The influence of atomizing media on the quality of the combustion of liquid fuels

Abstract

The aim of the work was to experimentally investigate the influence of atomizing medium on combustion properties of methyl-ester of rapeseed oil. Reserves of the fossil fuels are decreasing every day. This is the reason why the huge effort is devoted to finding out an alternative fuel to fulfil the energy demand of the world. Methyl-ester of rapeseed oil is one of the best available sources. The experiments were carried out in a watercooled horizontal combustion chamber. The pneumatic atomization using the effervescent atomizer was used for tests. Compressed air and superheated steam were chosen as the atomizing media. The tests were performed at three levels of the gas-to-liquid (mass flow rate) ratio (GLR), namely 15, 20 and 25 %. The experiments were focused on the investigation of flame characteristics, quality of combustion, NOx and CO emissions, temperature of flue gas, heat transfer and stability of combustion. Results revealed that the heat transfer was higher for about 6 % when the compressed air was used for the oil atomization. This is most likely caused by the exothermic reaction between the fuel and compressed air (air is the reactant, steam is the inert). On the other hand, the atomization by compressed air led to higher NOx emissions due to higher in-flame temperatures. The distribution of heat fluxes along the flame was very similar for both atomizing media. Combustion was observed stable without pulsation and fuel deposition at the bottom of the combustion chamber for all settings. The flue gas temperature was higher for about 20 °C during the atomization by the compressed air (compressed air - 653 °C, superheated steam - 635 °C). As for the flame characteristics, increasing GLR caused the reduction of the flame length and "sharper" flame.