Emission control: Do we have a problem?

Several years ago, Roger Hansen had good reason to worry about the federal mandates to lower exhaust pollution levels for diesel-powered trucks, buses and other equipment. As fleet manager for the San Diego Unified School District, Hansen feared switching his fleet of 500 buses from diesel to an alternative fuel, such as propane or compressed natural gas (CNG), would be prohibitively expensive.

“We were looking at millions and millions of dollars to convert our fleet to run on something like CNG,” Hansen says. “We’re not just talking about the cost of the vehicle conversions, either. We would have had to install new refueling systems, new fuel storage tanks, and make changes to our maintenance facility.”

Rather than use CNG, San Diego’s school bus fleet switched to clean diesel in 1999 as part of a green diesel technology program initiated by Chicago-based International Truck & Engine to help its products meet tighter diesel emission rules. Thirteen of Hansen’s buses were retrofitted with diesel particulate filters (DPFs) and started using ultra low sulfur diesel (ULSD) — fuel with a sulfur content of 15 parts per million (ppm), compared to today’s on-road counterpart at 500 ppm and 1,000 ppm for off-road fuel.

Today, Hansen has equipped 170 buses with DPFs and operates the entire fleet on ULSD, which reduces exhaust emission levels while minimizing both the cost and operational impact. “One of the best things about [clean diesel] technology is there’s been no decrease in engine power or performance, reduction in fuel mileage or less range,” he says.

Hansen believes that using clean diesel is far cheaper than converting to other clean air alternatives. “The cost of our switch is really minimal compared to going to CNG,” he says. “For example, just take refueling. We allocate between six and 10 minutes of refueling time per bus per day from our 30 dispensers. With CNG, because of the range limitations, we’d have to refuel twice per day. And, it takes longer to refuel. Even if we spent all night refueling, we couldn’t get it done with the staff and dispensers we have now.”

Controlling emissions

Because the Environmental Protection Agency (EPA) has targeted diesel exhaust as a major contributor to air pollution, fleets that operate diesel-powered trucks are being subjected to ever-more stringent emission rules (see “The engine emissions timeline,” p. 44). Diesel exhaust contains particulate matter, black carbon, sulfur dioxides, nitrogen oxides and more than 40 chemicals that the Clean Air Act classifies as hazardous air pollutants. And while diesel-powered trucks make up only 2 percent of vehicles in the country, their exhaust is responsible for more than 60 percent of all particulates and nearly half of all nitrogen oxides, according to EPA.

EPA mandated ULSD as the primary diesel fuel starting June 1, 2006, because using it reduces particulate matter (PM) by up to 13 percent, hydrocarbons (HC) by 13 percent, carbon monoxide (CO) by 6 percent and nitrogen oxide (NOx) by 3 percent. If ULSD is used with diesel oxidation catalysts (DOCs), PM emissions can be cut by 20 percent to 50 percent, toxic hydrocarbons by more than 70 percent and carbon monoxide by more than 90 percent, according to EPA. Using DPFs in conjunction with ULSD reduces emissions even more, cutting PM, CO, HC and toxic HC levels in the engine’s exhaust stream all by 90 percent or more.

Emission compliance is not cheap. EPA says ULSD can cost between 3 and 50 cents more per gallon compared to regular 500-ppm diesel fuel, depending on how close the fleet is to ULSD suppliers. The aftertreatment technology is expensive, too, with DOCs costing about $1,500 to $2,500 each and DPFs ranging between $5,000 and $8,000 each, according to the Seattle-based Puget Sound Clean Air Agency (PSCAA). The agency believes those prices will decrease sharply as more DOCs and DPFs are produced to fill 2007 orders.

Many government fleets are using ULSD and aftertreatment systems retrofitted to older trucks or purchased in new vehicles, to get advance data on operational effects. However, few report significant problems from using either ULSD or aftertreatment technology. Tacoma, Wash.’s Fleet Services Division, for example, retrofitted 48 of its refuse trucks in October last year with DOCs, at $2,000 each, using a $100,000 grant from the PSCAA.

It also is switching to a ULSD/biodiesel fuel blend this year from its current fuel mix — 80 percent regular diesel and 20 percent biodiesel — as a way to further cut emissions at a relatively low cost, says Fleet Manager Steve Hennessey. “The technology switch was very easy, no more difficult than changing a muffler,” he says. “We replaced the exhaust stack with a DOC at night while the trucks were parked, and we had them all converted in a month.”

