Optical investigations of alternative fuel combustion in common rail compression ignition engine

The increasing global energy demand and the decreasing fossil-energy resources are enhancing the interest in the combustion characteristics of alternative fuels for diesel engines. Alternative-fuel combustion has been studied in detail in light-duty diesel engines, even if the comparison of test results from different chemical nature fuels obtained by integrated optical methodologies is lacking. Thus, it is the primary objective of the present study to characterize the combustion of selected alternative fuels in an optical common rail compression ignition engine by high-speed luminescence imaging and natural emission spectroscopy. The effects of the fuels on in-cylinder spray combustion and soot formation were investigated through UV-visible digital imaging and natural emission spectroscopy. Experiments were performed in a single cylinder high swirl compression ignition engine. The test engine was optically accessible and equipped with a common rail multi-jets injection system. Several injection pressures and timings at two EGR rates were tested. Digital imaging allowed characterizing the evaporating spray and the combustion process. UV-visible emission spectroscopy was used to follow the evolution of the combustion process chemical markers. Chemiluminescence signal due to OH was identified. The soot spectral feature in the visible wavelength range was correlated to soot engine out emissions. Conventional and optical data related to diesel fuel blended with gasoline and butanol were compared