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What are fuel mapping computers?

2009-03-25T06:58:00.000-07:00

Hybrid Car Image Gallery

Yoshikazu Tsuno/AFP
Toyota unveils the 2005 Prius, complete with new hybrid engine unit, in Tokyo. See more pictures of hybrid cars.

Before we can get into a discussion about fuel mapping, you have to have to know a bit about electronic fuel injection (EFI). What's that? To put it simply, it's a computerized system that takes over where your old carburetor left off, regulating the mix of air and fuel in your engine to keep it running smoothly. Too much fuel, and you're wasting gas. Too little, and you could damage your engine.

For decades, fuel regulation was handled by the carburetor. In the late 1950s, cars with optional electronic fuel injection came on the scene, and by the 1990s, EFI was common. Today, almost all new cars have EFI systems instead of carburetors.

The fuel map is the EFI system's setting for regulating the air/fuel mix. The map has three goals:

Optimize performance -- for better speed and acceleration

Optimize fuel economy -- to get the best gas mileage

Optimize emissions -- to eliminate as many waste particles from the tailpipe as possible

Next, we'll map out the parts that make up this intricate

Parts of the EFI System

Yoshikazu Tsuno/AFP
Would you put the brains of your car under its seats?

Understanding fuel mapping technology is much easier if you know the territory. The center of the whole EFI system, which controls the fuel map, is the engine control unit (ECU). Think of this component as the car's brain. Sensors located in the engine and throughout the rest of the vehicle send information to the ECU. The ECU interprets this information and uses it to keep the car working at its best.

The ECU looks like a black plastic box with the electronic brains inside. Its location varies wildly by manufacturer. Some put the ECU in the engine compartment near the battery, some put it near the glove box or steering column in the passenger compartment. Some even put it under one of the seats.

The ECU, though, is useless without its sensors, just like our brains wouldn't be much good at interpreting the world around us without our senses. While there are dozens of sensors in a car that feed information to the ECU like the one that triggers that annoying "Check Engine" light, we'll just list the ones that create the fuel map.

Mass Air Flow (MAF) Sensor: This sensor measures the amount of air coming into the engine. Less air is drawn into the engine when it's idling, so less fuel is needed. More air is drawn into the engine once the car's in motion, so more fuel is needed from the injectors.
Oxygen (O₂) Sensors: Located in the exhaust system, these sensors detect the amount of unburned oxygen and fuel coming from the engine. The ECU can adjust the amount of fuel injected into the engine to increase efficiency.
Throttle Position Sensor (TPS): This sensor tells the computer how hard and how quickly the driver pushes on the gas pedal. The farther and faster the pedal is pushed, the wider open the throttle moves, increasing the amount of fuel that needs to be added to the engine for speed.
Manifold Absolute Pressure (MAP) Sensor: This sensor measures changes in the engine's manifold pressure, which tells the ECU how much load the engine needs to bear (towing or going uphill) and how fast it needs to happen (speeding up or slowing down). If the sensor reads high pressure, the ECU will lower the engine vacuum and add more fuel. If there is low pressure, the ECU will raise the vacuum and dial down the fuel injection.
Vehicle Speed Sensor (VSS): This tells the ECU how fast the car is moving and adjusts the fuel accordingly. This sensor also sends signals to the speedometer and the cruise control computer.

The Fuel Map

Stephen Oliver
Would you like to know what a fuel map looks like? Start here.

While the car's ECU doesn't need to visualize the fuel map, it's helpful for us humans to picture how this computer comes to its conclusions. You don't need a physical piece of graph paper, but imagining one will make it easier. The fuel map looks a lot like something you'd learn in a junior high school math class.

Imagine that piece of graph paper and draw a simple X-Y axis on it: one line going across (the X) and one line going up and down (the Y). The numbers along the X axis represent the engine's revolutions per minute (rpm). That's how fast the engine's internal components are turning to do whatever the driver needs -- speeding up, slowing down, waiting at a red light or even towing a boat. The Y axis represents the load on the engine, or the energy required by the engine to do the task at hand.

Now imagine points scattered all along that graph paper that represent different driving situations. That's the fuel map. At each point -- and there are hundreds of possible combinations -- the ECU decides what to tell the fuel injectors to do.

Pulling a fifth-wheel camper up the Rocky Mountains at highway speed, for example, puts the engine under a huge load and requires a lot of energy. The ECU gets input from all of the sensors on vehicle speed, air intake, pressure, and temperature and plots a specific point on the imaginary graph. The computer is programmed to tell the fuel injectors what to do at that very point on the fuel map, and it sends out the appropriate message -- without any more input from the driver.

Once the ECU has received the information from the sensors and figured out what to do based on the fuel map, it can change three basic things to make the engine run at its best -- the fuel flow rate, spark timing, and idle speed.

But what can you, the car owner, do to change these things? Change the ECU and sensors, of course. We'll look at improvements and troubleshooting for the fuel mapping system on the next page.

Changing the Fuel Map

Blaine Franger
You'll need your ECU to regulate the air/fuel mix in your engine to make this job easier.

There are basically two types of people who'd want to make changes to the fuel map: Performance hounds and fuel misers.

Performance-minded people who are interested in eking every last hundredth of a second from their cars can reprogram the ECU's fuel map to deliver more fuel. There may be some fuel wasted and a lot more unburned fuel in the exhaust, but that's the price you pay for a win at the Saturday night drag races.

