This is for Jason and Kerry
This is for Jason and Kerry regarding DEF.
There's a lot of bad information out there in regards to DEF. Diesel exhaust fluid is API (American petroleum institute) regulated substance that consists of 32.5% pure urea and 67.5% deionized water. Same people that regulate oil standards. Let's start with the DPF as theres confusion on those too. in 2008 the EPA mandated on road diesel regulations to have a substantial decrease in particulate matter (soot). The DPF is a filter that traps the soot so the exhaust is clean. Then when the filter gets plugged heat is required to remove the blockage. The engines then go through a regeneration process which essential dumps raw fuel into the exhaust, the fuel hits the diesel oxidation catalyst, produces temperatures about 1100 degrees F, that heat burns the soot out of the filter and turns it into an invisible gas, therefore cleaning the filter. When diesel burns the significant by products (besides awesome) are nitrogen oxides NO2, and particulate matter. NO2 = acid rain, particulate matter= our lungs don't like it (basically, I'm not a chemist). Increasing the combustion temperatures will more fully burn the fuel which will reduce the soot (soot is kind of unburned fuel). When you increase the combustion temperatures you successfully produce less soot and the end result is higher NO2 emissions. So, 2008+ manufactures used DPF's to catch the soot, then ramped up the combustion temperature with an air intake butterfly valve. This means theres less need for regeneration, though it pushes the NO2 emissions up substantially. Luckily, prior to 2008 there was a NO2 emissions EPA regulation which is what put EGR (exhaust gas recirculation) systems into our diesel. So, with added NO2, via the goal to decrease regeneration needs by decreasing soot, they increased the amount of EGR. EGR is dumb as it puts exhaust into the intake manifold which is... well, dumb. Well, here comes 2011! EPA says you diesel engine manufacturers need to decrease your NO2 outputs dramatically. Oh, no... now what?!. SCR!!! Sorry this is so long, I just want to help people understand what these systems are for. SCR stands for selective catalyst reduction. The diesel oxidation catalyst (DOC) reacts with the diesel fuel to make high amounts of heat to clean the DPF (diesel particulate filter). The SCR system in 2011-current (except 6.7 Cummins, they're so awesome and efficient they didn't have to use SCR until like 2014) diesels consists of a catalyst as well. The catalyst in the SCR system reacts with the NO2 that the diesel produces and converts it to hydrogen and water. The DEF does that as well. I think the catalyst and the DEF work together to produce an acceptable decrease. I think... Im confident... Certainly theres specifics in all of this but in a nutshell this is why we have what we have.
So, to recap; Diesel burns, makes power, soot, and nitrogen oxides. Soot and NO2 are bad for everybody and everything. The leaders that try to do the right thing and set the standard for the rest of the world (America and I guess European Union) decided that we need less soot and NO2. The DPF was born to trap the soot. The SCR (DEF) was born to decrease the NO2. Diesels are now more efficient, and less of a hinderance on the environment than gas engine.
All this emissions stuff can be bothersome at times. Sometimes problematic since there a lot of sensors and wires and algorithms that could hiccup. Sometimes when you remove those emission systems and retune the ECM's, you get an unbelievable amount of potential out of engines that are otherwise choked down. Some places you can get away with it, some can't.