Combustion process investigations in a high speed diesel engine fuelled with n-butanol diesel blend by conventional methods and optical diagnostics

The use of alternative fuels, as biodiesel and ethanol, for light duty CI engines to approach the target of ultra low NOx and PM emissions without fuel economy penalty has been widely investigated. Recently it is growing the interest in the butanol as a viable alternative either single or blended with conventional based fuels both to reduce the demand for fossil fuel and to reduce emissions of particulate matter without significantly increasing NOx. In this paper, butanol effects on combustion processes were investigated through conventional methods and optical diagnostics. First, blends of diesel and n-butanol were used in a common rail DI diesel engine running at different operating conditions. Exploration management of the timing and injection pressure were carried out to achieve conditions in which the almost total amount of fuel was delivered before ignition. This experimental activity was performed on a four cylinder, turbocharged, water cooled, DI diesel engine, equipped with a common rail injection system. Successively, the blends effects on combustion process were studied in the combustion chamber of a single cylinder compression ignition engine equipped with the same common rail multi-jets injection system. Spray combustion and pollutant formation were investigated by UV-visible digital imaging and natural emission spectroscopy. UV-visible emission spectroscopy was used for the detection of the chemical markers of combustion process. Chemiluminescence signals, due to OH, HCO and CO2 emission bands were detected. OH emission was correlated to NO measured at the exhaust. The soot spectral feature in the visible wavelength range was related to the engine out soot emissions.