Petroleum Fuels, II
Petroleum fuels have a number of characteristics and properties of interest to the user. Easy ignition is one of them and they all have a common composition, they consist of hydrocarbon (hydrogen and carbon) molecules and some small amounts of additives.
A basic understanding of aviation fuels is required as the pilot in command is responsible for the safe operation of the aircraft and this includes the refueling process and safe handling of these volatile fuels.
Additives are used to reduce fuel consumption, lower the cost of maintenance, reduce emissions and deposits. Fuels are formulated with an additive package depending on the application. The precise content of the package is usual proprietary to the manufacturer, think Shell V-Power or BP Ultimate. Additives are usually approved by the American Society of Testing and Materials (ASTM) or military standards (MIL).
Some commonly used fuel additives are:
- Alkyl lead is used in gasoline to raise its octane rating for use in higher compression engines to reduce the risk of knock. Mogas used to contain about 1 gram per liter of alkyl lead (1000 ppm). Unleaded Mogas now contains only a few ppm lead. AVgas still contains lead.
- Antioxidants are used to prevent gum in gasolines and aviation fuels.
- Biocide additives are used to control microbial growth in the fuel system.
- Conductivity additives are used to increase the conductivity of the fuels reducing the buildup of static electricity during transfer.
- Corrosion inhibitors will guard against corrosion during transfer and storage of the fuel. Some improve lubricity which reduces the friction of the movings parts in a fuel pump or injector.
- Detergent additives will like antioxidants help against gum, keeping fuel filter clean. Usually found in Mogas and diesel fuels.
- Icing inhibitors mainly for aviation fuels preventing ice crystal formation during flight at high altitudes. Diethylene glycol monomethyl ether is used for this.
- Metal de-activators will prevent metal contaminants from oxidizing with hydrocarbons and clogging the system.
- Oxygenates boost the octane rating of Mogas, thereby reducing the smog forming tendencies and suppresses knock. Also, the increased oxygen in the fuel provides for a more complete combustion. Ethanol is used for this.
- Thermal stability additives mainly used in JET fuel to stabilize the fuel in hot environments preventing carbon build up in engine nozzles, burners etc.
Below some commonly used terms and their explanations as used in the fuel and petroleum industry.
- Alcohol - Organic compound with an oxygen hydrogen (OH) group bonded to a hydrocarbon group.
- Bio-degradation - The reduction in quality of the petroleum by naturally residing microorganisms.
- Boiling Point - Temperature at which a liquid changes state to a vapor or gas.
- Crude Oil - The oil as found in the crust of the earth.
- Gasoline - Refined product for use in spark ignited engines.
- Hydrocarbons - Organic compounds composed of hydrogen and carbon. Petroleum products are complex combinations of hydrocarbons.
- Kerosene - Colorless, low sulfur, low smoke producing petroleum product mainly used in JET fuels.
- Petroleum - Naturally occurring, oily, flammable liquid made of hydrocarbons and found with gas in underground reservoirs, oil wells.
- Vapor Pressure - The pressure at which a liquid and its vapor are in equilibrium at a given temperature. The more volatile a liquid and the lower its boiling point, the higher its vapor pressure is.
- Viscosity - The resistance of a fluid to flow. The more viscous a liquid, the more it will resist to flow. It usually decreases with increasing temperature of the liquid.
- Volatility - Indicates how quickly a substance forms a vapor at a defined temperature and pressure.