2012 DURAMAX 6.6L TURBO DIESEL (LML/LGH)

Vehicle Applications

· Chevrolet Silverado 2500HD / 3500HD (LML)

· Chevrolet Express (LGH)

· GMC Sierra 2500 HD / 3500HD / Denali HD (LML)

· GMC Savana (LGH)

· Chevrolet and GMC chassis cab and box-delete trucks (LGH)

Product Highlights

· Strong cylinder block with induction-hardened cylinder walls

· Piston-cooling oil jets

· Lightweight aluminum cylinder heads

· Common-rail fuel injection with piezo injectors

· Variable-geometry turbocharger that enhances smart engine brake system

· B20 biodiesel capability

· 397 horsepower (296 kW) and 765 lb.-ft. of torque (1,037 Nm) – LML version

· 335 horsepower (249 kW) and 685 lb.-ft. of torque (928 Nm) – LGH version

Overview

With nearly 1.3 million Duramax diesel engines in operation since the engine was launched in 2000, no other automaker has as much diesel engine development experience in meeting the demands of the heavy-duty truck customer as General Motors.

In 2011, GM raised the bar with a new version of the Duramax 6.6L turbo diesel engine that was stronger, more powerful and more efficient than previous models, while retaining features such as common rail fuel injection and aluminum heads with a six-bolt-per-cylinder design that helped cement the Duramax’s foundation years ago. Digital modeling and simulation tools were used to raise the new engine’s durability benchmarks.

The new Duramax returns unchanged for 2012 and is offered on the Chevrolet Silverado 2500HD and 3500HD trucks, as well as GMC Sierra Denali HD, 2500HD and 3500HD. Known by its LML engine code, it is rated at 397 horsepower (296 kW) at 3,000 rpm and 765 lb.-ft. of torque (1,037 Nm) at 1,600 rpm.

A slightly different version of the Duramax 6.6L is offered in full-size vans, chassis cab and box-delete trucks. It is based on the same improved architecture and includes most of the same features as the LML, but is engineered to meet federal certification standards for incomplete vehicles, including the incorporation of a robust EGR system. It is rated at 335 horsepower (249 kW) at 3,100 rpm and 685 lb.-ft. of torque (928 Nm) at 1,600 rpm.

Cylinder Block and Rotating Assembly

The new Duramax block features a revised casting enhanced to support smoother and quieter engine operation. It continues to use a strong cast iron foundation known for its durability, with induction-hardened cylinder walls and five nodular iron main bearings. A deep-skirt design (the block extends below the crankshaft centerline) and four bolts per main – two vertical and two horizontal bolts – help ensure the block’s strength and enable more accurate location of the rotating assembly. Also, a die-cast aluminum lower crankcase strengthens the engine block and serves as the lower engine cover, while also reducing the engine’s overall weight.

The new Duramax engine also features a revised oiling circuit that includes a dedicated feed for the turbocharger to provide increased pressure at the turbo and faster oil delivery. There is also a new oil pump that delivers 21-percent greater capacity, for increased oil pressure at lower speeds. The main bearings’ profiles are changed, too, to increase oil film thickness, which enhances durability.

Working within the cylinder block is a robust rotating assembly that features a forged steel crankshaft, forged steel connecting rods and forged aluminum pistons. The crankshaft is surface-hardened by nitriding, a process widely acknowledged as the most effective means of limiting wear and ensuring durability.

The pistons are redesigned without pin bushings to reduced reciprocating weight, which helps the engine rev quicker and respond more immediately to throttle changes. The pistons also feature a revised head profile that helps lower the engine’s compression ratio to 16.0:1. New connecting rods are used with the pistons and feature a smaller-diameter pin bore on the small end to support the strengthened pistons. This is another component of the Duramax’s improved durability.

Piston-cooling oil jets are located at the bottom of the cylinder bores and spray engine oil on the bottom of the pistons.

