At a time when most auto manufacturers are hedging their bets on the future of diesel engines in the U.S. market thanks to cumbersome emission regulations, General Motors is drawing a line in the sand, announcing it plans to introduce a newly developed diesel powertrain in its light-duty full-size pickups sometime after 2009. While details on the engine remain sketchy—GM won’t even disclose the displacement of its V8 prototype engine, other than to say it will be between the 3.0-liter diesel it sells in Europe and the 6.6-liter Duramax engine designed for heavy-duty truck applications—the automaker is willing to say that the new engine will achieve a 25% reduction in fuel consumption over current gasoline V8 engines, along with a 90% reduction in particulates and NOx compared with today’s diesels. Both a particulate filter and a urea-based after treatment system are to be used.
The engine was designed and developed in-house through extensive use of math modeling by GM’s Powertrain organization. Engineers began by developing the combustion system by modeling a single cylinder, then expanding it by seven more. The engineers exceeded their development targets, says Charles Freese, GM executive director, Diesel Engineering. “We beat the targets with the single cylinder, which is almost unheard of. Then we went to the multi-cylinder and we beat those targets and then we went to the vehicle and we beat those targets. Every step of the way we had the precision modeling capability to do that,” says Freese. While perfecting the combustion process, the team also spent a fair amount of time working to reduce the noise, vibration and harshness characteristics of the engine. The design features aluminum cylinder heads with an integrated manifold, compact graphite iron block and fracture-split main bearing caps and connecting rods for precise fit. The engine utilizes a high-pressure, common-rail fuel system, along with a regenerative particulate filter that should last upwards of 150,000 miles, depending on the operating cycle, before the ash would have to be flushed out of the system. The liquid urea-based after treatment system has a capacity of up to 5 gallons, which Freese says would need to be topped off at each maintenance interval.—KMK