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 APIo, is used

to measure the specific gravity.

5.1315.141

SGAPI o

Fuel hydrometer.

Ideal Combustion

All of the H in fuel is converted to H20.

All of the C in fuel is converted to CO2.

Air is 21% O and 79% N by volume.

Combustion of Gasoline

Stoichiometric Air/Fuel Mixture

For gasoline…

1:1.15

1

54.1151.3/

FA

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.