NASHVILLE, Tenn. - Exhaust Gas Recirculation (EGR).Learn the term if you don't know it already, because of all the new emissions technologies being discussed for diesels, EGR looms closest. By all acc...
NASHVILLE, Tenn. – Exhaust Gas Recirculation (EGR).
Learn the term if you don’t know it already, because of all the new emissions technologies being discussed for diesels, EGR looms closest. By all accounts, it will be complex and it will be expensive.
By Oct. 1, 2002, most domestic makers of light-, medium- and heavy-duty diesels will apply an EGR apparatus to their products to meet the next round of emissions standards mandated by the U.S. Environmental Protection Agency (EPA). Because Canadian authorities quickly pick up the EPA’s regulations, EGR is what we’ll see as well, though not on everything.
By 2007, builders will go to exhaust “aftertreatment” using catalytic converters, not unlike those used for many years on the exhaust of gasoline engines. To avoid fouling the converters, they will also need ultra-low-sulfur fuel, which the EPA has mandated to be available by summer of 2006. Refiners are fighting this, but it may happen anyway.
Builders say EGR gear will include more complex turbochargers, plus valves, sensors, coolers and piping. This will weigh about 50 lb. per system and cost many hundreds of dollars per truck.
However, most imported trucks and domestics with Caterpillar, General Motors and some International diesels will not have EGR. GM and the imports won’t need EGR for another 14 months, and Cat and International have announced they will meet the regulations using other combustion technologies.
The EPA’s next lowering of the limits – and thus the need for EGR – is actually scheduled for January 2004. That’s when nitrogen oxide, or NOx, is to be lowered from the current 4 grams per brake hp/hr to 2.5 grams of both NOx and carbon monoxide. But the EPA is punishing the builders it forced to sign an infamous Consent Decree in 1998 by requiring them meet the ’04 limits 14 months sooner.
For practical purposes, the October 2002 limit will be 2 to 2.2 grams, a decrease in NOx of nearly 50 per cent, says Bob Jorgensen, director of product environmental management at Cummins, one of those affected by the decree.
Others are Caterpillar’s Engine Division, Detroit Diesel, Mack Trucks, Renault VI, Navistar International and Volvo Trucks North America. All had to sign the decree and pay fines totaling tens of millions of dollars for supposedly cheating on EPA emission rules. The agency claimed that they programmed their engines to pass the certification tests, yet illegally polluted under other conditions (mostly highway cruising).
Builders denied the charges, but buckled under because they feared they’d be shut down while fighting the decree in court. All but Cat and International will need EGR in ’02 to meet the new limits.
International Engine, whose transgressions the EPA viewed as less serious, will not need EGR on its in-line DT466 until ’04. But a new small V-8 diesel (which will replace the T444E/Ford PowerStroke) will begin using it as soon as it’s introduced in the ’02 to ’03 time frame, said Scott Peterson, an applications engineer.
The new 6-liter V-8 diesel won’t need EGR in ’02 but will in ’04. And Ford wants to avoid a running change in ’04, especially in its light trucks, which will use most of the new engine production.
Most foreign builders did not violate emissions laws and were not pushed into the Consent Decree, so do not have to lower their NOx emissions by October of ’02. Only Renault VI, which builds Mack’s Mid-Liner midrange trucks, will apparently have to use EGR.
Isuzu of Japan and its General Motors partner are not affected by the decree. So neither Isuzu’s imported diesels nor domestic engines jointly developed by Isuzu and GM – the 6.6- and 7.8-litre DuraMax diesels – will use EGR in ’02, according to Mike Eaves, an assistant product manager in GM’s truck operations.
Like the EPA’s other regulations and the U.S. Clean Air law on which they’re based, the agency’s decree only sets exhaust emissions limits. The EPA does not tell engine makers how to meet the limits, just that they must. Most diesel builders agree that with technology they’ve been able to develop, EGR will have to be used sooner or later.
Cummins and Mack have both issued statements expressing confidence in EGR as an effective way to meet the upcoming limits. But both are reluctant to talk about their systems in detail.
Detroit Diesel has been much more open, partly because it has EGR-equipped engines already running in commercial service. These are heavy-duty engines in transit buses.
