Mathematical Expressions Relating Evaporative Emissions from Motor Vehicles without Evaporative Loss-Control Devices to Gasoline Volatility

A program was undertaken to study the effects of fuel volatility characteristics on evaporative emissions from motor vehicles without evaporative loss-control devices. The ultimate objective of this study was to derive a simple mathematical expression relating evaporative emissions from an urban car population to gasoline volatility parameters. Since development of the necessary data base for such a program through direct experimentation would have been quite inefficient, an alternate approach was taken in deriving a set of mathematical models to calculate evaporative emissions from carburetors and fuel tanks of motor vehicles. These models were verified by comparison with limited experimental data.

Information available on daily urban area vehicle use and data on how fuel system temperatures vary with vehicle, vehicle use, and ambient temperature were then used to develop a general model that would calculate daily evaporative emissions from a vehicle population, given the ambient temperature conditions and fuel volatility parameters. Linear regression analyses on these calculated data resulted in a simple mathematical expression for predicting the daily average evaporative emission from motor vehicles. Such an expression is of interest in studying the effects of changes in gasoline volatility characteristics on evaporative emissions from uncontrolled motor vehicles.