Challenge

DATTCO’s School Bus Division provides school transportation and charter services to municipalities, school systems, and other public and private organizations. Serving large cities and small towns alike, DATTCO is one of New England's leading school bus operators, providing transport services for 12 school systems and 65,000 school children.

Diesel particulate matter (PM) poses a serious health risk and according to the EPA, aggravates asthma and allergies or can cause other serious health problems including lung cancer. To reduce exposure of harmful emissions exposure to children on school buses in Westport and Plainville, Connecticut, DATTCO installed full-wall DPFs to achieve the highest protection against PM.

However, in low-temperature applications such as this, DPFs quickly collect soot, which causes the cordierite substrate pores to clog. The dry nature of the soot from EGR engines tends to exacerbate this problem, forming a hard carbon cake that only oxidizes at elevated temperatures. As the filter clogs, backpressure continues to rise until the unit is either removed and cleaned or regenerated in place. Until filters are serviced, the increased backpressure results in poor engine performance and lower fuel efficiency, increasing overall fleet operations costs.

Since school bus exhaust does not run hot enough to enable passive regeneration, once the backpressure reached 5-6 psi, DATTCO would remove and bake the filters for six hours to oxidize the entrained soot. Aside from being an energy-consuming and costly process, it also required that buses be removed from service more frequently than desired. Combined with the lower fuel efficiencies and escalating diesel prices, the DPF program became more expensive than originally anticipated.

Alternatively, DATTCO could have deployed an active DPF, whereby diesel fuel is injected in front of the filter and ignited to raise the temperature enough to initiate regeneration. While this does not require removal of the filter for cleaning, active systems run the risk of run-away regeneration, which can cause unacceptable consequences such as significant thermal stress. This in turn can affect substrate integrity and damage the DPF, ultimately shortening the life of the device.

Run-away regeneration also creates the possibility of flames jetting out of school bus exhaust system. In addition, active systems tend to have higher upfront and operating costs, making them less attractive economically.

With passive DPFs installed on the existing Westport and Plainville fleet, DATTCO sought a solution to ease its maintenance issues and operating costs while providing school systems with the healthiest environment for their children.

Solution

Clean Diesel’s Platinum Plus® DFX-DPF fuel-borne catalyst acted as a “problem solver” for DATTCO, ensuring filter performance without increased costs. With a quick, straightforward installation, the buses were equipped with an onboard dosing system to automatically blend Platinum Plus with diesel fuel on the engine intake.

Specifically formulated for use with DPFs, Platinum Plus DFX-DPF delivers benefits at multiple levels.

Complete passive regeneration initiated by loading the engine between 2250-2450 rpm.

A. Typical urban driving with exhaust temperatures ranging between 225-300oC
B. Driving for 15 min at highway speeds increased temperatures to the 300-350oC range and initiated passive low-temperature regeneration
C. Over the course of regeneration, backpressure dropped from a high of 4.5-5.5 psi to 0.5 psi
D. Stable backpressure between 0.5-1.0 psi; after five months of operation, backpressure on the Platinum Plus-treated system remained below 3 psi