To be introduced at the upcoming Geneva Motor Show in March, the 2.2-liter Clean Power engine offers 130 kW (175 hp) of power and 400 Nm (295 lb-ft) of torque, while producing levels of NOx and PM emissions that are respectively around 50% and 80% below Euro-4 standards. (See chart to right. The D-4D 180 Clean Power refers to the concept car noted above.)
The Clean Power engine uses a new, high-pressure piezoelectric common-rail injection system.
The principle of piezoelectricity describes the capacity of certain materials to deform upon the application of an electrical current and to return to their original state when the current is removed. In a piezoelectric fuel injection system, each injector is composed of a stack of piezoelectric ceramic elements. When an electric current is applied to the stack, the elements expand almost instantaneously, allowing the fuel coming from the common-rail into the cylinder.
This technique allows larger volumes of fuel to be injected in a shorter time than would be possible with solenoid injectors. It also results in greater fuel atomization to enable more efficient combustion across the range of the engine.
The Clean Power engine also uses Toyota’s D-CAT (Diesel Clean Advanced Technology) package as standard. The D-CAT emissions technology is already available in the Avensis model.
D-CAT consists of a number of elements, but at its heart is the DPNR (Diesel Particulate NOx Reduction system) 4-way catalyst that reduces NOx and PM simultaneously. (Schematic illustration of D-CAT components to the right.)
The DPNR catalyst relies on the engine management system to vary the air-fuel ratio in the exhaust gasses.
To achieve this, a fifth injector, known as Exhaust Port Injector (EPI), has been added and placed in the exhaust port. At the critical moment, fuel is injected into the exhaust gas flow in order to create stoichiometric conditions in the DPNR catalyst. This ‘rich spike’ allows the DPNR catalyst to reduce NOx and PM.
The EPI also performs the sulfur discharge control. When the sulfur accumulated in DPNR catalyst reaches a certain level, the EPI will increase the catalyst’s bed temperature in order to release the sulfur.
Toyota D-CAT also adopts a high-efficiency EGR (Exhaust Gas Recirculation) cooler to increase the density of the exhaust gasses being recirculated into the combustion chamber by reducing their temperature.
Along with the 2.2-liter Clean Power engine, Toyota is introducing another 2.2-liter engine in the mid-power range, offering 110 kW (148 hp) of power and 310 Nm (229 lb-ft) of torque.
Fuel consumption figures are not yet available. However, the current production Avensis using a 2.0-liter diesel with D-CAT consumes 5.8 liters per 100 km (combined), or 40.5 mpg (US), with CO2 emissions of 155 g/km.
At the introduction of the Clean Power concept last year, Toyota also indicated that it would extend the engine range down to 1.9 liters, 2.2 liters being the current top-end.
It will be interesting to see Toyota’s approach to the North American market with these Clean Power diesels. I haven’t seen any statements regarding their potential introduction here. I assume that Toyota will monitor the acceptance of diesels in the NA market and decide accordingly.