Exhaust gas recirculation (EGR) lowers the engine's combustion temperature, thus lowering nitrogen oxide (NOx) levels.
Exhaust gas recirculation (EGR) lowers the engine's combustion temperature, thus lowering nitrogen oxide (NOx) levels.

Complete Review of the Dodge Ram 1500 and the Ford F-150 Lariate Edition.

There's one silver lining in our current downturn. With so many trucks operating at less-than-full capacity, fleet managers have the time to study what their purchasing options will be for the next engine update. Luckily, the effect of the engine emission upgrade will hit about the time our economy will be rising to full throttle.

The crux of the choice is the type of emission reduction strategy that is best for your fleet. To understand the differences, one needs a short review of diesel exhaust pollutants and how each emissions reduction strategy helps achieve EPA limits.

In October 2002, when, due to penalties for earlier violations, EPA forced most enginemakers to reduce nitrogen oxides (NOx) to meet the 2004 standard of 2.5 grams per horsepower-hour (g/hp-hr), exhaust gas recirculation (EGR) was the universally accepted strategy.

EGR drew exhaust gas from the tailpipe, cooled it in an under-hood heat exchanger using engine coolant, and introduced the exhaust gas back into the cylinders through the intake air. This diluted the intake air with inert exhaust, slowing the process and lowering the engines' combustion temperatures. That reduced NOx.

But EGR raised under-hood temperatures and put added stress on cooling systems. Components had to be redesigned to withstand higher temperatures.

The next emissions restrictions in 2007 required 90% less particulate matter (PM), including soot. The limits, which were 0.10 g/hp-hr, dropped to 0.01 g/hp-hr.

Control of PM is done in a diesel particulate filter (DPF). Exhaust flows into a diesel oxidation catalyst (DOC) that starts the chemical conversion of soot to inert carbon dioxide (CO2). Any remaining solids are then trapped in an ultra-fine ceramic filter. When the filter starts to clog, raw diesel fuel is sprayed over another catalyst, raising the internal temperature enough to oxidize the carbon soot and convert it to CO2 in an active regeneration process. The ongoing catalytic conversion is passive regeneration.

In Europe, where NOx has been targeted in recent years, truck manufacturers have used selective catalytic reduction (SCR). This process injects diluted urea into an exhaust after-treatment device. The urea is a catalyst to help chemically change the oxides back to pure nitrogen and oxygen, the two major components of air.

As urea levels drop, warnings are issued to the driver. If the urea is not replenished in a timely manner, engine power is reduced until more is added. In North America, the urea is called diesel emission fluid, or DEF.

Preferring EGR over SCR

In a survey conducted by Braun Research, of more than 300 class 5 to 8 truck operators with purchasing authority, 51% preferred EGR only; 24% preferred SCR. Their reasons were higher engine prices, reliability, added maintenance costs and new maintenance requirements, and added weight. Navistar commissioned the study.

At its press conference during the World of Concrete, executives from Navistar announced their decision to use EGR in International Trucks with proprietary MaxxForce engines. International will use only Advanced EGR to meet 2010 EPA diesel exhaust emission standards. That means Cummins engines, which will use SCR in addition to EGR, will not be offered in their 2010 trucks.

Jim Hebe, senior vice president of Navistar, aggressively defended Advanced EGR, despite all competitors' decisions to use SCR. The added SCR equipment adds weight and complexity and makes the operator, not the manufacturer, responsible for achieving compliance, said Hebe. Urea forms slush at 13º F, requiring thermostat-controlled heaters as part of the SCR equipment. (If the DEF becomes frozen, EPA allows idling until enough fluid is liquefied by the heater.)

Competitors counter they will use the same proven engine architecture as the 2007 engines, but with improved fuel economy. SCR requires less cooling than EGR, saving as much as 300 pounds. Fuel economy with SCR is claimed to be as much as a 4% to 5% improvement.

Preliminary estimates from Volvo, parent of Mack Trucks, indicate prices for 2010 trucks with SCR will range from $6000 to $10,000 higher than current models.

Another factor in the selection process is DEF availability. Over-the-road operators have concerns about DEF availability and drivers keeping DEF tanks full. But these concerns may not be as valid for domiciled fleets, such as concrete producers'.

The marketplace will ultimately determine the success or failure of either strategy, as the economy recovers and truck purchasers make their decisions. But now is the time you should ask questions.

Paul Abelson is a former director of the Technology and Maintenance Council of the American Trucking Association and is currently on the Board of Truck Writers of North America. To contact him, e-mailtruckwriter@anet.com.