Investigations and Analysis of Working Processes of Two-Stroke Engines with the Focus on Wall Heat Flux

Small displacement two-stroke engines are widely used as affordable and low-maintenance propulsion systems for motorcycles,
scooters, hand-held power tools and others. In recent years, considerable progress regarding emission reduction has been reached.
Nevertheless, a further improvement of two-stroke engines is necessary to cover protection of health and environment. In addition, the
shortage of fossil fuel resources and the anthropogenic climate change call for a sensual use of natural resources and therefore, the fuel
consumption and engine efficiency needs to be improved.
With the application of suitable analyses methods it is possible to find improving potential of the working processes of these engines.
The thermodynamic loss analysis is a frequently applied method to examine the working process and is universally adaptable. Within
this paper, a series production small displacement two-stroke engine is experimentally investigated on the test bench and adapted with
measuring equipment in order to analyze the working process with focus on the wall heat flux. Due to high speed and vibrations, these
investigations are complex. This publication considers an assessment of correlation predictability of heat transfer models, which are
used in the thermodynamic loss analysis, by means of a comparison with experimental data. Thereto the measurement technique based
on the surface temperature method applied to a small two-stroke engine is explained. From these investigations, the thermodynamic
loss analysis regarding wall heat loss is reassessed and improvement potential is pointed out. Finally, an alignment of the
thermodynamic loss analysis for small displacement two-stroke engines regarding the wall heat losses is performed. The results of the
thermodynamic loss analysis demonstrate the occurring efficiency losses and therewith improvement strategies concerning the working
process can be deduced.