การสันดาบแบบเมโสของเชื้อเพลิงเหลว

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The purpose of this project was to lay the foundations to design, build and test a meso scale combustor. A conference paper about this work was presented at the MIER 2013 conference while a journal paper has been submitted to the Chiang Mai University Journal on Natural Sciences and after having gone through several revisions is currently awaiting publication. A meso combustion system is a system capable of burning gasoline or other liquid fuel within a range of flow rates between 10 – 70 mg/sec. The reason for this is to provide future power for small portable devices in the 100 – 1000 W range. This is more power than most portable batteries can deliver but less power than small internal combustion engines. If such a product existed, the list of uses for such a product is quite extensive but not limited to: ? Power/electricity for homes in remote regions ? Power for billboards or signs in remote regions ? Portable power for military applications, powering soldiers communication devices ? Auxiliary power in automobiles, power for the DVD player, AC …etc ? Power for telecom cabinets in remote areas ? Traffic light power or road lighting in remote regions ? Clean, low emission start up for vehicles It was the purpose of this proposal to lay the foundation for a meso scale power device that can deliver power, cleanly, inexpensively and reliably. The first step was to develop a method of delivering power to it by vaporizing liquid fuel in small quantities. The primary source of this power was intended initially to be gasoline. The combustion should be continuous and not intermittent making it cleaner than an automobile engine thus suitable for indoor use. Sterling engines and Tesla turbine are two potential energy conversion devices that could potentially use this heat to produce work output. ง In order to combust this flow rate of fuel an experiment outline and an initial design of a novel vaporizer was prepared. The first step of this project involved mapping out the performance of a novel low flow, efficient flow blurring nozzle initially developed by Alfonso. This has the potential to be ideally suited to meso scale applications because it can supposedly overcome the high flow rate problems of plain nozzles and also the complexity problems of the electrostatic nozzle. The purpose of this research was to fully understand the performance of the nozzle and then implement its design into various meso power applications. Table 1 provides a summary of previous research and shows that the combination of fuel and air is different for this project than anything other previous research. Researchers Nozzle Type Combustion (Yes/No) Fuel Flow Rate (ml/min) Air/Fuel Ratio Sadasivuni et al. Flow Blurring Yes 0.3 16 < AF < 21 Kyritsis et al. Electrostatic Yes 0.23 5 < AF < 11 Alfonso Flow Blurring No 20 0.5 < AF < 90 Benjamin et al. Flow Blurring No 40 1 < AF < 4 Nguyen et al. Air Blast No 0.6 0.25 < AF < 1.5 This Project Flow Blurring Yes 10 1 < AF < 4 Table 1: Summary of Previous Research It was the goal of this research to test the suitability of this new injector type. It is desired to have an air/fuel ratio greater than 16 and a fuel flow rate of magnitude 10ml/min. This has never been done before with a burning mixture. In previous research, either the fuel flow rate is an order of magnitude lower or else the vaporization occurs without any combustion. An experiment was set up with the capability to deliver air and fuel to a nozzle head. The gap between the nozzle head and the fuel supply tube had the capability to be moved to within 10?m. Adjusting the gap distance and the fuel/air ratio whilst combustion occurred led to a set of results. จ Some of the positive results from this project were: 1) The first one is that the nozzle produced a flame within the meso-flow regime (10 – 70 mg/sec) that is of interest 2) The second is that this flame is stable and constant within a certain air flow range and gap size The negative aspects are as follows: ? The special flow blurring regime was not observed. This should have been a cleaner, stable, blue flame with this regime but the nozzle acted as a regular internal two fluid spray nozzle. ? The air flow rate into the nozzle head was too low for stoichiometric combustion. It was so low that the nozzle, in its present form, cannot be used in a closed combustion system without additional air supply. Increasing the air mass flow rate resulted increased the exit jet velocity and resulted in an unstable flame. Even with increasing nozzle geometry, the air velocity was too great for stability. ? The stable flames produced were not small, blue efficient flames but were yellow in color. They also had some soot visible at the flame ends. This usually signifies insufficient oxygen for a complete combustion reaction. There are several possible explanations for not observing a change in combustion when the nozzle enters the flow blurring regime: a. At these low flow rates the efficiency improvement in the flow blurring nozzle is small and may be not observable b. Even if the efficiency improvement was higher it may still not be possible to observe it by looking at the combustion flame c. Flow blurring only occurs at the higher air mass flow rates that produce liftoff and flame instability There are some conclusions that can be drawn from this research and some of the lessons learned are: ฉ I. If a meso scale combustion chamber is to be built around the flow blurring injector then two separate air streams are needed. One high pressure, low flow rate through the flow blurring nozzle and another low pressure, high flow rate to provide the combustion air. II. Any fuel flow rate greater than 1500W produces a large, 30cm, flame that requires a large combustion chamber. III. For the range of air flow that provides stable combustion the flow blurring injector does not operate in it most efficient region. If it is operated in its efficient regions the flame produced is unstable. IV. This may mean that the vaporization and combustion should occur in two separate stages. The fuel is first vaporized at high flow rates and then slowed down in a diffuser before entering the combustion chamber. This adds complexity to the overall design but is the approach taken by other researchers who have actually combusted the mixture. In short, there is a lot of extra work left to do. Presently, this nozzle cannot to be used in small power conversion devices, which is the ultimate end use for this project. More work needs to be done on different designs and operating parameters to get a working flow blurring nozzle. This research points to designs that are more complex for meso scale combustion devices than was originally envisioned. The author does not wish to give up on this line of research yet and hopefully if the complexity of the meso combustion devices is achievable then there is still opportunities for their practical use.

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