Hennessey says the 50 converted trash trucks work fine and that his drivers report no difficulties, either in vehicle performance or fuel mileage. “I expect it to be no different when we go to ULSD,” he says. “When we switched to biodiesel three years ago, I really was concerned, but we had no complaints then or now.”

The experiences of two other cities that have used ULSD should reassure Hennessey about using the fuel. Chicago Transit Authority’s (CTA) bus fleet operates on ULSD without a problem, according to William Mooney, vice president of bus operations. With 2,000 buses covering 152 routes totaling 2,273 miles daily, the CTA is the country’s second largest public transit agency. It began using ULSD from British Petroleum in 2003 to lower exhaust pollution from buses, but Mooney has seen no vehicle performance fallout from the switch.

“We are achieving the same level of performance with the bus fleet using ULSD as with No. 1 diesel fuel,” Mooney says. “Maintenance changes, such as oil change intervals, have occurred from [newer] engine technology but not from the use of the ULSD fuel. Also, the transition to ULSD was seamless for our drivers. They had no issues either from a vehicle performance or environmental standpoint.”

Mooney notes that the reduction in emissions was one of the major goals behind making the switch to ULSD, and that has been achieved as well. “The use of ULSD fuel, in combination with particulate matter filters, has enabled CTA’s newest buses to experience a 90 percent to 95 percent reduction in emissions,” he says. “Even older model buses — those without particulate filters — experienced emission reductions from 5 percent to 15 percent as a result of the conversion. For us, it’s all about lowering emissions.”

Craig Allen, fleet manager for the Lansing, Mich.-based public bus fleet Capital Area Transportation Authority (CATA), was required to “go green.” Needing to buy 60-foot articulated transit buses in 2003, the agency could only purchase units equipped with exhaust gas recirculation (EGR) Series 60 Detroit Diesel engines and DPFs that could only be operated on ULSD. “Buses that large [must be] ‘50-state approved’ vehicles, meaning they must meet all emission regulations, including California’s, currently the most stringent,” Allen says. “So we had to use ULSD if we were going to buy a diesel-powered bus that large.”

Yet Allen has found integrating those low-emission vehicles to be far less taxing than expected. “In terms of maintenance, we adjusted our preventive maintenance schedule down to 3,000 miles from 5,000 miles, in part, because of the greater soot buildup in the engine oil — a byproduct of EGR,” he says. “Other than that, there’s been no operational differences at all.”

Fuel issues

Switching to ULSD reduces the fuel’s energy content and lowers the mileage per gallon (mpg) between 1 percent to 4 percent, according to the U.S. Department of Energy. But Allen says in some cases CATA’s new buses’ fuel economy actually increased after the switch to ULSD. “It was minor — from 3.9 mpg to between 4 mpg and 4.1 mpg. That’s significant savings to us over time,” he says. “The real key is that we’re not having to change anything. We get the same range, and the drivers get the same performance from their vehicles.”

While ULSD’s higher price generally has been a concern, CATA’s 12-month fixed contract price has turned out to be a major cost control tool. “Typically, ULSD runs anywhere from 8 to 12 cents more per gallon in our area, but since we can buy it at a fixed price for a year, we were protected from those high fuel prices in 2004,” Allen says. Even paying higher fuel prices this year, he is grateful for a contract. “This year it’s $1.67 a gallon, [which still amounts to a] big savings compared to the market price.”

“Frankly, I expected a lot more problems when we switched” to ULSD, says David Kerrigan, Seattle’s fleet manager. The city has been using ULSD in its fleet since July 2001. “Initially, we had a problem because our supplier used the wrong additive in our ULSD. ULSD can’t work without additives, because of the reduced sulfur content,” he says. “But once we got that fixed, it’s been a pretty seamless transition. We don’t do anything different operationally than we used to, and our 800 trucks are running just fine on it.”

Equipment differences

As state and local government fleets use a variety of diesel-powered equipment — from medium-duty trucks and buses to Class 8 tractors, refuse packers, bulldozers and road graders — many worry that ULSD and aftertreatment systems could significantly impact their operations. So far, though, that does not seem to be the case.

“In 2002 we made the switch to ULSD for all of our equipment, from long haul trucks to bulldozers, and we haven’t had a problem,” says Frank Van der Linden, project/program manager for King County, Wash.’s Solid Waste Division. “This year, we’re switching to ULSD with a 5 percent biodiesel additive, to help further reduce harmful exhaust emissions from our fleet.”

