COLUMBUS, Ind. - Top engineering and marketing people at Cummins have bared their plans for equipping upcoming diesels to meet the next round of North American exhaust limits.While they insist the pro...
HOW IT’S PLUMBED: Seen here is Cummins’ answer to the EPA. A: The start of the EGR equipment. B: The variable geometry turbo and control valve.
FLEXIBILITY: The vanes move in and out of exhaust flow, applying variable force to the compressor.
COLUMBUS, Ind. – Top engineering and marketing people at Cummins have bared their plans for equipping upcoming diesels to meet the next round of North American exhaust limits.
While they insist the products will work well, they concede they’ll cost more to buy and operate.
High-tech turbochargers and other air-handling devices, plus high-pressure cooling systems, will be among the devices fitted to Cummins products as of October 2002. All models will be equipped and certified except the N14E, which will be withdrawn as a truck engine at that time.
Fuel economy will stay about the same or worsen slightly, they estimate. Durability and longevity should be unaffected, and oil change intervals should stay about the same, even with more soot and other contaminants deposited in the crankcase, because (they insist) a new, more capable grade of motor oil will be available by the time the engines go to market.
Huge radiators – an expected necessity of exhaust gas recirculation (EGR), the chosen path toward lower emissions – will not be needed, engineers said during a briefing for the trade press in early May. The engines are going to run hotter, however, which will affect components under the hood.
Cummins is working with truck builders to install the newly configured diesels and test their effects on under-hood accessories and materials. The company pledges to be ready to meet the deadline set by the U.S. Environmental Protection Agency, executives say.
However, Cummins people are perplexed and skeptical of recent claims by Caterpillar Engine that it will not need “cooled EGR” to meet the regulations. Every diesel maker but Cat plans to use cooled EGR. Cummins’ government relations executives and engineers note research that says EGR is the only way to achieve the necessary low emissions.
Caterpillar is either using weird science or relying on “back room maneuverings” with the EPA to meet the next exhaust emissions limits, Cummins people think. And they said they will go to court if it appears Cat is getting special considerations by government officials.
Could it be something more sinister – nefarious negotiations with the EPA, giving Cat special breaks for on-highway diesels if it makes its off-highway diesels extra clean, Cummins people wonder?
If that’s the case, Cummins will challenge the side bargain in court.
Like most domestic engine builders, Cummins was accused by EPA of using illegal emissions control methods in the early to mid 1990s, and was forced in 1998 to sign a punishing consent decree. It was either that, or fight EPA’s dictates in court – during which EPA would probably have shut down engine production, putting them out of business, executives recalled.
Aside from paying stiff fines, the builders agreed to meet emissions reductions scheduled for January 2004 in October 2002. EPA calculated that reducing diesel pollutants 14 months early would make up for the period of “cheating,” relates Tina Vujovich, Cummins’ government relations vice-president.
“We disagreed with the decree then and we disagree with it now,” she says, “but when you sign a decree you agree on a going forward strategy.”
Cummins committed itself to meeting the deadline and will, and it is publicly insisting that all its competitors, including Cat, also meet it.
Nitrous oxide (NOx) and particulates will be drastically cut by the new limits, but NOx is the more difficult to handle.
It will be reduced from the current four grams per brake horsepower-hour to 2.5 grams, but that includes non-methane hydrocarbons, another pollutant. NOx alone will have to be cut to about 2.1 grams, explains John Wall, a company v-p. NOx is produced during high combustion temperatures, so temps must be lowered. The best way is “cooled EGR,” Wall says. This is done by forcing small amounts of hot exhaust gas into the chambers to displace oxygen. Less oxygen lowers the burn temps, and cooling the exhaust gas before it goes into the chambers further cuts temperatures so less NOx can form during combustion.
Special plumbing carries the gas from the “hot” side of the turbocharger to the engine’s intake manifold. The plumbing wraps around the rear of the cylinder head on ISX and Signature 600 engines; on all other heavy and midrange models the plumbing wraps around the front of the cylinder head.
Sensors and valves measure and modulate the gas flow; all are wired to the engine’s electronic control module (ECM), which considers data sent to it by sensors and adjusts the output of both the valves and turbocharger.
The same ECM will be used on all engine models, but turbos and valves will vary some. Malfunctions anywhere will be signaled through the electronic diagnostics.
The turbo is of the variable geometry (VG) type, which is also controlled by engine electronics.
It keeps the right amount of pressure on the engine’s inlet side to maintain a balance between recirculated exhaust and compressed inlet air.
The unit has an extra set of vanes that move into and out of the flow of gas from the exhaust manifold; more exposure of the vanes speeds up the turbo and compresses more inlet air, while less exposure reduces turbo speed and compressor action.
Among the precise devices is an EGR control valve, which is closed when the engine is cold to prevent exhaust gas from condensing and forming sulfuric acid, Wall says. After warm-up, the valve opens variably, depending on the pressure and temperature of the exhaust gas.
Temperature of the exhaust gas varies from 200 to 1,100 degrees Fahrenheit. But temps drop hundreds of degrees as the gas passes through a jacketwater cooler, plumbed directly to the engine’s liquid cooling system. Excess heat is absorbed by the coolant and transferred to the radiator, where it is blown into the atmosphere.
This is the “heat rejection” feared by truck builders because it will require extra cooling capacity – perhaps through a larger radiator – and the possible resulting damage to under hood components.
But “heat rejection is your friend,” Wall insists, because it means the system is working to reduce NOx and improve fuel economy. Without EGR, engine timing would have to be retarded to reduce NOx – translating into a substantial hit to fuel economy.
Radiator cores won’t be much larger than now, indeed they cannot be, because “no one is changing the hood lines for these engines,” said Ric Kleine, executive director, customer engineering. Fans may have to be more powerful, but this takes power and consumes fuel, so fans should not run any more than now.
Operating pressures and temperatures will be higher, Kleine says. Pressure will more than double, from the current seven pounds-per-square-inch (psi) to 15 psi; and temperatures will rise by 10 to 20 degrees, to 230 degrees Fahrenheit on the Signature 600 and to 225 degrees on all other models.
The Holset variable geometry turbo is complex and will be twice as costly as today’s turbochargers, says Sam Pringle, an ex-Holset executive who now directs Cummins’ air handling efforts. But its up side is fast response and strong pickup from lugging speeds – something that test drivers have praised.
A brief test spin in a heavy-duty tractor-trailer rig with an EGR-equipped engine confirmed these claims. The 11-litre ISM showed snappy acceleration beyond what its 400-hp rating would seem capable of, and the VG turbo, which works harder at lower revs than today’s turbos, is mostly responsible, engineers say.
VG turbos, valves and sensors to be used by Cummins are already being manufactured for use on cars and light trucks in Europe, so they are known devices, Wall says. Cummins is using the same designs for all engines, but will scale them to fit the various medium- and heavy-duty diesels. There will be some part commonality among various models, which will simplify parts distribution and stockage by dealers and fleets.
Will Cummins’ cooled EGR system be less troublesome than “low-flow cooling” used in the mid ’80s on Cummins’ Big Cam IV engines?
“I lived through that,” Wall comments wryly, insisting that engineers are working har
d to make cooled-EGR much more reliable.
What will the EGR-equipped products cost? Truck builders will set final prices, Cummins executives says, but it appears that heavy-duty EGR engines will cost $1,800 to $2,500 more than now, and a medium-duty model will add at most an additional $1,500. n