| Biodiesel is a superior and alternative fuel for fossil diesel. Development and research of biodiesel have been paid more attention to in the last decade all over the world. Since there are many feedstocks of biodiesels, properties of biodiesels and diesel leads to different characteristics of atomization, evaporation and ignition. Although using biodiesel will improve the emissions of diesel engine except NOx emission, characteristics of unregulated emissions when biodiesel used may be different from those of diesel. Therefore, necessary research should be carried out to understand these characteristics. This paper, investigates the characteristics of spray, combustion and emissions are also researched of biodiesel and diesel engine. The main works and conclusions are summarized as follows:1. Firstly, spray field of bio-diesel and mixed fuel with 0# diesel in a model gas cylinder were measured by Phase Doppler Particle Analyzer (PDPA). Lots of useful data were achieved such as distributions of the velocity vectors and the droplet diameters of fuel drop and concentration in the spray field of biodiesel. The results show that the diameter of nozzle hole gives a great impact on atomization after the core area of the spray. The smaller of the orifice diameter, the better spray effect. Compared with fossil diesel fuel, biodiesel performed a worse spray effect. Sauter mean diameter of biodiesel is bigger than that of fossil diesel fuel under the same operating condition. The higher engine speed is, the smaller droplet diameter and fluctuation velocity of droplet are.2.This study was presented a comparative spray characteristics difference between different biodiesel and 0# diesel by using a commercial high pressure common rail injection system. The spray macroscopic characteristics such as spray penetration, spray angle, and spray volume were studied in a constant volume vessel with a high-speed camera. Fuel spray injection pressure was varied from 60MPa to 150MPa, and ambient gas (N2) density range from 12.60 kg/m3 to 35.6 kg/m3. Results show that diesel spray geometric parameters such as spray volume are larger than that of jatropha fuel and palm fuel at the same spray injection pressure and ambient gas density. To achieve the same spray atomization level, time spent of diesel spray is least at the same condition.3. This study, by using the dynamic visual test device of multi-purpose spray combustion, is carried out through comparison testing on spray & combustion mechanism of biodiesel and conventional diesel, and a comparative analysis of the two fuels. Results show that for the biodiesel, fuel injection timing is earlier, combustion phasing advances, and its combustion is faster in the initial pre-mixed combustion stage, but slower in the spread combustion stage compared with the diesel fuel. Analyzed the effects of three factors, fuel characteristics, engine speed and injection pressure on biodiesel injection and combustion processes, following conclusions are reached:for the mixed fuel, injection timing and combustion phasing advance, the max. combustion pressure of mixed fuel B5 is the highest and occurs a little earlier. With injection pressure increasing, the ignition delay and the combustion duration become shorter.Auto-ignition characteristics and gaseous emissions are investigated Soybean methyl ester (SME), with higher cetane number(CN) than diesel, has a 10% decrease of ignitiondelay (ID) and Wasted oil methyl ester (WOME), with similar CN to diesel,has a 5% increase of ID compared with diesel. In addition, ID of biodiesel blends decreases at first and then increases with the increase of blend concentration, which may be due to the conjunct effects of lower chemical ID from higher cetane number and higher physical ID from poor atomization and evaporation. This also indicates that the effect of chemical properties on ignition is higher than the effect of physical properties on the poor atomization.4. Fuel modification (Micro-emulsion) is one of the methods of fuel redesign for reducing NOX emission, and also one important way to save energy and reduce greenhouse gas emission.The experiment study of engine performance and emissions fueled with the standard diesel, WOME biodiesel, microemulsified diesel, microemulsified biodiesel on the YZ4102ZLQ engine were completed. The results show that, the specific fuel consumption of different fuels change with the different modes based on the same diesel engine speed and power. The emission of NOx and smoke emission decrease obviously, but HC and CO increase using micro-emulsified biodiesel.
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