Cylinder Heads

The new Duramax diesel retains its signature aluminum cylinder head design, with six head bolts per cylinder and four valves per cylinder. The cylinder head design for the new Duramax remains similar to previous models, except for provisions for new, piezo-type fuel injectors.

The aluminum material of the heads helps reduce the engine’s overall weight, while the six-bolt design provides exceptional head-clamping strength – a must in a high-compression, turbocharged application.

Excellent airflow through the engine is achieved with the four-valve configuration. The intake valves measure 1.30 inches (33 mm) in diameter and the exhaust valves are 1.22 inches (31 mm) in diameter.

2000-Bar Fuel System with Piezo Injectors

The Duramax continues to use a common-rail direct injection fuel system. An increase of injection pressure from 1,800 bar (26,100 psi) to 2,000 bar (29,000 psi) improves fuel atomization, for a “cleaner” burn that promotes a reduction of particulate emissions. New piezo injectors allow a more precise metering of the fuel, especially for very small quantities of injected fuel, which leads to a smoother idle and lower combustion noise.

To further optimize the combustion process for the two versions of the Duramax (LML and LGH), the injection nozzles have different numbers of spray holes: eight holes in LML injectors and seven holes in LGH injectors. The shape of the spray holes is optimized to increase the hydraulic efficiency of the nozzles, which also helps reduce emissions.

Variable Geometry Turbocharging System

A new variable-vane turbocharger is employed on the 2011 Duramax 6.6L, advancing the engine’s legacy of state-of-the-art, variable-geometry boosting. The new turbo is designed to bolster a new smart engine brake system with the Allison 1000 six-speed automatic transmission, which creates added backpressure in the exhaust, resulting in negative torque during deceleration and downhill driving, enhancing driver control and prolonging brake pad life.

With the variable-geometry turbocharger, the engine delivers more power with lower exhaust emissions and no decrease in overall fuel efficiency. The system uses self-adjusting turbine vanes and sophisticated electronic controls to automatically adjust boost pressure and exhaust backpressure. The vanes, which can be opened and/or closed to vary boost pressure, direct exhaust gas at the turbocharger's turbine blades. This design enables boost to be controlled more precisely, with a greater range of modulation, than with a fixed-blade turbine. It also eliminates the need for a conventional wastegate.

During low-load conditions, such as idling for extended periods and low-speed driving, the temperature of the exhaust falls. To increase the load on the engine during those periods, a throttle is added to the intake system, upstream of the turbocharger. It is operated by the engine control module as an additional control for combustion temperatures.

As with previous models, the new Duramax’s turbocharger is mounted in the “V” area of the engine, between the cylinder heads, where it is cooled by the engine’s coolant system.

Emissions and Particulate Control Technology

The Duramax diesel features the latest in emission control technology, making it the cleanest Duramax engine ever produced, with NOx emissions reduced by at least 63 percent with the LML version, compared to the 2010 model. NOx emissions are controlled via a Selective Catalyst Reduction (SCR) aftertreatment system that uses urea-based Diesel (Emission) Exhaust Fluid (DEF). The DEF is housed in a 5.3-gallon (20 L) tank and needs to be replenished about every 5,000 miles (8,000 km). Three electrically heated lines – with heating controlled by the engine control module – feed the DEF to the emission system to ensure adequate delivery in cold weather.

Two new NOx sensors monitor the in and out levels of NOx of the SCR system for proper urea dosing, enabling very low levels of emissions. Two additional exhaust gas temperature sensors were added to provide temperature feedback to the control system for optimum diesel oxidation catalyst and SCR performance. This optimum performance provides increased durability for the aftertreatment system and promotes very low levels of emissions.

