DEF is mostly water, and it needs to be converted to heated ammonia at a minimum temperature of around 400 F vapor to be effective in a Selective Catalytic Reduction (SCR) catalyst. That means the exhaust gases entering it need to be hotter to compensate for the higher volume and that means slightly lower engine efficiency. There is also a chance that the SCR would need to be larger and more expensive.
I was on a major power project once that had a couple of big gas turbines with SCRs that used aqueous ammonia instead of DEF (ammonia is formed from decomposition of the Urea in DEF and is the active ingredient for a SCR). Some corporate genius for the owner of the plant used to work for General Electric the company who designed and guaranteed the turbines. He had the GE passwords for the control system and tweaked the settings to save some ammonia before we did the final commissioning checks. When we ran the numbers, the plant did not pass emissions. It took about 10 days and lot of money to figure out what was wrong and they finally undid the change and the plant passed. Changing factory control parameters invalidated the warranty and the owner had to pay GE to fix the problem along with lots of subcontractors.
The allowable emissions numbers out the tailpipe for diesels (and new gas turbine powerplants) is incredibly low. The SCR system is very complex and has to be spot on to get the removal efficiency required during all phases of operation, so it all comes down to money, what is the least cost smallest package that will meet the limits but not beyond? My guess was Cummins was having issues meeting the requirements so they tweaked some things in the controls to make it pass.
I have been in one of those meetings a couple of times where a half a million-dollar SCR will not pass the emissions testing and the owners are screaming at the contractor to get it fixed. Lots of things are put on the table and tweaking the software is usually the first thing that gets tried but in the background is the state air environmental department making sure that the tweaks result in the plant staying below the permit limits.
One of the big diesel engine companies got in trouble about 15 or 20 years ago when they elected not to go with SCRs and went with very complicated controls to avoid them. They sold a lot of big rigs that just plain would not run worth a darn and it was found that the rigs were going out of compliance soon after leaving the factory. They ended up paying a large fine and had to do expensive upgrades to the trucks. Some of the contractors I knew had bought some of those trucks and dumped them quick as they were going into "limp home mode" all the time and were in the shop all the time. They were for sale for cheap on the market.
I was on a major power project once that had a couple of big gas turbines with SCRs that used aqueous ammonia instead of DEF (ammonia is formed from decomposition of the Urea in DEF and is the active ingredient for a SCR). Some corporate genius for the owner of the plant used to work for General Electric the company who designed and guaranteed the turbines. He had the GE passwords for the control system and tweaked the settings to save some ammonia before we did the final commissioning checks. When we ran the numbers, the plant did not pass emissions. It took about 10 days and lot of money to figure out what was wrong and they finally undid the change and the plant passed. Changing factory control parameters invalidated the warranty and the owner had to pay GE to fix the problem along with lots of subcontractors.
The allowable emissions numbers out the tailpipe for diesels (and new gas turbine powerplants) is incredibly low. The SCR system is very complex and has to be spot on to get the removal efficiency required during all phases of operation, so it all comes down to money, what is the least cost smallest package that will meet the limits but not beyond? My guess was Cummins was having issues meeting the requirements so they tweaked some things in the controls to make it pass.
I have been in one of those meetings a couple of times where a half a million-dollar SCR will not pass the emissions testing and the owners are screaming at the contractor to get it fixed. Lots of things are put on the table and tweaking the software is usually the first thing that gets tried but in the background is the state air environmental department making sure that the tweaks result in the plant staying below the permit limits.
One of the big diesel engine companies got in trouble about 15 or 20 years ago when they elected not to go with SCRs and went with very complicated controls to avoid them. They sold a lot of big rigs that just plain would not run worth a darn and it was found that the rigs were going out of compliance soon after leaving the factory. They ended up paying a large fine and had to do expensive upgrades to the trucks. Some of the contractors I knew had bought some of those trucks and dumped them quick as they were going into "limp home mode" all the time and were in the shop all the time. They were for sale for cheap on the market.
