An Optical Investigation of Diesel-Pilot and Methane Dual-Fuel Combustion

The study investigated dual fuel combustion, where late-cycle diesel-pilot injection ignites the premixed methane-air mixture at light load in a single cylinder heavy-duty diesel engine, modified for optical access. The high-speed natural luminosity technique was employed to visualize the combustion processes at varying methane lambda values and different pilot ratios. Several methane lambda values were tested and to obtain different lambda values, methane quantity was varied while keeping other parameters the same. Methane was injected into the cylinder through intake manifold along with the air. In addition, three different pilot ratios were tested, obtained by varying the diesel-pilot amount. The results show that the flame front propagation becomes more prominent at methane lambda values closer to stoichiometric condition and evidence of flame front propagation could be seen in NL-images. In terms of the pilot ratio, it is observed that an increase in the pilot amount causes a rapid combustion and improves flame front propagation. The trends of ignition delay in dual fuel combustion for conducted tests were also analysed.