Gasoline Combustion and Corresponding Quality Criteria

The density and the volatility, expressed by the distillation curve and the vapor pressure, constitute the most important physical characteristics of motor fuels for obtaining satisfactory operation of a vehicle in all circumstances. 

Density is generally measured at 15°C using a hydrometer in accordance with the NF T 60-101 method it is expressed in kg/1 with an error of 0.0002 to 0.0005 according to which category of hydrometer is utilized. However, in practice only three decimal places are usually retained. 

The density varies with the temperature according to the relationship  

Although they are small in absolute value, these fluctuations must be taken into account in the various commercial transactions related to storage and distribution of gasoline. 

Several parameters come into the relation between density and equivalence ratio. Generally, the variations act in the following sense a too-dense motor fuel results in too lean a mixture causing a potential unstable operation a motor fuel that is too light causes a rich mixture that generates greater pollution from unburned material. These problems are usually minimized by the widespread use of closed loop fuel-air ratio control systems installed on new vehicles with catalytic converters. 

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