Volvo’s pursuit of lower CO2 figures for its diesel engines has led to the introduction of two new five-cylinder units, each of 2.4-L capacity. The single-turbo 2.4D and the twin-turbo D5 will power S80, V70, XC60, and XC70 models.
In the XC70, the new 2.4D offers 159 g/km (according to preliminary figures), compared to 199 g/km for the engine it replaces; the D5 emits 185 g/km vs. 199 g/km previously. Power of the D5 is upped by 15 kW (20 hp) to give 151 kW (202 hp) and that of the 2.4D by 9 kW (12 hp) to 129 kW (173 hp). Both engines have maximum torque of 420 N·m (310 lb·ft).
Now entering production, the engines will be available by late spring. "Reducing emissions and particulates was one of the basic requirements when the new engine was being developed," said Derek Crabb, Volvo’s Vice President, Powertrain Engineering.
The aluminum D5 engine uses two turbochargers of different sizes operating in sequence to help achieve linear power delivery over a broader rev range. Together they provide a boost pressure of 1.8 bar (26 psi). Maximum torque is delivered from 1500 to 3250 rpm. Volvo claims that there is no perceptible turbo lag.
Higher levels of EGR (exhaust gas recirculation) are also achieved. The system’s volume has been upped, and cooling fins have improved heat dissipation efficiency by some 25%, leading to reduced NOx emissions to meet Euro 5 requirements.
Both engines use piezoelectric injectors delivering seven injections per cycle with an injection pressure up to 1800 bar (26.1 ksi). Compression ratio of the D5 is 16.5:1.
A particular focus of Volvo’s engineering development team was to reduce internal friction and pumping losses. Both engines get ceramic glow plugs for faster warm-up and reduced emissions; they reach 1000°C (1832°F) in 2 s. At very low engine revs, the plugs are used to increase in-cylinder temperature to support more efficient combustion. The D5's high-pressure pump system has two pump elements instead of the three used for the previous-generation engine. There is no dipstick. Oil-level information is supplied by a dashboard display, and the amount needed to top up is also given. To enhance engine smoothness, new mountings were developed, supplemented by a third torque rod to provide added stability under hard acceleration.