On the opposite end of the scale are those drivers who are willing to sacrifice performance for fuel economy. A leaner fuel/air mixture is going to sap some power from the engine, but burning less fuel means higher miles per gallon and less fuel wasted in the process. There are even adjustable MAP sensors on the market specifically aimed at the fuel-saving crowd.

Which brings us to one last point: You must remember that the information in the vehicle's brain is only as good as what the sensors are telling it. If a sensor is bad and sending faulty information, the ECU will not adjust the fuel injectors correctly. Failure usually occurs due to a dusty sensor or a corroded or loose electrical connection. Occasionally, the sensor itself will just go bad and send incorrect signals.

To stick with our earlier example of an engine under very heavy load -- the camper on the highway in the Rockies -- let's think about what would happen if one of those sensors were bad. If the Mass Air Flow (MAF) sensor, for example, wasn't working correctly, it might tell the ECU that there wasn't a lot of air moving into the engine. This would move the point on the fuel map, and the ECU wouldn't know to send a signal to the fuel injectors to increase the amount of fuel in the mix to make up for all that air. The engine would seem sluggish, since it wasn't getting the energy it needed to do such a difficult job.

The fuel map inside the ECU is able to adjust the air/fuel mix for maximum efficiency and performance in any condition - that is, as long as the sensors are giving it the right information.

Why is summer fuel more expensive than winter fuel?

2009-03-25T06:56:00.000-07:00

Unfortunately for drivers, gas prices often go up during the summer, starting around Memorial Day [Source: EPA]. There are many reasons behind the increase in summer fuel prices, and some are fairly logical. More people traveling, especially on family vacations and road trips, increases demand. Also, in the spring months, energy companies conduct maintenance on their refineries, shutting them down and limiting capacity until late May. Because of these disruptions, oil supplies can become stretched. In addition, natural disasters, like hurricanes, can increase prices by disrupting transport routes and damaging refineries and other infrastructure.

But did you know that the gasoline sold during the summer is actually different -- and more expensive to produce -- than that sold in the winter? In this article, we'll take a look at why summer fuel prices are higher, focusing on the annual shift from winter-grade fuel to summer-grade fuel.

Photo courtesy: David New
Gas stations start selling summer-grade fuel, around Memorial Day weekend. This marks the beginning of the summer travel season.

Twice every year in the United States, the fuel supply changes. It's known as the seasonal gasoline transition. This change is the biggest reason for the price hike in summer gasoline. Depending on the time of year, gas stations switch between providing summer-grade fuel and winter-grade fuel. The switch started in 1995 as part of the Reformulated Gasoline Program (RFG), which was established through the 1990 Clean Air Act Amendments. The Environmental Protection Agency (EPA) started the RFG program in order to reduce pollution and smog during the summer ozone season, which occurs from June 1 to Sept. 15 [Source: EPA].

In order to reduce pollution, summer-blend fuels use different oxygenates, or fuel additives. These blends, the EPA claims, burn cleaner and also help compensate for a limited oil supply. The EPA says this practice of using seasonal blends also encourages the development of alternative fuels [Source: EPA]. (Remember that gasoline isn't just made up of processed crude oil -- it's a blend of refined crude oil and different compounds and additives.)

So what's the difference between summer-grade fuel and winter-grade fuel? Summer-grade fuel is more expensive for two reasons -- because of the ingredients it contains and because refineries have to briefly shut down before they begin processing it. Summer-grade fuel also burns cleaner than winter-grade fuel. This just means that it produces less smog and releases less toxic air pollutants, which we'll talk about more [source: EPA]. The actual difference in cost of production varies. One estimate claims an increase of only 1 cent to 2 cents per gallon [Source: Slate], while another states 3 cents to 15 cents per gallon [Source: Reason]. No matter the difference in production costs, the increase at the pump is even greater, owing to the summer driving season, dips in supply, maintenance costs and companies' converting to production of summer blends.

Summer-grade versus Winter-grade Fuel

During the summer, pollution is a frequent concern due to increased levels of smog and ozone, which can harm the lungs. Summer heat boosts the formation of ozone, while the appearance of an inversion layer -- an immobile layer of air -- can trap pollutants in the lower atmosphere [source: EPA].

Summer-grade fuel has a different Reid Vapor Pressure (RVP) than winter-grade fuel, which contributes to its being (marginally) more eco-friendly. RVP is the vapor pressure of gasoline measured at 100 degrees Fahrenheit. Fuels with higher RVP evaporate more easily than those with lower RVP. A particular fuel blend's RVP is based on the combined RVP of the ingredients that make up the blend. Regulators worry about this evaporation because it contributes to ozone formation.

Photo courtesy: VisionsofAmerica/Joe Sohm
Oil refineries like this one in California shut down for a few months every year. This is another reason why summer fuel prices are higher than winter fuel prices.

Gasoline must have an RVP below 14.7 PSI (pounds per square inch), which is normal atmospheric pressure; if a fuel's RVP were greater than 14.7 PSI, excess pressure would build up in the gas tank, and the fuel could boil and evaporate. Depending on the part of the country, the EPA's standards mandate an RVP below 9.0 PSI or 7.8 PSI for summer-grade fuel. Some local regulations call for stricter standards. Because of these varying RVP standards, up to 20 different types of boutique fuel blends are sold throughout the U.S. during the summer [Source: Slate].

Because RVP standards are higher during the winter, winter-grade fuel uses more butane, with its high RVP of 52 PSI, as an additive. Butane is inexpensive and plentiful, contributing to lower prices. Summer-grade fuel might still use butane, but in lower quantities -- around 2 percent of a blend [Source: The Oil Drum].

