Liquid Fuels

Crude Oil  Found in rock formations that were ocean floors.  Organic matter from seas became trapped by sediments at ocean floor.  Cracking of the molecules and elimination of oxygen turned organic matter into petroleum.

Crude Oil  Petroleum is made of 86% carbon and 14% hydrogen.  Hydrocarbon molecules are accompanied by dirt, water, sulfur and other impurities.  Crude oil must be refined to produce suitable engine fuels.

Fig. 5.1: Molecular Structures of Some Hydrocarbon Fuel Families

Fuel Properties  Standards Organizations SAE – Society of Automotive Engineers ASTM – American Society for the Testing of Materials API – American Petroleum Institute

Specific Gravity  A measure of the density of liquid fuels at 15.6 C as compared with water at the same temperature.  API devised the following scale,  where SG is the specific gravity.  A hydrometer, calibrated in API o, is used to measure the specific gravity.

Fuel hydrometer.

Ideal Combustion  All of the H in fuel is converted to H 2 0.  All of the C in fuel is converted to CO 2.  Air is 21% O and 79% N by volume.

Combustion of Gasoline

Stoichiometric Air/Fuel Mixture  For gasoline…

Table 5.2: Representative Fuel Molecules

Diesel Air/Fuel Ratios  Stoichiometric air/fuel mixture for CI engines 14.9:1.  However, most CI engines are operated with a leaner air/fuel ratios and therefore free oxygen is often found in the exhaust.