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Heat transfer in internal combustion engines is taking on greater importance as manufacturers strive to increase efficiency while keeping pollutant emissions low and maintaining adequate performance. Wall heat transfer is experimentally evaluated using temperature measurements both on and below the surface using a physical model of conduction in the wall. Three classes of model inversion are used to recover heat flux from surface temperature measurements: analytical methods, numerical methods and inverse heat conduction methods; the latter method has not been previously applied to engine data. This paper details the inherent assumptions behind, required steps for implementation of, and merits and weaknesses of these heat flux calculation methods. The analytical methods, which have been most commonly employed for engine data, are shown to suffer from sensitivity to measurement noise that requires a priori signal filtering.

This paper presents a theoretical analysis of the fuel and air flows within the idle circuit found in simple carburetors. The idle circuit is modeled numerically using a dynamic model that considers the resistances of the flow paths as well as the inertia of the fuel. The modeling methodology is flexible, in that the organization and techniques can be applied to any configuration and geometry. The numerical model calculates the fuel flow response of carburetor idle/transition circuits to pressure variations associated with air flow through the venturi and around the throttle plate. The model is implemented for a typical small engine carburetor and the nominal results are presented for this specific design.