Driving the new cooled exhaust gas recirculation engines is a pleasure. Not only do worries about performance appear to be unfounded, but the integration of new technology has actually improved performance, which amounts to a good tradeoff for the hit on pricing and a small loss in fuel efficiency.
While testing the engines, I spoke with drivers who have their doubts about the new technology. “I wonder about performance, especially on grades,” says driver Jim Howard, who is training with The Mickow Corp. “And I wonder about durability.”
Robert Vantassel, an owner-operator for A to Z Trucking of Pennsauken, N.J., says, “We’re going to lose power with all that new emissions technology.”
However, test drives of the heavy-duty engines that will use EGR – the system chosen by four of the five major diesel manufacturers to meet emissions standards effective Oct. 1 – show that performance is surprisingly strong. EGR requires more exhaust back-pressure to push the hot exhaust back through the recirculation system and into the intake manifold. Also, the greater boost in pressure is required so both the exhaust and the same amount of air will be forced into the engine. This requirement for higher air intake pressure is what has made it necessary to incorporate more powerful turbos.
Sweet spots have not moved. Torque curves tend to be flat, although this is not a result of new emissions technology; they have flattened in the past four or five years, says Mark Conover at Cummins. Thus, the right final gearing and throttle feathering make it easy to find the most fuel-efficient rpm. Detroit Diesel, for example, recommends 3.7 rears for its 430-hp and 500-hp engines.
The test drives of these engines, none longer than 350 miles, cannot answer questions about durability. The four EGR engine makers say their products are expected to have the same longevity as current models. Tighter oil change intervals and the price of the new CI-4 oils being brought out to handle increased amounts of soot and acids may add to preventive maintenance costs, particularly where bigger pans have been introduced. Mack has increased the capacity of its pan by 8 quarts, for example. But, as with measuring miles per gallon, the increased costs associated with preventive maintenance depend to a great degree on the application.
Manufacturers and the U.S. Environmental Protection Agency say the new technology will add $3,000 to $5,000 to the engine’s price; fuel consumption will rise between 3 percent and 5 percent over comparable late-model engines. It is possible some operations using older engines will realize increases in fuel mileage. Most experts agree fuel efficiency, price and maintenance account for an estimated $10,000 to $15,000 in extra costs over the life of an EGR engine.
Turbo technology is the heart of EGR. Cummins and Detroit use a variable nozzle that forces air across fixed vanes, while Mack’s system uses variable turbo blades. Volvo’s V-Pulse system captures the pressure wave created when the exhaust valve in each cylinder opens, controlling its flow into the system with two simple EGR valves. The variable turbos can also spin at much higher rates, and the variable nozzle adjusts to changes in throttle, allowing the three manufacturers using variable geometry to boost engine brake performance and spool the turbo up much more quickly to provide that increased throttle response. Volvo’s system, like the others, increases pressure on the inlet side, resulting in the same performance upgrade.
Overdrive road tests find the heavy-duty EGR engines pack powerful turbos, pick up quickly and sacrifice no pulling power to the god of smogless skies.
Engine makers have decreased parasitic power loss caused by air conditioning, fan use, air compressors and other systems dependent upon horsepower to run. At Mack, for example, fan technology has decreased fan noise and on-time considerably, says Mack lab tech Neal Biser. Adding EGR hardware increased engine weight at Mack and Cummins, but Volvo stayed the same and Detroit managed to lose weight.
The electronic control module creates the particular mix of exhaust gas recirculation and performance that keeps the feds and the drivers happy. The ECM also interprets EGR system data for faults such as coked valves and conditions like high condensation, high temperature or low barometric pressure. Condensation causes the formation of sulfuric acid, a leading contributor to engine wear, while low barometric pressure can indicate a turbo gasping for air at high altitudes, according to Chuck Blake at Detroit Diesel. All manufacturers now have more fault codes that show up with diagnostic tools and as a reading on the dash, generally only seen as “check engine.”
Another major concern of buyers is the increased under-hood temperature. Estimates range from 5 degrees at Mack to 20 degrees at Cummins, but test drives showed no effect on cab comfort or performance. Engine makers have increased their cooling systems to handle higher engine temperatures.
If these changes seem overly dramatic for the simple purpose of reducing emissions, consider the challenge. The new engines cannot emit more than 2.5 grams of nitrous oxide and non-methane hydrocarbons per horsepower/hour. This is a 90 percent reduction from current standards. It’s also a prelude to even stricter standards taking effect between 2007 and 2010.
This variable geometry turbo used by Cummins has a variable nozzle that forces air across fixed vanes. The turbo technology used in all four EGR engines increases pressure on the inlet side, resulting in the same performance upgrade.
HOW EGR WORKS
Cooled exhaust gas recirculation uses back-pressure to force the exhaust into a cooler, lowering its temperature from about 1,100 degrees to 450.
The cooled gas runs into a mixer where it meets cooled air from the charge air cooler and is forced into the cylinder head. These cooled gases lower the combustion temperature and keep nitrous oxide from forming.
This eliminates much of the need to retard timing, a procedure with negative impact on performance. Generally speaking, manufacturers still have had to retard timing, though not as much as before EGR. The late timing plus the EGR add to the formation of soot and acids during combustion.
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