Akademik Veri Yönetim Sistemi
Fuel, cilt.347, 2023 (SCI-Expanded)
Accelerated by the harms and depletion risk of fossil fuels, transition to low-carbon or renewable fuels have become an urgent need for combustion engines to decarbonize transport sectors. Natural gas-diesel dual-fuel combustion is a promising method to achieve these goals by allowing the usage of natural gas in diesel engines. However, this concept has drawbacks of low combustion efficiency, high unburned hydrocarbon (HC) emissions and high cyclic variations at low engine loads. These drawbacks hinder the benefits of dual-fuel such as low NOx and soot emissions. To find solutions to these drawbacks, split diesel injections with variable injection timings and mass split ratios (ratio of first injection diesel mass to total diesel mass) were investigated experimentally and numerically on a medium speed marine engine at low load using constant natural gas and diesel amounts. Experimental results of the split injection were compared to single injection dual-fuel and conventional diesel operation. Single injection case resulted in slightly lower HC emissions and cyclic variations and higher NOx emissions than split cases in a narrow injection timing interval. Apart from that, split injections increased combustion efficiency and decreased cyclic variations in a broader timing interval. For split cases, early first injection timing prevented high premixed heat release peak, suppressed NOx emissions and knocking. Especially, using 70% split ratio with retarded second injections increased combustion efficiency, decreased knocking level and provided simultaneous reduction of HC and NOx emissions compared to lower split ratio cases. In short, despite not giving the minimum values at all conditions, split injection showed potential to find a remedy to high HC emissions and cyclic variations issues by keeping robust operation in a wider injection timing interval. The numerical results support the experiments in which better combustion and decreased HC emissions are attained using sufficiently early diesel injections. Simulations show that, compared to late single injection, early single injection dual-fuel case enables more homogeneous temperature distribution and better oxidization of methane near the cylinder wall and central region above the piston crown. Besides, split injection shows improved methane oxidation near the cylinder wall and inside top-land crevice volume.