Experiments and multi-dimensional simulation of dual-fuel Diesel/natural gas engines

Dual-fuel engines, based on the use of natural gas (NG) as the main fuel in internal combustion engines (ICE) and using diesel injection as the ignition source instead of the spark plug, are one of the possible ways to reduce the trade off PM-NO\dX problem of traditional diesel engines. The high octane number (NOR) of NG allows to easily covert existing diesel engine, without varying the original compression ratio, with great advantages in terms of costs. The only modifications concern with the introduction of feeding system for NG and the reduction of diesel quantity injected into the combustion chamber, by acting on injection pump control. For high degrees of substitution, diesel oil can be considered only as the ignition source for the fresh air/NG mixture, with consequent beneficial effects on PM emissions. The real drawback regarding dual-fuel engines is the wide increase in HC and CO emissions and efficiency worsening, especially under part-load conditions. To reduce such emissions, further devices like intake throttle, three-way catalyst and EGR were utilized during experimental tests. In this paper the experimental results concerned with the conversion of the IVECO 8360.46R diesel engine, used for public transportation, to dual-fuel operations are argued. Experiments were performed to define engine performance and to reduce exhaust emissions. Experimental pressure data also were used to develop numerical tools, characterized by a mixed 1D-3D approach. A 1D code was utilized to calculate the real boundary inflow and outflow pressure conditions. Concerning with 3D simulation, a modified version of KIVA-3V code was used to simulate the whole working cycle of the engine. The examined test-case is characterized by low admission of diesel fuel so to represent diesel ignition and NG combustion.