Konstruktionstudie av en ångexpander

Sammanfattning

This thesis applies to a novel steam expander, one part of a steam engine system, a wobble plate

engine. The piston in the expander moves axially with the outgoing rotating shaft and is located

on a plate, why the engine type is called axial engine. When steam is applied to the plungers the

plate wobbles creating a rotation on the shaft going thru the wobble plate. The steam expander is

supposed to be used in exhaust gas recovery (bottoming cycle) applications and small scale

energy production. The commissioner is Ranotor Utveckling AB. The purpose with this thesis is

to evaluate the design of the expander and if possible give advise on the reasonability of the

concept from a mechanical point of view. The pre study concerns the history of wobble plate

engine as an internal combustion engine and steam expander, the engine’s principal layout and

usage, applications today and other information that concerns the engine. A number of

components are selected for further studies namely the piston and piston rod, the ball joint and

the wobble plate with bearings. The piston and piston rod is FE-modelled as a design

optimization. It is evaluated by measuring von Mises stress in different evaluation surfaces. The

study shows how the shape should be mass optimized and how this study can be valuable in the

future. The ball joint is studied as a part that should be bought as a separate part and tested at the

required loads and environment. The component can’t be lubricated with oil (oil can have effect

the function of other components of the system negative) why lot of the attention is put on

finding a joint that works well without lubrication or with water in the contact. The wobble plate

is studied by finding a kvasi-static operation point from a dynamic load modell of the steam

expander and applying these in static FE-modelled simulations. The wobble plate is equipped

with two bearings why an analytic study is made to find out how the position of the bearings

changes the load. The modell is verified by using a FE-modell and bearings are selected. The rest

of the study of the wobble plate is made on evaluating different kinds of supports for the

bearings in a FE-modell and giving general advise concerning the solid mechanics of the

component and how the study should proceed.