Gentlemen, Start Your EnginesWritten By: Steve Sturgess
Article Date: 04-03-2006
Copyright(C) 2008 Associated Equipment Distributors. All Rights Reserved.
It's important to thoroughly understand this new piece in the emissions puzzle.
With the on-highway diesel emissions regulations set to change in January 2007, it's no surprise that it's been standing room only at industry meetings whenever engines are on the agenda.
There's a lot to know about them - not the least of which is the fact that they're going to cost $7,000 to $10,000 more. And there's more complexity and much misconception.
Basically, the technology path is similar to the changes for the 10.02 engines: exhaust gas recirculation (EGR), but at increased flow rates.
EGR is used because the spent gases displace oxygen in the incoming air and keep down the flame temperature during combustion, thereby limiting NOx. And because EGR has been used for three years, the experience has allowed manufacturers to address many of the early "bugs."
Even Caterpillar, which has been the single stand-out and vocal opponent of EGR, is going down the same road with its ACERT technology, though because of the way it routes the exhaust gas, the company refers to it as a clean air system.
How it differs is in the tapping off point for the exhaust: downstream of the diesel particulate filter (DPF). And that's a new component everyone will have to deal with on the post '07 trucks, whatever the make of engine.
It's important to thoroughly understand this new piece in the emissions puzzle because there's a lot of misconception about DPFs, most of it surrounding the maintenance that will be required and much about the "regeneration" cycles.
The filter is there to deal with the microscopic carbon particles that exit the combustion chamber and from January '07 are effectively outlawed in diesel exhausts. The filter element is a ceramic monolith that is a bundle of ceramic tubes closed at one end or the other. Exhaust enters the open tubes from the engine and the only way out to the exhaust stack is through the ceramic walls of the monolith into neighboring tubes open at the other end, leaving carbon particles in the ceramic.
Just upstream of the filter monolith is an oxidizing catalyst stage. This serves two purposes, one of which is to oxidize the nitrous oxide (NO) which is a component of the NOx stream in the exhaust to nitrogen dioxide (NO2), another NOx component.
The enriched NO2 moves from the oxygen catalyst stage and enters a second process in the filter where the carbon particles and the additional NO2 in the exhaust react in the presence of a different catalyst. The carbon then comes off the ceramic walls as carbon dioxide gas and the NO2 reverts to NO. This process is known as passive regeneration and requires the heat of the exhaust to proceed.
All this goes on without the driver being aware of it, and the filter remains free of carbon buildup. However, this second reaction only occurs in the hot stream of exhaust typically seen when an engine is under load. Applications like over-the-road trucking require sufficient load factor and throttle position that passive regeneration goes on all the time. Others, like vocational applications, dumps, utility trucks, urban delivery vehicles, trash packers and so on may not have a hot enough exhaust stream, so need active regeneration.
Active regeneration is the oxidation catalyst's other task. If, through sensors, the engine electronics detect a buildup of back pressure as the carbon loads up without passive regeneration, a rich fuel mixture is fed into the exhaust, impinges on the oxidation catalysts and builds up heat in the stream to initiate the regenerative process.
This fuel may come from clever injection timing or it may be simply injected into the exhaust just downstream of the turbocharger. Yes, the exhaust heats up, but no, there's no flame.
Again, this is undetectable by the driver and the exhaust is little hotter than the exhaust from an engine working under load.
There's quite a lot of misunderstanding about active regeneration: Will it set fire to trees? What about a fuel hauler sitting at the fuel rack? What happens if the driver keys off in mid-regeneration? Won't the filter housing get extremely hot?
The answer is that, in general, there will be no more heat than you see from an engine working under load (as in the passive regeneration). And the engine manufacturers have thought it through as well, for instance, not permitting a regeneration event when the truck is stationary or below a threshold speed.
Misunderstanding number two surrounds the amount of maintenance the DPF will require.
Unfortunately, along with the spent combustion gases, coming out of the engine are minute traces of ash from additives in the oil. These ashes do not regenerate and so build up in the DPF over time. They have to be removed in a cleaning process.
Again, there's good news coming out of the engine companies: This cleaning could be in the 200,000- to 400,000-mile interval range. For an over-the-road fleet turning trucks at 36 or 42 months, this may be a one-time event. For other applications, maintenance may be required more regularly, but the federal mandate says this cannot be less than 100,000 miles (150,000 miles in California) to the first cleaning.
And the maintenance is easy and, if a fresh clean filter monolith is available, can be completed in one and a half to two hours.
There's considerable concern over the cost of the cleaning machines - you are not going to be able to tap the filter on the workshop floor to get the ash out. Most will be cleaned by air pulsing. (Detroit Diesel recommends an ionized water cleaning process and those machines are as much as $30,000.)
So it's likely dealers and engine distributors will be investing in the cleaning machines and fleets will carry new or reconditioned and cleaned filters on the shelf.
Caterpillar is pursuing a different tack, making the filter serviceable while still on the truck. That, though, means removing inlet and exhaust pipes and piping the filter up to what amounts a very powerful vacuum cleaner. It sounds simpler, but the construction of the DPFs we've see to date is such that the filter monolith can be very easily serviced.
So yes, there will be cost for the filter maintenance and a little additional maintenance, but nothing like the fears expressed in those standing-room-only meetings.
There's a little more complexity and everyone who runs trucks on the highway needs to understand as much as they can about the implications of the '07 engines. Armed with good information and the right questions when making truck purchase decisions, the fears will go away.
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