General Motors’ all-new 4.5-L Duramax diesel V8 slated for late-2009 production is sailing smoothly through its Gamma development phase, according to Director of Diesel Engineering Charlie Freese. In the GM Powertrain development process, Gamma denotes final testing with production-intent hardware.
“I’m very pleased with progress,” Freese told AEI in early February. “We have vehicles running, and calibration configurations are on track. This is the part of the program where we ‘tune’ the engine to integrate it into the vehicle and make sure it’s an overall powertrain package that meets expectations.”
Freese is particularly happy with the performance of the engine’s innovative cylinder heads, which feature inboard exhaust ports and internal intake ports. In this configuration, the exhaust ports face toward the valley where the single turbocharger is located. And the intake ports are located inside the two-tiered head. They are fed pressurized charge directly through the tops of the intake camshaft covers. This design allows the exhaust manifolds to be integrated into the aluminum head casting.
“Our analytical data on the heads has proven out in the hardware,” Freese said. “We’re seeing many advantages including reduced part count—we’ve saved more than 70 parts by going to the inboard exhaust, compared with other Vee diesels in our portfolio.”
Fewer parts bring mass savings and lower assembly times, which helps lower cost, he noted. The design also optimizes airflow in the engine and reduces restrictions from having crossover pipes that carry exhaust from the outside to the inside where EGR coolers are located.
“This layout gives us the ability to tune the amount of volume needed in the exhaust system within the configuration of the cylinder head manifold, which is integral,” Freese explained. “And we don’t need to have any more exhaust passage volume than what’s needed just to hook up to the turbocharger.”
The DOHC V8 diesel was planned specifically for light-truck applications. Its narrow 72º cylinder angle allows it to fit the same ultra-compact box volume as GM’s small-block V8s. Besides the unique cylinder-head arrangement, the new Duramax boasts a compacted-graphite-iron (CGI) cylinder block, piezo-type common rail fuel injectors operating at 2000 bar (29,000 psi), and a selective catalytic reduction aftertreatment system that Freese calls “the best choice” for reducing NOx (oxides of nitrogen) to meet the new EPA Tier 2 Bin 5 emissions regulations. It is also package-protected for closed-loop cylinder pressure monitoring.
Rated output is targeted at more than 310 hp (231 kW), or 68 hp/L (51 kW/L), and 520 lb·ft (705 N·m).
As the new Duramax moved from early proof-of-concept and Beta development phases to its current configuration, engineers have made a number of changes. They have tested extensively ribbed, reinforced-plastic camshaft covers (the Gamma-level engine wears cast-aluminum covers; Freese will not reveal the production material). They have also redesigned the engine’s accessory drive, revised the turbocharger outlet tract for improved airflow, and tweaked the oil cooler mounting, among other changes.
When it reaches production, the 2010 Duramax may turn out to be the fastest clean-sheet diesel development program yet in Freese’s career.
“It was up and running quickly, and the design has evolved quite well, given the high level of innovation,” he said. Using genetic algorithms to optimize the combustion process before reaching the single-cylinder test stage was a big advantage, he noted.
“Simulating thousands of combustion chambers and accurately modeling the real physical behavior of the combustion system allowed us to eliminate all the bad ideas,” Freese said. “We then centered on one design from which we cut hardware, and moved forward with a high degree of confidence.”