By Paul Abelson
Senior Technical Editor
At the annual fall meeting of the Technology & Maintenance Council, the biggest question was, “How are the 2007 engines performing?” The answer is, there’s good news and there’s bad news.
The good news is that the engines seem to be doing well. The bad news is that many of the accessories are not.
While all engines manufactured after Jan. 1, 2007, had to be compliant with the 2007 EPA emissions regulations, a large number of engines were built in 2006 in anticipation of the pre-buying that did, in fact, take place. The surplus of engines built in 2006 was put in the vast majority of trucks shipped during the first half of 2007.
There were several hundred test engines bought by some of the larger fleets as early as the second half of 2006 and put in service for evaluation. Most of the fleets involved in the tests are TMC members. Most of those doing testing report having 75,000 to 85,000 miles on their engines.
What’s the problem?
To understand the problems encountered, it is important to understand how these new engines differ in their approach to cleaning their exhaust.
The two major groups of pollutants managed are particulate matter and oxides of nitrogen – abbreviated NOx. Particulate matter consists of partially burned fuel or soot, unburned hydrocarbon fuel and ash from motor oil. The most recent round of emissions reductions in the October 2002 emission standards-compliant engines concentrated on controlling NOx. The 2007 engines build on that and go after particulate matter.
Normally, particulate matter could be controlled by increasing combustion temperatures to the point where all hydrocarbon material is burned completely, turning it into carbon dioxide and water vapor.
But, when air is subjected to high heat and pressure, the nitrogen and oxygen in it combine to form NOx, a precursor to smog and acid rain.
Unfortunately, the technology required to control one group of pollutants creates more of the other. Cool the flame to limit NOx and particulate matter increases. Raise combustion temperature to limit particulate matter and NOx increases.
Finding a solution
Nitrogen oxide was controlled in October 2002-compliant engines by taking some of the exhaust gas and mixing it in with the incoming air. Particulate matter was limited by increasing the amount of intake air and controlling fuel injection with higher injection pressures along with variable timing of multiple injection pulses.
The exhaust gas was cooled using engine coolant, and re-circulated in measured amounts through the intake manifold. This exhaust gas recirculation – called EGR for short – limited nitrogen oxide but added soot to the engine and greatly increased the heat that the cooling system had to manage. Heat taken into the cooling system is dissipated through the radiator. The heated air then flows back under the hood, heating the engine compartment even more.
To meet 2007 standards, the amount of exhaust re-circulated was increased, raising under-hood temperature even more. That put even more soot into the crankcase oil, requiring the new CJ-4 oil formulation or shorter drain intervals.
To manage the increased particulate matter, a new device called a diesel particulate filter, or a DPF, was developed. Porous ceramic traps particulate matter, letting only exhaust gases escape. The solids build up inside the DPF and have to be cleaned out periodically.
Cleaning is done automatically when conditions warrant. The engine controller determines how much backpressure has increased. When cleaning, which is called regeneration, is needed, fuel is injected onto a precious metal catalyst.
That raises the temperature to between 1,100 and 1,200 degrees, converting all soot to carbon dioxide. The system can be de-activated 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 is that the new engines and DPFs are operating as they should. Occasional problems with DPF dosing valves were reported, but they seem to have more to do with fuel quality than with system function.
At 60 mph, a fully loaded rig’s engine will generate 1.5 million Btu per hour. More than half the energy is lost to the cooling system or out the exhaust. That used to be more than 66 percent just 25 years ago.
The 2007 engines return up to 30 percent of exhaust heat to the coolant through EGR, forcing the radiator to manage as much as 680,000 Btu per hour. With that as background, here’s the bad news.
The bad news
In this hot environment, serious problems have been noticed with bearings in alternators, air conditioner clutches and power steering pumps. Whether seals are failing, 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 the time it takes to leak down 5 psi. Some fleets report not being able to pressurize charge-air coolers beyond 7 psi.
One fleet manager stated he would not pressurize a defective part to 30 psi, fearing a catastrophic failure that could injure a technician. He commented it could also be an OSHA violation.
The manager said, “We wouldn’t tolerate a radiator leaking 5 psi every few minutes. Why should we accept it with charge-air coolers?” Original equipment manufacturers accept it because turbochargers put out enough air to compensate.
Heat from under-hood and from under-cab DPFs have increased cab floor temperatures. Some managers claim you can cook food on some cab floors. To have dual exhausts, you need an under-cab DPF with a Y-pipe. Vertical DPFs keep cabs cooler. You may want to add a non-functional pipe just for looks.
DPF regeneration has caused problems for drivers. New trucks have three-position switches for automatic, manual on and prevent-regeneration modes. Drivers turn off regeneration to prevent the high temperatures in dangerous areas. When they forget to switch back to automatic operation, DPF backpressure can increase to limits requiring regeneration. Beyond that it can build to a point requiring power reduction or even shutdown. Drivers complain of low power, but it isn’t the engine. Training overcomes this.
Far less commonplace, but certainly worthy of note, fleet managers also reported a growing number of truck fires. We think of diesel as having a much higher flash point than gasoline, but high under-hood heat has raised return line fuel temperature significantly.
In turn, fuel in the tank is heated closer to diesel’s 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. As has always happened, I think the engineering talent assigned to correcting these problems will, in time, succeed. The question is, when?
New designs using new materials will correct these problems, most likely before truck operators start the next round of pre-buying prior to the introduction of 2010 models. Then, engines will have to meet even more stringent regulations.
Until then, caveat emptor. Let the buyer beware. LL
Paul Abelson may be reached at firstname.lastname@example.org