EXPERIMENTAL INVESTIGATION OF HCCI COMBUSTION PROCESS WHEN USING BIOETHANOL

HCCI combustion has the potential to be highly efficient and to produce low emissions. HCCI engines can have efficiencies as high as compression-ignition, di-rect-injection  engines,  while  producing  ultra-low  oxides  of  nitrogen  and  particulate matter emissions. But this process is difficult to keep under control by changing en-gine 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 0 C and λ = 1.9. When air-fuel ratio is more or less than 1.9, the start of com-bustion 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 o C the heat release rate was 107,3 and 201,0 kJ/(m3 deg). The cyl-inder 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 reac-tion increases the CO and CH emissions. The minimum of CO and HC emissions was 512 and 660 ppm. Smoke opacity was < 3,5 %.