Operating costs (e.g., fuel) for the new Euro-4 engines are, according to Scania, comparable to those of their Euro-3 cousins, despite the lower emissions levels.

Scania will use SCR (Selective Catalytic Reduction) selectively on high-output V8 engines to allow customers to benefit now from tax and toll incentives for Euro-5 class engines, prior to Scania’s accomplishing the EGR development that will deliver the same level of emissions reductions.

Emissions control techniques on Scania’s current range of truck engines

Ultimately, however, Scania EGR and XPI injection will feature on the full range of Euro-5 engines.

The choice of emission technology is part of Scania’s strategy to provide an integrated powertrain that secures the best possible operating economy for the customer in any type of transport.

Exhaust Gas Recirculation. EGR has been in use for several decades, in cars as well as heavy-duty vehicles. EGR takes a portion of the exhaust gases, cools it and feeds it back into the combustion chamber toserve as a filuent to lower the oxygen concentration and also to increase the heat capacity of the air/fuel charge.

The cooled gas minimizes combustion temperatures, and the reduced oxygen denisty slows combustion, therey reducing NO_x emissions. Typical EGR NO_x reductions are about 50% percent.

However, PM emissions may increase and fuel economy may decrease as a result. Finding and maintaining the proper balance of EGR and temperature is key. Scania uses its high-pressure injection system and combustion management to reduce particulates and maintain or improve fuel efficiency.

Scania EGR systems extract up to 18% of the exhuast flow for Euro-4 engines and 25% for Euro-5. A flow meter and an EGR valve controlled by the engine management system determine the exact amount under different conditions.

The exhaust gases pass through a cooler that is integrated in the engine’s cooling system and led into the intake manifold. The intake air, after passing through the turbocharger and charge-cooler, is pressurised at this point. Depending upon the engine’s basic deisgn, this is done either with or without turbocompounding.

On non-turbocompound engines, the intake manifold has a venturi valve at the point where the exhaust gases enter. The manifold has a constriction that speeds up the flow past this point, creating a suction effect that pulls the exhaust gases into the intake air flow.

To vary the size of the constriction, depending on engine revs and the amount of exhaust gas needed, the Scania venturi has two positions.

On turbocompound engines (higher horsepower versions of 420 hp and 470 hp), the extra turbocompound turbine means that the pressure is higher on the exhaust side, high enough to overcome the pressure in the intake manifold. No venturi valve is needed. Exhaust gas is supplied to the intake manifold in amounts regulated by the EGR valve.

Where an SCR-based system might add an additional 200kg in vehicle weight, the venturi valve for non-turbocompound engines adds 20 kg, and the turbocompound/EGR system adds 80kg.

In the full range of Euro-4 engines available this fall, Scania also uses a maintenance-free oxidizing catlayst.

For now, Scania will use SCR (selective catalytic reduction) to achieve Euro 4 on its more powerful V8 engines. These vehicles are likely to operate in areas where the infrastructure for the urea additive has been extended, or carry extra supplies on-board.

The Euro-4 engines are available this fall, the first Euro-5 engines will be available in 2006. Scania promises a full line of Euro 5 engines well prior to the 2009 legal requirements.

Looking beyond that, to what could be Euro 6, Scania expects testing methods betwen Europe and North America to be harmonized, and that Euro 6 emissions levels would be based closely on the EPA 10 standards in the US from 2010.

For the longer term, Scania is looking to developments in HCCI (homogeneous charge compression ignition).