Seal Beach, California-based Clean Energy Fuels Corp (CEFC) and US truck manufacturer Navistar have launched a ‘joint offensive’ to promote the use of natural gas (NG) as a heavy-duty truck fuel. By way of an incentive, CEFC says it is prepared to install, at its expense, NG storage/refuelling facilities at fleet depots where trucking companies commit to purchasing (unspecific) ‘large numbers’ of gas-fuelled trucks.
Interestingly, the NG engines installed in pre-production class 8 Navistar vehicles are from Cummins-Westport. This represents a re-establishment of customer-supplier relations between Navistar and Cummins, which were broken off, somewhat abruptly, about three years ago when the engine maker decided to adopt urea-fed SCR (selective catalytic reduction) technology for controlling its diesels’ NOx emissions. That move went against Navistar’s loudly-trumpeted policy of relying on EGR (exhaust gas recirculation) alone to hold down NOx levels.
Navistar says it has submitted its 12.4 litre MaxxForce 13 diesel, built under licence from MAN in Germany, for full EPA 2010 certification. It expresses confidence that the latest version of the engine, still without the SCR employed by all its rivals, will meet the requirements.
The announcement of Navistar’s NG deal with CEFC helped to draw attention away from the less positive news that Navistar would soon run out of the emission credits it has been using to allow its continuing sale of trucks with EPA 2007 compliant engines beyond January 2010, when much tighter NOx (and particulate) limits came into force. The EPA (Environmental Protection Agency) has said that, with credits eliminated, a fine of US$1900 will be imposed for each non EPA 2010 compliant engine supplied by Navistar. Several competitors have welcomed the news, while calling for much heavier fines.
Typically, Navistar is unfazed, saying it has submitted its 12.4 litre MaxxForce 13 diesel, built under licence from MAN in Germany, for full EPA 2010 certification. It expresses confidence that the latest version of the engine, still without the SCR employed by all its rivals, will meet the requirements, albeit with some exceedance during warm-up which, it claims, occurs with some competitive engines anyway.
What is different about this latest MaxxForce 13 variant? Navistar Chief Executive Dan Ustian says “essentially, there’s no change in the engine. It’s all in the controls. The customer won’t even know the difference.” His most contentious assertion, however, is that “there will be no change in fuel efficiency”.
In Europe, MAN has largely abandoned its ‘EGR only’ NOx control strategy in order to meet Euro 6 emission limits, which are roughly comparable to those of EPA 2010.
Observers involved in diesel engineering over recent years will be sceptical about that fuel efficiency claim, following on from Ustian’s assurance that “it’s all in the controls”. The well-proven way to cut NOx using engine controls, ie fuel system management, is to retard net injection timing. And such timing retardation always brings with it a fuel penalty. ‘Before and after’ specific fuel consumption curves for the MaxxForce 13 would be revealing. However, US engine manufacturers, unlike their European counterparts, tend not to allow such data into the public domain.
It is worth pointing out that, in Europe, MAN has largely abandoned its ‘EGR only’ NOx control strategy in order to meet Euro 6 emission limits, which are roughly comparable to those of EPA 2010. Its D26 engine in Euro 6 form, virtually identical to the MaxxForce 13, features SCR as well as EGR. Many predict that Navistar will, before too long, follow suit.
The opinions expressed here are those of the author and do not necessarily reflect the positions of Automotive World Ltd.
Alan Bunting has a background in engineering, and has been writing on commercial vehicle and powertrain related topics since the 1960s. He has been an Automotive World contributor since 1996.
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