Characterization of Ash Emissions from Diesel Engine Combustion


Exhaust ash particles are formed from the non-combustible fraction of diesel aerosol which is derived from metallic lube oil additives and engine wear metals. These metallic particles tend to ‘decorate’ carbonaceous exhaust particles, but may form separate particles at sufficiently high metal to soot ratios. Ash causes build-up and plugging of diesel particulate filters (DPF), resulting in reduced fuel economy and increased cleaning frequency. Ash also deposits in 3-way catalyst leading to poisoning.

We have developed a high temperature oxidization method (HTOM) to measure the ash emissions in real-time. In HTOM, the diesel exhaust is passed through a tube furnace where the soot and hydrocarbons are oxidized. Stable metallic compounds and other refractory metal compounds survive the furnace and are measured using real-time particle instruments. Results suggest significant ash emission during engine transients, both up and down in load and speed.

To reduce ash emissions, lubricant manufacturers face the challenge of producing blends of lube oil that reduce ash production without compromising the efficacy of lubricating oil. Since there is a correlation between ash production and lubricant oil consumption real-time measurement of ash has significant advantages over measuring accumulation of ash in a DPF, which is time consuming and costly.