M.S. in Chemical Engineering
Henry M. Rowan College of Engineering
Hesketh, Robert P.
Bhatia, Krishnan K.
Diesel motor exhaust gas; School buses
This thesis evaluated the contributions of school bus self pollution from both the crankcase and the tailpipe emissions to in-cabin levels of fine and ultrafine particulate matter, and determined the effectiveness of commercially available retrofit technologies towards reducing levels of particulate matter inside the school bus passenger compartment. Mobile tests were conducted with a school bus powered by an International DT466E engine on an outdoor test track. Measurements of fine and ultrafine particle concentrations within the cabin of a school bus were performed with and without retrofit technologies.
The tests utilized a drive cycle using data from actual school bus routes. In-cabin particulate matter concentrations were measured using three Thermo Electron DataRAM- 4 units, and three TSI P-Trak ultrafine particle counters. Tailpipe gaseous emissions, as well as engine parameters were measured using the Sensors SEMTECH-D system. Tests were conducted using the original school bus configuration without installed retrofit technology, a single retrofit technology and combinations of a closed crankcase ventilation system (CCVS) and a tailpipe retrofit. The two tailpipe retrofits tested included a Diesel Particulate Filter (DPF) and a Flow Through Filter (FTF). All the tests were performed using ultra-low sulfur diesel fuel. At minimum three runs were completed for each test configuration.
This thesis presents the results of two studies. The initial study was conducted using a bus that had several leaks through faulty seals in the bus. A total of 69 runs were conducted in this initial study. In the final study 19 runs were conducted with the same bus after sealing the leaks and establishing a new testing protocol.
An analysis of variance was conducted on the results to determine statistical difference among technologies. It was found that operating the bus with the windows open resulted in low concentrations of particulate matter in the cabin of the bus. Operating the bus with the windows closed resulted in higher particulate matter concentrations in the cabin of the bus compared to the particulate matter concentrations in the ambient air outside of the bus. This study confirmed that the use of tailpipe retrofit technologies resulted in large emission reductions of gaseous pollutants normally emitted from the tailpipe. All tailpipe retrofit technologies reduced CO approximately 50-65% and hydrocarbons were reduced by approximately 92 to 97%.
It was found that three retrofit technology combinations reduce in-cabin net PM2.5 mass concentrations. The most effective technology was the combined DPF and CCVS. The results from the final study show that if only a DPF was used then it was 70% as effective as the combined DPF and CCVS. If the combination of FTF and CCVS were employed then this retrofit was approximately 50% as effective as the combined DPF-CCVS retrofit technology. The CCVS with no tailpipe retrofit was approximately 30% as effective as the DPF-CCVS.
In-cabin net ultrafine particle concentrations as measured by the P-Trak decreased with increasing engine oil temperature. From the analysis of the ultrafine data as a function of engine oil temperature it was determined that the use of a CCVS reduces the particle count concentrations from 50 to over 100% compared to the cases without the CCVS. The DPF or FTF used without a CCVS did not significantly reduce in-cabin net ultrafines concentrations. This study gives evidence that a major source of ultrafines into the school bus is from the crankcase vent.
Martinez-Morett, David, "Diesel particulate matter quantification and reduction strategies for school buses" (2009). Theses and Dissertations. 645.