Storing Fuel Out of Season Because of the way winter and summer fuels react under different atmospheric pressures, particularly in terms of evaporation, it's important to use summer and winter fuels during their respective seasons. Fuel that's stored out of season can evaporate. It can also hurt engine performance.

We know that gas prices go up during the summer, generally around Memorial Day, but when do companies start producing these different summer fuels? The EPA defines April to June as the "transition season" for fuel production [Source: EPA]. Refineries switch over to summer-blend production in March and April [Source: EPA]. Gas stations have by June 1 to switch to selling summer-grade gas, while terminals and other facilities "upstream" from pumping stations have to switch by May 1 [Source: EPA]. Following the summer driving season, companies switch back to winter blends beginning in September, with the first winter increase in RVP allowance occurring on Sep. 15.

In a 2001 report, the EPA claimed that "roughly 75 million Americans breathe cleaner air today due to [the seasonal fuel] program" [Source: EPA]. Still, the increased price, combined with the use of controversial additives like ethanol (which is less energy efficient than gasoline and produces more smog) and methyl tertiary butyl ether (MTBE), means that the program may still have its detractors.

How Fuel Gauges Work

2009-03-25T06:48:00.000-07:00

If you're like me, you like to squeeze every last mile you can out of your tank of fuel. If you could get 20 miles extra from each tank, that could save you two or three trips to the gas station over the course of a year.

The main impediment to stretching your mileage is the fuel gauge on your car, which makes you think you have less fuel than you actually do. These devices are notoriously inaccurate, showing empty when there are gallons left in the tank and showing full for the first 50 miles.

In this article, we'll learn why our fuel gauges behave the way they do. There are two main parts to a fuel gauge: the sender, which measures the level of fuel in the tank, and the gauge, which displays that level to the driver. First, let's see how a typical sender works.

The Sending Unit

The sending unit is located in the fuel tank of the car. It consists of a float, usually made of foam, connected to a thin, metal rod. The end of the rod is mounted to a variable resistor. A resistor is an electrical device that resists the flow of electricity. The more resistance there is, the less current will flow. In a fuel tank, the variable resistor consists of a strip of resistive material connected on one side to the ground. A wiper connected to the gauge slides along this strip of material, conducting the current from the gauge to the resistor. If the wiper is close to the grounded side of the strip, there is less resistive material in the path of the current, so the resistance is small. If the wiper is at the other end of the strip, there is more resistive material in the current's path, so the resistance is large.

When the float is near the top of the tank, the wiper on the variable resistor rests close to the grounded (negative) side, which means that the resistance is small and a relatively large amount of current passes through the sending unit back to the fuel gauge. As the level in the tank drops, the float sinks, the wiper moves, the resistance increases and the amount of current sent back to the gauge decreases.

Running on Empty You may be surprised at how much fuel you actually have left when the needle is on empty. To find out, check your owner's manual for the exact volume of your fuel tank. Then, the next time your needle shows empty, find the nearest gas station and fill 'er up. Subtract the number of gallons it takes to fill your tank from the volume stated in the owner's manual, and you'll know just how much farther you can go when the gauge hits empty.

This mechanism is one reason for the inaccuracy of fuel gauges. You may have noticed how your gauge tends to stay on full for quite a while after filling up. When your tank is full, the float is at its maximum raised position -- its upward movement is limited either by the rod it's connected to or by the top of the tank. This means that the float is submerged, and it won't start to sink until the fuel level drops to almost the bottom of the float. The needle on the gauge won't start to move until the float starts to sink.

Something similar can happen when the float nears the bottom of the tank. Often, the range of motion does not extend to the very bottom, so the float can reach the bottom of its travel while there is still fuel in the tank. This is why, on most cars, the needle goes below empty and eventually stops moving while there is still gas left in the tank.

Another possible cause of inaccuracy is the shape of the fuel tanks. Fuel tanks on cars today are made from plastic, molded to fit into very tight spaces on the cars. Often, the tank may be shaped to fit around pieces of the car body or frame. This means that when the float reaches the halfway point on the tank, there may be more or less than half of the fuel left in the tank, depending on its shape.

The Gauge

The gauge is also a simple device. The current from the sender passes through a resistor that either wraps around or is located near a bimetallic strip. The bimetallic strip is hooked up to the needle of the gauge through a linkage.

The bimetallic strip is a piece of metal made by laminating two different types of metal together. The metals that make up the strip expand and contract when they are heated or cooled. Each type of metal has its own particular rate of expansion. The two metals that make up the strip are chosen so that the rates of expansion and contraction are different.

When the strip is heated, one metal expands less than the other, so the strip curves, with the metal that expands more on the outside. This bending action is what moves the needle.

Some newer cars, instead of sending the current directly to the gauge, use a microprocessor that reads the output of the resistor and communicates with the dashboard. These systems actually help improve the accuracy of the gauge. Let's take a look at one of these systems.

Microprocessor-controlled Gauges

Some newer cars have a microprocessor that reads the variable resistor in the tank and communicates that reading to another microprocessor in the dashboard. Carmakers can tinker with the gauge movement a little -- they can compensate for the shape of the tank by comparing the float position to a calibration curve. This curve correlates the position of the float with the volume of fuel left in the tank. This allows the gauge to read more accurately, especially in cars with complicated gas-tank shapes.

