Toyota Unveils Cleaner, More Efficient Diesels

Toyota Motor Corp. says its new 2.4- and 2.8-liter diesel engines are cleaner, quieter and more powerful than the "KD" powertrains they replace.

The direct-injection "GD" four-cylinder engines are the first Toyota diesels to use a selective catalytic reduction system, which the company notes can eliminate 99% of nitrogen oxide emissions. The carmaker also made design improvements and other changes that enabled a 30% reduction in catalyst size and cut the number of its global exhaust system layouts from 18 to just three.

Toyota also is launching a new thermal "swing wall" insulation technology in the next-generation diesels. The system allows the 2.8-liter mill to achieve 44% thermal efficiency, which Toyota touts as "one of the most thermally efficient in existence." By comparison, the Toyota Prius' engine has a thermal efficiency of 37%.

The new insulation system coupled with the use of silica-reinforced porous anodized aluminum (SiRPA) on the pistons reduces cooling loss during combustion by about 30%, according to Toyota. It describes SiRPA as a high insulation and dissipation material that is easy to heat and cool.

Other improvements include:

• a new piston combustion chamber shape and a common-rail fuel injection system that allows for higher pressure.
• more precise control of fuel injection pressure.
• a port shape design that improves airflow to the engine.
• coordinating pilot injection to the state of the ambient air before primary fuel injection to shorten ignition delay.

The new diesel engines increase high-end torque by as much as 25% and boost fuel economy by about 15%. The new 2.8-liter diesel generates 174 hp and 332 lb-ft of torque, while the smaller oil burner makes 148 hp and 243 lb-ft.

The engines employ a new turbocharger that is 30% smaller than that used on current KD engines. Toyota says the design is more efficient and produces nearly instantaneous response, thus maximizing torque over a broader engine range.

Both engines are available in the Land Cruiser Prado midsize SUV that bowed this week in Japan. The 2.8-liter mill was launched in Thailand earlier this spring in the new Hilux small pickup truck.