Year

2009

Degree Name

Master of Engineering (Mechanical)

Department

School of Mechanical, Materials and Mechatronics Engineering - Faculty of Engineering

Abstract

A Computational Fluid Dynamics (CFD) simulation of an opposed piston Internal Combustion (IC) engine, also known as the NuStroke engine, has been developed. The thesis focuses on the design and analysis of this particular engine using ANSYS CFX, a commercial CFD tool. The primary objectives of this thesis are to analyse the gas flow, effect of heat transfer, and combustion process on the engine performance. The engine geometry is modelled and meshed in ANSYS Workbench V11.0 to minimize any exporting errors that may creep in and cause serious mesh issues during mesh deformation simulation. Several researchers for a wide range of cases, justifying its application in the present study, have extensively validated different versions of the CFD code. At the initial stage of the project, the engine is modelled with single inlet and exhaust ports, the piston motion is prescribed with a sinusoidal profile, and a polynomial profile based on cam profile motion. The model does not include the combustion process. It is validated against an air-standard cycle process model developed in spreadsheet form. Similar spreadsheet models have been developed and extensively validated against experimental results of other engines by the author as a part of another thesis. To analyse the effects of combustion, the Domain Source Method (DSM) is employed in the CFD model, by which energy of combustion is explicitly fed to the engine model. A further improved CFD model with multiple inlet and exhaust ports is then applied. This enables the engine CFD model to closely simulate a real world engine, with the combustion model based on the DSM. The results obtained are then compared with the previous modelling results and spreadsheet results. The initial work on using Burning Velocity Model (BVM) and Eddy Dissipation Model/Finite Rate Chemistry (EDM/FRC) models to simulate combustion in the model is done and some results from these models are presented. The in-cylinder flow fields and pressure waves observed show significant vortex generation and heat transfer through the gas and combustion chamber walls. The present modelling of the engine using CFD techniques, and the analysis are the first attempts of this kind for this particular engine. The advantage of polynomial cam profile in controlling the performance of this engine is observed to be outstanding. The analysis of the obtained pressure and temperature, and the incylinder mid-plane pressure and velocity streamline plots show that both the spreadsheet model and CFD model agree qualitatively. These observations lead to a conclusion that the project, if extended further with experimental analysis, will give results that are comparable to the spreadsheet and CFD model results. The current work successfully presents a numerical simulation of an opposed piston engine. This study has enough potential to boost further research attempts in similar engine configurations, as the opposed piston engines have not been widely used nowadays in industries due to difficulties in attaining a successful design and balancing issues despite of the fact that they are low cost and less complicated engines. At this stage of the thesis, experimental results are not available for a more extensive validation, but at a later stage, if possible, this could be done to validate the current CFD model. Further extensive research on similar engine configurations with the help of good computing facilities and CFD simulation tools would make it possible to develop a successful, designer-friendly, and eco-friendly engine, which could eventually set up a new revolution in the entire engine industry.

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