What's the Gasoline role in Engine Performance

 GASOLINE:  What's the gasoline?!

Gasoline

DEFINITION :

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. Gasoline and air burns in the cylinder of the engine and produces heat and pressure, which is converted to rotary motion inside the engine and eventually powers the drive wheels of a vehicle. When combustion occurs, carbon dioxide and water are produced if the process is perfect and all of the air and all of the fuel are consumed in the process.

CHEMICAL COMPOSITION:

Gasoline is a combination of hydrocarbon molecules that have between five and 12 carbon atoms. The names of these various hydrocarbons are based on the number of carbon atoms and include:

•  Methane —one carbon atom
•  Ethane —two carbon atoms
•  Propane —three carbon atoms
•  Butane —four carbon atoms
•  Pentane —five carbon atoms
•  Hexane —six carbon atoms
•  Heptane —seven carbon atoms (Used to test octane rating– has an octane rating of zero)
•  Octane —eight carbon atoms (A type of octane is used as a basis for antiknock rating)

The crude oil refining process showing most of the major steps and processes.

REFINING:

Refining Gasoline

read also: History of Diesel Engine

TYPES OF CRUDE OIL

Refining is a complex combination of interdependent processing units that can separate crude oil into useful products such as gasoline and diesel fuel. As it comes out of the ground, petroleum (meaning “rock oil”) crude can be as thin and light colored as apple cider or as thick and black as melted tar. A barrel of crude oil is 42 gallons, not 55 gallons as commonly used for industrial barrels.

Typical terms used to describe the type of crude oil include:

•  Thin crude oil has a high American Petroleum Institute (API) gravity, and therefore, is called high-gravity crude.
•  Thick crude oil is called low-gravity crude. High-gravity-type crude contains more natural gasoline and its lower sulfur and nitrogen content makes it easier to refine.
•  Low-sulfur crude oil is also known as “sweet” crude.
•  High-sulfur crude oil is also known as “sour” crude.

DISTILLATION:

In the late 1800s, crude was separated into different products by boiling in a process called distillation. Distillation works because crude oil is composed of hydrocarbons with a broad range of boiling points. In a distillation column, the vapor of the lowest-boiling hydrocarbons, propane and butane, rises to the top. The straight-run gasoline (also called naphtha), kerosene, and diesel fuel cuts are drawn off at successively lower positions in the column.

Why Do I Get Lower Gas Mileage in the Winter?

Several factors cause the engine to use more fuel in the winter than in the summer, including:

•  Gasoline that is blended for use in cold climates is designed for ease of starting and contains fewer heavy molecules, which contribute to fuel 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.

VOLATILITY:

Gasoline-Volatility-Requirements-from-WWFC

DEFINITION OF VOLATILITY 

Volatility describes how easily the gasoline evaporates (forms a vapor). The definition of volatility assumes that the vapors will remain in the fuel tank or fuel line and will cause a certain pressure based on the temperature of the fuel.

REID VAPOR PRESSURE (RVP) 

Reid vapor pressure (RVP) is the pressure of the vapor above the fuel when the fuel is at 100°F (38°C). Increased vapor pressure permits the engine to start in cold weather. Gasoline without air will not burn. Gasoline must be vaporized (mixed with air) to burn in an engine.

A gasoline testing kit

SEASONAL BLENDING

 Cold temperatures reduce the normal vaporization of gasoline; therefore, winter-blended gasoline is specially formulated to vaporize at lower temperatures for proper starting and driveability at low ambient temperatures. The American Society for Testing and Materials (ASTM) standards for winter-blend gasoline allow volatility of up to 15 pounds per square inch (PSI) RVP. At warm ambient temperatures, gasoline vaporizes easily. However, the fuel system (fuel pump, carburetor, fuel-injector nozzles, etc.) is designed to operate with liquid gasoline. The volatility of summer-grade gasoline should be about 7.0 PSI RVP. According to ASTM standards, the maximum RVP should be 10.5 PSI for summer-blend gasoline.

DISTILLATION CURVE

 Besides Reid vapor pressure, another method of classifying gasoline volatility is the distillation curve. A curve on a graph is created by plotting the temperature at which the various percentage of the fuel evaporates.

the distillation curve

References:

- Automotive Technology_ Principles, Diagnosis, and Service (4th Edition)  

- Writes for James D. Halderman.