The Effect And Mechanisms Of A Homogeneous Combustion Catalyst In The Reduction Of Emissions From Diesel Combustion In Compression Ignition Engines

A ferrous picrate based homogeneous combustion catalyst has shown significant effectiveness in improving the fuel economies in compression ignition (diesel) engines. However, there has been a lack of knowledge of the effect and the working mechanisms of the catalyst in reducing the pollutant emissions, which has hindered the widespread application of the catalytic technology in diesel engines. The present research aimed to systematically assess the efficacy of the ferrous picrate catalyst in emission reductions from diesel engines and to further the understanding of the mechanisms behind the catalytic effect in diesel combustion processes. More specifically, this thesis work has successfully addressed the following specific research objectives: To confirm and quantify the effect of the catalyst in improving fuel consumptions and reducing pollutant emissions (UHC, CO, NOx and smoke) from a diesel engine fuelled with diesel and biodiesel; To investigate the effect of the catalyst on the key characteristics of soot particles from diesel engine combustions, including soot oxidation properties, soot nanostructure and particle size, soot chemical and elemental compositions; To ascertain the morphology and the ultimate fate of iron in the catalyst during diesel combustion process; and To reveal the mechanisms of the working of the catalyst in diesel soot formation during the combustion processes. To assess the effectiveness of the catalyst, a series of tests was performed on a laboratory diesel engine and a large-scale diesel engine facility as a function of engine speed, load and catalyst dosage. The beneficial effects were also examined with the engine fuelled with biodiesel fuel to realise the full potential of the catalyst. The tests consistently demonstrated a fuel saving of 1.1% - 3.8% over the range of conditions examined. The mechanisms of the catalyst in diesel engine combustions were studied by determining the differences in the characteristics of soot particles using a combination of several advanced analytical techniques, including TGA, SEM/TEM-EDS, FT-IR, NMR and elemental analyser. The evolution of iron in the catalyst during diesel combustion was also investigated to provide additional evidence for the understanding of the role of the catalyst in diesel combustion processes. Laboratory diesel engine tests with diesel fuel have showed the addition of the catalyst was able to reduce up to 39.5% smoke, 22.5% CO and 15.3% unburned hydrocarbons (UHC), as well as 3.8% specific fuel consumptions. As a consequence of the improved combustion efficiency, NOx was found to be elevated by up to 8.3% under the experimental conditions. Results from large-scale diesel engine tests showed that the use of the catalyst reduced up to 20.7% CO and 22.8% UHC at the cost of 5.3% increase in NOx. In biodiesel combustion, the smoke, CO and UHC emissions were reduced by up to 24.4%, 17.3% and 3.8% with the fuel consumptions saved by up to 2.8%, by the addition of the catalyst. It was also found that the NOx and CO2 from the biodiesel combustion were increased by up to 4.5% and 2.5% due to the enhanced combustion efficiency associated with the use of the catalyst...