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| Volvo D5 twin-turbo diesel engine. Click to enlarge. |
Featuring sequential twin turbochargers, ceramic glow-plugs and piezoelectric fuel injectors, the new engine applied in the S80 delivers 205 hp (153 kW) of power and 420 Nm (310 lb-ft) of torque, with fuel consumption of 6.2 liters/100 km (38 mpg US) and CO2 emissions of 164 g/km.
The previous engine generation has undergone constant development in a series of stages and had reached the end of its potential. We therefore decided to start with a clean sheet of paper and harness the advanced technology to which we have access today. The result is even better than we dared hope. What is more, this engine has been developed entirely in-house at Volvo.
—Derek Crabb, Vice President, Powertrain Engineering
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| The twin turbo system. Click to enlarge. |
The two turbochargers are of different sizes and together deliver boost pressure of 180 kPa (1.8 bar), across a broad rev range. The smaller turbocharger is used primarily at lower revs. It reacts more alertly than the larger one and provides immediate response to quick throttle movements. At higher revs, the larger turbocharger takes over to provide more propulsion when accelerating at higher speeds. In addition to increased performance and reduced fuel consumption, the twin-turbo approach makes it possible to exploit the EGR system more efficiently than before.
By increasing the volume of the EGR cooler and equipping it with effective cooling fins, it has been possible to increase heat dissipation efficiency by 25%. This in turn gives the returning exhaust gases far lower temperature, thus reducing emissions of nitrogen oxides (NOx) to Euro 5 requirements.
The piezoelectric fuel injectors are used in combination with an 1,800 bar (180 MPa) injection system. The piezoelectric injector nozzles can deliver up to seven separate injection events during each operating cycle. Due to this speed and the high fuel delivery pressure, the injector nozzle can provide short pre-delivery injections even when engine revs exceed 3000 rpm, contributing to reduced engine noise.
The piezoelectric injector nozzle can also produce extremely short post-delivery injections of fuel after the main injection sequence. As a result, the particulate filter can be regenerated even when the engine is running at low revs.
The fuel pump is a high-pressure unit with two pump elements instead of three as in the previous D5 engine generation. This makes the pump spin more easily, thus reducing the load on the various components. A more easily driven pump also reduces fuel consumption.
Ceramic glow-plugs provide excellent starting properties. They are heated up extremely quickly and reach 1,000 °C two seconds after a cold start. Maximum operating temperature is 1,300 °C, about 30% higher than that of a conventional glow-plug. With ceramic glow-plugs, the engine can be started immediately without pre-heating, even at temperatures as low as -30 °C (-22 °F).
Instead of using an oil dipstick the driver is alerted via the information display when it is time to top up with oil. The system even specifies how much oil is needed.
The engine mountings have been further developed and tailored to suit the high torque levels. They are supplemented with a third torque rod to stabilize the engine during firm acceleration.
When the project got under way, our goal was to bring fuel consumption down to 6.4 liters/100 km in the Volvo S80, which after all is a relatively large car. As the work progressed we saw that we could beat that target and today we are actually down to 6.2. With an automatic gearbox we have been able to reduce the consumption with more than 8 percent, from 7.3 to 6.7, which is a significant improvement.The new five-cylinder diesel is the first engine from Volvo’s new project office for diesel engine development. The entire process from receiving the design brief to installing the first engine in a car took less than three years.
—Derek Crabb
