Diesel hybrids: OEMS are combining the two fuel saving technologies to meet both demands for better fuel economy and lower emissions

Automotive Industries, Feb, 2005 by Bill Siuru

As the rivalry continues between the American-favored hybrid electric vehicles and European-favored diesels, Ford, General Motors and DaimlerChrysler brought prototypes that combine both technologies to the 2005 North American International Auto Show (NAIAS). These are the Mercury Meta One, Opel Astra Diesel Hybrid and Mercedes-Benz S-Class Hybrid. Diesels are already the most common power source in hybrid electric trucks and buses, driven partly by military interest in hybrids running on a single battlefield fuel, JP-8, that can be used in both ground and air vehicles.

Mercury Meta One

The Mercury Meta One, a showcase for many advanced technologies, features a 2.7L V6 diesel mated to a Modular Hybrid Transmission (MHT). The twin-turbocharged, intercooled, DOHC, 24-valve, 60-degree V-6 has a compacted graphite iron block and aluminum heads.

This engine is used in the new Jaguar S-Type Diesel sold outside North America. With the MHT, the torque converter of the 6-speed automatic transmission is replaced by a high-voltage electric motor and two hydraulic clutches so the motor can operate independently of, or with, the diesel engine. The 35-kW, three-phase motor also serves as the flywheel, starter, alternator and traction motor to drive the front wheels. The layout required minimal change to the base transmission, thus reducing the complexity and cost compared to other hybrid systems.

The MHT can operate in an assist mode to supplement the engine's output for additional power for acceleration and under conditions where a diesel pollutes most. For example, them is a short burst in soot emissions as a typical diesel's turbocharger speeds up when accelerating. Tuning a diesel engine to minimize this spike usually compromises throttle response The MHT provides a momentary burst of power for a quick takeoff with very low emissions. Electrical energy is stored in a 325-Volt, 6-Amp-hour nickel metal hybrid (NiMH) battery. Working together, the diesel and electric motor, the 2.7L- V-6 makes 248hp at 4,000 rpm and 431 ft. lb. of torque at 1,900 rpm--almost as much as the Ford's 6.8L Triton V-10--but sips rather than guzzles fuel.

Also helping fuel economy is a start-stop system that shut down the diesel engine during stops.

The Mercury Meta One is the first diesel hybrid that meets stringent Partial Zero Emission Vehicle (PZEV) requirements accomplished by combining hybrid and advanced exhaust after-treatment technologies. The latter includes (1) dual pre-turbo metallic oxidation catalysts for faster light-off and reduced cold-start emissions, (2) oxidation catalysts to reduce hydrocarbon and carbon monoxide, (3) urea selective catalytic reduction system to control nitrogen oxide, (4) catalyzed particulate filter, (5) dual-wall, air-gap exhaust pipes to retain heat in the after-treatment system and improve its efficiency, and (6) hands-free, capless fuel filler. According to Graham Hoare, director of Powertrain Research and Advanced Engineering, "By applying our full arsenal of advanced emissions-reduction technologies, we have demonstrated that it is possible for diesel engines to have emissions even lower than many gasoline engines on the road today. With its tremendous low-end torque, this turbo-diesel packs a strong, but clean, punch."

The Mercury Meta One's engine can run on a biomass-based diesel furl that minimizes carbon dioxide emissions being explored by Ford in partnership with BP. The renewable furl is produced via the Fischer-Tropsch process from feedstocks like grasses, waste wood, food crop residues and municipal solid waste. This furl can be blended with conventional diesel fuel to reduce life cycle greenhouse gas emissions. Since the furl comes from biological feedstocks that absorb carbon dioxide while growing, the furl doses the "carbon loop" as the carbon dioxide emissions are offset by the carbon dioxide absorbing furl production. Unlike biodiesel, this fuel is not susceptible to water contamination and microbial growth in storage tanks. It is also naturally sulfur-free, vital for use with emission control catalysts and filters.

With a focus on preventing and reducing the severity of accidents, Ford has developed several active safety technologies included in Meta One. These include Lane Departure Warning providing a visual, audible and vibration in the driver's seat if the vehicle departs from a lane without activation of a turn signal. A Crash Mitigation by Braking system uses a video camera and radar to sense vehicles on the road ahead. If the on-board system determines an imminent collision and the driver fails to react, brakes are applied automatically. Other high-tech electronics include a Reconfigurable Display so drivers can customize the size and location of displays, Wi-Fi integrated radio and SIRIUS satellite video that provide streaming video entertainment to passengers. The SmartNav system not only receives real-time traffic and weather information, but also communicates with roadside sensors about traffic and weather conditions that in turn communicate with a central computer system. This system informs all SmartNav-equipped vehicles in the region to suggest alternate routes.