Optical studies of spray development and combustion of water-in-diesel emulsion and microemulsion fuels

Physical properties, spray behaviour and combustion characteristics of a water-in-diesel emulsion, a water-in-diesel microemulsion and a conventional diesel fuel were investigated. The size of the drops, in the water-containing fuels, was measured by NMR diffusometry. Spray development and combustion were studied by optical methods in an optically accessed combustion vessel at conditions similar to those in a diesel engine. High speed shadowgraphs were employed to measure break-up, droplets penetration, vapour penetration and start of combustion. Combustion duration, flame temperature and relative soot concentration were determined by emission-based methods. Differences in spray behaviour suggest an enhanced atomisation for the water-containing fuels compared to regular diesel fuel. Moreover, reduced soot concentrations and flame temperature with increased combustion duration were noticed for the water-in-diesel fuels than for the regular diesel fuel.