Abstract
Traditionally, the favourable operating conditions to obtain the CAITM combustion mode are experimentally determined based on a sweeping of all operating commands controlling the engine. Among the most popular commands for a given engine speed are the valve timing, the valve lift or the fuel/air equivalence ratio.
This experimental way of study of the combustion mode is mainly limited by the engine design choices that were themselves based on the a priori knowledge of the favourable operating conditions. Consequently, some of the limitations observed during operation are (or may be thought to be) the consequences of the engine design and not an actual limitation of the combustion mode itself.
The present study proposes to reverse the reasoning by numerically determining the favourable conditions leading to a successful combustion without any limitation imposed by a pre-defined engine design. In this manner, our virtual engine is operated on all imaginable operating conditions to define the most favourable ones. And, only after that, the choices for engine design are made to convert a standard engine to an engine able to deliver the needed operating conditions.
The favourable operating conditions are defined by analysing the stationary operating points obtained with various initial conditions and by limiting the operating range to the points implying acceptable pollutant emissions (NOx, CO and uHC) and noise level (criterion based on pressure gradient).
Keywords: Controlled Auto-IgnitionTM, Simulation, Fuel Consumption, Spark Ignition Engine, Negative Valve Overlap