Hitting the road
“The trucks we are driving are about as responsive as a truck could be, are getting great fuel mileage for a 16-liter engine, and the reliability, comfort, and functionality are about as good as it gets,” he says.
Bill Parry of Giant Eagle, a supermarket chain, says the company has been running five pre-production SCR trucks from Volvo since 2007. “Volvo initially shipped us DEF, but we soon found a local supplier and buy it in 250-gallon totes. We’ve found that SCR is no different from any other new technology. There seems to be a lot of smart engineering that has gone into the system. When you look at the exhaust pipe, it is amazingly clean, and the drivers think the response (of the engine) is better.”
Ed Saxman, Volvo’s drivetrain product manager, says, “Some of our competitors are introducing new, common-rail injection systems with 2010. Our injection system is pretty much as it was in ’07. We had a 35,000 psi system even then.
“We’ve seen about a 5 percent increase in fuel economy. It comes from reduced EGR combined with other things. The most important of those is our ‘no regen solution.’”
Volvos do without regeneration under virtually all on-road driving conditions, Saxman says, for several reasons.
Volvo’s 2007 engine redesign allowed it to tolerate higher levels of EGR. The injection system was improved, in part to allow increased injection pressures and generate less soot. It was also re-programmed to allow multiple injections for each power cycle, which helps control both soot and NOx.
Fortunately, NOx in the exhaust helps the passive regeneration of soot in the DPF. With SCR to get rid of that pollutant at the end of the process, it’s practical to allow the engine to produce some NOx and send it into the DPF. So, a three-part strategy resulted: One, an engine that produces minimal soot; two, control of the combustion to give the correct ratio between soot and NOx in the exhaust headed for the DPF; and, three, control of exhaust temperature to keep it hot enough to regenerate the DPF without adding fuel with the doser in the DPF.
The MX engine, using SCR, is not on the road yet but has been extensively tested. The engine will displace 12.9 liters, use compacted graphite iron for both the block and cylinder head, and the maximum rating will be 485 hp with 1,650 lb.-ft. of torque, according to marketing materials. Mounting the gear train on the rear of the engine, and designing the mounting system so the oil pan “floats,” will minimize noise and vibration.
Paccar says an unusual “fractured cap” design for the bearing caps allows greater strength in the engine’s bottom end and longer torque and power curves.
The engine will have the camshaft located high in the block and driving unit injector pumps. These electronically controlled pumps will provide 36,000 psi injection pressures through high-pressure piping to electronically controlled injection valves located in the head. Improvements in such piping, plus the engine computer’s ability to coordinate the valves on the pumps with the opening and closing of the injectors electronically, allows a high-performance injection system of unusually simple design. n