According to an article issued by NIOSH’s George Schnakenberg Jr, MSHA approval of an engine does not in itself imply that DPM emissions are low and MSHA approval alone does not ensure that the engine is a “clean” engine. Instead, Schnakenberg advises mines to check the Particulate Index (MSHA) or the g/bhp-hr (EPA) for newly introduced engines.

Many mines are considering repowering or replacing some of their underground fleet as a means to reduce diesel particulate matter (DPM) concentrations in order to comply with the diesel rules. MSHA requires that newly introduced underground diesel powered equipment utilize either MSHA- or EPA Tier 1- or Tier 2-approved diesel engines.

To meet the new regulations the Ventilation Rate (VR) and the Particulate Index (PI) of the engine should be checked to indicate emission performance. VR refers to gaseous emissions and the PI gives the DPM emissions.

“For most modern engines the VR is determined by nitric oxide (NO) emissions, not carbon monoxide (CO) emissions. The PI is the ventilation rate (dilution air quantity) needed to reduce emitted DPM to 1 mg/m3, approximately 2 times the standard for Total Carbon (TC is 80% of DPM). Again many of the MSHA approved engines have a high PI and are to be avoided by selecting instead an engine of the desired horsepower with a low PI,” said Schnakenberg.

Likewise, he advised meeting EPA Tier 1 and Tier 2 certifications does not guarantee low particulate matter emissions.

“The selection strategy for EPA Tier certified engines is to select the one in the horsepower range which has the lowest emission rate in grams/brake horsepower-hour (g/bhp-hr). Additionally, for new engines above 100 hp only those that are Tier 2 should be considered, since Tier 2 is currently applicable to those engines,” he said.

Another variable for DPM emissions that should be taken into account is all certification tests by MSHA and EPA are performed at low elevations. Schnakenberg said recent experience demonstrated EPA certification does not guarantee a limit on emission levels of nitrogen oxides for modern, electronically controlled engines operated at elevation.

He said this finding was being investigated by MSHA, and it is currently unknown at what altitude and for which engines this happens, and what the remedy may be. Additionally a New-Engine Subcommittee of the Coal Diesel Partnership has been formed to mitigate the dearth of engines available for use at elevation in coal mines caused by this issue.