Scania is to start introducing its Euro 5 EGR engine during 2007 using Scania’s XPI common-rail fuel injection system, starting in the mainstream long-haulage segment, according to research chief Hasse Johansson. He reckons the engines meet Euro 5 standards “without any fuel penalty”.
Scania’s EGR engine uses a system known as turbo-compounding to generate extra power out of less fuel. It recycles gases rather than expelling them straight away through an exhaust pipe. Heat is extracted from the exhaust gases by a second exhaust turbine downstream from the turbocharger. The second turbo (the turbo-compound turbine) spins at 55,000 r/min, the movement of which is passed through turbine gears and a hydraulic coupling, then through the timing gears to the crankshaft. Stepping down the revs produces a boost in torque, which when reaching the flywheel adds momentum and helping the engine to run more smoothly and evening out the rhythmic pressures induced by combustion. Exhaust gases enter the manifold at a temperature around 700ºC, and are then used to drive the conventional turbocharger.
These exhaust gases, instead of being directed out into the atmosphere, are pushed into the turbo compound unit, still at a temperature of around 600ºC. The energy is used to spin the second turbine at up to 55,000 r/min. After passing this point, the gases are cooler, somewhere around 500ºC, and are expelled via a conventional exhaust system and silencer.
The revolutions of the turbine are stepped down in various stages by mechanical gears and a hydraulic coupling. The hydraulic coupling balances out variations between the rotation of the flywheel and the turbo-compound turbine.
By the time drive reaches the crankshaft, the rate of rotation is down to around 1,900 r/min. The flywheel’s momentum is increased, and its rotation becomes more stable and even.