EXPERIMENTAL INVESTIGATION OF HCCI COMBUSTION PROCESS WHEN USING BIOETHANOL

Abstract

HCCI combustion has the potential to be highly efficient and to produce low emissions. HCCI engines can have efficiencies as high as compression-ignition, direct-injection engines, while producing ultra-low oxides of nitrogen and particulate matter emissions. But this process is difficult to keep under control by changing engine load and speed. The effects of intake air temperature and mixture concentration on HCCI combustion characteristics and emissions were analyzed in this paper. The bioethanol – air mixtures start burning probably when air temperature is 100 0C and λ = 1.9. When air-fuel ratio is more or less than 1.9, the start of combustion occurs later. At λ = 2.4, the start of combustion takes place at TDC. When operating at λ > 1.74, the knocking burning was observed. The higher temperature of the combustible mixture before compression stroke gives higher heat release rate and cylinder pressure data. At the temperature of 100 and 120 oC the heat release rate was 107,3 and 201,0 kJ/(m3 deg). The cylinder pressure was equal to 53,3 and 60,9 bar. At low combustion temperature NOx emissions are not high. When oxidation reaction is stable, NOx emission at many measurement points was not higher than 10 ppm. But at higher relative air/fuel ratio the NOx emission increased to 74 ppm. The reason of this result was the knocking combustion. The low temperature reaction increases the CO and CH emissions. The minimum of CO and HC emissions was 512 and 660 ppm. Smoke opacity was < 3,5 %.