The internal combustion engine with compression ignition is still the most important power plant for heavy duty transport, railway transport, marine applications and generator sets. Fuel cost and emission regulations drive manufacturers to switch to alternative fuels. The understanding and prediction of these fuels in the spray and combustion process will be very important for these issues. In the past, lot of research was done for conventional diesel fuel by optically analyzing both spray and combustion. However comparison between different groups is difficult since qualitative results and accuracies are depending in the used definitions and methods. The goal of present research is to verify the behavior pure oils compared to more standard fuels while paying lot of attention to the interpretation of the measurement results.
Spray formation from a pump-line-nozzle diesel fuel injection system through a multi-hole injector, used for medium speed applications, is studied in an optically accessible constant volume combustion chamber using digital high speed shadowgraphy. A nitrogen atmosphere up to 80bar and 150°C was used for the non-reacting injection environment. This work compares non-evaporating sprays of diesel, rapeseed methyl-ester and rapeseed oil. In the first part the acquisition and processing of the optical measurements is evaluated and discussed in detail: results might differ depending on the used techniques which makes it not straight forward comparing results from other authors. The difficulty of image interpretation as well as the high standard deviation of the obtained results is pointed out. A second part discusses the influence of the fuel on the fuel injection system. Finally, the comparison for the different fuels is made between the different spray parameters for non-evaporating sprays, such as spray angle and penetration. It was found that the higher viscosity and bulk modulus of the oil significantly increases the injection pressure, shortens the injection delay and reduces the atomization. The spray angle and penetration progress approximately stayed the same at the later stage of the injection. The spray structure however differs for the highly viscous oil, suggesting that another parameter to characterize the spray is required.