DETERMINATION OF LAMINAR FLAME SPEED OF DIESEL FUEL FOR USE IN A TURBULENT FLAME SPREAD PREMIXED COMBUSTION MODEL

One of the key challenges facing diesel engine system modelers lies in adequately predicting the fuel burning rate profile given the direct relationship between energy release and key performance parameters such as fuel economy, torque, and exhaust emissions. Current state-of-the-art combustion sub-models employed in such system simulation codes rely heavily on empiricism and successful application of such sub-models for new engine designs is highly dependent on past experience with similar combustion systems. One common approach to address this issue is to expend great effort choosing associated empirical coefficients over a range of similar combustion system designs thus improving the potential predictive capability of a given empirical model. But, continual combustion system development and design changes limit the extrapolation and application of such generic combustion system dependent coefficients to new designs due to various reasons including advancements in fuel injection systems, engine control strategy encompassing multiple injections, and combustion chamber geometry.

In order to address these very difficult challenges, an extensive effort has been applied toward developing a physically based, simplified combustion model for military-relevant diesel engines known as the Large Scale Combustion Model (LSCM). Recent effort has been spent further refining the first stage of the LSCM two stage combustion model that is known as the premixed phase sub-model. This particular sub-model has been compared with high-speed cylinder pressure data acquired from two relevant direct injection diesel engines with much success based on a user defined parameter referred to as the laminar flame speed by the combustion community. It is a physically significant parameter that is highly dependent on local temperature, pressure, and oxygen concentration but little experimental effort has been spent determining its behavior for diesel fuel due to ignition constraints. This submission will discuss one approach of indirectly determining this key combustion parameter.