Systems like this can also trigger a fuel light that signals when fuel is getting low. Most of these lights come on while there are still a couple of gallons of gas left in the tank, giving you plenty of time to stop for fuel.

The microprocessor can also provide some damping to the needle movement. When you go around a turn, or up a hill, the fuel can slosh to one side of the tank and quickly change the float position. If the needle were to respond quickly to all of these changes, it would be bouncing all over the place. Instead, software calculates a moving average of the last several readings of the float position. This means that changes in needle position occur more slowly. You may have noticed this when filling up your car -- you'll finish filling the tank long before the needle reaches full.

While fuel gauges are far from exact, they err on the conservative side.

For more information on fuel gauges and related topics, check out the links on the next page.

How Gasoline Works 2

2009-03-25T06:40:00.000-07:00

What is octane?

If you've read How Car Engines Work, you know that almost all cars use four-stroke gasoline engines. One of the strokes is the compression stroke, where the engine compresses a cylinder-full of air and gas into a much smaller volume before igniting it with a spark plug. The amount of compression is called the compression ratio of the engine. A typical engine might have a compression ratio of 8-to-1. (See How Car Engines Work for details.)

The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine. Knocking can damage an engine, so it is not something you want to have happening. Lower-octane gas (like "regular" 87-octane gasoline) can handle the least amount of compression before igniting.

The compression ratio of your engine determines the octane rating of the gas you must use in the car. One way to increase the horsepower of an engine of a given displacement is to increase its compression ratio. So a "high-performance engine" has a higher compression ratio and requires higher-octane fuel. The advantage of a high compression ratio is that it gives your engine a higher horsepower rating for a given engine weight -- that is what makes the engine "high performance." The disadvantage is that the gasoline for your engine costs more.

The name "octane" comes from the following fact: When you take crude oil and "crack" it in a refinery, you end up getting hydrocarbon chains of different lengths. These different chain lengths can then be separated from each other and blended to form different fuels. For example, methane, propane and butane are all hydrocarbons. Methane has a single carbon atom. Propane has three carbon atoms chained together. Butane has four carbon atoms chained together. Pentane has five, hexane has six, heptane has seven and octane has eight carbons chained together.

It turns out that heptane handles compression very poorly. Compress it just a little and it ignites spontaneously. Octane handles compression very well -- you can compress it a lot and nothing happens. Eighty-seven-octane gasoline is gasoline that contains 87-percent octane and 13-percent heptane (or some other combination of fuels that has the same performance of the 87/13 combination of octane/heptane). It spontaneously ignites at a given compression level, and can only be used in engines that do not exceed that compression ratio.

Gasoline Additives

During WWI, it was discovered that you can add a chemical called tetraethyl lead to gasoline and significantly improve its octane rating. Cheaper grades of gasoline could be made usable by adding this chemical. This led to the widespread use of "ethyl" or "leaded" gasoline. Unfortunately, the side effects of adding lead to gasoline are:

Lead clogs a catalytic converter and renders it inoperable within minutes.
The Earth became covered in a thin layer of lead, and lead is toxic to many living things (including humans).

When lead was banned, gasoline got more expensive because refineries could not boost the octane ratings of cheaper grades any more. Airplanes are still allowed to use leaded gasoline, and octane ratings of 115 are commonly used in super-high-performance piston airplane engines (jet engines burn kerosene, by the way).

Another common additive is MTBE. MTBE is the acronym for methyl tertiary butyl ether, a fairly simple molecule that is created from methanol.

MTBE gets added to gasoline for two reasons:

It boosts octane.
It is an oxygenate, meaning that it adds oxygen to the reaction when it burns. Ideally, an oxygenate reduces the amount of unburned hydrocarbons and carbon monoxide in the exhaust.

MTBE started getting added to gasoline in a big way after the Clean Air Act of 1990 went into effect. Gasoline can contain as much as 10 percent to 15 percent MTBE.

The main problem with MTBE is that it is thought to be carcinogenic and it mixes easily with water. If gasoline containing MTBE leaks from an underground tank at a gas station, it can get into groundwater and contaminate wells. Of course, MTBE isn't the only thing getting into the groundwater when a tank leaks -- so is gasoline and a host of other gasoline additives.

According to this page at the EPA:

Although there is no established drinking-water regulation, USEPA has issued a drinking-water advisory of 20 to 40 micrograms per liter (µg/L) on the basis of taste and odor thresholds. This advisory concentration is intended to provide a large margin of safety for noncancer effects and is in the range of margins typically provided for potential carcinogenic effects.

The most likely thing to replace MTBE in gasoline is ethanol -- normal alcohol. It is somewhat more expensive than MTBE, but it is not a cancer threat.

Problems With Gasoline

Gasoline has two problems when burned in car engines. The first problem has to do with smog and ozone in big cities. The second problem has to do with carbon and greenhouse gases.

When cars burn gasoline, they would ideally burn it perfectly and create nothing but carbon dioxide and water in their exhaust. Unfortunately, the internal combustion engine is not perfect. In the process of burning the gasoline, it also produces:

Carbon monoxide, a poisonous gas
Nitrogen oxides, the main source of urban smog
Unburned hydrocarbons, the main source of urban ozone

Catalytic converters eliminate much of this pollution, but they aren't perfect either. Air pollution from cars and power plants is a real problem in big cities.

Carbon is also a problem. When it burns, it turns into lots of carbon dioxide gas. Gasoline is mostly carbon by weight, so a gallon of gas might release 5 to 6 pounds (2.5 kg) of carbon into the atmosphere. The U.S. is releasing roughly 2 billion pounds of carbon into the atmosphere each day.