Van der Linden says all 500 pieces of equipment in his fleet run fine on ULSD, with no loss of fuel economy or performance. Also, the fleet has retrofitted 12 of its tractors with DPFs, and Van der Linden says those work fine as well.

“We had some minor glitches when we started using them,” he says. “We have electronic devices on the exhaust system, monitoring the exhaust backpressure to see if the filter is getting plugged, and we had some issues with the wiring harnesses for those systems. But once we worked that out, they’ve functioned just fine.”

Van der Linden says that the DPFs have to be cleaned every 60,000 miles to remove soot and ash deposit build- up. But instead of cleaning the filters inhouse, mechanics replace clogged filters with spares and then ship the clogged ones back to the fleet’s engine dealer for cleaning. “That means no downtime for filter maintenance on these trucks,” he says.

John Hunt, fleet manager for Fresno, Calif., also has had few problems. His fleet has been using ULSD for all of its equipment — from bulldozers to buses — since January 2003 without “a lick of problems.” “The fuel itself is transparent, so none of our operators even know we are using it,” he says. The city’s 62 buses and 40 refuse vehicles equipped with DPFs and ULSD in their tanks also have had no problems.

“It’s almost uncanny how smooth the transition has been,” he says. “The two big things we initially worried about were the higher price of ULSD and the potential damage a ‘misfuel’ could cause if we used higher sulfur fuel in one of our retrofitted vehicles. However, since we began using ULSD, the price premium has come down from 15 cents to 6 cents extra per gallon — just from an increase in the number of suppliers.”

Fresno decided to first switch to ULSD across the board, mixing it with the higher-sulfur fuel already on hand until the older fuel had been fully “flushed” from the system. It began retrofitting its refuse trucks and buses after that, he says. “It saved us the expense of cleaning out our tanks,” Hunt says. “We could use that ULSD/regular diesel mix without harming any of our vehicles, and it proved the simplest and safest way to transition our operation to the cleaner fuel. We haven’t missed a beat.”

Switching to ULSD in conjunction with DPFs also has helped reduce emissions, says Joseph Oldham, Fresno’s fleet acquisition manager. “The vehicles equipped with DPFs and using ULSD have seen PM emissions drop 85 percent and NOx cut 25 percent,” he says. “As a result, we’ve also noticed a huge improvement in the air quality at our equipment yard and [maintenance] facility. Our drivers don’t complain about that diesel smell anymore, and our mechanics don’t complain about the smoke from vehicles in the shop.”

Another unexpected benefit: the trucks and buses are cleaner, especially around the exhaust stack where soot used to collect in the exterior, Oldham says. “Without that soot, we aren’t washing the vehicles as much, and they are staying cleaner longer. These are costs you don’t think about until they are gone and you don’t have to pay for it. It’s hard to put a value on that.”

Sean Kilcarr is senior editor at American City & County’s sister publication, Fleet Owner.

The engine emissions timeline

On Oct. 1, 2002, the Washington-based U.S. Environmental Protection Agency (EPA) required new heavy-duty diesel engines to emit no more than 0.1 grams per brake horsepower hour (g/bhp-hr) of particulate matter (PM), 2 g/bhp-hr of nitrogen oxide (NOx), and between 0.4 and 0.5 g/bhp-hr of non-methane hydrocarbons (NMHC). The NOx and NMHC measurements typically are combined for testing at 2.5 g/bhp-hr. In 2004, the rules were expanded to include medium- and light-duty diesel truck engines.

By 2007, emission level requirements for new diesel engines will become even stricter. PM emission levels will decrease to 0.01 g/bhp-hr, NOx to 0.2 g/bhp-hr and NMHC to 0.14 g/bhp-hr. The PM requirement will be implemented fully in 2007, while the NOx and NMHC requirements will be phased in between 2007 and 2010. As a result, new diesel engines in 2010 will produce less than 10 percent of the emissions of 2001 models.

To meet the 2007 rules, fuels will be changing. Starting in June 2006, the diesel sulfur content will drop to 15 parts per million (ppm) from the current 500 ppm. The EPA is requiring 80 percent of diesel fuel sold in 2006 to meet the 15 ppm standard and is increasing the requirement to 100 percent by 2010.

In 2002, most engine manufacturers believed that major aftertreatment devices would be required by 2007, adding significantly to the cost of new heavy-duty trucks. However, after two years of intensive work, engine makers believe far less aftertreatment will be needed.
— Sean Kilcarr