SPECIAL REPORT: Navistar pursues ammonia-based ‘SCR’ solution
Posted: August 1, 2014
WARRENVILLE, Ill. — Is selective catalytic reduction (SCR) in Navistar’s future? Perhaps — although, with a twist.
The Chicago truck and engine maker has entered into a development and supply agreement with a Danish emissions-reduction provider to produce an SCR-based solution for the diesel market in years to come.
It remains unclear what Navistar’s system will look like exactly, if it’s used at all, but the staple technology currently produced by Amminex in Denmark differs little in principle from that seen on SCR engines used by Navistar’s competitors to meet the EPA’s 2010 nitrogen-oxide emission reduction targets. Both rely on ammonia released in a catalyst downstream of the DPF to create a chemical reaction that turns NOx into clean nitrogen and water vapour. The difference is in the ammonia storage and release systems.
Unlike today’s SCR engines — in which urea-based diesel exhaust fluid (DEF) is meshed with the hot exhaust stream in a catalyst, forming ammonia — Amminex’s AdAmmine system uses a solid, namely crystallized salt ammonium. It’s stored in a cartridge, which is heated to create "on-demand" ammonia in the catalyst, triggering the same sort of NOx conversion as with DEF. The cartridge would simply be replaced — as an OEM part — at every oil change.
While AdAmmine is effectively an SCR treatment technology with an alternate ‘reductant’ storage and dispensing mechanism, Navistar says it "fits perfectly into (its) Advanced EGR prime path — eliminating the need for customers and third parties to invest in a new infrastructure for liquid urea."
"While other commercial truck manufacturers have limited their investment in emissions technology, declaring liquid urea-based SCR to be the solution for NOx reduction, Navistar continues to invest in new technologies that support our philosophy that emission control is the responsibility of the manufacturer," said Eric Tech, president, Navistar Engine Group.
AdAmmine at work from Amminex webiste
The truckmaker has heavily criticized SCR many times in the past because of the requirement for drivers to replenish DEF.
It is instead going with an in-cylinder emission control solution, "advanced" EGR, for 2010, although its MaxxForce engines will come up short of the 0.2 grams NOx per brake horsepower per hour benchmark mandated by the EPA. (The company is permitted to use banked ’emissions’ credits to sell those engines for some time beyond the Jan. 1, 2010 deadline).
Although Amminex has developed and tested the technology over 80,000 km in six cars and one medium-duty truck, a working system for a heavy-duty diesel engine doesn’t yet exist and is still under development.
Navistar spokesman Roy Wiley admits that a MaxxForce engine with this technology, if it happens, is not imminent.
He doesn’t deny that, technically, AdAmmine functions like an SCR system, but without DEF.
This isn’t the first time Navistar has aligned itself with SCR technology, though. As todaystrucking.com revealed in August, the company’s Brazilian MWM International Motores subsidiary is employing SCR in its NGD 9.3E medium-duty engine for use by other truck makers in the South American market.
Reiterating recent comments from Navistar execs, Wiley says the company’s objection isn’t with SCR per se, but specifically with the responsibility placed on the customer to keep the DEF tank full.
As for the requirement to replace AdAmmine cartridges, Wiley suggests that such maintenance doesn’t place any more burden on truckers than changing oil filters or tires. (What remains unclear is the best way to dispose of ammonia cartridges, however).
Of course, OEMs marketing SCR engines this New Year commonly respond to Navistar’s concerns about DEF by saying that the replenishment of the liquid is no more burdensome for drivers than filling up windshield washer fluid.
While it appears there would still be a certain degree of hands-on involvement by the end-user, one benefit claimed for AdAmmine is that the system needs 2.5 times less packaging space. The cartridge is also said to have a much longer shelf life than DEF. And it’s said to avoid the rare problem of urea concentration variations.