If it were solid carbon, it would be extremely noticeable -- it would be like throwing a 5-pound bag of sugar out the window of your car for every gallon of gas burned. But because the 5 pounds of carbon comes out as an invisible gas (carbon dioxide), most of us are oblivious to it. The carbon dioxide coming out of every car's tailpipe is a greenhouse gas. The ultimate effects are unknown, but it is a strong possibility that, eventually, there will be dramatic climate changes that affect everyone on the planet (for example, sea levels may rise, flooding or destroying coastal cities). For this reason, there are growing efforts to replace gasoline with hydrogen. See How the Hydrogen Economy Works for details.

How Gasoline Works

2009-03-25T06:36:00.000-07:00

In the United States and the rest of the industrialized world, gasoline is definitely a vital fluid. It is as vital to the economy as blood is to a person. Without gasoline (and diesel fuel), the world as we know it would grind to a halt. The U.S. alone consumes something like 130 billion gallons (almost 500 billion liters) of gasoline per year!

Justin Sullian
The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites.

What is it in gasoline that makes it so important? In this article, you will learn exactly what gasoline is and where it comes from.

What is gasoline?

Gasoline is known as an aliphatic hydrocarbon. In other words, gasoline is made up of molecules composed of nothing but hydrogen and carbon arranged in chains. Gasoline molecules have from seven to 11 carbons in each chain. Here are some common configurations:

     H H H H H H H
    | | | | | | |
  H-C-C-C-C-C-C-C-H         Heptane
    | | | | | | |
    H H H H H H H


    H H H H H H H H
    | | | | | | | |
  H-C-C-C-C-C-C-C-C-H       Octane
    | | | | | | | |
    H H H H H H H H


    H H H H H H H H H
    | | | | | | | | |
  H-C-C-C-C-C-C-C-C-C-H     Nonane
    | | | | | | | | |
    H H H H H H H H H


    H H H H H H H H H H
    | | | | | | | | | |
  H-C-C-C-C-C-C-C-C-C-C-H   Decane
    | | | | | | | | | |
    H H H H H H H H H H

Typical molecules found in gasoline

When you burn gasoline under ideal conditions, with plenty of oxygen, you get carbon dioxide (from the carbon atoms in gasoline), water (from the hydrogen atoms) and lots of heat. A gallon of gasoline contains about 132x10⁶ joules of energy, which is equivalent to 125,000 BTU or 36,650 watt-hours:

If you took a 1,500-watt space heater and left it on full blast for a full 24-hour day, that's about how much heat is in a gallon of gas.
If it were possible for human beings to digest gasoline, a gallon would contain about 31,000 food calories -- the energy in a gallon of gasoline is equivalent to the energy in about 110 McDonalds hamburgers!

Where does gasoline come from?

Gasoline is made from crude oil. The crude oil pumped out of the ground is a black liquid called petroleum. This liquid contains hydrocarbons, and the carbon atoms in crude oil link together in chains of different lengths.

It turns out that hydrocarbon molecules of different lengths have different properties and behaviors. For example, a chain with just one carbon atom in it (CH4) is the lightest chain, known as methane. Methane is a gas so light that it floats like helium. As the chains get longer, they get heavier.

The first four chains -- CH4 (methane), C2H6 (ethane), C3H8 (propane) and C4H10 (butane) -- are all gases, and they boil at -161, -88, -46 and -1 degrees F, respectively (-107, -67, -43 and -18 degrees C). The chains up through C18H32 or so are all liquids at room temperature, and the chains above C19 are all solids at room temperature.

The different chain lengths have progressively higher boiling points, so they can be separated out by distillation. This is what happens in an oil refinery -- crude oil is heated and the different chains are pulled out by their vaporization temperatures. (See How Oil Refining Works for details.)

The chains in the C5, C6 and C7 range are all very light, easily vaporized, clear liquids called naphthas. They are used as solvents -- dry cleaning fluids can be made from these liquids, as well as paint solvents and other quick-drying products.

The chains from C7H16 through C11H24 are blended together and used for gasoline. All of them vaporize at temperatures below the boiling point of water. That's why if you spill gasoline on the ground it evaporates very quickly.

Next is kerosene, in the C12 to C15 range, followed by diesel fuel and heavier fuel oils (like heating oil for houses).

Next come the lubricating oils. These oils no longer vaporize in any way at normal temperatures. For example, engine oil can run all day at 250 degrees F (121 degrees C) without vaporizing at all. Oils go from very light (like 3-in-1 oil) through various thicknesses of motor oil through very thick gear oils and then semi-solid greases. Vasoline falls in there as well.

Chains above the C20 range form solids, starting with paraffin wax, then tar and finally asphaltic bitumen, which used to make asphalt roads.

All of these different substances come from crude oil. The only difference is the length of the carbon chains!

What is the Strategic Petroleum Reserve?

2009-03-25T06:33:00.000-07:00

With oil prices rising, the U.S. government has decided to tap into its Strategic Petroleum Reserve to help make sure that people who use oil to heat their homes will have plenty and that the price will not be too high. President Clinton authorized the Department of Energy, which manages the reserve, to release up to 30 million barrels of oil in a swap with oil companies. The companies will take the oil in fall 2000 but will have to return the oil by fall 2001. The government hopes that the companies will use the oil to keep supplies adequate this winter.

