CFD Analysis of the Injection Strategy of a Dual Fuel Compression Ignition Engine Supplied with Hydrogen

Although in the latest years the use of compression ignition engines has been a thread of discussion in the automotive field, it is possible to affirm that it still will be a fundamental producer of mechanical power in other sectors, such as naval and off-road applications. However, the necessity of reducing emissions requires to keep on studying new solutions for this kind of engine. Dual fuel combustion concept with methane has demonstrated to be effective in preserving the performance of the original engine and reducing soot, but issues related to the low flame speed forced researcher to find an alternative fuel at low impact of CO2. Hydrogen, thanks to its chemical and physical properties, can be a perfect candidate to ensure a good level of combustion efficiency; however, this is possible only with a proper management of the in-cylinder mixture ignition by means of a pilot injection, preventing uncontrolled autoignition events as well. Moreover, an effective injection strategy can be beneficial for a further reduction of carbonous pollutants from the diesel fuel pilot. Therefore, this work is aimed to numerically analyze the sensitivity of the combustion development in a diesel engine converted to operate in dual fuel mode, where hydrogen is injected in the intake manifold and diesel pilot is directly injected in the cylinder. Starting from a test case at a constant engine speed of 2000 rpm experimentally validated, numerical simulations are carried out with the software ANSYS Forte, using a Turbulence- Kinetics interaction model and the Autoinduced Ignition Flame Propagation model for diesel and hydrogen, respectively. Lookup tables were specifically implemented for the evaluation of the laminar f lame speed through H2/ air mixtures.