Next round of emissions regs will dictate OEM cooling-system designs
Until now, changes in heavy-truck emissions regulations have only impacted engine design. That's about to change. Perhaps drastically.
But let's back up to what the fuss is all about. As the industry is well aware, the next round of federal regs - which come into effect on October 1, 2002 - will require a substantial reduction in nitrogen oxide (NOx) emissions.
Engine makers pretty much concur they will use exhaust-gas recirculation (EGR) to meet the tighter 2002 limits. EGR is already a proven technology in other applications so few fear it won't work on heavy-duty trucks.
Be that as it may, there is at least one drawback to EGR. It produces more heat for the engine to dissipate, or "transfer," as engineers like to put it.
As a result, changes are expected to be made under the hood - and in some cases, to the hood or front end of vehicles to accommodate those adjustments.
Because of the greater heat EGR engines will throw off, each OEM will likely re-engineer its cooling system to one degree or another. If those changes are extensive enough, manufacturers may have to adjust the design of their cabs to fit the cooling package into the engine compartment.
Naturally, no OEM is eager to compromise all the hard work and money it has sunk into shaping aerodynamic profiles for its trucks over the last 15 or more years.
That none of this may be easy to achieve - or because it may involve highly proprietary engineering fixes - may explain why only three major OEMs of over-the-road Class 8 trucks responded in depth to our queries on this topic.
A fourth, Freightliner Corp., through a spokesperson regretted it could not discuss details at this time, but asserted that all engines it offers to comply with the 2002 regs "will have the same performance and fuel economy" as its customers now enjoy.
How each OEM will accomplish this with minimum fuss and expense will make a great engineering story, once each completely tells it.
But for now, conclusions can be drawn by considering the rough outlines drawn by OEM experts who were willing to discuss how they expect to proceed in tackling this fast-approaching challenge.
According to Steve Homcha, executive vp-engineering & product planning for Mack Trucks, cooling capacities will indeed have to increase on 2002 engines.
"On our own engines," Homcha reports, "we're moving in the direction of favoring EGR as the emissions solution. The engineering for this is more complicated than just recirculating exhaust gas. We also have to cool it before putting it back into an air stream that itself should be cool. That's what will drive increased demand on the cooling system.
"As a result," he continues, "we may have to adjust radiator design, rework the fins and tubes, or make changes to the fan. This may include making the fan more 'aggressive' by giving it a more curved profile or putting more pitch on the fan blades. Both approaches would pull in more air to run across the radiator surface."
Homcha says none of these changes would be considered shocking or revolutionary. "We're not forecasting the height of hoods will rise," he says. "We may see the unit end up 20 to 50 lb. heavier, though.
"Our engine development for 2002 is moving well along," Homcha continues, "so we are where we need to be - even though we didn't plan for meeting these emissions as soon as we now must."
He emphasizes that none of the work that has to be done is mystifying to engine makers or OEMs. "The industry won't see anything like a second radiator mounted in there," he jokes. "Rather, the tight deadline just means we'll put more people on it and work more hours on an accelerated schedule."
"It's still early to make all the determinations that will be needed to meet the 2002 emissions regs," states Preston Feight, program manager at Kenworth Truck Co. From an OEM perspective, we expect heat will increase in a range, depending on engine make and model.
"We'll need to have prototype engines for evaluation before we can determine what the specific solutions will be - and to make them robust without negatively impacting performance or cost of operation for the truck owner."
He notes that even without test engines in place, Kenworth is working "hand in hand" with engine suppliers to "make sure the solutions are holistically designed."
According to Feight, the effect adjustments to the cooling system may have on vehicle aerodynamics is a potential concern. "How that plays out will be engine- and horsepower-dependent," he explains. "The solutions will have to be developed engine by engine, and truck by truck.
"The areas we're considering involve addressing heat transfer out of the radiator and the charge-air cooler. We'll increase cooling efficiency by enlarging the surface areas of these units or by increasing the air flow," he reports.
"Certainly," says Feight, "our goal remains offering the end user the most economical and best-performing trucks possible. And as we get further along in our development efforts, we'll be able to tell the industry more about our solutions."
"Using EGR to meet the 2002 emission requirements results in 30% to 40% more heat that must be transferred from the engine," points out Keith Brandis, director of product strategy for Volvo Trucks North America.
"Truck OEMs will have to work on a parallel path with engine makers as they provide us with information on their developments," he says. "They are already sharing preliminary data from early tests, which of course are subject to change."
According to Brandis, a key challenge will be cooling 1,100 degrees F exhaust air down to 300 degrees F before putting it back into the intake manifold.
At the same time, he says, "there are certain limits on radiator design because we've all learned the value of aerodynamics. The radiator opening in the hood dictates a big part of making the truck more slippery.
"So," he continues, "if there are changes up front to the radiator or charge air cooler, it could affect the shape and dimensions of the hood, which could in turn impact the aerodynamic profile of the truck. The old tombstone-style radiator will likely have great difficulty meeting EGR cooling demands."
But Brandis reports Volvo believes it has come up with a solution. "One solution we're investigating involves mounting the fan in the center of the radiator and using a fan ring that moves together with the fan.
"This setup would close the clearance gap between the fan and shroud to a quarter inch, which would pull more air through the radiator opening," he continues. "We've used this design on our VN Series trucks since '96, and seen it effective at handling the cooling demands of engines ranging up to 600 hp."
Whatever solutions are implemented, Brandis says Volvo's goal it to meet the 2002 regs while maintaining the aerodynamic efficiency of its trucks.
Eventually, time will tell which of the possible solutions to the EGR cooling issue will pan out as the most effective. Stay tuned for further developments.
Cooling-system supplier Horton Inc. already has some ideas about how EGR engines can best be cooled down.
According to Steve Clancey, manager of product planning, cooling systems on EGR engines will have to deal with 20% to 40% more heat rejection.
Although it's still early in the game, he says it's already "pretty clear engine and truck OEMs will have to do a number of things" to handle the extra heat. Clancey says these may include:
* Increasing the square-inch area of radiators. "Greater cooling area of the radiator will be part of the solution."
* Larger diameter fans. "This is most direct route to increasing cooling efficiency. We may in fact see a movement to 32-in. fans, now found on high-horsepower engines."
* Increase the rate fans spin. "Spinning fans at a higher ratio will produce more air flow for cooling."
* Higher-capacity fan drives and more efficient fan designs. "The goal would be to provide a fan package that uses less horsepower at a given rate of air flow."
* Shroud design. "A well-designed fan shroud can enhance air flow. The idea is to keep the clearance between the fan tip and shroud to a minimum. This alone can yield a 10% or more improvement in air flow."
Summing up, Clancey says some combination of more efficient fan/shroud designs and higher-torque fan drives, along with improved radiators, "will get us over the hump" posed by the effect 2002 emissions regs will have on cooling systems.