Engine Notebook: Volvo Tier 3 engines

As the world’s largest producer of heavy-duty diesel engines, Volvo has both the resources and the need to stay at the forefront of emissions control.

U.S. EPA regulations for on-highway engine emissions will take a rigorous step up starting next year. To meet those standards, the new D11, D13 and D16 engines from Volvo Trucks North America will use sophisticated versions of standard hardware to reduce oxides of nitrogen 50 percent from current levels. They’ll also come with diesel particulate filters to slash particulate matter emissions by 90 percent.

Volvo’s sliding nozzle variable geometry turbocharger has electronic actuation. Exhaust gas recirculation volume and flow are controlled by hydraulically actuated valves. A delta-pressure EGR flow sensor measures changes in EGR flow and provides communication between the EGR valve and the variable geometry turbocharger actuator through Volvo’s VECTRO engine management system. This setup is responsible for curbing NOx.

As with other diesel particulate filters, Volvo’s will provide passive regeneration when the duty cycle generates sufficiently high exhaust gas temperatures to reduce the soot to ash. Under other duty cycles the filter will provide active regeneration. In active mode, diesel fuel is added to the exhaust stream to raise temperature inside the particular filter to allow oxidation of the soot. Active regeneration takes about 15 minutes and uses about a half-gallon of fuel. A dash light alerts the driver that active regeneration is about to occur or is underway. The driver can delay the process if the timing is inconvenient, such as just before the vehicle is parked and shut off.

Volvo will offer a back-of-cab diesel particulate filter, but the standard configuration will be a compact DPF that mounts to the frame under the right side of the cab. The compact DPF allows the use of a straight pipe behind the cab, which may allow moving the trailer closer to the cab for improved aerodynamics and fuel economy.

Accumulated ash will have to be periodically removed from the DPF. This will likely be a dealer function for small fleets; large fleets may choose to invest in the necessary equipment. Intervals for the DPF will be at least 100,000 miles for the first servicing and at least 150,000 for subsequent servicing. The process takes about 90 minutes.

As with other ’07-compliant engines, Volvo’s units will require the use of ultra-low-sulfur diesel fuel. Restricted to no more than 15 parts per million sulfur, ULSD will be introduced in October of this year.

To cover the additional emissions technology, the surcharge for ’07 Volvo engines is $7,500. This applies to Volvo’s three engines as well as the Cummins ISX Volvo offers.

Off-Highway solutions
Volvo Advanced Combustion Technology is the term for the emissions-reduction package on Tier 3 off-highway engines. Within that package, two components stand out.

First is the new generation electronic fuel injector. Inside an injector is a needle. The tip of that needle fits into a hole at the end of the injector. When the needle lifts from the hole, fuel flows. When the needle drops back into the hole, fuel flow is shut off.

By providing fuel pressure on both sides of the needle and with the use of twin pulse-width-modulated solenoids, the opening and closing of the needle is much more tightly controlled. “Ten years ago injection started around 24 degrees before top dead center with a needle opening pressure of 150 bar,” says Bill Rix, technical trainer for Volvo. “Now it occurs around 2 or 3 degrees BTDC with a needle opening pressure of up to 1,800 bar. The needle opening pressure and injection timing are controlled by Volvo’s EMS52 electronic controller.”

These new injectors are used on engines of more than 250 horsepower. Engines below that output use a common rail fuel injection system.

The other standout feature in V-ACT is internal exhaust gas recirculation. The I-EGR process can be controlled for optimizing performance and emissions. On all but the D9 and D12 engines, I-EGR is integrated with the engine brake. On those two engines, I-EGR employs a double rocker on the exhaust valve. The hydraulically actuated secondary rocker lifts the exhaust valve during the engine’s intake stroke to allow a measured amount of exhaust gas back into the cylinder. The process is electronically controlled by the engine management system.

The Future
The next level of on-highway standards arrives in 2010, and off-highway Tier 4 arrives in 2011. Much of the Volvo preparation for this has been to consider several emissions reduction strategies and, by process of elimination, arrive at the ones that hold the most promise.

“The next step for construction equipment engines has to be treatment of exhaust gases,” Rix says.

One possible solution is selective catalytic reduction. SCR injects urea into the exhaust stream. The urea converts to ammonia and combines with NOx to form harmless water and nitrogen gas. To reduce NOx by one gram per brake horsepower hour requires injecting urea roughly equivalent to 1.5 percent of the fuel used. Even so, refilling the tank “is not a daily thing,” says Rix. And the matter of infrastructure – which is a big issue to the trucking industry – is less of a concern to an industry where fuel trucks are refilling equipment at the site already.