The new Duramax 6.6L also includes GM’s second-generation diesel particulate filter system, which regenerates its diesel particulate filter using a downstream injection of diesel fuel directly into the exhaust stream and can travel up to 700 miles (1,125 km) between regenerations – a 300-mile (482 km) increase over the previous Duramax engine. The use of downstream injection also helps improve engine life by eliminating concerns surrounding the possibility of diesel fuel contaminating engine oil, which can happen when fuel used for regeneration is introduced directly into the cylinder.

A complex ceramic-type exhaust gas filter is installed behind the oxidizing catalyst already in the exhaust system. The filter replaces the conventional muffler and consists of hundreds of small, porous tubes blocked at one end, which forces the exhaust gas through the walls of the tubes, which trap particulate matter. The trapped particles are then burned off by the heat of the exhaust, which reaches 550 degrees C. Sensors detect the differential pressure between exhaust gas entering and exiting the filter, and signal the engine control module to adjust combustion to maintain the exhaust gas temperature.

B20 Biodiesel Capability

The LML Duramax 6.6L turbo diesel is capable of running on B20 biodiesel, a fuel composed of 20 percent biodiesel and 80 percent conventional diesel. B20 helps lower carbon dioxide emissions and lessens dependence on petroleum. It is a domestically produced, renewable fuel made primarily of plant matter – mostly soybean oil

Extensive testing and validation was performed on the Duramax 6.6L using B20 that meets ASTM International’s standard D7467, which covers biodiesel blends between B6 and B20. To make the Duramax 6.6L and its fuel system compatible with B20, GM upgraded some seals and gasket materials to withstand the ester content of biodiesel and included an upgraded fuel filter that includes a coalescing element. It improves the separation of water that may be present in the fuel, because biodiesel can attract and absorb water. Also, additional heating of the fuel circuit was added to reduce the chance of fuel gelling or waxing that could plug filters.

The Duramax 6.6L’s diesel particulate regeneration system features a downstream injector that supplies fuel for the regeneration process. This greatly reduces potential oil dilution, which is important when using biodiesel. Downstream injection saves fuel and works better with B20 than in-cylinder post injection.

Fuel Filter

A unique filtration medium inside the fuel filter canister provides excellent separation of emulsified water in the fuel, reducing the likelihood of water entering the high-pressure fuel system. Compared to earlier filter designs, this one can extend filter life by up to 33 percent.

Easy underhood access to the fuel filter remains a hallmark of the new Duramax 6.6L. It is easily changed in Chevrolet and GMC HD pickups without putting the vehicle on a lift; it is accessible by simply leaning into the engine compartment.

Quietness

The LML Duramax 6.6L improves on an already low-noise reputation with double-pilot injection, a strengthened block and, in some conditions, lower rail pressure, contributing to a nearly 30-percent noise reduction noise at the engine level. A new piezo-actuated fuel injection system – capable of operating on ASTM grade B20 biodiesel – ensures more precise fuel delivery, improving emission performance and playing a crucial role in reducing high-speed noise, vibration and harshness.

Cold Weather Performance

The new Duramax continues to provide outstanding cold-weather performance, with microprocessor-controlled glow plugs capable of gas engine-like start performance in less than three seconds in temperatures as low as -20 degrees F (-29 C), without a block heater.

Duramax for Commercial Trucks

The LGH Duramax for full-size vans, chassis cab and box-delete truck models is based on the same improved architecture and includes most of the same features as the LML version, but is engineered to meet federal certification standards for incomplete vehicles. Mostly, that means the LGH is emissions-certified separately from the rest of the vehicle, while the LML is certified in the vehicle, with all of the exhaust and emissions equipment.

To meet the more stringent emissions requirements for 2011, the LGH Duramax features a robust EGR cooling system, along with revised turbocharger tuning that helps enhance EGR performance (the LML has an EGR bypass) and different injector nozzles. The LGH also has a larger-capacity selective catalytic reduction system. Although it differs slightly from the LML version, the LGH Duramax offers the same key features and benefits, including the exhaust brake system, B20 biodiesel capability and excellent cold-start performance.

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