Search Results

The current study was focused on flow field measurements of diesel sprays. The global fuel spray characteristics, such as spray penetration, have also been measured. Particle Image Velocimetry (PIV) was utilized for flow field measurements and the global spray characteristics were recorded with high-speed back light photographing. The flow field was scanned to get an idea of the compatibility of PIV technique applied to dense and high velocity sprays. It is well proven that the PIV technique can be utilized at areas of low number density of droplets, but the center of the spray is way beyond the ideal PIV measurement conditions. The depth at which accurate flow field information can be gathered was paid attention to.

Three-dimensional diesel engine combustion simulations with single-step chemistry have been compared with two-step and three-step chemistry by means of the Laminar and Turbulent Characteristic Time Combustion model using the Star-CD program. The second reaction describes the oxidation of CO and the third reaction describes the combustion of H2. The comparisons have been performed for two heavy-duty diesel engines. The two-step chemistry was investigated for a purely kinetically controlled, for a mixing limited and for a combination of kinetically and mixing limited oxidation. For the latter case, two different descriptions of the laminar reaction rates were also tested. The best agreement with the experimental cylinder pressure has been achieved with the three-step mechanism but the differences with respect to the two-step and single-step reactions were small.

Non-evaporating diesel sprays have been simulated utilizing the ETAB and the WAVE atomization and breakup models and have been compared with experimental data. The experimental penetrations and widths were determined from back-lit spray images and the droplet sizes have been measured by means of a Malvern particle sizer. The model evaluation criteria include the spray penetration, the spray width and the local droplet size. The comparisons have been performed for variations of the injection pressure, the gas density and the fuel viscosity. The fuel nozzle exit velocities used in the simulations have been computed with a special code that considers the effect of in-nozzle cavitation. The simulations showed good overall agreement with experimental data. However, the capabilities of the models to predict the droplet size for different fuels could be improved.

The objective of this paper is to analyse the performance and the combustion of a large-bore single-cylinder medium speed engine running with hydrotreated vegetable oil. This fuel has a paraffinic chemical structure and high Cetane number. These features enable achievement of complete and clean combustion with different engine setups. The main benefits are thus lower soot and nitrogen oxides emissions compared to diesel fuel. The facility used in this study is a research engine, where the conditions upstream the machine, the valve timing and the injection parameters are fully adjustable. In fact, the boundary conditions upstream and downstream the engine are freely controlled by a separated supply air plant and by a throttle valve, located at the end of the exhaust pipe. The injection system is common-rail: rail pressure, injection timing and duration are completely adjustable.

Soot modeling has become increasingly important as diesel engine manufacturers are faced with constantly tightening soot emission limits. As such the accuracy of the soot models used is more and more important but at the same time 3-D CFD engine studies require models that are computationally not too demanding. In this study, soot Phi-T maps created with detailed chemistry code have been used to develop a soot model for engineering purposes. The proposed soot model was first validated against detailed chemistry results in premixed laminar environment. As turbulence in engines is of major importance, it was taken into account in the soot oxidation part of the model with the laminar and turbulent characteristic time- type of approach. Finally, the model was tested in a large bore Diesel engine with varying loads. Within the steps described above, the proposed model was also compared with the well-known Hiroyasu-Magnussen soot model.

Hydrotreating of vegetable oils or animal fats is an alternative process to esterification for producing biobased diesel fuels. Hydrotreated products are also called renewable diesel fuels. Hydrotreated vegetable oils (HVO) do not have the detrimental effects of ester-type biodiesel fuels, like increased NOx emission, deposit formation, storage stability problems, more rapid aging of engine oil or poor cold properties. HVOs are straight chain paraffinic hydrocarbons that are free of aromatics, oxygen and sulfur and have high cetane numbers. In this paper, NOx - particulate emission trade-off and NOx - fuel consumption trade-off are studied using different fuel injection timings in a turbocharged charge air cooled common rail heavy duty diesel engine. Tested fuels were sulfur free diesel fuel, neat HVO, and a 30% HVO + 70% diesel fuel blend. The study shows that there is potential for optimizing engine settings together with enhanced fuel composition.