RESUMO
Carbon based metallic additives were widely researched to improve combustion charecteristics of spark ignition and compression ignition engines. It was proven that carbon nanotube additive shortens ignition delay period and improves combustion characteristics especially in diesel engines. HCCI is a lean burn combustion mode which provides high thermal efficiency and simultaneously low NOx and soot emission. However it has drawbacks such as misfire at leaner mixtures and knocking at high loads. Carbon nanotube could be used to improve combustion for HCCI engines as well. The aim of this study is to investigate the effects of multi-walled carbon nanotube addition to ethanol and n-heptane blends on HCCI engine performance, combustion and emission by experimentally and statistically. During the experiments, the mixed fuels formed with %25 ethanol, %75 n-heptane and 100, 150 and 200 ppm MWCNT additives were used. The experiment of these mixed fuels was carried out at different lambda and engine speed values. Response Surface Method was implemented to determine optimal additive amount and operation parameters of the engine. The variable parameter values to be used in the experiments were created with the central composite design, and a total of 20 experiments were performed. According to the obtained results, IMEP, ITE, BSFC, MPRR, COVimep, SOC, CA50, CO and HC response parameter values were obtained. Response parameter values were entered into the RSM environment and optimization studies were carried out depending on the response parameters targets. Among the optimum variable parameter values, the MWCNT ratio was determined as 102.16 ppm, lambda 2.7 and engine speed 1124.439 rpm. Response parameter values after optimization were determined as IMEP 4.988 bar, ITE 45.988 %, BSFC 227.846 g/kWh, MPRR 2.544 bar/CA, COVimep 1.722 %, SOC 4.445 CA, CA50 7 CA, CO 0.073 % and HC 476.452 ppm.