Development of Next Generation Optical Engines
Examensarbete för masterexamen
Applied mechanics (MPAME), MSc
Optical engines are used as research and development tools to study the combustion inside internal combustion engines. Conventional optical engines uses an extended piston in order to be able to observe the combustion chamber from below, through the piston. This extended piston, or Bowditch piston, limits the load and speed in which the engine can operate due to its geometrically weak design and considerable mass. This master thesis proposes a design for a new type of optical engine that has significantly higher mechanical performance compared to conventional optical engines. The new design may provide an engine speed increase of up to 100%. Optical engines are often single cylinder internal combustion engines, fitted with transparent parts providing optical access to the combustion chamber. Using the optical access, various processes taking place in the combustion chamber may be studied optically which becomes more and more important in today's advanced engines, some of which are direct injected. The optical engine can be fitted with a transparent liner providing optical access from the side of the combustion chamber, together with the Bowditch piston providing access from below. These pistons are known for their high weight and low stiffness, frequently limiting engine speeds and cylinder pressures to low or moderate. For a standard optical engine with car engine specifications, maximum speeds can be around 2500RPM. By summer 2014 Anders Dahl and Kristoffer Clasén came up with the idea of how to replace the Bowditch piston in an optical engine. By reconfiguring the conrod and crankshaft, optical access was achieved from beneath the piston rather than inside, making the piston shorter, lighter and therefore stronger. The reconfiguration also resulted in higher force absorption, which is a key feature since increasing engine speed drastically increases the piston acceleration and hence the reaction forces. The concept was consumed by Bohus Automotive AB and a master thesis in collaboration with the division of combustion at Chalmers was initiated. The work was divided in two parts; development and validation of the piston, and development of an engine comprising the piston. The aim of the piston validation was to determine a first estimate of the mechanical performance. A piston design was created using the CAD-software Inventor and an iterative approach. When the design had matured it was analysed by FEM with regard to stress, using the commercial FE-software Ansys Workbench Mechanical. Parallel to the piston an engine design was developed using the same software and iterative approach. The aim of the engine development was to establish a suitable engine layout comprising the piston concept. Without an engine, the piston has no use. Much of the engine was created using engineering intuition to be able to create a whole engine design within the project time, and the engine will need its own verification in the future. The piston analyses showed promising results, indicating a performance increase of up to 100% in engine speed compared to the Bowditch design. Likewise, a successful engine with a compact design was established that fulfilled the demands on ease of use and accessibility. A few simplifications and assumptions have been implemented in the analyses, and more work is needed in the future to verify other components such as crankshaft and conrods. The transparent parts have been excluded from the analyses since they would inevitably limit the performance. Normally the transparent liner would be the first component to break. There is however a configuration option of the new engine that excludes the transparent liner which would allow much higher loads than usual.
Energiteknik , Hållbar utveckling , Energi , Transport , Energy Engineering , Sustainable Development , Energy , Transport