Combustion Instability during Starting of Turbocharged Diesel Engine Including Biofuel Effects

Abstract

A series of starting tests was conducted on a turbocharged diesel engine to investigate combustion instability for various coolant temperatures, ranging from 20 to 80°C, and fuel blends (neat diesel, blend of diesel with 30% biodiesel, and blend of diesel with 25% n-butanol). A statistical analysis was performed in order to quantify the effects of the coolant temperature and fuel properties on the extent of the instability phenomena. As expected, the engine thermal status was found to play an influencing role, with cold starting leading to combustion instability; a difference up to 38 bar between successive cycles was documented. The biodiesel blend exhibited higher instability and the n-butanol one showed higher absolute pressures but somewhat more stable operation. Both biofuel blends led to higher in-cylinder pressure irregularities compared to the neat diesel operation. For all examined blends, instability phenomena were still apparent even after several seconds from the engine start-up.