Continued In theory, this ratio is an air–fuel mixture of 14.7 to 1. The ratio is actually a compromise between power and economy.
The heat produced by the combustion process is measured in 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 temperature of one gram (g) of water one Celsius degree.
As the altitude increases, atmospheric pressure drops. Octane rating does not need to be as high because the engine cannot take in as much air. This will reduce the compression pressures.
Continued Figure 52–12 Photo of gasoline pump taken in a high-altitude area. Note the lower than normal octane ratings. The “ethanol” sticker reads that all grades contain 10% ethanol from November 1 through February 28 each year to help reduce CO exhaust emissions. In mountainous areas, gasoline(R + M)/2 octane ratings are two or more numbers lower than normal (about one octane number per 1,000 ft or 300 m altitude).
Reformulated gasoline ( RFG ) helps reduce emissions. Refiners reformulate by using additives that contain at least 2% oxygen by weight and reducing benzene to a maximum of 1% by volume. Two other major changes done at the refineries are as follows:
Reduce light compounds . Refineries eliminate butane, pentane, and propane, which have a low boiling point and evaporate easily. These are released to the atmosphere during refueling and through the fuel tank vent, contributing to smog formation.
Reduce heavy compounds . 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 converter
Top-tier gasoline is gasoline that has specific standards for quality, including enough detergent to keep all intake valves clean. The standards were developed by the four automobile manufacturers, including BMW, General Motors, Honda, and Toyota. Top-tier gasoline exceeds the quality standards developed by the World Wide Fuel Charter ( WWFC ) that was established in 2002 by vehicle and engine manufacturers. The gasoline companies that agreed to make fuel that matches or exceeds the standards as a top-tier fuel include Chevron Texaco and Conoco Phillips. Ford has specified that BP fuel, sold in many parts of the country, is the recommended fuel to use in Ford vehicles. What is Top-Tier Gasoline? Figure 52–13 T he gas cap on a Ford vehicle notes that BP fuel is recommended.
Fuel is a major expense in vehicle operation cost. Proper operation of the engine depends on clean fuel of proper octane rating and vapor pressure for atmospheric conditions. Some guidelines:
Purchase fuel from a busy station to help ensure that it is fresh and less likely to be contaminated with water or moisture.
Keep the fuel tank above one-quarter full, especially during seasons in which the temperature rises and falls by more than 20°F between daytime highs and nighttime lows. This helps to reduce condensed moisture in the fuel tank and could prevent gas line freeze-up in cold weather.
NOTE: Gas line freeze-up occurs when the water in the gasoline freezes and forms an ice blockage in the fuel line.
Do not purchase fuel with a higher octane rating than is necessary. Try premium high-octane fuel to check for operating differences. Some drivers compromise by using midgrade (plus) fuel to benefit from the engine power and fuel economy gains without the cost of using premium fuel.
Avoid using gasoline with alcohol in warm weather. If warm-engine stumble, stalling, or rough idle occurs, change brands of gasoline.
Do not purchase fuel when a tanker truck is filling the underground tanks. Dirt, rust, and water may be stirred up in the underground tanks and pumped into your vehicle.
Don’t overfill the tank. After the nozzle clicks off, round up to the next dime. Adding additional gasoline will cause the excess to be drawn into the charcoal canister. This can lead to engine flooding and excessive exhaust emissions.
Be careful when filling gasoline containers. Always fill a gas can on the ground to help prevent the possibility of static electricity build-up during the refueling process.
Figure 52–14 Many gasoline service stations have signs posted warning customers to place plastic fuel containers on the ground while filling. If placed in a trunk or pickup truck bed equipped with a plastic liner, static electricity could build up during fueling and discharge from the container to the metal nozzle, creating a spark and possible explosion. Some service stations have warning signs not to use cell phones while fueling to help avoid the possibility of an accidental spark creating a fire hazard.
