Challenge

The Lane Regional Air Protection Agency (LRAPA) located in Springfield, Oregon, is dedicated to protecting public health, quality of life and the environment as a leader and advocate for the continuous improvement of air quality in Lane County. One of its duties includes reducing emissions produced by school buses in the county. When LRAPA was granted an award through the US EPA’s Clean School Bus USA Program, they began researching solutions for emissions reduction that wouldn’t increase expenses or maintenance requirements.

The Clean School Bus USA program was created by the EPA to reduce air pollution from school buses and lessen children's exposure to diesel exhaust. Children’s exposure to harmful emissions is significant, with approximately 24 million American children spending an average of 90 minutes in a school bus every day. Additionally, school buses drive more than four billion miles each year, creating a considerable amount of air pollution, including particulate matter (PM), oxides of nitrogen (NOx), carbon moNOxide (CO) and unburned hydrocarbons (HC).

The challenge in providing PM reduction solutions for most school bus applications is the need to compensate for low-temperature exhaust. In low exhaust temperature applications, when high-temperature self-cleaning is not possible, soot is collected in filters, causing increased backpressure and lower fuel efficiency. As a result, filters must be cleaned manually, requiring buses to be removed from service for unscheduled maintenance.

In order to meet the requirements of the EPA’s Clean School Bus USA Program, LRAPA sought an EPA ETV-verified solution that provided the benefits of reduced PM for children and bus operators, without increasing the maintenance schedule. To accomplish this, they turned to Clean Diesel for the solution.  

Solution

While a challenge to most wall-flow DPFs, this is an ideal application for Clean Diesel’s Purifier e3. Purifier e3 is a durable filter solution that provides emissions reduction in low exhaust temperatures. In addition to PM, CO and HC reductions, Purifier e3 lowers NOx emissions, with no increase in NO2.

      
Purifier e3 EPA
ETV-Verified Reductions:
   
PM 76%
CO 66%
HC 89%
NOx 9%

With the assistance of Northside Trucks & Equipment of Portland, Oregon, five systems were installed during spring break in March, 2006. Each installation included a monitoring system set up to give the operator a warning signal when backpressure reached 3 psi and a stop signal when backpressure exceeded 3.5 psi.

As of July 2008, each bus had been driven more than 30,000 miles, with none of the devices requiring removal for cleaning. Furthermore, data monitoring showed that none of the buses reached a backpressure of 3.5 psi and rarely exceeded the 3.0 psi warning value. The few times it exceeded 3.0 psi, the fleet manager instructed the drivers to simply drive the bus up a steep hill. This process generated temperatures high enough to cause regeneration of the filter, without the need to remove it for cleaning. In addition, buses drivers noted a visible reduction of  exhaust smoke.

Backpressure and Temperature for Bus #15