Diesel Combustion Process BED Multi-component Fuel Use

As alternative fuels to petroleum diesel fuel, biodiesel and ethanol have been widely researched in many countries and regions. There exist some problems in the process of these researches. The main problems were as follows:the poor fuel atomization effect of biodiesel, the increased NOx emissions, the poor solubility of diesel fuel and ethanol, the inconsistent study conclusions of the emissions and the lack of systematic research and so on. Aiming at the above problems, the biodiesel-ethanol-diesel (abbreviated as BED) multi-component fuel was prepared with certain proportions of biodiesel, ethanol and diesel fuel by using the physicochemical properties complementarity of the three fuels. Taking into account the advantages of biodiesel and ethanol and the technical potential of high pressure common rail system, the researches on the effect of the BED multi-component fuel on the engine performance and it’s combustion control law were performed, and the effect of different altitude levels on the combustion process was studied when the BED multi-component fuel was used by the organic combination of alternative fuel and control technology. The researches were investigated as follows:(1) Conducting the investigation on stability and physicochemical properties of the BED multi-component fuelAiming at the problem of poor solubility of ethanol and diesel fuel, the biodiesel was added to the ethanol-diesel fuel. And the experimental investigation on stability and three phase solubility of the BED multi-component fuel at different temperatures was carried out. The effect of different proportions of biodiesel and different temperatures on the stability of the BED multi-component fuel was studied. And the effect of the blending ratio of the biodiesel and ethanol on the main physicochemical properties of the BED multi-component fuel was researched and analyzed.(2) Conducting the experimental investigation on the engine performance when the BED multi-component fuel was usedThe comparative experiments were performed on a high pressure common rail diesel engine fueled with pure diesel and the BED multi-component fuel with10%-25%biodiesel and3%-5%ethanol in volume percentage at81kPa atmospheric pressure. The effect of the BED multi-component fuel with different proportions of biodiesel, ethanol and diesel fuel on engine power, fuel economy, emissions and combustion characteristics and the difference between the BED multi-component fuel and the diesel fuel were analyzed. The difference of the spray and combustion process between the BED multi-component fuel and the diesel fuel was analyzed by comparing the fields’distribution.The test results showed that if the engine was kept unchanged, the engine power was lower than that of pure diesel when the BED multi-component fuel was used. And the fuel economy was improved by1.3%-2.1%when the proportion of biodiesel in the BED multi-component fuel was kept within15%. On the meanwhile, the CO, THC, soot and PM emissions decreased, while the NOx emissions had increasing trend with a maximum of17%. If the volume percentage of biodiesel reached25%, the fuel consumption increased, the improving effect of the BED multi-component fuel on emissions was weakened and the emissions even increased. Retarding injection timing and using EGR technology can reduce the NOx emissions of the BED multi-component fuel effectively. The cylinder pressure and combustion temperature were decreased. There was no significant difference in the start of combustion. And the combustion duration was shortened obviously. With the increase of biodiesel component in the BED multi-component fuel, the peak heat release rate increased.(3) Researching the combustion control law of the BED multi-component fuelThe effects of the key fuel injection control parameters including the pilot injection timing and quantity, the main injection timing and quantity and the injection pressure on the combustion characteristics of the diesel engine were investigated when the BED multi-component fuel was used.The results indicated that if the pilot injection timing was retarded properly, the intensity of the main injection fuel combustion process would reduce. The increased pilot injection quantity was helpful to improve the cylinder pressure, while the peak heat release rate and the maximum rate of pressure rise increased. The advanced main injection timing led to the advanced start of combustion and higher values in the maximum cylinder pressure, the maximum combustion temperature and the peak heat release rate, and they would appeared in advance. The rate of pressure rise increased, which resulted in a violent combustion process. With the increase of the biodiesel and ethanol components in the BED multi-component fuel, the peak heat release rate in the main injection phase increased firstly and then decreased as the main injection was made in advanced timing. Both of the maximum cylinder pressure and the peak heat release rate increased with the increasing main injection quantity. The combustion duration extended accordingly. As the injection pressure increased, the maximum cylinder pressure and the peak heat release rate both increased. And the combustion duration was shortened. The heat release rate increased firstly and then decreased at the early stage of the combustion, leading to the same trend in the cylinder pressure.(4) Researching the effect of different altitude levels on the combustion process of the BED multi-component fuelThe experiments on the high pressure common rail diesel engine fueled with the BED multi-component fuel at different altitude conditions were performed. The experimental results indicated that when the engine was kept unchanged, the influence of atmospheric pressure variation on the engine power was not significant on the whole. At low loads, with the increase of atmospheric pressure, the improvement of fuel economy was not significant and the fuel consumption even increased. At high loads, the fuel economy was improved. With the increase of atmospheric pressure, the CO and THC emissions decreased basically, and the NOx emissions decreased at medium and low loads while increased at full load. The PM emissions decreased at full loads. With the decrease of the altitude level and the increase of atmospheric pressure, the maximum cylinder pressure, the maximum combustion temperature and the peak heat release rate were all increased. The degree of their increase varied with the different variation intervals of the atmospheric pressure. The burning speed was accelerated and the combustion duration was shortened. The rate of pressure rise increased, but still within the scope of smooth running.(5) Researching the effect of different types of oxygen content variation on the engine performanceA further comparison of the different effects of fuel oxygen content in the BED multi-component fuel and intake oxygen content caused by altitude variation on diesel engine performance was made. The results indicated that when the pure diesel fuel was used, the influence of altitude variation on the engine power was not significant and the brake specific fuel consumption (BSFC) decreased with the increase of atmospheric pressure. When the BED multi-component fuel were used, the engine power and brake specific fuel consumption reduced with the increase of fuel oxygen content, and the effective thermal efficiency was improved. Compared to the effect of increasing atmospheric oxygen content by altitude variation, the improvement in fuel consumption due to the increase of BED multi-component fuel’s oxygen content was greater.