SCR aces the test
The restyled 2011 Prevost H3-45 turns heads while Volvo powertrain and SCR eases operators’ minds
By David Hubbard
When the Environmental Protection Agency (EPA) imposed its most recent round of heavy-duty diesel emission standards, Volvo chose Selective Catalytic Reduction (SCR) as the technology that most efficiently solved the problem of nitrogen oxides.
Already proven in Europe, Prevost believes the SCR approach combines the best aspects of Exhaust Gas Recirculation (EGR) with a Diesel Particulate Filter (DPF) and selective catalytic reduction to provide the best possible solution, which it says exceeds the 2010 EPA NOx emissions requirements. Volvo says it has over 250,000 vehicles using SCR, which since 2004 have traveled 50 billion proven miles.
The integrated Volvo powertrain takes advantage of the distinctive coordination between the Volvo D13 engine and I-Shift transmission, which Prevost says results in fuel savings and easier service scheduling.
Cosmetic changes to the exterior of the H-Series focus on the sleek redesign at the rear of coach to complement the previous redesign to the front end. New aesthetic touches to the wheel wells also make the 2011 H3-45 more eye-catching.
For added driver comfort as well as passenger safety, the 2011 H3-45 features a new steering wheel with built-in easy-access message center display and radio controls fully integrated through the multiplex electrical architecture.
The new version also offers Prevost AWARE Adaptive Cruise Braking (ACB), which according to Prevost protects drivers and passengers in two ways. First, AWARE helps drivers maintain a safe following distance by sounding an alert if the distance between the coach and the vehicle ahead closes. Second, with cruise control-activated the automatic throttle reduction and brake application assistance acts to help the driver safely slow the vehicle. Adjustable alert settings allow flexibility for varying driving conditions. The ACB system also records and stores valuable driving data for analysis and driver training.
Integrated into the dashboard, the ACB system minimizes driver distraction that can lead to an accident. Prevost says the system also can actually increase fuel efficiency by helping drivers operate in cruise control for a longer period of time.
SCR put to the test
Prevost outfitted two 2010 H3-45s with the EPA 2010 Volvo D13 with SCR technology engine for preliminary testing.
David Annett, president of Annett Bus Lines, Sebring, FL, had the opportunity to put one in service in a three-month trial period this past summer; as did Ugo Barrette, director of Autobus Maheux, Rouyn-Noranda, QB, Canada.
David Annett and his brother, Brian, operate the charter company with a 48-coach fleet that is 100 percent Prevost. Five of the 37 H-Model Prevosts are 2010 models equipped with the EPA 2007 Detroit Diesel engine, purchased as a pre-buy prior to the new engines becoming mandatory.
“We based our decision first of all on cost, but also with the SCR technology being new to us, we were not entirely sure what would happen,” says Annett. “It is natural to wonder.”
Annett put the test coach right alongside the new 2010 models on a number of charters from Florida to Washington, D.C.
“We logged approximately 25,000 miles during this three-month period and purposely tried to put the coach into challenging driving situations such as city driving and short distance driving in high temperatures,” he says. “This put us in excellent position to compare the performance of the EPA 2010 engine with the US 2007 Detroit Diesel engines.”
According to Annett Bus Lines, the technology performed flawlessly in all types of situations during the three-month trial.
“During one month-long assignment to Washington, D.C. the US 2010 engine never required a stationary manual regeneration,” he says. “On the other hand, our US 2007 engines running on the exact itinerary required on average one regen per week.”
He says his company could not fully evaluate fuel mileage because of the automatic transmission. But he did report the coach returning around seven miles per gallon on the highway and 6.7 mpg overall for the entire trial using an Allison transmission.
The obvious additional consideration for the SCR engine is the need to monitor the level of urea, or diesel exhaust fluid (DEF).
“Although we were perhaps a little hyper sensitive to monitoring the level in the 16-gallon tank, we found this really to be a very non-intrusive part of a driver responsibilities,” says Annett. “Our coach returned approximately 200 miles per gallon of urea during the trial, which equates to approximately 3,200 miles between required fill ups.”
Annett reports that because the coach can travel such a long distance on a full tank of urea without consequence, drivers can easily plan well in advance to locate additional urea while on the road.
“Even with an empty DEF tank situation, we understand there is ample time —up to 10 hours — to operate the coach before locating and restocking the DEF. We also found most truck stops were well stocked with supplies of urea.”
Annett says based on what he saw during the test period his company believes the US 2011 Prevost H3-45 with the US 2010 Volvo D13 will offer enhanced performance both in terms of economy and efficiency, particularly when mated with the Volvo I-Shift transmission.
Autobus Maheux operates a fleet of 125 buses intercity, school and charter bus services, which includes 23 Prevost H3-45, one a 2010 model. Barrette assigned his early production coach to the regular intercity routes. Like Annett, he says his maintenance team and driver were at first concerned for problems stemming from the use of urea.
“The diesel engine fluid can freeze, and with the minus-30 to 35 Celsius temperatures we get in our region, we had good reason for concern,” says Barrette. “However, our worries are unfounded. The product indeed freezes, but the reheating system in this engine is very efficient.”
He notes with the addition of a new reservoir, drivers must get used to another set of dashboard lights that alert them to low fluid levels. He says the drivers adapted quickly to the new dashboard, as well as the new engine and transmission. According to Autobus Maheux, driving improved as a result of improvements to ergonomics and lighting in the driver compartment. BR