Just saying ‘no’ to NOx: no easy matter
To comply with EPA’s emissions reduction mandate, all enginemakers except Caterpillar use exhaust gas recirculation, known as ‘EGR.’

by Paul Abelson, technical editor

At the International Trucking Show, Detroit Diesel displayed its latest Series 60, designed to meet the emissions regulations due in October. With that introduction, all heavy-duty engine builders have described the emissions-reducing technologies. The new regulations call for 2.4 grams per horsepower-hour (g/hp-hr) of combined oxides of nitrogen (NOx) and non-methane hydrocarbons (NMHC) and 0.10g/hp-hr of soot. Current engines produce about 0.4g/hp-hr of NMHC, so the October engines reduce 50 percent NOx from today’s 4.0g/hp-hr standard, effective since 1998. 

But the Environmental Protection Agency (EPA) claimed the engines were “rigged” to allow better fuel economy and greater performance while spewing forth more NOx. Even though they passed test procedures that EPA devised, the enginemakers agreed to pay penalties rather than try to fight EPA. They also agreed to advance the next deadline for emissions cut by 15 months.

The dilemma
High combustion temperatures are needed to burn diesel so it does not create soot. Those same high temperatures cause nitrogen and oxygen, the main gases in air, to combine and form NOx. Raise temperatures to eliminate particulate matter (pm), and you create NOx. Lower temperatures to avoid making NOx and you get more pm. 

All enginemakers except Caterpillar use exhaust gas recirculation (EGR). Exhaust is inert. It dilutes oxygen to lower peak combustion temperature. Computers can control fuel injection for a pulsed burn, so fuel is more completely used, but temperatures stay low to avoid forming NOx. Up to 15 percent of exhaust goes back to the intake. The exhaust gas is upwards of 1,800 degrees F. It must be cooled before it can be used. A heat exchanger draws heat from the gas and transfers it to engine coolant. The coolant transfers heat to the radiator where it transfers to underhood air. That system is called “cooled EGR.” Cummins, Detroit Diesel and Mack use it. Exhaust flow is metered by computer-controlled valves. To assure there is sufficient exhaust pressure, most enginemakers use either variable-geometry turbochargers or turbos with waste gates. Both techniques result in more responsive engines with minimal turbo lag. 

Volvo uses pressure to divert the gas. Every time an exhaust valve opens, pressure travels through the manifold, forcing some of the exhaust to the cooler. Simple flapper valves prevent back flow. Mack uses uncooled internal EGR in its vocational engines. Internal EGR is done with valve timing. The exhaust is kept open during the intake stroke, drawing exhaust back from the manifold into the cylinder. This only works when engine speed varies. Mack uses cooled EGR for on-highway engines. 

Caterpillar believes EGR is only a short-term fix, and it will not be viable in 2007, when standards call for even more drastic cuts, to 0.2g/hp-hr NOx and 0.01g/hp-hr particulates. Cat is using higher pressure fuel injection, split injection timing, a “smart” wastegated turbocharger and a diesel oxidation catalyst near the muffler. Their Clean Power II engines are close to meeting 10/02 standards. They have said they will absorb any EPA penalties. Their ACERT (Advanced Combustion Emissions Reduction Technology) engines will be ready by 2003.

Today, a typical diesel uses 44 percent of the fuel’s energy for propulsion. The remaining 56 percent either goes out the exhaust (33 percent) or into the coolant (23 percent). With cooled EGR, engine efficiency will remain at about 44 percent, but about 7 percent of the heat lost in exhaust will be added through the EGR cooler to the 23 percent in the cooling system, raising it to 30 percent of the fuel’s energy. It increases the load on the cooling system by 30 percent. To compensate, cooled EGR engines must have larger radiators, up to 1,500 square inches, and as many as eight rows of cooling tubes, rather than today’s four. Fans will be larger in diameter, with up to 11 blades. They will consume up to 55 hp. Shrouds will be redesigned. 

So far, I’ve driven three trucks with 10/02 engines; two with Cummins’ ISX and one with Cat’s C-12. They are responsive and enjoyable to drive. The big questions are: Will they last? What will happen to maintenance intervals? Will engines still be able to go a million miles? No one knows yet, and won’t for another few years. That’s why major fleets have put their purchases on hold. 

I won’t advise against buying a new truck, since the enginemakers say their products will last. Detroit claims years of EGR experience in their Series 50 bus engines. My advice is that if you need to replace your truck or add another, make sure you get an extended warranty. You might want to do what the big fleets do — negotiate the longest warranty you can to cover the truck for as long as you plan to own it. If (as everyone is predicting) sales drop drastically, you may be able to get a long-term warranty for little or no added cost. This could become even more of a buyer’s market. Whatever you decide, good luck.