Study On Combustion Process And Emission Characteristics For CNT And MoO₃ Nano-diesel

In order to meet the demand of stringent regulations about emissions, efficient control of diesel engine emissions has become an important topic about environment pollutions. Exploring proper additives added to diesel fuel to improve its quality is an important solution to realize high efficient combustion and emissions reduction without any engine structure modification. As the diesel additives, nano-particles have superior thermal conductivity due to their nanometer scale and surface effect, which help to enhance the spray atomization and evaporation, increase the combustion efficiency and reduce emissions. In order to comprehensively understand the reaction mechanism of nano-fuel bends, carbon nanotubes（CNT） and nano molybdenum oxide（MoO₃） are chosen as additives added to diesel fuel. Then the oxidation properties are investigated under thermogravimetric analyzer, the combustion and emission properties are studied based on engine tests. The main research contents and conclusions are as follows:（1） The morphology of CNT and MoO₃ is investigated using field emission scanning electron microscope（SEM）. The SEM images show that CNT particles are about 40 nm in diameter with tubular structure and MoO₃ particles are about 80 nm in size with layered structure.（2） Nano-fuel blends with the dosing level of 50mg/L and 100mg/L are prepared by proper physical and chemical dispersion methods. According to the different applications, nano-fuel blends with tetradecane（C14） and neat diesel as liquid medium are respectively labeled as C50 CNT, C100 CNT, C50 Mo, C100 Mo and D50 CNT,D100CNT, D50 Mo, D100 Mo.（3） Thermogravimetric test is conducted to investigate the oxidation process of C50 CNT, C100 CNT, C50 Mo and C100 Mo. The temperature, reaction time and the average reaction rates to different weight loss rates are compared to evaluate the oxidation properties of nano-fuel blends. Due to the favorable heat transmission ability of CNT and the excellent catalytic oxidation ability of MoO₃, in addition to their nanometer scale and surface effect, the oxidation reaction rates of nano-fuel blends areincreased. The results show that the TG and DTG profiles of nano-fuel blends move to low temperature region compared to C14, and the tendency is more obvious with the increase in dosing level of CNT and nano-MoO₃. In total, CNT is more efficient than nano-MoO₃ in oxidation promotion of C14.（4） The combustion process and emissions of D50 CNT, D100 CNT, D50 Mo and D100 Mo are explored in diesel engine tests. Due to the favorable oxygen storage ability of CNT and the excellent heat transmission ability of MoO₃, in addition to the enhancement in spray atomization and evaporation by nano-particles in fuel, the ignition timing of nano-fuel blends is advanced and the combustion is accelerated as well. As a result, in the rated operating mode, the ignition timing are advanced by 0.8, 1.8, 0.4 and1.0°CA for D50 CNT, D100 CNT, D50 Mo and D100 Mo respectively, as compared to the reference diesel, and the peak of heat release is reduced by 5.5%, 15.1%, 1.6% and10.7%, and the effective thermal efficiency are increased by 3.3%, 5.2%, 1.5% and2.3%. Emissions such as CO, HC, NO_x and soot for CNT-diesel and MoO₃-diesel are all reduced to different levels. In total, CNT-diesel is more efficient than MoO₃-diesel in improving combustion and reducing emissions.