The pickup inside the fuel tank can help keep water from being drawn into the fuel system unless water is all that is left at the bottom of the tank. Over time, moisture in the air inside the tank can condense, causing liquid water to drop to the bottom of the tank (water is heavier than gasoline—about 8 lb per gallon for water and about 6 lb per gallon for gasoline). If alcohol-blended gasoline is used, the alcohol can absorb the water and the alcohol–water combination can be burned inside the engine. However, when water combines with alcohol, a separation layer occurs between the gasoline at the top of the tank and the alcohol–water combination at the bottom. When the fuel level is low, the fuel pump will draw from this concentrated level of alcohol and water. Because alcohol and water do not burn as well as pure gasoline, severe driveability problems can occur—stalling, rough idle, hard starting, and missing. Why Should I Keep the Fuel Gauge Above One-Quarter Tank?
Gasoline fuel tanks have an expansion volume area at the top. This expansion area is equal to 10% to 15% of the volume of the tank. It is normally not filled with gasoline, but is designed to provide a place for the gasoline to expand into, if the vehicle is parked in the hot sun and the gasoline expands. This prevents raw gasoline from escaping the fuel system. A small restriction is usually present to control the amount of air and vapors that can escape the tank and flow to the charcoal canister. This volume area could be filled with gasoline if the fuel is slowly pumped into the tank. Since it can hold an extra 10% (2 gallons in a 20-gallon tank), some people deliberately try to fill the tank completely. When this expansion volume is filled, liquid fuel (rather than vapors) can be drawn into the charcoal canister. When the purge valve opens, liquid fuel can be drawn into the engine, causing an excessively rich air–fuel mixture. This liquid fuel can harm vapor recovery parts, and overfilling can also cause the vehicle to fail an exhaust emission test, particularly during an enhanced test when the tank could be purged while on the rollers. Do Not Overfill the Fuel Tank
Ethanol Also called ethyl alcohol or grain alcohol , ethanol is usually made from grain and is the type of alcohol found in alcoholic drinks such as beer, wine, and distilled spirits like whiskey. Ethanol is composed of two carbon atoms and six hydrogen atoms with one added oxygen atom.
Figure 52–16 The ethanol molecular structure showing two carbon atoms, six hydrogen atoms, and one oxygen atom. Continued
Conventional ethanol and cellulose ethanol are the same product, but cellulose ethanol is produced using the nonfood portion of the feedstock. Ethanol derives from grains, such as corn, wheat, or soybeans. Corn is converted to ethanol in a dry or wet milling process. In dry milling, liquefied cornstarch is produced by heating cornmeal with water and enzymes. Wet milling separates the fiber, germ (oil), and protein from the starch before it is fermented into ethanol. Cellulose ethanol can be produced from agricultural plant wastes (corn stalks, cereal straws), plant wastes from industrial processes (sawdust, paper pulp), and energy crops grown for fuel production. These nongrain products are often referred to as cellulosic biomass .
Separating these complex structures into fermentable sugars is needed to achieve efficient and economic production of ethanol. Two processing options are employed to produce fermentable sugars from cellulose biomass:
Acid hydrolysis is used to break down the complex carbohydrates into simple sugars.
Enzymes are employed to convert the cellulose biomass to fermentable sugars. The final step involves microbial fermentation, yielding ethanol and carbon dioxide.
NOTE: Grain-based ethanol uses fossil fuels to produce heat during the conversion process, generating substantial greenhouse gas emissions. Cellulose ethanol production substitutes biomass for fossil fuels. The green-house gases produced by the combustion of biomass are offset by the CO 2 absorbed by the biomass as it grows in the field.
The majority of the ethanol in the United States is made from:
In Brazil, the world’s largest ethanol producer, it is made from sugarcane.
Production of ethanol is referred to as being carbon neutral because the amount of CO 2 released during production is equal to the amount of CO 2 that would be released if the corn or other products were left to decay. Does Ethanol Production Harm the Environment?
E-85 Manufacturers have available vehicles capable of operating on a combination of gasoline and ethanol called E - 85 , composed of 85% ethanol and 15% gasoline.
Continued NOTE: The octane rating of E-85 depends on the exact percent of ethanol used, which can vary from 81% to 85%, as well as the octane rating of the gasoline used. E-85 has less heat energy than gasoline. Gasoline = 114,000 BTUs per gallon E - 85 = 87,000 BTUs per gallon Fuel economy is reduced by 20% to 30% if E-85 is used. Pure ethanol has an octane rating of about 113, whereas E-85, which contains 35% oxygen by weight, has an octane rating of about 100 to 105 compared to a regular unleaded gasoline rating of 87.
