An experimental-numerical approach to reduce emissions of a dual fuel Diesel-natural gas engine

Conversion from diesel to dual fuel (diesel and natural gas) operation may represent an attractive retrofit technique to get a better PM-NOx trade-off in a diesel engine, with no major modifications of the original design. In the proposed paper, an Euro 2 heavy duty diesel engine, converted for dual fuelling, has been studied and tested to reduce pollutant emissions. Throttled stoichiometric with EGR and lean burn technologies have been selected as control strategies. A mixed experimental-numerical approach has been utilized to analyze the engine behavior by varying key operating conditions such as throttling, natural gas/diesel oil percentage and EGR. The model, based on a 3D approach, has been used mainly to understand the evolution of the distribution of the most important parameters in the combustion chamber. The use of stoichiometric mixtures, throttling and EGR, together with the adoption of a TWC, has been finally chosen as it allows to get very low gaseous and PM emissions, even if at the cost of a lower global efficiency than lean burn operation. Final emissions have been verified with respect to the ECE R49 13 mode steady state cycle. Dual fuelling allows to get a reduction in the order of 75% of NOx and PM, and higher than 30% of HC and CO.