No abstract

While extensive research has been done on improving diesel engines, much less has been done on auxiliary heaters, which have their own design challenges. The study analyzes how to optimize the combustion performance of an auxiliary heater, a 6 kW diesel burner, by investigating key parameters affecting diesel combustion and their properties. A model of a small diesel heater, including a simulation of fuel injection and combustion process, was developed step-wise and verified against experimental results that can be used for scaling up to 25 kW heaters. The model was successfully applied to the burner, predicting the burner performance in comparison with experimental results. Three main variables were identified as important for the design. First, it was concluded that the distance from the ring cone to the nozzle is essential for the fluid dynamics and flame location, and that the ring cone should be moved closer to the nozzle for optimal performance. Second, the design of the swirl co-flow is important, and the swirl number of the inlet air should be kept above 0.6 to stabilize the flame location for the present burner design. Finally, the importance of the nozzle diameter to avoid divergent particle vaporization was pointed out.

There is global interest in utilization of biomass energy through thermochemical processes such as gasification. The crucial step in many gasification processes is the upgrading of the produced gas, removing for example problematic components, such as tar, preferably with a flexible solution that adapts to several feedstock compositions, gasification technologies, and conditions. The present work focuses on the underpinning modeling for the development of a burner for partial combustion in an autothermal tar reformer. A design and modeling study considering the effect of the burner geometry and inlet locations on flame stability was performed. The model and the constructed burner is verified and validated against experimental results, displaying a successful operation of the combustion zone, verifying and validating the developed model against specific requirements. The verified model was finally applied for an extended process window.

The formation of soot in a swirling flow is investigated experimentally and numerically in the context of biogas combustion using a CO 2 -diluted methane/oxygen flame. Visualization of the swirling flow field and characterization of the burner geometry is obtained through PIV measurements. The soot particle size distributions under different fuel concentrations and swirling conditions are measured, revealing an overall reduction of soot concentration and smaller particle sizes with increasing swirling intensities and leaner flames. An axisymmetric two-dimensional CFD model, including a detailed combustion reaction mechanism and soot formation submodel, was implemented using a commercial computational fluid dynamics (CFD) code (Ansys Fluent). The results are compared with the experiments, with similar trends observed for the soot size distribution under fuel-lean conditions. However, the model is not accurate enough to capture soot formation in fuel-rich combustion cases. In general, soot particle sizes from the model are much smaller than those observed in the experiments, with possible reasons being the inappropriate modeling in Fluent of governing mechanisms for soot agglomeration, growth, and oxidation for CH 4 -CO 2 mixtures.