In-depth comparison between pure diesel and diesel methanol dual fuel combustion mode

Diesel Methanol Dual Fuel (DMDF) could achieve high efficiency and low emissions simultaneously at part of engine conditions, but the reason of this has not been clarified. In order to find the reason behind this phenomenon, Pressure-Volume (P-V) map, equivalence ratio (φ)-temperature (T) map and three-dimensional simulation software were used to compare diesel and DMDF mode, and two test conditions were selected to fulfill in-depth comparison of two combustion modes. Based on the analysis of P-V map, the reason of higher thermal efficiency at DMDF mode is as follows: lower cylinder pressure in compression stroke contributes to compression work reduction. Meanwhile, higher combustion rate of DMDF mode could reduce cylinder temperature and pressure in the late power stroke, which would further decrease exhaust loss and heat loss. Based on the analysis of φ-T map, higher methanol substitution percent could reduce the intersection area between cylinder φ-T map and nitric oxide & soot generation region. And after analyzing in-cylinder temperature, hydroxy mole fraction together with the equivalent ratio three-dimensional cloud map, it is found that the inhibitory effect of methanol on diesel low-temperature combustion prolongs diesel ignition delay, which helps to form the homogeneous charge in the cylinder. Under DMDF mode, fuel rich areas are significantly reduced, so is the maximum in-cylinder temperature. This is the key to achieve ultra-low nitrogen oxides and soot emissions for DMDF mode.