Truck builders frustrated
Freightliner and Peterbilt Truck executives have expressed frustration, complaining that time is short and that they’ve been given little information by engine makers on how EGR systems will fit into their trucks.
But Cat’s ACERT announcement in early March caused Peterbilt’s general manager, Nick Panza, and Freightliner’s president and chief executive officer, Jim Hebe, to breathe sighs of relief. ACERT will have little or no effect on heat rejection or any other operating or installation aspects, Cat has assured truck makers. And it will not use “hot EGR,” as some outside of Caterpillar have speculated.
If this proves true, Cat medium and heavy diesels could become the favored engines at those and probably other builders. The “preferred supplier” agreement that Paccar, parent to Peterbilt and Kenworth, has signed with Cummins may therefore be worth less to Cummins than it hoped.
Freightliner and its sister company, Sterling, also use diesels from their German sister, Mercedes-Benz. Mercedes was not involved in the EPA’s decree, so is also exempt from the ’02 punishment and will not need EGR then.
Some engine builders are busily earning Clean Air “credits” by producing cleaner-than-required engines now. This includes Cat’s installation of catalytic converters on trucks equipped with its 3126E and Cummins’ reprogramming of existing heavy-duty N14E+ and ISX diesels (which it is doing with the consent of some users). Both actions reduce nitrous oxides now and will lessen what the builders must do to cut NOx in ’02 and ’04.
One provision of the infamous consent decree allows each builder to strike its own deal with the EPA, executives have said. Cat’s ACERT will work partly because of on-going negotiations with the environmental watchdog.
How it works
Gasoline engines have been using EGR since the 1970s, and for them it’s a relatively simple process. It takes a few per cent of exhaust gas and sends it back to the cylinders to be burned again. The most complicated thing in the system is a cheap EGR valve, which over time gets dirty and sometimes stuck; cleaning or replacement is the fix.
Diesels are different. For more than nine years they have used other means to meet increasingly stringent pollution limits. This time they’ll need EGR to lower the amounts of NOx, a principal cause of smog.
Exhaust gas in the cylinders will reduce the amount of oxygen available for combustion, Cummins’ Jorgensen explained.
Less oxygen means cooler combustion, which results in less production of NOx.
The amount of exhaust gas required in diesels will range from a small percentage to about 30 per cent, depending on operating conditions, says Steve Homcha, Mack executive vice president for Class 8. The amount will be electronically metered, based on sensor readings of engine pressures and temperatures, and will come through a precision EGR valve at the turbocharger.
A “variable geometry” turbo will get constantly varying amounts of exhaust gas to work with – even with no change in combustion rate or exhaust flow. The method of turbo variation will vary among builders and even by the size of engine, says Cummins’ Jorgensen. But the effect will be the same: better handling of changing conditions and control emissions.
Exhaust gas is hot, so must be cooled on its way to the intake manifold by a special EGR heat exchanger. Most builders will use a water-to-gas type, which uses engine coolant, or “jacketwater,” to carry off unwanted heat. Jacketwater will thus g
et hotter than now (when it carries only extra heat from combustion). The extra heat will have to be shrugged off by higher air flow and probably a larger radiator.
The engine will still need its charge-air cooler. This is the air-to-air heat exchanger mounted ahead of the radiator, which cools the clean, compressed, inlet air from the turbo. Inlet air is mixed with the cooled, recirculated exhaust gas just before both are forced into the cylinders. The turbo, acting on orders from the engine’s electronic control module, keeps both air and exhaust streams pressurized.
Higher heat rejection from EGR will mean more heat under the hood – one of the worries expressed by Peterbilt.
In view of the likely higher price tags on EGR-equipped trucks, will fleets “pre-buy” trucks without EGR to avoid trouble and expense?
“No, we haven’t heard that,” answers Steve Homcha at Mack.
“What we have heard from customers is, ‘Are you going to be there on time and what will the impact on fuel economy be?’ But we haven’t heard about pre-buying. More likely, if there’s a question, they’ll hold their current products longer” before trading them in, he says.
Will the lower prices of trucks without EGR make them bargains that buyers won’t be able to resist?