A mathematical model of the fuel system of an automotive engine has been constructed, utilizing the basic engineering principles of fluid flow, heat and material balances, and the vapor-liquid equilibria characteristics of the fuel components. This model, when implemented on a digital computer, can be used to study such aspects of the steady state and dynamic behavior of an automotive fuel system as vapor locking tendencies, carburetor icing, hydrocarbon evaporative emissions, and with modifications, cold starting, warmup, hot starting, hot idle, and so forth.Mathematical models of this type, by defining the parameters to be evaluated using selected experimental programs, permit the rapid accumulation of more useful and realistic information than can be obtained by an empirical approach. Two versions of this type of model have been implemented.PART 1: VAPOR LOCK MODELS - The first model deals with the volatility behavior of gasoline, defined by trueboiling-point analysis. The model is used with specified automotive engine and operating conditions. The vapor locking tendency under any given steady state or dynamic condition (for example, acceleration) may be determined. The computer program output includes time graphs of car speed and fuel content of the carburetor.PART 2 - CARBURETOR ICING MODEL - A dynamic mathematical model of carburetor icing in automotive fuel systems (DYNIM) has been developed and programmed for a digital computer. It defines the relationships among gasoline composition, operating conditions, ambient conditions, car characteristics, and tendency for forming ice in the carburetor. The model can also be used to study the effect of additives used as anti-icing agents. Although the conventional icing test sequence of acceleration, steady state, deceleration, and idle is employed in the model as described, any desired sequence may be specified.