Diesel Exhaust Fluid (DEF)
The Environmental Protection Agency was created in the footsteps of the Clean Air Act of 1970. For 46 years the EPA has been constantly evolving and enacting laws to address the environmental needs of this country. For many years owners of three-quarter and one-ton light duty pickup trucks enjoyed no additional smog equipment on their vehicles. All of that changed in 2008 with the EPA required the use of diesel particulate filters on all three-quarter-ton and larger trucks as well as required biannual smog tests which included a visual inspection of the vehicle to make sure the DPF parts were still on the truck. In 2010 the regulations got even tighter.
Many thought that the era of big power and torque were over and vowed to never purchase a new truck ever again. However, something spectacular happened and the complete opposite thing occurred. It turns out that Americans truly do adapt and overcome. Every one of the manufacturers figured out a way to cut down on the NOx levels all the while making more horsepower and torque than ever before. Innovation is bread out of strife.
The engineering breakthrough reaction torque sensor through the use of the selective catalytic reduction. The vast majority of these systems use diesel exhaust fluid (mixture of urea and deionized water) sprayed into the exhaust system to break down the generated NOx into harmless nitrogen and water molecules. Since the DEF (Diesel Exhaust Fluid) is introduced in the exhaust, also called after-treatment technology, the manufacturer is free to build as much power as they want. The DEF is stored in a separate tank which is insulated and heated and is marked by a blue filler cap.
Still there are two factions of diesel guys out there; those who have accepted to the EPA changes and those who are still vehemently against any regulations whatsoever despite the work around technological advancements. For those not willing to accept the changes there has been a shift to older used diesel engines or remanufactured diesel engines that have been grandfathered in. This article aims to go over the cold hard facts about DEF and educate the populace into making smarter diesel operator decisions.
- What exactly is Diesel Exhaust Fluid (DEF)?
From a strictly chemical disposition DEF is a mixture of 67.5% deionized water and 32.5% urea. Urea is a compound in Nitrogen that turns to ammonia when heated and is used in a variety of industries. Urea is technically derived from a byproduct of urine but for mass production purposes it is synthetically made. Most DEF products are regulated by the American Petroleum Institute. Lets take a look at the science behind DEF when mixed with exhaust. Chemically, DEF is firstly comprised of (NH2)2CO; and when injected into the hot exhaust gas the water evaporates leaving ammonia and isocyanic acid.
STEP 1: DEF Becomes Ammonia and Isocyanic Acid: (NH2)2CO → NH3 + HNCO
STEP 2: The Isocyanic Acid chemically breaks down with water into Carbon Dioxide and Ammonia:
HNCO + H2O -> CO2 + NH3 overall which is this: (NH2)2CO + H2O -> 2NH3 + CO2
STEP 3: At this point during the chemical reaction Ammonia will, in the presence of oxygen and a catalyst, will reduce nitrogen oxides:
2NO + 2NH3 + ½O2 -> 2N2 + 3H2O and 3NO2 + 4NH3 -> 7/2N2 + 6H2O
STEP 4: The overall reduction of NOx by urea is:
2(NH2)2CO + 4NO + O2 -> 4N2 + 4H2O + 2CO2 and 2(NH2) 2CO + 3NO2 -> 7/2N2 + 4H2O + 2CO2
- How Often Do You Need To Fill Up the DEF Tank?
That question specifically depends on miles per gallon and usage of the diesel truck in question. No matter how heavy the load, according to the OE manufacturer, the typical average light duty truck will consume 2-3 gallons of DEF per 800 miles. However, most new trucks with an average miles per gallon rating of 20+mpg will go roughly 8,000-10,000 miles on a tank full (10 gallons) of DPF. Each truck is different, for example on a Dodge Ram there is a gauge readout of exactly how much DEF is left in the tank, GM has a digital readout and Ford has a simple low DEF light.
Medium Duty and Heavy Duty Fuel models will vary but according to Cummins Filtration DEF consumption will be approximately 2% of the fuel consumed. For every 50 gallons of diesel fuel burned you will use 1 gallon of DEF. Each truck engine is different and you will get a feel of how much DEF your engine will use on a regular basis.
- Where can you buy DEF?
Don’t be fooled into thinking you can buy DEF just anywhere. DEF is mostly sold at truck stops in big jugs containing multiple gallons of the stuff. Some gas stations will carry DEF but don’t count on it if you are in a pickle. It is important to understand if you don’t refill an empty DEF tank the engine will automatically shut down. You don’t want to be stranded somewhere with an empty DEF tank because it is not sold everywhere. Common places to buy DEF include TravelCenters of America, Walmart, Target, Love’s Travel Shop, SAPP Brothers, Flying J Truck Stops, Petro Stopping Centers and Pilot Travel Centers, O’Reilly’s, NAPA and Advanced Auto.
- What are the Pros and Cons of a DEF Truck?
There are very few cons with DEF as it is a fairly simple procedure to deal with. However when it comes to Diesel Particulate Filter (DPF) and Selective Catalytic Reduction (SCR) there can be many maintenance and repair issues since they prone to clogging. These systems are complicated in design and a simple clogged filter can cause pressure and temperature differentials that can affect the whole performance of the engine.
The only cons to DEF include the additional upfront cost to the truck, added nominal weight and some additional room to store an extra gallon of the fluid. The pros are better fuel economy, increased horsepower, more optimized combustion, fewer regenerations issues, less wear on the engine and in addition it only releases nitrogen and water vapor into the air.
- Is emissions production really an important issue?
Whether it is a big deal or not is not really not up for debate considering all 2008 light-medium diesel and up have to comply with the EPA Regulations. NOx has been blamed for smog, a rise in greenhouse gasses and acid rain. The DEF as part of the Selective Catalytic Reduction system (SCR) turns NOx into pure nitrogen and water vapor. Climate change is a heated debate but we can all agree that spewing more gasses of any kind into the environment isn’t something we need more of. For those users who don’t want to mess with emissions issues used diesel engines or remanufactured engines are still available and have been grandfathered into the EPA Tier Ratings Program.