Saturday, 11 April 2015
End of the road in sight for EGR
Diesel engine makers for trucks in the US are closely watching the legislators as they mull implementing reductions in greenhouse gas (GHG) emissions that will come on top of EPA 2017 requirements.
US diesel engine makers with strong European connections may be aware of Scania's intention to manage without EGR systems for its larger engines - the Swedish company has already eliminated EGR on its lower-powered diesel engines.
The trend in Europe with Euro 6 in place, as initiated by Fiat's truck-making arm, Iveco, looks to be set in the direction eliminating EGR systems altogether in favour an SCR-only exhaust treatment system. This follows in the face of advancing technologies surrounding the atomisation of Adblue (urea).
It will be recalled that some time ago Iveco declared it could meet Euro 6 requirements on its larger diesel-powered truck models using SCR alone, but not without the added cost of much heavier AdBlue consumption.
It is reckoned that Adblue consumption of Iveco engines could be as much as six percent of fuel consumption, although this on-cost is offset somewhat by the improved fuel consumption offered by SCR-only engines.
Now Scania has joined the fray as Mikael Björkstrand, Scania’s chief engineer responsible for all its five- and six-cylinder in-line diesels, admits the days of EGR could be numbered. Presumably others could follow.
Interviewed recently by UK's Commercial Motor magazine, Björkstrand has said the potential of SCR as a NOx suppressant is increasing continually, thereby diminishing EGR’s role.
According to Björkstrand, Scania has 60 engineers at its Södertälje engine laboratory working on AdBlue injection and mixing.
He claims the reductant can now be injected and atomised successfully into the exhaust stream at lower temperatures without the usual urea crystallisation taking place around the spray nozzle.
The net result is an improvement in SCR performance and reliability, leading to a substantial reduction in AdBlue consumption for a given NOx reduction. This is important as the engine maker edges Adblue consumption towards two per cent - a big improvement over Iveco’s performance.
EGR has the benefit of reducing peak combustion temperatures and thereby restricting NOx formation is detrimental to fuel economy and increases PM (particulate matter) emissions.
However, by eliminating EGR and allowing higher NOx levels to be dealt with downstream, gives engineers the opportunity to advance net injection timing. This in turn enables ever-higher levels of fuel injection pressures which in turn yield improvements in fuel economy.
It is this improvement in fuel economy, albeit on the back of higher Adblue consumption that could be one reason why executives of North American Diesel engine makers could be asking their engineers "Hey you guys, what's going on in Europe?"
US legislators are pushing for improved GHGs, notably better CO2 emissions (fuel economy) from diesel-powered trucks and SCR-only engines could be one way out.
Engineers at Detroit Diesel Corporation (Daimler Trucks of North America) in Detroit, Michigan, Mack Powertrain North America (Volvo) heavy duty diesel engine, transmission and driveline plant in Hagerstown, Maryland, and Paccar (Daf) in Columbus, Mississippi will be aware of developments at Iveco and Scania through their internal links.
Engineers at Cummins Inc. in Columbus, Indiana no doubt too will be aware through their counterparts in the UK of the company’s mid-range ISB engines which use EGR and SCR to meet Euro 6. These engines are supplied to Daf.
On the other hand, Navistar International’s engineers are somewhat at an arms-length disadvantage, despite former links with MAN in Germany and depending how open are present lines of communication. Although following the Lisle, Illinois company’s decision to go cap-in-hand to Cummins for large SCR six-cylinder diesel powertrains following the abrupt retirement in August 2012 of company boss Daniel Ustian, its powertrain engineers will now be closer to the SCR debate than previously they were ever allowed to be.
Diesel engines makers in the country need to meet EPA 2010 in terms of NOx and PM limits as well as reduce CO2 emissions. But in the face of even tougher legislation to meet GHG limits they could find themselves having to adopt SCR-only engines.
But if SCR-only engines do appear in North America, almost certainly operators will have to counter any gains in fuel economy with the increased costs associated with a higher consumption of Adblue.
The question on both sides of the Atlantic could be: Will the SCR-only engines be cheaper than their forebears which had EGR and SCR? Eliminating EGR hardware will simplify engine design and build but it will be interesting to see if any savings from hardware reduction are passed on to customers.
Europe is already mulling a computerised system for monitoring CO2 consumption through its Vecto program which is seen as a means of assessing and/or regulating CO2 emissions from trucks and buses without separate regard to the CO2/fuel consumption of the engine.
Thus, there appears to be two quite different lines of attack towards CO2 emissions. In Europe, the thinking seems to be in terms of ‘whole vehicle’ assessment whereas in the US the problem is being tackled at the powertrain.
Diesel engine makers in the US integrated with truck builders, namely Detroit Diesel, Volvo/Mack and Paccar might well prefer the European Vecto system, whereas being an ‘outsider’ Cummins might probably prefer a system that relates to its products rather than to the whole vehicle. Navistar which, as it moves through its own rationalisation programme, is becoming increasingly less vertically integrated and thus increasingly reliant on Cummins Inc. despite its link with MAN, might well take sides with the Columbus-based company - its new-found 'friend'.