Experimental determination of fuel evaporation rates using IR-thermography

Abstract

The scope of the present work is to experimentally investigate the heat and mass transfer phenomena occurring in the case of pure liquid as well as FAME-diesel fuel mixture droplets evaporating in a constant temperature and constant air velocity environment. Experiments have been performed to record the time evolution of droplet diameter and surface temperature. An ultrasonic droplet acoustic levitator has been operated in order to suspend the isolated droplets in air. A fast CCD camera and an infrared camera have been used to record droplet diameters and droplet surface temperatures, respectively. The produced experimental data can be used in the validation of computational and empirical models for single, pure liquid or multicomponent droplet evaporation. Oil fired furnaces and boilers, diesel engines and gas turbines utilize liquid fuel sprays in order to increase the fuel surface area and thus accelerate the vaporization and combustion rates. Conventional technologies, used to burn a liquid fuel, inject the fuel into the combustion chamber through a nozzle that atomises it, producing a spray comprising a large number of droplets, typically of the order of a few tens of micron to a few hundreds of micron in diameter. The droplets, subjected to the high temperatures of the combustion chamber, are evaporated and burnt in a sequential process. In order to study and examine the evaporation behaviour of a spray, one can focus on a single droplet, evaporating in a convective environment. Study of such a case may yield invaluable information for the modelling of the evaporation process. The scope of the present work was to experimentally investigate the heat and mass transfer phenomena occurring in the case of a droplet evaporating in a constant temperature and constant velocity air environment, aiming to the creation of an experimental database useful for the computational modelling of the evaporation process. The experimental device used was an acoustic levitator, which is a valuable tool in order to study the heat and mass transfer phenomena occurring at the surface of an evaporating droplet, since it allows an almost steady “hanging” of the droplet without any mechanical supports. Examined fuels included both pure liquids (decane, ethanol and n-heptane) as well as multicomponent mixtures, consisting of industrial diesel oil (type EL) – FAME (Fatty acid methyl ester) blends. The commercial use of such mixtures (containing FAME up to 20% per volume) is expected to raise in the near future, since FAME are considered renewable energy sources and there is a worldwide trend towards the extension of the application of such fuels.