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The flow of diesel fuel through multi-hole injection nozzles is well understood. There are, however, no comprehensive experimental results for the design of injection nozzles for alternate fuels. A steady state flow generator was designed and employed to analyze the effects of the physical fuel properties and the needle lift on the discharge coefficient for the nozzle orifice. Three fuels were tested: diesel reference fuel, a 50/50 mixture of diesel fuel and sunflower oil, and 100%. sunflower oil. The fuel viscosities range from 3.0 cS to 30.0 cS at 40°C. Five injection pressures ranging from 3.5 to 13.8 MPa, and eight increments of needle lift between 0.031 and 0.940 mm were used in this investigation. A significant influence of needle lift, injection nozzle pressure, and physical properties of fuels on the flow coefficient in the normal operating range of a typical diesel engine was proven.

The effect of increased clearance between the needle and its guides in a fuel injection nozzle on the rate of lacquer deposit formation from neat sunflower oil was investigated. Bosch fuel injection nozzles were tested on a fuel v injection calibration stand. The needle clearance reduction due to deposit buildup was monitored with a pneumatic leak test. Two test series of 100 hours duration each were performed at a temperature of 350°C. Each series consisted of ten 10-hour segments with a complete system shutdown after each segment. For the first test series the system was allowed to cool down before each shutdown. During the second test series the system was stopped while still hot. For fuels with physical and chemical properties similar to those of neat sunflower oil, excessive residue on the internal surfaces of the injection nozzles is likely to occur with the ultimate result of complete needle immobility.

The development of a fuel-air injection nozzle that injects a premixed fuel and air and then a quantity of clean air into the combustion chamber is described. The new injection nozzle provides better controllability of fuel-air mixing and fuel evaporation. Additionally, the clean air injection following the fuel-air mixture injection prevents stagnant fuel accumulations in the nozzle tip. Therefore, the fuel-air injection nozzle is of particular advantage for use with difficult fuels such as plant oils for long term operation. The fuel-air injection nozzle was tested in an engine running on sunflower oil giving significant reduction in carbon buildup. No engine modifications were necessary for the fuel-air injection nozzle installation.

An unmodified, direct-injected diesel engine was operated on diesel fuel and three blends of diesel fuel and sunflower oil. Heating of the fuels was used to change their viscosities. At normal fuel temperatures, specific fuel consumption and smoke emission increased for any power as sunflower oil content increased. Overall efficiency and exhaust temperature showed virtually no changes with fuel composition. Increasing fuel temperature caused a shift of best overall efficiency from high to low speeds, the magnitude of the shift depending on the plant oil concentration of the fuel. Thus fuel heating as a means of viscosity control may result in an efficiency penalty in the normal operating range of an engine. Typical plant oil induced engine contaminations such as wet stacking, excessive carbon accumulations, nozzle orifice blocking, and lubrication oil gelling were experienced.

The effect of temperature on the rate of lacquer deposit formation from neat sunflower oil on the needles of fuel injection nozzles was investigated. Boson fuel injection nozzles were tested on a fuel injection calibration stand. A pneumatic leak test was developed to monitor the needle clearance reduction due to deposit buildup. For fuels with physical and chemical properties similar to those of neat sunflower oil, excessive residue on the internal surfaces of the injection nozzles is likely to occur with the ultimate result of complete needle immobility. The rate of the lacquer buildup on the needle increases with temperature. Prior to final needle sticking, delay in start of injection, sluggish needle lift, increases in duration of injection, maximum, final residual, and maximum residual line pressures, and decrease in maximum needle lift can be observed. Based on the obtained results, the temperature of injection nozzles handling plant oil fuels should be kept as low as possible.