Numerical Investigation of Dual Fuel Combustion on a Compression Ignition Engine Fueled with Hydrogen/Natural Gas Blends

The present work aims to assess the influence of the composition of blends of hydrogen (H2) and Natural Gas (NG) on Dual Fuel (DF) combustion characteristics, including gaseous emissions. The 3D-CFD study is carried out by means of a customized version of the KIVA-3V code. An automotive 2.8 L, 4-cylinder turbocharged diesel engine was previously modified in order to operate in DF NG-diesel mode, and tested at the dynamometer bench. After validation against experimental results, the numerical model is applied to perform a set of combustion simulations at 3000 rpm-BMEP = 8 bar, in DF H2/NG-diesel mode. Different H2-NG blends are considered: as the H2 mole fraction varies from 0 vol% to 50 vol%, the fuel energy within the premixed charge is kept constant. The influence of the diesel Start Of Injection (SOI) is also investigated. Simulation results demonstrate that H2 enrichment accelerates the combustion process and promotes its completion, strongly decreasing UHC and CO emissions. Evidently, CO2 specific emissions are also reduced (up to about 20%, at 50 vol% of H2). The main drawbacks of the faster combustion include an increase of in-cylinder peak pressure and pressure rate rise, and of NOx emissions. However, the study demonstrates that the optimization of diesel SOI can eliminate all aforementioned shortcomings.