Ask the Expert/FAQ's

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. So what's the real chemical difference between gasoline, kerosene and diesel? It has to do with their boiling points.

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. 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!

­In theory, diesel engines and gasoline engines are quite similar. They are both internal combus­tion engines designed to convert the chemical energy available in fuel into mechanical energy. This mechanical energy moves pistons up and down inside cylinders. The pistons are connected to a crankshaft, and the up-and-down motion of the pistons, known as linear motion, creates the rotary motion needed to turn the wheels of an automobile forward.

Both diesel engines and gasoline engines covert fuel into energy through a series of small explosions or combustions. The major difference between diesel and gasoline is the way these explosions happen. In a gasoline engine, fuel is mixed with air, compressed by pistons and ignited by sparks from spark plugs. In a diesel engine, however, the air is compressed first, and then the fuel is injected. Because air heats up when it's compressed, the fuel ignites.

The diesel engine uses a four-stroke combustion cycle just like a gasoline engine. The four strokes are:

• Intake stroke -- The intake valve opens up, letting in air and moving the piston down.
• Compression stroke -- The piston moves back up and compresses the air.
• Combustion stroke -- As the piston reaches the top, fuel is injected at just the right moment and ignited, forcing the piston back down.
• Exhaust stroke -- The piston moves back to the top, pushing out the exhaust created from the combustion out of the exhaust valve.

Remember that the diesel engine has no spark plug, that it intakes air and compresses it, and that it then injects the fuel directly into the combustion chamber (direct injection). It is the heat of the compressed air that lights the fuel in a diesel engine.

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• needs to demonstrate its ability to consistently provide product that meets customer and applicable statutory and regulatory requirements
• aims to enhance customer satisfaction through the effective application of the system, including processes for continual improvement of the system and the assurance of conformity to customer and applicable statutory and regulatory requirements.

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Diesel engines convert chemical energy into mechanical power. The diesel fuel is then injected under pressure into the engine cylinder, where it mixes with air and combustion occurs. Diesel engines produce relatively high levels of gaseous emissions of nitrogen oxides (NOx) and particulate emissions, often referred to as diesel particulate matter (DPM).

DPM is a complex aggregate of materials that includes:

Dry carbon particles (or soot) and inorganic oxides (primarily sulfates)

• A soluble organic fraction that results from incomplete combustion of diesel fuel and engine lubricating oils and tends to adsorb or condense onto the carbon particles
• A gaseous component consisting mainly of CO, NOx and sulfur dioxide (SO2)

Diesel emissions are very fine. The total concentration of pollutants in exhaust from diesel engines is just a fraction of a percent.