Stuart Daw

Physical Properties of Bio-Diesel and Implications for Use of Bio-Diesel in Diesel Engines

In this study we identify components of a typical biodiesel fuel and estimate both their individual and mixed thermo-physical and transport properties. We then use the estimated mixture properties in computational simulations to gauge the extent to which combustion is modified when biodiesel is substituted for conventional diesel fuel. Our simulation studies included both regular diesel combustion (DI) and premixed charge compression ignition (PCCI). Preliminary results indicate that biodiesel ignition is significantly delayed due to slower liquid evaporation, with the effects being more pronounced for DI than PCCI. The lower vapor pressure and higher liquid heat capacity of biodiesel are two key contributors to this slower rate of evaporation. Other physical properties are more similar between the two fuels, and their impacts are not clearly evident in the present study. Future studies of diesel combustion sensitivity to both physical and chemical properties of biodiesel are suggested.

Impact of rail pressure and biodiesel fueling on the particulate morphology and soot nanostructures from a common-rail turbocharged direct injection diesel engine

An investigation of the impact of rail pressure and biodiesel fueling on exhaust particulate agglomerate morphology and primary particle (soot) nanostructure was conducted with a common-rail turbocharged direct injection diesel engine. The engine was operated at steady state on a dynamometer running at moderate speed with both low (30%) and medium–high (60%) fixed loads, and exhaust particulate was sampled for analysis. The fuels used were ultra-low sulfur diesel and its 20% v/v blends with soybean methyl ester biodiesel. Fuel injection occurred in a single event around top dead center at three different injection pressures. Exhaust particulate samples were characterized with transmission electronic microscopy imaging, scanning mobility particle sizing, thermogravimetric analysis, Raman spectroscopy, and X-ray diffraction analysis. Particulate morphology and oxidative reactivity were found to vary significantly with both rail pressure and biodiesel blend level. Higher biodiesel content led to an increase in the primary particle size and oxidative reactivity but had no impact on nanoscale disorder in the as-received samples. For particulates generated with higher injection pressures, the initial oxidative reactivity increased, but there was no detectable correlation with primary particle size or nanoscale disorder.

Experimental analysis and visualization of spatiotemporal patterns in spouted fluidized beds.

A numerical characterization based on experimental data of the spouting regime in a two-dimensional fluidized bed is presented. The aspect ratio of the bed allowed for good visualization of the spouting and solids circulation as the spouting jet gas velocity was varied to highlight the visited bifurcation sequence. Digital video sequences were recorded and then preprocessed for numerical analysis. In this paper, the proper orthogonal decomposition (POD) was applied to these data sets in order to identify and separate the dominant spatial features from the temporal evolution of the spouting dynamics. The results indicate that the overall spatiotemporal dynamics can be captured by a few POD eigenfunctions, and that the POD amplitudes can be used to distinguish between varying degrees of spouting.

Flamedoctor™: Nonlinear Burner Diagnostic System

Utility power plants are employing advanced control systems to improve performance over the load range. The performance of the boiler combustion system is critical to the overall performance. Flame Doctor™, which has been developed by McDermott Technology, Inc. and Oak Ridge National Laboratory under sponsorship of Electric Power Research Institute, performs diagnostics on an individual burner basis. The system consists of analogue‐to‐digital signal conversion and conditioning hardware, analysis software, and a graphical user interface. Time varying voltage signals from all of the burner flame scanners on a boiler are analyzed simultaneously. Nonlinear techniques such as symbolization and time asymmetry along with linear techniques such as power spectral analysis are used. The nonlinear techniques discriminate stability features in the combustion dynamics not possible with the linear techniques alone. The assessments for a variety of flame conditions are collected in a reference library. Libraries have be...

Low‐Order Bubble Model for Bubbling Fluidized Beds — A Case Study of Ozone Decomposition

A dynamical model for bubble behavior in fluidized beds was developed by Daw and Halow [1] based on experimental observations of bubble interactions. The model is a set of nonlinear, ordinary differential equations, each equation representing the time rate of change of the vertical position for a given bubble. This model has been used for near realtime simulation of 3‐D fluidized beds and studied extensively. This agent‐based model has been extended for chemical reactions and ozone decomposition in fluidized beds is reported in this paper. The results from these simulations predict the conversion data of ozone decomposition (Fryer and Potter, 1976). This talk will also discuss the next steps and how this model can be extended to design and control fluidized beds.