CFD Analysis of the Combustion Process in Dual- Fuel Diesel Engine

Dual-fuel technology has the potential to offer significant improvements in the emissions of carbon dioxide from light-duty compression ignition engines. The dual-fuel (diesel/natural gas) concept represents a possible solution to reduce emissions from diesel engines by using natural gas (methane) as an alternative fuel. Methane was injected in the intake manifold while the diesel oil was injected directly into the engine. The present work describes the results of a numerical study on combustion process of a common rail diesel engine supplied with natural gas and diesel oil. In particular, the aim is to study the effect of increasing methane concentration at constant injected diesel amount on both pollutant emissions and combustion evolution. The study of dual-fuel engines that is carried out in this paper aims at the evaluation of the CFD potential, by a 3-dimensional code, to predict the main features of this technology. In fact, to better understand the phenomena that take place during the dual-fuel operation (flame propagation throughout the premixed methane-air medium activated by the early self-ignition of the diesel fuel), the fluid-dynamic calculations could be extremely useful. The model calibration has been done referring to experimental data obtained in a single cylinder of an optically accessible engine. The experiments provided reference data in terms of pressure cycles, pollutant and unburned species and detailed visualization of the combustion development. Such data represented an effective validation check of the CFD based calculations. The latter allowed a deeper investigation of the combined diesel oil - methane combustion process. The numerical results also confirm that the OH radical plays a significant role for the detection of the regions with the highest combustion reactivity.