Characterization of Liquid Fuel Evaporation of a Lifted Methanol Spray Flame in a Vitiated Coflow Burner


Book Description

An experimental investigation of lifted spray flames in a coflow of hot, vitiated gases is presented. The vitiated coflow burner is a spray flame that issues into a coaxial flow of hot combustion products from a lean, premixed H2/Air flame. The spray flame in a vitiated coflow emulates the combustion that occurs in many advanced combustors without the detailed fluid mechanics. Two commercially available laser diagnostic systems are used to characterize the spray flame and to demonstrate the vitiated coflow burner's amenability to optical investigation. The Ensemble Particle Concentration and Size (EPCS) system is used to measure the path-average droplet size distribution and liquid volume fraction at several axial locations while an extractive probe instrument named the Real-time Fuel-air Analyzer (RFA) is used to measure the air to fuel ratio downstream of the spray nozzle with high temporal and spatial resolution. The effect of coflow conditions (stoichiometry) and dilution of the fuel with water was studied with the EPCS optical system. As expected, results show that water retards the evaporation and combustion of fuels. Measurements obtained by the RFA extractive probe show that while the Delavan manufactured nozzle does distribute the fuel over the manufacturer specified spray angle, it unfortunately does not distribute the fuel uniformly, providing conditions that may result in the production of unwanted NOx. Despite some limitations due to the inherent nature of the experimental techniques, the two diagnostics can be readily applied to spray flames in the vitiated coflow environment. Cabra, Ricardo and Dibble, Robert W. and Chen, Jyh-Yuan Glenn Research Center NASA/CR-2002-212083, NAS 1.26:212083, E-13736










Evaporation of Jet Fuels


Book Description

Determining the fate and transport of JP-8 jet fuel is a complex and important problem. As part of the startup procedures for jet engines, fuel is passed through aircraft engines before combustion is initiated. Because of the extremely low temperatures at northern tier Air Force bases, the unburned fuel does not evaporate readily and may come into contact with ground crew. To determine the amount and duration of contaminant contact, the evaporation of the emitted fuel must be modeled. The amount and composition of the fuel upon reaching the ground crew may be determined by droplet evaporation models that have already been developed. The evaporation of the fuel after adhering to the skin needs to be modeled. This knowledge of the fuel's fate may then be used to determine source terms for use in toxicological studies. This research involves the comparison of two existing droplet evaporation models and the calculation of the evaporation of a film of jet fuel from a surface. The existing models are compared in order to make recommendations on which model to use to predict the amount and composition of fuel reaching the ground crew. To make the surface evaporation problem amenable to modeling, simplifying assumptions are made. The fuel is assumed to be a uniformly distributed mixture of representative hydrocarbon groups. Due to the complexity of the mixture of aviation fuels, a mixture of the predominant species were chosen as representatives to approximate the physical behavior of the entire fuel mixture. The goal of this research is to determine the most appropriate model for predicting the amount and composition of jet fuel reaching the ground crew and to extend the more appropriate fuel droplet evaporation model to describe the evaporation of a film of fuel from a surface. A validation of the resultant model is then performed by comparing the calculations to experimental data.







Experimental Investigation of Fuel Vaporization on Combustion Efficiency. Quarterly Progress Report, October-December 1979


Book Description

The initial set of experiments have been performed in the test stand with the basic configuration described in the last progress report. With this experimental set-up, the temperature measurements on the firing tube (and oil evaporation surface) indicated insufficient and a much too low heating rate with the preheat nozzle (0.75 gph). A number of remedies were attempted to increase the gas temperature in the recirculation region around the firing tube. These remedies were intended to increase the flame angle and consisted of various size discs, washers and flame impellers located relative to the nozzle. A qualitative picture of the flow flame-configuration pattern is also shown. These were not successful in increasing the evaporization surface temperature. Moreover sooting was enhanced. To significantly reduce the heat-up time with the preheat nozzle, the contribution from the various heating modes are assessed here. An element of the firing tube and evaporation surface is shown. The various heat transfer modes to this surface with and without vaporization spray are indicated.




Experiments and Numerical Simulations of Turbulent Combustion of Diluted Sprays


Book Description

This book reflects the results of the 2nd and 3rd International Workshops on Turbulent Spray Combustion. The focus is on progress in experiments and numerical simulations for two-phase flows, with emphasis on spray combustion. Knowledge of the dominant phenomena and their interactions allows development of predictive models and their use in combustor and gas turbine design. Experts and young researchers present the state-of-the-art results, report on the latest developments and exchange ideas in the areas of experiments, modelling and simulation of reactive multiphase flows. The first chapter reflects on flame structure, auto-ignition and atomization with reference to well-characterized burners, to be implemented by modellers with relative ease. The second chapter presents an overview of first simulation results on target test cases, developed at the occasion of the 1st International Workshop on Turbulent Spray Combustion. In the third chapter, evaporation rate modelling aspects are covered, while the fourth chapter deals with evaporation effects in the context of flamelet models. In chapter five, LES simulation results are discussed for variable fuel and mass loading. The final chapter discusses PDF modelling of turbulent spray combustion. In short, the contributions in this book are highly valuable for the research community in this field, providing in-depth insight into some of the many aspects of dilute turbulent spray combustion.