Optimal dead space in axial-type expander

Abstract: In this thesis a method for determining optimal dead space in an axial-type expander is developed. The axial-type expander in question is for use in a steam engine, a environmental friendly and fuel-agnostic alternative to the ICE-engine. Optimal dead space is of importance as an increase in the dead space lowers the efficiency of the engine, however, is needed to ensure operation of expander as the piston could otherwise collide with the expander chamber top surface. The model for determining the optimal dead space in this thesis is based on vectorial tolerance models used for kinematic assemblies, and include the effect of thermal expansion, clearances at joints, manufacturing tolerances and deformations. With resulting tolerances and safety factors, a safe position of the expansion chamber top surface can then be established by Monte Carlo analysis. With input of design variables and the effect from factors mentioned and their effect on the minimal safe distance is calculated using the model in this thesis. From numerical analysis, the factors having the most contribution on the dead space are concluded to be thermal expansion of piston and piston rod, dimensional manufacturing tolerances of piston and piston rod, clearance at ball joints, axial clearance at shaft and bending of Z-shaft.