Novel combustion technologies, which de-throttle the gasoline spark ignition (SI) engine, show high potential in reducing the fuel consumption. Technologies like variable valve actuation and/or gasoline direct injection, allow new strategies to run the SI engine unthrottled with early inlet valve closing (SI-VVA), charge stratification (SI-STRAT) and controlled auto ignition (CAI), also known as gasoline homogeneous charge compression ignition (HCCI). These diverse combustion concepts show thermodynamic gains that stem from several, often different, sources.
A multitude of definitions of thermodynamic gas exchange potentials arise when looking at the various publications concerning de-throttled combustion concepts. This paper shows a summary and comparison of these definitions and points out which one can be applied in general to evaluate various combustion concepts under the same basis of evaluation.
Additionally, a comparison between de-throttled gasoline combustion concepts at two representative engine operating points and a load sweep for the SI-VVA combustion concept is shown to illustrate the different interpretations of thermodynamic analysis of the gas exchange process. Advantages of the different combustion concepts are analyzed using thermodynamic split of losses method, which starts its potential analysis with the ideal constant volume cycle. A combustion concept comparison regarding these thermodynamic potentials, especially concerning gas exchange losses, is also performed.
The purpose of this paper is to propose a clear definition of thermodynamic benefits of de-throttled gasoline combustion concepts.
