Multidimensional Simulations of Combustion in Methane- Diesel Dual-Fuel Light-Duty Engines

The adoption of gaseous fuels for Light Duty (LD) engines is considered a promising solution to efficiently reduce greenhouse gases emissions and diversify fuels supplies, while keeping pollutants production within the limits. In this respect, the Dual Fuel (DF) concept has already proven to be, generally speaking, a viable solution, industrially implemented for several applications in the Heavy-Duty (HD) engines category. Despite this, some issues still require a technological solution, preventing the commercialization of DF engines in wider automotive fields, including the release of high amounts of unburned species, possibility of engine knock, chance of thermal efficiency reduction. In this framework, numerical simulation can be a useful tool, not only to better understand specific characteristics of DF combustion, but also to explore specific geometrical modifications and engine calibrations capable to adapt current LD architectures to this concept. Once the general DF concept is tailored for LD compression ignition engines, respecting practical functional limits, an optimal operating map displays, at different engine load values, a considerable variability in the optimal extent of Diesel substitution and Diesel injection strategies. As a result, some operating conditions significantly differ from the classic DF mode implemented in HD architectures. Thus DF models proposed to resemble combustion in HD engines could not be suitable for LD ones. The present work aims at evaluating the applicability of modeling approaches already consolidated for Diesel combustion to the DF operation of a LD engine. The validation activity is carried out thanks to a wide experimental campaign on a single cylinder Diesel engine, properly modified to work in Dual-Fuel mode. Three characteristic operating conditions have been selected to be reproduced numerically by means of the LibICE library, relying on the OpenFOAM software platform, employing detailed chemical reaction kinetics. Numerical results properly capture the main features of all the examined conditions, ranging from a reference Diesel mode at medium load to a pure DF condition with 95% of premixed methane.