The 15% gasoline in this blend helps the engine start, especially in cold weather. Vehicles equipped with this capability are commonly referred to as alternative fuel vehicles ( AFVs ), flex fuels , and flexible fuel vehicles , or FFVs .
Figure 52–17 A vehicle emission control information (VECI) sticker on a flexible fuel vehicle indicating the percentage of ethanol with which it is able to operate. NOTE: E-85 may test as containing less than 85% ethanol if tested because it is often blended according to outside temperature. A lower percentage of ethanol with a slightly higher percentage of gasoline helps engines start in cold climates. Using E-85 in a flex fuel vehicle can result in a power increase of about 5%. A engine rated 200 hp using gasoline or E-10 can produce 210 hp using E-85.
GM, Ford, Chrysler, Mazda, and Honda are offering E-85 vehicles. These vehicles use fuel system parts designed to withstand alcohol content, modified driveability programs that adjust fuel delivery and timing to compensate for the various percentages of ethanol fuel, and a fuel compensation sensor that measures percentage of ethanol blend and temperature of the fuel. This sensor is also called a variable fuel sensor . See Figures 52–18 and 52–19.
Figure 52–18 The location of the variable fuel sensor can vary, depending on the make and model of vehicle, but it is always in the fuel line between the fuel tank and the fuel injectors.
Flex-fuel vehicles are equipped with a sensor to detect presence and percentage of ethanol…
Figure 52–19 A cutaway view of a typical variable fuel sensor. … and match fuel injector on-time and ignition timing to match the fuel. Continued
Many General Motors flex fuel vehicles do not use a fuel compensation sensor and instead use the oxygen sensor to detect the presence of the lean mixture and the extra oxygen in the fuel. The power train control module (PCM) then adjusts the injector pulse width and the ignition timing to optimize engine operation to the use of E-85. This type of vehicle is called a virtual - flexible fuel vehicle abbreviated V - FFV The virtual-flexible fuel vehicle can operate on pure gasoline, E-10, E-85, or any combination. How Does a Sensorless Flex Fuel System Work? Continued
Most E-85 vehicles are very similar to non-E-85 vehicles. Fuel system components may be redesigned to withstand the effects of higher concentrations of ethanol. Since the stoichiometric point for ethanol is 9:1 instead of 14.7:1 as for gasoline, air–fuel mix has to be adjusted for the percentage of ethanol present in the fuel tank. To determine this percentage of ethanol in the fuel tank, a compensation sensor is used. The benefits of E-85 vehicles are less pollution, less CO 2 production, and less dependence on oil. Ethanol-fueled vehicles generally produce the same pollutants as gasoline vehicles; however, they produce lower CO and CO 2 emissions. See Figure 52-20.
Figure 52–20 A pump for E-85 (85% ethanol and 15% gasoline). There are few, if any, of these pumps in many states. NOTE: For additional information on E-85 and for the location of E-85 stations in your area, go to www.e85fuel.com Visit www.e85fuel.com on the World Wide Web Continued
Lowland types —grow up to 12 feet tall and are typically found on heavy soils in bottomland sites
Switchgrass ( Panicum virgatum ) is a summer perennial grass that is native to North America. It is a natural component of the tall-grass prairie, which covered most of the Great Plains, but was also found on the prairie soils in the Black Belt of Alabama and Mississippi. Switchgrass is resistant to many pests and plant diseases, and is capable of producing high yields with very low applications of fertilizer. This means that the need for agricultural chemicals to grow switchgrass is relatively low. Switchgrass is also very tolerant of poor soils, flooding, and drought, which are widespread agricultural problems in the Southeast. There are two main types of switchgrass: Better energy efficiency is gained because less energy is used to produce ethanol from switchgrass. What is Switchgrass? Continued
Starting in 2006, General Motors vehicles designed to operate on E-85 do not use a fuel compensation sensor, but instead use the oxygen sensor and refueling information to calculate the percentage of ethanol in the fuel. The PCM uses the fuel-level sensor to sense that fuel has been added and starts to determine the resulting ethanol content by using the oxygen sensor. However, if a service technician were to reset fuel compensation by clearing long-term fuel trim, the PCM starts the calculation based on base fuel, which is gasoline with less than or equal to 10% ethanol (E-10). If the fuel tank has E-85, the fuel compensation cannot be determined unless the tank is drained and refilled with base fuel. Therefore, avoid resetting the fuel compensation setting unless it is known that the fuel tank contains gasoline or E-10 only. Avoid Resetting Fuel Compensation Continued
Light, volatile, colorless, tasteless, flammable, poisonous, with a very faint odor; used as an antifreeze, solvent, and fuel. Methanol burns in air, forming CO 2 ( carbon dioxide ) and H 2 O ( water ).