The Strategic Petroleum Reserve is the United States' emergency oil stockpile, and it is the largest emergency petroleum supply in the world. The reserve stores about 570 million barrels of crude oil in underground salt caverns at four sites along the Gulf of Mexico. A barrel contains 42 gallons or 159 liters of oil. To create the caverns, workers drill into a salt dome and then put water into the hole to dissolve the salt. Each cavern is about 2,000 feet deep and holds about 10 million barrels of oil. The government uses salt caverns because it costs less than storing oil in aboveground tanks and because the pressure from the earth will seal up any leaks that might develop. The Energy Department also says that the temperature difference in the caverns, which are 2,000 feet below the surface of the earth, keeps the oil circulating so that the petroleum maintains its quality.

The government chose to put the oil near the Gulf of Mexico because there are many oil refineries nearby and because shipping is readily available. The sites are Bryan Mound near Freeport, Texas; Big Hill near Winnie, Texas; West Hackberry near Lake Charles, La.; and Bayou Choctaw near Baton Rouge, La. The reserve could store up to 700 million barrels. Most of the oil in the reserve comes from Mexico and the North Sea.

It costs the federal government $21 million a year to maintain the oil reserve, and about 1,150 people work for the oil reserve. About 125 are government employees, and the rest are contracted workers. In the coming budget year, the Energy Department will get about $157 million to buy oil for the reserve.

The United States started the petroleum reserve in 1975 after oil supplies were cut off during the 1973-74 oil embargo. The embargo was a shock to the U.S. economy, and the government decided that the country should never be caught short again. The United States uses almost 19 million barrels of petroleum every day, and more than half of that oil comes from imports. A reserve of 60 days' worth of petroleum could help keep the oil flowing in case of a cutoff. The last time that the United States used oil from the reserve was during the Persian Gulf War in 1991 to keep oil plentiful and prices stable. That drawdown is different from the exchange authorized recently because the companies who bid for it will return the oil this time.

What's the difference between gasoline, kerosene, diesel, etc?

2009-03-25T06:27:00.000-07:00

The "crude oil" pumped out of the ground is a black liquid called petroleum. This liquid contains aliphatic hydrocarbons, or hydrocarbons composed of nothing but hydrogen and carbon. The carbon atoms link together in chains of different lengths.

It turns out that hydrocarbon molecules of different lengths have different properties and behaviors. For example, a chain with just one carbon atom in it (CH₄) is the lightest chain, known as methane. Methane is a gas so light that it floats like helium. As the chains get longer, they get heavier.

The first four chains -- CH₄ (methane), C₂H₆ (ethane), C₃H₈ (propane) and C₄H₁₀ (butane) -- are all gases, and they boil at -161, -88, -46 and -1 degrees F, respectively (-107, -67, -43 and -18 degrees C). The chains up through C₁₈H₃₂ or so are all liquids at room temperature, and the chains above C₁₉ are all solids at room temperature.

So what's the real chemical difference between gasoline, kerosene and diesel? It has to do with their boiling points. We'll get into that on the next page.

Carbon Chains in Petroleum Products

The chains in the C₅, C₆ and C₇ range are all very light, easily vaporized, clear liquids called naphthas. They are used as solvents -- dry cleaning fluids can be made from these liquids, as well as paint solvents and other quick-drying products.

The chains from C₇H₁₆ through C₁₁H₂₄ are blended together and used for gasoline. All of them vaporize at temperatures below the boiling point of water. That's why if you spill gasoline on the ground it evaporates very quickly.

Next is kerosene, in the C₁₂ to C₁₅ range, followed by diesel fuel and heavier fuel oils (like heating oil for houses).

Next come the lubricating oils. These oils no longer vaporize in any way at normal temperatures. For example, engine oil can run all day at 250 degrees F (121 degrees C) without vaporizing at all. Oils go from very light (like 3-in-1 oil) through various thicknesses of motor oil through very thick gear oils and then semi-solid greases. Vasoline falls in there as well.

Chains above the C₂₀ range form solids, starting with paraffin wax, then tar and finally asphaltic bitumen, which is used to make asphalt roads.

All of these different substances come from crude oil. The only difference is the length of the carbon chains!

Still curious about petroleum uses and processing? Check out the links on the next page for related articles and quizzes to test your knowledge.

How Oil Drilling Works 3

2009-03-25T06:18:00.000-07:00

Extracting the Oil

After the rig is removed, a pump is placed on the well head.

Photo courtesy California Department of Conservation
Pump on an oil well

In the pump system, an electric motor drives a gear box that moves a lever. The lever pushes and pulls a polishing rod up and down. The polishing rod is attached to a sucker rod, which is attached to a pump. This system forces the pump up and down, creating a suction that draws oil up through the well.

In some cases, the oil may be too heavy to flow. A second hole is then drilled into the reservoir and steam is injected under pressure. The heat from the steam thins the oil in the reservoir, and the pressure helps push it up the well. This process is called enhanced oil recovery.

Photo courtesy California Department of Conservation
Enhanced oil recovery

With all of this oil-drilling technology in use, and new methods in development, the question remains: Will we have enough oil to meet our needs? Current estimates suggest that we have enough oil for about 63 to 95 years to come, based on current and future finds and present demands.

For more information on oil drilling and related topics, including oil refining, check out the links on the next page.

