Department of Mechanics, University of Palermo. 26 p. (год публикации не указан)
Abstract
It is well known that the spark advance is one of the most important parameters influencing the efficiency of a S.I. engine. A change in this parameter causes a shift in the combustion phase, whose optimal position, with respect to the piston motion, implies the maximum brake mean effective pressure (bmep), for given operative conditions.
In this work the most significant parameters involved with the optimal combustion phase position are taken into consideration. In particular, the influence of the combustion duration, of the heat release law, of the heat transfer to the combustion chamber walls and of the mechanical friction losses are evaluated.
The theoretical conclusion, experimentally proven by many authors, is that the central point of the combustion phase (known as the location of the 50% of mass fraction burnt, here called MFB50) must be delayed with respect to the TDC as a consequence of both heat exchange between gas and
chamber walls and friction losses.