Figure 52–22 This sign on a methanol pump shows that methyl alcohol is a poison and can cause skin irritation and other personal injury. Methanol is used in industry as well as a fuel source. Continued A methanol flame is almost colorless. Methanol is often called wood alcohol because it was once produced as a by-product of destructive distillation of wood.
The biggest source of methanol in the United States is coal. Using a reaction between coal and steam, a gas mixture called syn - gas ( synthesis gas ) is formed. Components of this mixture are carbon monoxide and hydrogen, which, through an additional chemical reaction, are converted to methanol. Natural gas can also be used to create methanol and is re-formed or converted to synthesis gas, which is later made into methanol. Biomass can be converted to synthesis gas by a process called partial oxidation, and later converted to methanol. Electricity can be used to convert water into hydrogen, which is then reacted with carbon dioxide to produce methanol. Methanol is toxic and can cause blindness and death. It can enter the body by ingestion, inhalation, or absorption through the skin.
M-85 Some flexible fuel vehicles are designed to operate on 85% methanol and 15% gasoline. Methanol is very corrosive and requires that the fuel system components be constructed of stainless steel and other alcohol-resistant rubber and plastic components. The heat content of M - 85 is about 60% of that of gasoline.
Propane Normally a gas, propane is easily compressed into liquid and stored in inexpensive containers. Known as liquefied petroleum gas ( LPG ) or LP - gas because propane is often mixed with about 10% of other gases such as butane, propylene, butylenes, and mercaptan to give the colorless and odorless propane a smell. Propane is nontoxic, but if inhaled can cause asphyxiation through lack of oxygen. Propane is heavier than air and lays near the floor if released into the atmosphere. Propane is commonly used in forklifts and other equipment used inside warehouses and factories because exhaust from the engine using propane is not harmful.
Propane comes from a by-product of petroleum refining of natural gas. In order to liquefy the fuel, it is stored in strong tanks at about 300 psi (2,000 kPa). The heating value of propane is less than gasoline; more is required, which reduces the fuel economy.
Figure 52–23 Propane fuel storage tank in the trunk of a Ford taxi. Continued
Compressed Natural Gas ( CNG ) Another fuel often used in fleet vehicles is compressed natural gas , or CNG , and vehicles using this fuel are often referred to as natural gas vehicles ( NGVs ). Look for the blue CNG label on vehicles designed to operate on compressed natural gas.
Figure 52–24 The blue sticker on the rear of this vehicle indicates that it is designed to use compressed natural gas. Continued
Natural gas has to be compressed to about 3000 PSI (20,000 kPa), so weight and the cost of storage container is a major factor when it comes to preparing a vehicle to run on CNG. Compressed natural gas is made up of a blend of methane, propane, ethane, N-butane, carbon dioxide, and nitrogen. Once processed, it is at least 93% methane. Natural gas is lighter than air and will rise when released into the air. Since CNG is already a vapor, it does not need heat to vaporize before it will burn, which improves cold start-up and results in lower emissions during cold operation. Because it is already a gas, it does displace some air charge in the intake manifold, leading to about a 10% reduction in engine power. Natural gas also burns slower than gasoline; ignition timing must be advanced more when the vehicle operates on natural gas. Natural gas has an octane rating of about 115 octane.
The stoichiometric ratio, the point at which all the air and fuel is used or burned, is 16.5:1 compared to 14.7:1 for gasoline. This means that more air is required to burn one pound of natural gas than is required to burn one pound of gasoline.
