Q & A > Question Details
When you have a scenario of low sulfur diesel (50 ppm), what is the impact of Diesel viscosity at 40°C on vehicle emissions?
19/06/2012 A: keith bowers, B and B Consulting, kebowers47@gmail.com
Viscosity (at 40C) of a 'low sulfur diesel stream is not a factor in vehicle emissions 'except' that more viscous molecules are more likely to be complex hetero-aromatics with sulfur atoms 'hidden inside' which are nearly impossible to remove except by 'ring opening' hydro-treating/hydro-cracking- and because they ARE more complex, they burn much more slowly than naphthenes and paraffins. Hydrocarbon emissions, primarily as 'soot' , from diesel engines ARE potentially adversely effected by higher fuel viscosity. 'Diesel Index, Cetane Index, and Cetane Number ( measured on the ASTM CETANE Engine) are all indicators of how long it takes for the injected fuel spray to ignite and start burning. More viscous fuel would TEND to have a longer 'ignition delay' (due to both molecular types and the injected fuel droplet size) which would tend to result in higher amounts of soot emissions.
Actual soot emissions of a fuel are very highly engine specific. Older 'legacy' diesel engines emit much more soot than modern 'ultra-high pressure (>25,000 psig) computer controlled fuel rail injection system' engines.