In the skyrocketing fuel price situation, using natural gas by means of a diesel dual fuel (DDF) conversion technique is a promising technology as it is flexible for diesel trucks. However, DDF engines suffer from low engine efficiency and poor emission characteristics at low-to-medium load operations. In this study, two DDF concepts were proposed by using five operating parameters including 1) the number of injection pulses, 2) duration of each injection pulse, 3) injection timing, 4) throttle position, and 5) EGR. The first three parameters were varied in the first concept whereas all parameters were varied in the second one. Results from these two DDF conversion concepts were compared to the simple conversion where the operating parameters for diesel injections were fixed by the standard ECU of the OEM.
At light load (2000 rpm, 3.1-bar IMEP), the brake efficiencies in the first and the second concepts were improved from the simple conversion by 21% and 35%, respectively. Moreover, methane emissions were reduced by 51% and 90%. The main challenge found in these new concepts was the lower exhaust temperature, which tended to reduce the catalytic converter efficiency.