Figure 52–25 The fuel injectors used on this Honda Civic GX CNG engine are designed to flow gaseous fuel instead of liquid fuel and cannot be interchanged with any other type of injector. Continued Continued
Figure 52–26 A CNG storage tank from a Honda Civic GX shown with the fixture used to support it while it is being removed or installed in the vehicle. Honda specifies that three technicians be used to remove or install the tank through the rear door of the vehicle due to the size and weight of the tank.
Increased compression ratio
Strong pistons and connecting rods
Fuel injectors designed for gaseous fuel instead of liquid fuel
When completely filled, the CNG tank has 3600 PSI pressure.
When the ignition is turned on, the alternate fuel electronic control unit activates the high-pressure lock-off, which allows high-pressure gas to pass to the high-pressure regulator. The high-pressure regulator reduces high-pressure CNG to approximately 170 PSI, 1172 kPa and sends it to the low-pressure lock-off, activated at the same time. From the low-pressure lock-off, the CNG is directed to the low-pressure regulator. This two-stage regulator first reduces pressure to approximately 4 to 6 PSI in the first stage and then 4.5 to 7 inches of water in the second. From here, low-pressure gas is delivered to the gas mass sensor/mixture control valve. This valve controls the air–fuel mixture. The CNG gas distributor adapter then delivers the gas to the intake stream.
CNG vehicles are designed for fleets that usually have their own refueling capabilities. One drawback is the time it takes to refuel. The ideal method of refueling is the slow fill method, which compresses the natural gas as the tank is being fueled. This method ensures the tank will receive a full charge; however, this can take three to five hours to accomplish. If more than one vehicle needs filling, the facility will need multiple CNG compressors to refuel the vehicles. There are three commonly used CNG refilling station pressures: P24 —2400 PSI
The fast fill method uses CNG that is already compressed. However, as the CNG tank is filled rapidly, the internal temperature of the tank will rise, which causes a rise in tank pressure. Once the temperature drops in the CNG tank, the pressure in the tank also drops, resulting in an incomplete charge in the CNG tank. This refueling method may take only about five minutes; however, it will result in an incomplete charge to the CNG tank, reducing the driving range.
P-series alternative fuel is patented by Princeton University and is a non-petroleum-based fuel suitable for use in flexible fuel vehicles or any vehicle designed to operate on E-85 (85% ethanol, 15% gasoline). P-series fuels are blends of the following:
The ethanol and MTHF are produced from renewable feedstocks, such as corn, waste paper, biomass, agricultural waste, and wood waste (scraps and sawdust).
See the chart on Page 602 of your textbook. The components used in P-type fuel can be varied to produce regular grade, premium grade, or fuel suitable for cold climates. P-series fuels are not produced in large enough amounts to make this fuel a good alternative at the present time.
In Brazil, most vehicles are designed to operate on ethanol or gasoline or any combination of the two. In this South American country, ethanol is made from sugarcane, is commonly available, and is lower in price than gasoline. Compressed natural gas (CNG) is also being made available, so many vehicle manufacturers in Brazil, such as General Motors and Ford, are equipping vehicles to be capable of using gasoline, ethanol, or CNG. These vehicles are called tri-fuel vehicles. What is a Tri-Fuel Vehicle?
Biodiesel is domestically produced, renewable fuel manufactured from vegetable oils, recycled restaurant greases or animal fats.
Figure 52–27 Biodiesel is available at few locations. Safe, biodegradable, and reduces serious air pollutants such as particulate matter (PM), carbon monoxide, and hydrocarbons. Biodiesel is defined as mono-alkyl esters of long-chain fatty acids derived from vegetable oils or animal fats which conform to ASTM D6751 specs for use in diesel engines. Biodiesel refers to the pure fuel before blending with diesel fuel. Continued
Purchasing biodiesel in bulk quantities decreases the cost.
Biodiesel maintains similar horsepower, torque, and fuel economy.
Biodiesel has a higher cetane number than conventional diesel, which increases the engine’s performance.
Biodiesel has a high flash point and low volatility so it does not ignite as easily as petrodiesel, increasing the margin of safety in fuel handling. In fact, it degrades four times faster than petrodiesel and is not particularly soluble in water.
It is nontoxic, safe to handle, transport, and store. B20 vehicle and petrodiesel maintenance requirements are the same.