How Oil Drilling Works 2

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Oil Rig Systems

Once the equipment is at the site, the rig is set up. Here are the major systems of a land oil rig:

Anatomy of an oil rig

Power system
- large diesel engines - burn diesel-fuel oil to provide the main source of power
- electrical generators - powered by the diesel engines to provide electrical power
Mechanical system - driven by electric motors
- hoisting system - used for lifting heavy loads; consists of a mechanical winch (drawworks) with a large steel cable spool, a block-and-tackle pulley and a receiving storage reel for the cable
- turntable - part of the drilling apparatus
Rotating equipment - used for rotary drilling
- swivel - large handle that holds the weight of the drill string; allows the string to rotate and makes a pressure-tight seal on the hole
- kelly - four- or six-sided pipe that transfers rotary motion to the turntable and drill string
- turntable or rotary table - drives the rotating motion using power from electric motors
- drill string - consists of drill pipe (connected sections of about 30 ft / 10 m) and drill collars (larger diameter, heavier pipe that fits around the drill pipe and places weight on the drill bit)
- drill bit(s) - end of the drill that actually cuts up the rock; comes in many shapes and materials (tungsten carbide steel, diamond) that are specialized for various drilling tasks and rock formations
Casing - large-diameter concrete pipe that lines the drill hole, prevents the hole from collapsing, and allows drilling mud to circulate

Photo courtesy Institute of Petroleum
Circulation system - pumps drilling mud (mixture of water, clay, weighting material and chemicals, used to lift rock cuttings from the drill bit to the surface) under pressure through the kelly, rotary table, drill pipes and drill collars
- pump - sucks mud from the mud pits and pumps it to the drilling apparatus
- pipes and hoses - connects pump to drilling apparatus
- mud-return line - returns mud from hole
- shale shaker - shaker/sieve that separates rock cuttings from the mud
- shale slide - conveys cuttings to the reserve pit
- reserve pit - collects rock cuttings separated from the mud
- mud pits - where drilling mud is mixed and recycled
- mud-mixing hopper - where new mud is mixed and then sent to the mud pits

Drill-mud circulation system

Derrick - support structure that holds the drilling apparatus; tall enough to allow new sections of drill pipe to be added to the drilling apparatus as drilling progresses
Blowout preventer - high-pressure valves (located under the land rig or on the sea floor) that seal the high-pressure drill lines and relieve pressure when necessary to prevent a blowout (uncontrolled gush of gas or oil to the surface, often associated with fire)

Drilling

Photo courtesy Phillips Petroleum Co.
Rotary workers trip drill pipe

The crew sets up the rig and starts the drilling operations. First, from the starter hole, they drill a surface hole down to a pre-set depth, which is somewhere above where they think the oil trap is located. There are five basic steps to drilling the surface hole:

Place the drill bit, collar and drill pipe in the hole.
Attach the kelly and turntable and begin drilling.
As drilling progresses, circulate mud through the pipe and out of the bit to float the rock cuttings out of the hole.
Add new sections (joints) of drill pipes as the hole gets deeper.
Remove (trip out) the drill pipe, collar and bit when the pre-set depth (anywhere from a few hundred to a couple-thousand feet) is reached.

Once they reach the pre-set depth, they must run and cement the casing -- place casing-pipe sections into the hole to prevent it from collapsing in on itself. The casing pipe has spacers around the outside to keep it centered in the hole.

The casing crew puts the casing pipe in the hole. The cement crew pumps cement down the casing pipe using a bottom plug, a cement slurry, a top plug and drill mud. The pressure from the drill mud causes the cement slurry to move through the casing and fill the space between the outside of the casing and the hole. Finally, the cement is allowed to harden and then tested for such properties as hardness, alignment and a proper seal.

In the next section we'll find out what happens once the drill bit reaches the final depth.

Testing for Oil

Drilling continues in stages: They drill, then run and cement new casings, then drill again. When the rock cuttings from the mud reveal the oil sand from the reservoir rock, they may have reached the final depth. At this point, they remove the drilling apparatus from the hole and perform several tests to confirm this finding:

Well logging - lowering electrical and gas sensors into the hole to take measurements of the rock formations there
Drill-stem testing - lowering a device into the hole to measure the pressures, which will reveal whether reservoir rock has been reached
Core samples - taking samples of rock to look for characteristics of reservoir rock

Once they have reached the final depth, the crew completes the well to allow oil to flow into the casing in a controlled manner. First, they lower a perforating gun into the well to the production depth. The gun has explosive charges to create holes in the casing through which oil can flow. After the casing has been perforated, they run a small-diameter pipe (tubing) into the hole as a conduit for oil and gas to flow up the well. A device called a packer is run down the outside of the tubing. When the packer is set at the production level, it is expanded to form a seal around the outside of the tubing. Finally, they connect a multi-valved structure called a Christmas tree to the top of the tubing and cement it to the top of the casing. The Christmas tree allows them to control the flow of oil from the well.

Once the well is completed, they must start the flow of oil into the well. For limestone reservoir rock, acid is pumped down the well and out the perforations. The acid dissolves channels in the limestone that lead oil into the well. For sandstone reservoir rock, a specially blended fluid containing proppants (sand, walnut shells, aluminum pellets) is pumped down the well and out the perforations. The pressure from this fluid makes small fractures in the sandstone that allow oil to flow into the well, while the proppants hold these fractures open. Once the oil is flowing, the oil rig is removed from the site and production equipment is set up to extract the oil from the well.

How Oil Drilling Works

2009-03-25T06:00:00.000-07:00

Photo courtesy Phillips Petroleum Co.

