Visualizational Research On Spray, Combustion And Soot Formation Of Second Generation Biodiesel

With the increase of energy crisis, environmental pollution and further stringent emission control regulation. A clean combustion in diesel engine is an important facet to meet stringent emissions resulations and enhance the performance of diesel engine. Using alternative diesel fuel may represent a promising solution to achieve high efficiency and low polluting combustion. As a clean and alternative energy, the fatty acid methyl esters biodiesel can offer a lot of benefits, including available feedstock, reduction of greenhouse gas emissions and so on. However, the problem of lower heating value, poor stability and serious corrosion of first generation biodiesel and high cost of second generation biodiesel limit the application of biodiesel in diesel engine. The catalytic hydrogenation of second generation biodiesel which is mainly produced non-edible oils and besides, possessed good combustion and emission characteristics has become more attractive and promising for the sustainable production of biodiesel. Therefore, the aim of this work is mainly focused on the optical research on spray, combustion and soot formation of catalytic hydrogenation of second generation biodiesel to better understand their effect on the combustion processes and extract the maximum benefits from biodiesel. It will be provided theoretical basis for applying catalytic hydrogenation of second generation biodiesel in diesel engine.The emission characteristics of different blending ratios of diesel/ catalytic hydrogenation biodiesel were investigated which not only demonstrates that catalytic hydrogenation of second generation biodiesel can be used in diesel engine, but also indicate that it is important to study the spray, combustion and soot process of second generation biodiesel. Advanced optical technology is applied to study the spray, combustion and soot formation characteristics of catalytic hydrogenation of second generation biodiesel under various working conditions and different blend ratios in an optical constant volume combustion chamber under simulated, quiescent diesel engine. The time-resolved results of fuel spray, combustion and soot formation combined in temporal and spatial simultaneously. The 3D soot formation process and OH radical was studied using Diffused Background Light Extinction Imaging method. The innovative results of this thesis are as follows:1. Based on the results of ignition delay and flame lift-off length, the optimal number of injection and injection interval are acquired to reduce the cycle to cycle variation.2. The spray characteristics were obtained using Mie-scattering and schilieren technology. The experimental results indicate that liquid length goes up with increasing blending ratio of catalytic hydrogenation biodiesel. However, the injection pressure has a little effect on liquid length. It can be concluded that the development of liquid length is mainly depended on mass flow and entrainment ambient air. The injection rate and evaporation ratio of blended fuel determine the vapor penetration. While the blending ration of catalytic hydrogenation biodiesel has little influence on vapor penetration. As the ambient temperature rises, the vapor penetration increases when the injection pressure is higher than one value. 3. The PLIF and nature flame illumination method were applied to investigate combustion characteristics. The ignition delay and flame lift-off length decrease with increasing ambient gas temperature, oxygen content and blending ratio of catalytic hydrogenation biodiesel. While increasing injection pressure causes ignition delay to decline and flame lift-off length to rise. The evaporation process has a little effect on combustion when the flame liff-off length is longer than liquid length under high injection pressure. But the effects between liquid length and flame lift-off length are considerably when the the flame liff-off length is shorter than liquid length under low injection pressure. The results of OH radical indicate that an increasing blending ratio of catalytic hydrogenation biodiesel cause a larger high temperature reaction region. 4. The soot onset time decreases and the soot onset distance between nozzle tip and soot onset location increases with increasing injection pressure. However, the soot onset time and the soot onset distance decreases with increasing oxygen content. Meanwhile, the soot optical thickness(KL) declines with increasing injection pressure or decreasing oxygen content. As increase ambient gas temperature, the peak soot level in a flame rises while the soot onset time and onset distance decreases. It should be note that no soot can obtain when ambient gas temperature lower than one value. Comparing results of B0 and B50, the soot onset location of B50 is closer to nozzle tip than that of B0 under the same operation conditions. While under the quasi steady state conditions, the soot optical thickness of B0 is higher than that of B50.5. Based on experimental results, the empirical formulas of liquid length, vapor penetration, ignition delay and flame lift-off length were obtained using statistical analysis which can provide important experimental data to develop spray and combustion model. The emission characteristics of different blending ratios of diesel/ catalytic hydrogenation biodiesel were investigated which not only demonstrates that catalytic hydrogenation of second generation biodiesel can be used in diesel engine, but also have great meaning for engineering.