How are the 2007 engines performing? This was the biggest question at the Fall Meeting of the Technology and Maintenance Council. The good news: The engines seem to be doing well. The bad news: Many of the accessories are not.
Background: PM and NOx
Engines manufactured after Jan. 1, 2007, have to be compliant with 2007 EPA emissions regulations. The two major pollutants to be managed are particulate matter (PM) and oxides of nitrogen (NOx).
The last round of emissions reductions, in the 10/02 engines, concentrated on controlling NOx, which is a precursor to smog and acid rain. The 2007 engines build on that plus go after PM.
PM consists of partially burned fuel (soot), unburned hydrocarbon fuel, and ash from motor oil. Previously, it was controlled by increasing combustion temperatures to the point where hydrocarbon fuel is burned completely, turning it into carbon dioxide and water vapor. But when air, which is composed primarily of nitrogen and oxygen, is subjected to high heat and pressure—as inside a combustion chamber—the two elements combine to form NOx.
The strategies that control one create more of the other. Cool the flame to limit NOx and PM increases. Raise combustion temperature to limit PM, and NOx increases.
NOx was controlled in 10/02 engines by mixing some of the exhaust gas with incoming combustion air. By increasing the volume of intake air with two-stage or variable geometry turbo-charging and managing fuel injection with higher injection pressures and variable timing of multiple injection pulses, PM was limited. The exhaust gas was cooled with engine coolant, and recirculated in measured amounts through the intake manifold. This limited NOx but added soot to the engine and amplified the heat managed by the cooling system. That increased under-hood temperatures.
To meet the 2007 standards, exhaust gas recirculation was increased, raising under-hood temperature even more. More soot went into the crankcase oil, requiring a new oil formulation (CJ-4) or shorter drain intervals with CI-4+.
New diesel particulate filters (DPF) trap PM and let only gaseous exhaust escape. When cleaning—called regeneration— is needed, fuel is injected onto a precious metal catalyst. That raises the temperature to between 1100 and 1200F, converting all soot to carbon dioxide.
The automatic system can be deactivated to prevent regeneration under hazardous conditions, or regeneration can be manually initiated. Some engine makers prevent regeneration when traveling at low speeds or when stopped. Inert ash remains in the DPF, which must be cleaned out every 350,000 to 400,000 miles or so.
The Good News
Fleet managers testing 2007 engines and DPFs report that they are operating as they should. Occasional problems with DPF dosing valves occur, but they seem to be the result of fuel quality rather than system function.
The Bad News
In this hot environment, serious issues have been noticed with alternator, serpentine belt tensioner, air conditioner clutch, and power steering pump bearings. Whether seals are allowing grease to seep out, or the greases themselves are not standing up to the heat, has not yet been determined.
Charge air coolers seem to be leaking excessively, according to a number of fleets. Engine makers test charge air coolers by pressurizing them to 30 psi and measuring time to leak down 5 psi. Some fleets report not being able to pressurize beyond 7 psi. One fleet manager says he won't pressurize a defective part to 2 atmospheres of pressure, fearing a catastrophic failure that could injure a technician.
Heat from under the hood and from under-cab DPFs have increased cab floor temperatures. Some managers claim you can cook food on floors.
Many trucks have three-position DPF regeneration switches for automatic, manual-on, and prevent-regeneration modes. If a driver turns off regeneration to prevent operation in dangerous areas and forgets to switch back to automatic operation, DPF back pressure can cause the engine controller to derate the engine. The driver will complain of low power, but it isn't the engine. Training corrects this.
Fleet managers also report a growing number of truck fires. We think of diesel as having a much higher flash point than gasoline, but high under-hood heat raises return line fuel temperature significantly. In turn, fuel in the tank is heated closer to flash point, so ruptured lines and broken tanks are more likely to result in fires than ever before.
Those are the primary problems reported by the fleets testing the newest engines. Designs and materials to correct these problems will most likely appear before the introduction of 2010 models, when engines will have to meet even more stringent regulations.
Until then, caveat emptor. Let the buyer beware.
— Paul Abelson is a former director of the Technology and Maintenance Council of the American Trucking Associations, a board member of Truck Writers of North America, and active in the Society of Automotive Engineers.