INFLUENCE OF INTAKE AIR TEMPERATURE AND EXHAUST GAS RECIRCULATION ON HCCI COMBUSTION PROCESS USING BIOETHANOL

The combustion process and exhaust gas emission inside an internal combustion engine are adamantly dependent on the composition of the mixture and method of preparation. Better energy use results are obtained when the air-fuel mixture ignites spontaneously by increasing the temperature inside the cylinder. But in HCCI (homogeneous charge compression ignition) engines, the mixture is prepared outside the cylinder, and it is hard to control the process. The paper presents the thermodynamic characteristics of homogeneous air-bioethanol mixtures on HCCI engines performance. The experiment was carried out by changing the intake air temperature, exhaust gas recirculation and mixture composition. When the intake air was preheated up to 100 degrees C, and the relative air-fuel ratio (lambda) was 1.9, the air-bioethanol mixture started burning earlier. When the relative air-fuel ratio was higher or lower, the combustion started later. Stable burning was fixed in the range of lambda = 2.18-4.28, when the intake air temperature was 120 degrees C. The heat release rate and cylinder pressure were proportional to the temperature of air-bioethanol mixture. The heat release rate was 107.3 and 201 kJ. (m(3) CAD)-1 (CAD-crank angle degrees), and the cylinder pressure was 53.3 and 60.9 bar at a mixture temperature of 100 and 120 degrees C, respectively. The combustion temperature on HCCI engines was low due to small quantities of nitrogen oxides. During this experiment, the amount of NOx (nitrogen oxides) of many measurement points was not higher than 10 ppm. But with richer mixtures, the amount of NOx increased up to 74 ppm. The lowest quantity of CO (carbon monoxide) and HC (hydrocarbon) realized was 0.05 % and 0.06 %.