Biodiesel acts as a lubricant and this can add to the life of the fuel system components.
Biodiesel blends are denoted as “ BXX ” with “ XX ” representing the percentage of biodiesel contained in the blend (i.e., B20 is 20% biodiesel, 80% petroleum diesel). Blends of 20% biodiesel with 80% petroleum diesel (B20) can generally be used in unmodified diesel engines. Biodiesel can also be used in its pure form (B100), but may require certain engine modifications to avoid maintenance and performance problems. B20 costs 30 to 40 cents more per gallon than conventional diesel, often called petrodiesel .
Continued NOTE: For additional information on biodiesel and the locations where it can be purchased, go to visit www.biodiesel.org Visit www.biodiesel.org on the World Wide Web
I Thought Biodiesel Was Vegetable Oil? Biodiesel is vegetable oil with the glycerin component removed by means of reacting the oil with a catalyst. The resulting hydrocarbon esters are 16 to 18 carbon atoms in length, almost identical to petroleum diesel fuel atoms. This allows the use of biodiesel fuel in a diesel engine with no modifications needed. Biodiesel-powered vehicles do not need a second fuel tank, whereas vegetable-oil-powered vehicles do. There are three main types of fuel used in diesel engines. These are:
Petroleum diesel, a fossil hydrocarbon with a carbon chain length of about 16 carbon atoms.
Biodiesel, a hydrocarbon with a carbon chain length of 16 to 18 carbon atoms.
Vegetable oil, a triglyceride with a glycerin component joining three
hydrocarbon chains of 16 to 18 carbon atoms each, called straight vegetable oil ( SVO ).
Biodiesel…Vegetable Oil? Vegetable oil is not liquid enough at common ambient temperatures for use in a diesel engine fuel delivery system designed for the lower-viscosity petroleum diesel fuel. It needs to be heated to obtain a similar viscosity, meaning a heat source must be provided before the fuel can be used in a diesel engine. This is achieved by starting on petroleum diesel or biodiesel fuel until engine heat can be used to warm a tank containing vegetable oil. The use of vegetable oil in its natural state does eliminate the need to remove the glycerin component. Many vehicle and diesel fuel system suppliers permit biodiesel fuel certified as meeting testing standards. None permit use of vegetable oil in its natural state.
Pure Plant Oil ( PPO )—most often used in Europe to describe SVO
Waste Vegetable Oil ( WVO )—could include animal/fish oils from cooking
Used Cooking Oil ( UCO ) —used when the oil may or may not be pure vegetable oil
Other terms used when describing vegetable oil include:
E-diesel , called diesohol outside the US, is standard No. 2 diesel fuel with up to 15% ethanol. While E-diesel can have up to 15% ethanol by volume, typical blend levels are from 8% to 10%. Cetane Rating The higher the cetane number, the shorter the delay between injection and ignition. Normal diesel fuel has a cetane number of about 50. Adding 15% ethanol lowers the cetane number. To increase the cetane number back to that of conventional diesel fuel, cetane-enhancing additive is added to E-diesel. The additive used to increase the cetane rating of E-diesel is ethylhexylnitrate or ditertbutyl peroxide.
E-diesel has better cold-flow properties than conventional diesel. The heat content of E-diesel is about 6% less than conventional diesel, but the particulate matter (PM) emissions are reduced by as much as 40%, 20% less carbon monoxide, and a 5% reduction in oxides of nitrogen (NO X ).
The oxygen in oxygenated fuels, such as E-10, E-85, and E-diesel, is not in a gaseous state like the CO 2 in soft drinks. The oxygen is part of the molecule of ethanol or other oxygenates and does not bubble out of the fuel. Oxygenated fuels, like any fuel, have a shelf life of about 90 days. How Long Can Oxygenated Fuel Be Stored Before All of the Oxygen Escapes? E-diesel is considered to be experimental and can be used legally in off-road applications or in mass-transit buses with EPA approval.
Synthetic fuels have been in use since the 1920s. They convert coal, natural gas, and other fossil fuel products into a fuel that is high in quality and clean-burning. The process for producing Fischer-Tropsch fuels was patented by two German scientists, Franz Fischer and Hans Tropsch, during World War I. The Fischer-Tropsch method uses carbon monoxide and hydrogen (the same synthesis gas used to produce hydrogen fuel) to convert coal and other hydrocarbons to liquid fuels in a process similar to hydrogenation, another method for hydrocarbon conversion.
