Cat's ACERT Engines Promise To Be Formidable EGR Alternatives

Sept. 28, 2010

Most truck-engine manufacturers reached for exhaust-gas recirculation (EGR) to meet the Environmental Protection Agency's Oct. 1, 2002, emissions deadline. Only Caterpillar rejected EGR entirely, choosing instead to pay a steep fine for each Clean Power truck engine it has sold since October. But fines on the C9 stopped Jan. 17, when EPA certified it with elements of the exhaust-cleaning alternative called ACERT. And Cat's other mid-range ACERT offering, the C7 that replaces the on-road 3126E, was certified this spring.

ACERT is Caterpillar's acronym for Advanced Combustion Emissions Reduction Technology—an impressive-sounding name with a price tag estimated at well over $500 million.

"It has been the most expensive, largest development program Cat has undertaken," says Jim Parker, vice president of Cat's engine marketing division. "We've spent more on it than on development of the high-drive tractors."

ACERT is an assemblage of reasonably familiar componentry that might appear unspectacular compared to the attention this technology has garnered.

The C7 and C9 ACERT engines retain hydraulically actuated electronic unit injectors (HEUI), used on Cat mid-range engines since 1997. Electronically controlled waste-gate turbochargers and exhaust aftertreatment complete the mid-range ACERT package. Heavy-duty engines—the C11 (replacing the C-10), the C13 (replacing the C-12), and the C15—are expected to certify with mechanically actuated electronic unit injectors (MEUI), dual turbochargers, and exhaust aftertreatment.

Boost pressure from the dual turbochargers reaches over 40 psi, which not only reduces NOx, but also gives the driver faster throttle response. The turbos use electronically controlled wastegates and they are plumbed in series. The air charge tends to be hot. High-horsepower engines use jacket-water aftercoolers and air-to-air aftercoolers together, so ACERT will make use of the cooling systems truck makers designed for EGR.

Probably the boldest ACERT innovation is variable intake-valve actuation, and its electronic controls. Cat employs a solenoid adapted from HEUI which allows the on-board computer to work with the camshaft. Refinements to MEUI enable it to inject varying amounts of fuel several times during each compression stroke. The on-board computer adjusts the amounts and timing of air and fuel delivered to each cylinder for peak combustion. (Cat expects fuel economy equal to engines built in 2001.) Much less NOx leaves through the exhaust valve.

Cat's diesel oxidation catalyst traps particulate matter, the other diesel-emission villain, downstream. The aftertreatment technology has been used on Cat mid-range engines for years, and it was added to heavy-duty engines last October. Cat says the stainless-steel, muffler-type component has no moving parts, that it requires no service, and expects it to last as long as the engine. "Meeting emissions regulations without regard to customer impact is unacceptable at Caterpillar," says Parker. "It's a key reason we abandoned cooled EGR."

EGR reintroduces portions of the exhaust stream into the combustion chamber with intake air. ACERT engines don't breathe in exhaust. This is the key difference on which Cat has wagered its non-compliance fines, and its future. Parker quotes reports by the North American manufacturers of engines with cooled EGR to EPA that those products could require two to four more repairs in the first 500,000 miles than comparably rated engines designed in 2001. The makers of EGR also warned EPA that life to overhaul could be reduced by 25 percent.

These reports were made in 2001, while most manufacturers were still developing EGR technology (go to the website to read the report). Their accuracy might suffer from the advancement of EGR since then, but the numbers do provide some measure of operating cost. Parker estimates the per-repair cost, adds it to the cost of reduced life to overhaul, and ACERT's anticipated fuel savings.

Caterpillar engineers are confident that ACERT will deliver fuel economy 3 to 5 percent better than comparable EGR engines, as well as longer oil-change intervals. Adding Cat's typical resale-value advantage to those values, Parker estimates total cost in the first 500,000 miles of an ACERT engine's life will be about $10,000 less than comparably rated engines with EGR.

Cat's ACERT gambit already shows signs of paying off. Paccar (Kenworth and Peterbilt), Freightliner, and International have each limited their heavy-duty engine options to two. Caterpillar is one of the two choices offered in these trucks. Plus, ACERT promises to be a platform on which Cat can build lots of emissions-compliant products.

"ACERT will eventually touch almost all Cat engine applications, including earthmoving and construction equipment," says Tana Utley, medium- and heavy-duty product director with Cat's engine division. "And it gives us a clear line of sight to meeting the 2007 on-highway emissions regulations."