In 2005 alone, the United States produced an estimated 9 million barrels of crude oil per day and imported 13.21 million barrels per day from other countries. This oil gets refined into gasoline, kerosene, heating oil and other products. To keep up with our consumption, oil companies must constantly look for new sources of petroleum, as well as improve the production of existing wells.

How does a company go about finding oil and pumping it from the ground? You may have seen images of black crude oil gushing out of the ground, or seen an oil well in movies and television shows like "Giant," "Oklahoma Crude," "Armageddon" and "Beverly Hillbillies." But modern oil production is quite different from the way it's portrayed in the movies.

In this article, we will examine how modern oil exploration and drilling works. We will discuss how oil is formed, found and extracted from the ground.

Oil is a fossil fuel that can be found in many countries around the world. In this section, we will discuss how oil is formed and how geologists find it.

Forming Oil
Oil is formed from the remains of tiny plants and animals (plankton) that died in ancient seas between 10 million and 600 million years ago. After the organisms died, they sank into the sand and mud at the bottom of the sea.

Photo courtesy Institute of Petroleum
Oil forms from dead organisms in ancient seas.
(Click here for a larger image.)

Photo courtesy Institute of Petroleum
Close-up of reservoir rock
(oil is in black)

Over the years, the organisms decayed in the sedimentary layers. In these layers, there was little or no oxygen present. So microorganisms broke the remains into carbon-rich compounds that formed organic layers. The organic material mixed with the sediments, forming fine-grained shale, or source rock. As new sedimentary layers were deposited, they exerted intense pressure and heat on the source rock. The heat and pressure distilled the organic material into crude oil and natural gas. The oil flowed from the source rock and accumulated in thicker, more porous limestone or sandstone, called reservoir rock. Movements in the Earth trapped the oil and natural gas in the reservoir rocks between layers of impermeable rock, or cap rock, such as granite or marble.

Photo courtesy Institute of Petroleum
Oil reservoir rocks (red) and natural gas (blue) can be trapped by folding (left), faulting (middle) or pinching out (right).

These movements of the Earth include:

Folding - Horizontal movements press inward and move the rock layers upward into a fold or anticline.
Faulting - The layers of rock crack, and one side shifts upward or downward.
Pinching out - A layer of impermeable rock is squeezed upward into the reservoir rock.

Finding Oil

The task of finding oil is assigned to geologists, whether employed directly by an oil company or under contract from a private firm. Their task is to find the right conditions for an oil trap -- the right source rock, reservoir rock and entrapment. Many years ago, geologists interpreted surface features, surface rock and soil types, and perhaps some small core samples obtained by shallow drilling. Modern oil geologists also examine surface rocks and terrain, with the additional help of satellite images. However, they also use a variety of other methods to find oil. They can use sensitive gravity meters to measure tiny changes in the Earth's gravitational field that could indicate flowing oil, as well as sensitive magnetometers to measure tiny changes in the Earth's magnetic field caused by flowing oil. They can detect the smell of hydrocarbons using sensitive electronic noses called sniffers. Finally, and most commonly, they use seismology, creating shock waves that pass through hidden rock layers and interpreting the waves that are reflected back to the surface.

Photo courtesy Institute of Petroleum
Searching for oil over water using seismology

In seismic surveys, a shock wave is created by the following:

Compressed-air gun - shoots pulses of air into the water (for exploration over water)
Thumper truck - slams heavy plates into the ground (for exploration over land)
Explosives - drilled into the ground (for exploration over land) or thrown overboard (for exploration over water), and detonated

The shock waves travel beneath the surface of the Earth and are reflected back by the various rock layers. The reflections travel at different speeds depending upon the type or density of rock layers through which they must pass. The reflections of the shock waves are detected by sensitive microphones or vibration detectors -- hydrophones over water, seismometers over land. The readings are interpreted by seismologists for signs of oil and gas traps.

Although modern oil-exploration methods are better than previous ones, they still may have only a 10-percent success rate for finding new oil fields. Once a prospective oil strike is found, the location is marked by GPS coordinates on land or by marker buoys on water.

Preparing to Drill

Once the site has been selected, it must be surveyed to determine its boundaries, and environmental impact studies may be done. Lease agreements, titles and right-of way accesses for the land must be obtained and evaluated legally. For off-shore sites, legal jurisdiction must be determined.

Once the legal issues have been settled, the crew goes about preparing the land:

The land is cleared and leveled, and access roads may be built.
Because water is used in drilling, there must be a source of water nearby. If there is no natural source, they drill a water well.
They dig a reserve pit, which is used to dispose of rock cuttings and drilling mud during the drilling process, and line it with plastic to protect the environment. If the site is an ecologically sensitive area, such as a marsh or wilderness, then the cuttings and mud must be disposed offsite -- trucked away instead of placed in a pit.

Once the land has been prepared, several holes must be dug to make way for the rig and the main hole. A rectangular pit, called a cellar, is dug around the location of the actual drilling hole. The cellar provides a work space around the hole, for the workers and drilling accessories. The crew then begins drilling the main hole, often with a small drill truck rather than the main rig. The first part of the hole is larger and shallower than the main portion, and is lined with a large-diameter conductor pipe. Additional holes are dug off to the side to temporarily store equipment -- when these holes are finished, the rig equipment can be brought in and set up.

Depending upon the remoteness of the drill site and its access, equipment may be transported to the site by truck, helicopter or barge. Some rigs are built on ships or barges for work on inland water where there is no foundation to support a rig (as in marshes or lakes).

In the next section, we'll look at the major systems of an oil rig.