Characterizing ultrafine particles emissions from a heavy duty CNG engine through endurance tests

Paper #:
  • 2017-01-0778

  • 2017-03-28
In the light of major research work carried out on the detrimental health impacts of ultrafine particles (<50 nm), Euro VI emission standards incorporate a limit on particle number, of which ultrafine particles is the dominant contributor. With large reserves of natural gas available together with lesser fuel costs and emission impact, there has been a steady increase in the number of CNG vehicles on road .Considering the fact that CNG is a neat fuel, the dominant contributor toward particle emissions is due to combustion of the lubricant. The oil transport mechanisms into the combustion chamber vary with engine operating conditions as well as with the physico chemical properties of the lubricant. The present study investigates the mechanism of nucleation, effect of oil viscosity & ageing on the size as well as particle number concentration on a heavy duty 230hp Cummins gas engine. Endurance tests of 150 hrs duration each, using lubricants of two different viscometrics (20W-50 & 15W-40) were conducted in order to differentiate the nature of ultrafine particle emissions. Particle size distribution is measured using Engine Exhaust Particle Sizing Spectrometer (TSI EEPS Model 3090).Data is analyzed on a 50 hr interval for both the lubricants.GMD values for Oil A indicate a steady decline in particle diameter with a corresponding increase in surface area at the end of 150 hrs thereby showing a higher rate of nucleation .GMD values for Oil B indicate a decrease in surface area with oil ageing. A comparative study between the particle concentration and surface area reveal 2 major pathway mechanisms for generation of nano-particle vis-à-vis gas to particle conversion and adsorption of volatile particles on core nuclei. Exhaust particle morphology was analyzed using TEM/SEM and it was found that the core nuclei are metals (sourced from lubricant additive & engine wear) around which the volatile matter congregate. The size range of the core nuclei varies for the two lubricants and the rate of nucleation is found to be very sensitive to the exhaust flow conditions. The study underlines the importance of a concerted lubricant formulation, in cylinder combustion and after treatment strategy to counter the ultrafine particle emissions from gas fueled engines
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