The Fischer-Tropsch method uses carbon monoxide and hydrogen in a process similar to hydrogenation The process using natural gas, also called gas - to - liquid ( GTL ) technology, uses a catalyst, usually iron or cobalt, and incorporates steam reforming to give off the by-products of carbon dioxide, hydrogen, and carbon monoxide. The fuels contain a very low sulfur and aromatic content, produce virtually no particulate emissions and do not differ in fuel performance from gasoline and diesel. They are very expensive to produce on a large scale, although research is under way to lower processing costs. Diesel fuel created using the Fischer - Tropsch diesel ( FTD ) process is often called GTL diesel .
Coal to Liquid ( CTL) Abundant in the US, coal can be converted to a liquid fuel through a process called coal to liquid ( CTL ). The main obstacle to these CTL plants is huge cost. The need to invest $1.4 billion per plant before the product can be made is the reason why no one has built a CTL plant yet in the United States. Investors need to be convinced that the cost of oil is going to remain high in order to get them to commit this kind of money. A large plant might be able to produce 120,000 barrels of liquid fuel a day and would consume about 50,000 tons of coal per day. Such a plant would create about 6,000 tons of CO 2 per day. These CO 2 emissions and cost involved make CTL a new technology that is not likely to expand.
Two procedures can be used to convert coal to a liquid fuel:
Direct —In the direct method, coal is broken down to create liquid products. First the coal is reacted with hydrogen (H 2 ) at high temperatures and pressure with a catalyst. This process creates a synthetic crude, called syncrude , which is then refined to produce gasoline or diesel fuel. Indirect —In the indirect method, coal is first turned into a gas and the molecules are reassembled to create the desired product. This process involves turning coal into a gas called syngas. The syngas is converted into liquid, using the Fischer-Tropsch (FT) process. Continued
Figure 52–28 A typical coal-to-liquid plant. Russia has been using CTL by injecting air into the underground coal seams. Ignition is provided and resulting gases are trapped and converted to liquid gasoline and diesel fuel. This underground method is called underground coal gasification ( UCG ).
Methanol to Gasoline Exxon Mobil has developed a process for converting methanol (methyl alcohol) into gasoline in a process called methanol-to-gasoline ( MTG ). The process was discovered by accident when a gasoline additive made from methanol was being created. The process instead created olefins (alkenes), paraffins (alkenes), and aromatic compounds, which in combination are known as gasoline. The process uses a catalyst and is currently being produced in New Zealand
Future of Synthetic Fuels Producing gasoline and diesel fuels by other methods besides refining from crude oil has usually been more expensive. With the increasing cost of crude oil, alternative methods are now becoming economically feasible. Whether diesel fuel or gasoline is created from coal, natural gas, or methanol, or created by refining crude oil, the transportation and service pumps are already in place. Compared to using compressed natural gas or other similar alternative fuels, synthetic fuels represent the lowest cost.
ALTERNATE FUEL COMPARISON CHART See the chart on Page 602 of your textbook.
All fuels are flammable and many are explosive under certain conditions. When working around compressed gases of any kind (CNG, LNG, propane, or LPG), always wear personal protective equipment (PPE), and take precautions including:
SAFETY PROCEDURES WHEN WORKING WITH ALTERNATIVE FUEL VEHICLES Continued
Safety glasses and/or face shield.
Long-sleeved shirt and pants to help protect exposed skin from the freezing effects of gases under pressure in the event pressure is lost.
If any fuel gets on the skin, the area should be washed immediately.
If fuel spills on clothing, change into clean clothing as soon as possible.
If fuel spills on a painted surface, flush the surface with water and air-dry. If simply wiped off with a dry cloth, the paint surface could be permanently damaged.
As with any fuel-burning vehicle, always vent the exhaust to the outside. If methanol fuel is used, the exhaust contains formaldehyde , which has a sharp odor and can cause severe burning of the eyes, nose, and throat.
WARNING: Do not smoke or have an open flame in the area when working around or refueling any vehicle.