Gasoline

Octane – The octane number (also known as the anti-knock index or AKI) is a measure of a gasoline’s ability to withstand autoignition.  Under the right temperature and pressure conditions, the air-gas mixture within the engine cylinder can ignite ahead of time. This combustion results in an audible knocking sound in the engine and can reduce engine efficiency and potentially lead to engine damage if allowed to continue over a long period of time. The higher the octane number of the gasoline, the more resistant the fuel to this auto ignition. Please note – using fuel with a higher octane in an engine that is designed to use 87 octane gasoline will have no appreciable effect on the performance of that engine.

In the Fuel Quality Laboratory, the octane number of a gasoline sample is determined using octane engines operating under different conditions. The first engine is the Research Octane Number Engine (RON) and simulates conditions where an engine would not be under duress (such as idling at a stop light). The second engine is the Motor Research Engine (MON) and simulates conditions where an engine is under a significant load (going up a hill or towing a trailer). The octane numbers determined under the two conditions are averaged and the resulting value is the determined octane rating of the fuel. *Mention the sticker? Image?

Distillation – This test provides information regarding the fuels volatility or ability to be vaporized. This test is conducted by boiling the fuel and measuring the temperature of the distillate at different points during the test. The final distillation end point (or final boiling point) is one of the most important data points that is collected during this test. An elevated end point is the result of the fuel being contaminated with a higher boiling fuel such as diesel or kerosene and can lead to a vehicle engine shutting down.

Percent Ethanol by Volume – The volume of ethanol in gasoline is required by law to be displayed on the dispenser and is limited to specific volume ranges based on engine type. In the laboratory, these values are determined by gas chromatography using ASTM test method D4815 and ASTM D5501.

Vapor Pressure - The vapor pressure of gasoline is very important when it comes to understanding the volatility of a sample and how it will perform under certain conditions.  During the winter months, a higher vapor pressure gasoline assures that when you turn the engine over it will start as the temperature of the fuel in your tank will be cold and concentration of molecules in the vapor phase smaller. During the summer you want the gasoline to have a lower vapor pressure or it could potentially boil in the fuel line on a hot day shutting down the vehicle’s engine (a condition known as vapor lock). Thus, gasoline producers vary the composition of the fuel to meet the different seasonal requirements set forth by Federal law and we in turn make sure that the fuel sold in our State meets these vapor pressure mandates.

Water and Sediment – Water is the largest concern for consumers when it comes to fuel quality as its presence can result in poor engine performance and possible failure. Sediment can result in clogged fuel lines and filters that reduces engine performance. All samples are visually inspected to assure that they do not contain either of these contaminants during testing.

Phase Separation – With the widespread introduction of ethanol into gasoline roughly 15 years ago the problem of phase separation started to emerge. Unlike conventional or non-ethanol gasoline, the presence of ethanol allows the fuel to absorb a small amount of water with no effect. However, since ethanol is more chemically similar to water than the hydrocarbon components of gasoline, once the maximum amount of water is absorbed, any additional water added will result in the water stripping the ethanol out of the gasoline. What is left is a solution that has two distinct layers; a mixture of ethanol and water sits at the bottom of the tank and an ethanol depleted gasoline layer floats on top.  This ethanol and water mixture is very caustic and, in some cases, can lead to engine damage.  Inspectors visually inspect gasoline samples for the presence of phase separation and also check the storage tanks for its presence. Under current North Carolina code, the presence of phase separation in a storage tank is grounds for closure of the dispensed fuel product even if phase separation is not found coming through the dispenser.

Diesel, Biodiesel blends, and Kerosene

Cetane Number – This value is much like the octane number for gasoline and provides a way to measure the combustibility of a diesel fuel. The lower the cetane number, the longer the delay before the fuel combusts in the engines. Low cetane number fuels can result in engine knocking, poor performance, and in some cases engine damage. In the State of North Carolina, the minimum cetane number for diesel fuel is 40 as required per ASTM test method D975. In the lab this value can be estimated using the distillation and API gravity data from the sample (ASTM test method D4737), or it can be measured using ASTM test method D7668.

Flashpoint – The flashpoint is the temperature at which there are enough vapors above a liquid to support the combustion when a flame is introduced. This test is important in determining if a fuel is safe to use or if it contains a lower boiling fuel such as gasoline. The presence of gasoline in diesel or kerosene can lead to significant engine damage or a potential fire if used in a home heater. Inspectors check the flashpoint of all diesel and kerosene products offered for sale using a manual flashpoint unit following ASTM test method D56.

Distillation – This test provides information regarding the fuels volatility or ability to be vaporized. This test is conducted by boiling the fuel and measuring the temperature of the distillate at different points during the test. Elevation in the temperatures of the distillate at specific volume recovered are indicative of old stock or cross contamination with higher boiling fuels.

API Gravity – This test is not regulatory but can be used in conjunction with distillation data to calculate an estimated cetane index for a diesel fuel.

Dye – The United States Department of Revenue using red dye to mark diesel and kerosene products that have not been taxed. Diesel fuels that have been dyed red are restricted from road use and are primarily used for agricultural and construction applications. Please note that there is no difference in the physical properties or the performance characteristics between red dyed kerosene and clear kerosene products.  

Color – The color of clear kerosene can be used as an indicator as to whether the fuel is contaminated or if it has been sitting in a storage tank for a long period of time and has potentially started to degrade.

Sulfur – Sulfur is a naturally occurring element that is commonly found in petroleum products. During the combustion process, this element can form sulfur oxides that are known pollutants in the environment (acid rain). Much of it is removed when processing crude oil into fuels and our testing makes sure it does not exceed those amounts.

Percent Fatty Acid Methyl Ester (FAME) or % Biodiesel – At the lab we use infrared light to measure the percentage of biodiesel in biodiesel blends to verify that the concentration advertised on the dispenser matches that of the product being sold.

Water and Sediment – Water is the largest concern for consumers when it comes to fuel quality as its presence can result in poor performance and possible engine failure. Sediment is a growing concern as more diesel engines shift to utilize high pressure fuel systems and, in some cases, can result in significant damage to fuel delivery systems. All samples are visually inspected for the presence of water and sediment during testing.

Motor Oil

Kinematic Viscosity at 100°C – This test measures the API viscosity grade which represents the thickness of an oil at the operating temperature of the engine. The kinematic viscosity is represented by the number after the “W” on an oil bottle; for example, the API viscosity grade of a 10W30 motor oil is 30.

Apparent Viscosity – This test is used to determine the winter grade which describes the starting properties of an oil at low temperature.  The winter grade of an oil is represented by the number before the “W” on the bottle; for example, the winter grade of a 10W30 oil is 10W.

Percent Water in Motor Oil – This test uses distillation to separate water from an oil sample so that it can be collected and quantified to give the percentage of water in the sample.