GM's surprising new V8 diesel has no manifolds
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Right side of the new V8 shows lack of exhaust manifold. Intake route is straight into the top of the intake cam boxes.
General Motors has taken some of the wraps off of its 2010 Duramax diesel V8, revealing clever design features and technologies that clearly push the state-of-the-art in Vee-type compression-ignition engines.
Unveiled during a media briefing at its Milford, MI, Proving Grounds, the new 4.5-L powerplant will be one of the most powerful, lowest-emitting, and package-efficient light-duty V8 diesels in the marketplace, company engineers claimed.
The new Duramax is scheduled to enter production in late 2009 at GM's Tonawanda, NY, engine plant. It will power GM's full-size pickup trucks and utilities, among other potential applications. Rated output is targeted at more than 310 hp (231 kW), for 68 hp/L (51 kW/L), and 520 lb•ft (705 N•m).
The Duramax was designed to fit within the ultra-compact envelope of GM's small-block gasoline V8. Its NVH profile also targets the gas engine. These aggressive requirements drove many of the engine's innovations announced to date.
The new engine's aluminum cylinder heads' exhaust ports face inboard, toward the valley of the cylinder block. This allows the single variable-geometry turbocharger, exhaust-gas recirculation (EGR) cooler, and close-coupled oxidation catalyst to reside within the valley. The layout negates the need for separate exhaust manifolds while reducing overall width.
The reversed-head orientation also means the new diesel does not use a conventional intake manifold. Its intake ports are internal, rather than arrayed along an exterior face of the head as in common practice. The ports are fed pressurized charge directly through the tops of the intake camshaft covers.
The heads' unique two-tiered internal construction segregates the intake route, the chain-driven DOHC valvegear, and water jacket. (The fully dressed engine on display was not sectioned, so no internal details were revealed.)
Compacted graphite-iron (CGI) optimizes the cylinder block's strength and mass. The block's cylinder banks are splayed at 72º to achieve a narrow overall package with even firing, but the narrow vee requires a balance shaft for smooth running. GM studied aluminum block castings but determined that the light alloy would not deliver sufficient long-term durability and could not cope with the cylinder pressures planned for the new engine.
The main bearing caps are precision-fractured ("cracked"). This novel application of a feature that is commonly used for connecting rod big-ends enables closer crank-to-bearing tolerances with greatly improved assembly accuracy.
Piezo-type common-rail fuel injectors operating at 2000 bar (29,000 psi) are one of the keys to the new diesel meeting ultra-stringent U.S. Tier 2 bin 5 and California LEV2 emissions regulations. Another enabler is the engine's urea-based selective catalytic reduction system for reducing engine-out NOx (oxides of nitrogen) emissions.
The Duramax is package-protected for closed-loop cylinder pressure monitoring, a technology GM will introduce on its new 2.9-L turbodiesel V6 next year in Europe.
The initial concept for the new Duramax sprang from impromptu brainstorming sessions between GM's Director of Diesel Engineering, Charlie Freese, and the V8's Chief Engineer, Gary Arvan.
"It was totally clean-sheet," Freese recalled. "Starting with very rough sketches, our path to every technical solution began with a 'what if.' We ended up avoiding traditional approaches."
And Mountain Dew, rather than coffee, was the engineers' preferred beverage during the meetings, which stretched into many late evenings.
According to Arvan, one strategic goal was to eliminate the component duplications that make Vee-type diesels inherently more complex and costly. Hence the single turbocharger and absence of exhaust manifolds.
Another goal was "to shorten the typical long induction and exhaust paths and minimize surface area along the way, to quickly get the hot exhaust out of the heads and into the turbo," he noted.
Eliminating the intake manifold and employing internal exhaust-gas recirculation also reduces the number of noise-radiating surfaces, Arvan said. And the stout CGI block "is stiffer than any competitive cylinder block we've analyzed—and we've analyzed them all," Freese added.
The Duramax's bills of design and materials (BoD and BoM) were developed to achieve some commonality with the current-generation 6.6-L V8. Shared features include the quick-start system with intake air heater, electronic EGR, and some elements of the larger diesel's electronic control system. The 4.5-L engine will employ a new E86 engine controller.
GM will uncloak more of the V8's secrets this year, after the automaker establishes patents in a number of areas, said Freese.
Lindsay Brooke
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