Optical Analysis of Combustion and Soot Formation in a CI Engine Fuelled with Water in Diesel Emulsion through Microchannels Emulsification

Water in diesel emulsion (WiDE) is a viable solution for lowering both NOx and
Soot emissions from compression ignition (CI) engines. In this paper, the effect of WiDE on
the combustion process and exhaust emissions of a prototype optically accessible CI engine
was investigated through conventional in-cylinder pressure measurements and optical
diagnostics. The emulsion (9.1%v of water) was produced through a prototype designed
microchannels emulsifier with a small amount of nonionic surfactant. Commercial diesel was
set as reference fuel and compared to WiDE. The start of injection (SOI) was swept from 8 to
23 CAD BTDC. For diesel fuel, the injected mass and injection pressure were representative of
a medium load regime, WiDE injection interval was adjusted to keep constant the energy
content. Compared to Diesel, WiDE induced an increase in ignition time, enhancing the
air/fuel mixing with a simultaneous reduction in PM and NOx. 2D chemiluminescent emission
measurements highlighted a reduction in soot formation using WiDE, without significant
changes in soot oxidation rate.