Search Results

International concerns over small engine efficiency and emissions characteristics have lead to several efforts to develop improved internal combustion engine cycles, including investigation of Homogeneous Charge Compression Ignition (HCCI) and Premixed Charge Compression Ignition (PCCI) modifications to classic combustion cycles. Kashmerick Engine Systems LLC. has proposed a K6 cycle that moves the combustion process to an external continuous-combustion chamber to decrease the rate of combustion and allow optimization of the combustion chamber and piston-cylinder as a compression and expansion device separately to improve efficiency and reduce emissions. This paper describes 0-dimension modeling of both an air-standard dual-cycle model and an air-standard K6 cycle model in Engineering Equation Solver (EES) to compare the ideal performance of the two cycles.

The purpose of this research is to develop a prediction technique that can be used in the development of port fuel-injection (hereinafter called PFI) gasoline engines, especially for general purpose small utility engines. Utility engines have two contradictory desirable aspects: compactness and high-power at wide open throttle. Therefore, applying the port fuel injector to utility engines presents a unique intractableness that is different from application to automobiles or motorcycles. At the condition of wide open throttle, a large amount of fuel is required to output high power, and injected fuel is deposited as a wall film on the intake port wall. Despite the fuel rich condition, emissions are required to be kept under a certain level. Thus, it is significant to understand the wall film phenomenon and control film thickness in the intake ports.

This work presents a carburetor model written in FORTRAN and coded into a user routine object in a one-dimensional engine software program, GT-Power. The model was compared to experimental data from a single cylinder, carbureted, spark ignition, gasoline, air cooled engine. The model, which the user subroutine was coupled with, was the GT-Power model created and calibrated for the engine tested. The model gave an error of less than 15 percent compared with measured engine performance. When the user routine object was connected, the results compared between the GT-Power model and the experimental data showed good agreement of 20 percent error or less for the wide open throttle case.

A modified Brayton cycle is incorporated into a continuous combustion engine system. This 6-stroke engine system is described and illustrated with pressure-volume diagrams. Potential advantages over the traditional 4-stroke Otto cycle are reviewed in the areas of emissions, flexible-fuel use, energy conversion efficiency, and noise. A detailed 1-D air standard thermodynamic model of the K6 cycle is generated and used to investigate the potential efficiency of this cycle and analyzed from partial throttle to wide-open throttle power output. The affects of compression ratio and expansion variations on efficiency are evaluated. The power output and power density are estimated. Key assumptions in the analysis of the thermodynamic model are discussed. Comparisons are made to a similar level of analysis of an Otto cycle 4-stroke engine. A utility engine simulating this cycle operating on compressed air is described.

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.

Although each carburetor design is slightly different, it is possible to define some basic elements that can be used as building blocks to describe many carburetor designs. All carburetors designs use small metering orifices to constrain fuel and air flow through different circuits. This paper presents the CFD analysis of fuel flow across small metering orifices typically found in small engine carburetors. The analysis was divided into three parts: first, CFD simulations of liquid flow in square-edged orifices were performed. These simulations indicated the appropriate turbulent model and numerical parameters to be used in the study of orifices with more complex geometries. Second, inlet and outlet chamfers were added to the square-edged orifices, which allowed for understanding their effect on the characteristics of the flow. Finally, the simulations were performed on geometries that represented metering orifices found in real carburetors.

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.

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.

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.