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A commercial CFD package was used to develop a three-dimensional, fully turbulent model of the compressible flow across a complex-geometry venturi, such as those typically found in small engine carburetors. The results of the CFD simulations were used to understand the effect of the different obstacles in the flow on the overall discharge coefficient and the static pressure at the tip of the fuel tube. It was found that the obstacles located at the converging nozzle of the venturi do not cause significant pressure losses, while those obstacles that create wakes in the flow, such as the fuel tube and throttle plate, are responsible for most of the pressure losses. This result indicated that an overall discharge coefficient can be used to correct the mass flow rate, while a localized correction factor can be determined from three-dimensional CFD simulations in order to calculate the static pressure at locations of interest within the venturi.

The main circuits of a small engine carburetor can be represented as a complex, dynamic, two-phase flow fluid network. This paper presents the theoretical characterization of a dynamic one-dimensional model of fuel and air flow in small engine carburetors and its implementation into a one-dimensional engine simulation software package. This implementation allows for studying the effect of changes in individual carburetor parts on engine performance. The characterization of the model indicated that the dynamic behavior of the entire flow network can be captured by the solution of the instantaneous momentum balance equation on the single-phase liquid elements of the network, simplifying the dynamic model considerably. The second part of this work discusses the implementation into the one-dimensional engine simulation package, and shows examples of the studies that the coupled implementation allow for.

This work presents a complete model of the carburetor for small engines. It extends the previously published models by incorporating a detailed review of two-phase flow pressure drop, the effect of the fuel well on the control of airbleed flow, and unsteady flow. The homogenous two-phase flow model, which is commonly used in carburetor modeling, was compared with an empirical correlation derived from experiments in small pipes and found to be in poor agreement. In order to assess unsteady flow conditions, the model was extended by solving instantaneous one-dimensional Navier-Stokes equations in single-phase pipes. This strategy proved successful in explaining the mixture enrichment seen under pulsating flow conditions. The model was also used to derive a sensitivity analysis of geometries and physical properties of air and fuel.

This paper presents a theoretical study of different strategies of waste heat recovery in an internal combustion engine, operating in a hybrid vehicle (spark ignition engine and electric motor). Many of the previous studies of energy recovery from waste heat focused on running thermodynamic cycles with the objective of supplying air-conditioning loads. There are two elements of this study that are different from previous studies: first, the end use of the recovered waste heat is the generation of electric power, and, second, the implementation of these heat recovery strategies takes place in a hybrid vehicle. The constant load conditions for the SI-engine in the hybrid vehicle are a potential advantage for the implementation of a heat recovery system. Three configurations of Rankine cycles were considered: a cycle running with the exhaust gases, a cycle with the engine coolant system, and a combined exhaust-engine coolant system.