Using DEF properly

By |  October 13, 2014

A rundown of diesel exhaust fluid handling and an analysis of the events that led to its development.

Source: Thunder Creek Equipment

Source: Thunder Creek Equipment

The U.S. Environmental Protection Agency (EPA) established new emissions standards in 2010 requiring medium- and heavy-duty vehicles to significantly reduce engine emissions, particularly nitrous oxides (NOx) and particulate matter. To meet the new standards, makers of high-horsepower (174 to 750 hp) diesel engines adopted SCR, which injects DEF into engine exhaust to reduce harmful NOx emissions.

DEF is a colorless, nontoxic, nonhazardous and nonflammable liquid made of deionized water (67.5 percent) and highly pure synthetic urea (32.5 percent). It looks like water but smells slightly of ammonia. DEF is sprayed into the exhaust, breaking down NOx gases into nitrogen and water by means of an advanced catalyst system. Most new diesel trucks, pickups, SUVs and vans are fitted with SCR and have a DEF tank that must be refilled on a regular basis.

Small spills of DEF can easily be wiped up, and if DEF comes into contact with skin it can be washed off with water. DEF is, however, sensitive to chemical impurities and only cautious handling will prevent contamination. It’s far more likely to become contaminated than it is to damage equipment.

DEF freezes when stored below 12 degrees, but it won’t be damaged. It does expand when frozen, and full containers can burst when closed. Shelf life decreases the higher the constant storage temperature – up to 50 degrees for 36 months; up to 77 degrees for 18 months; and up to 86 degrees for 12 months. Temperatures around 95 degrees reduce the shelf life to about six months.

DEF tanks should be filled with every fill-up of diesel, and there’s no additional labor provided handling, transport and storage are done correctly. If not approached properly, the SCR system can become contaminated and cause the equipment problems. Remember: DEF is not an additive. It should never be added to diesel fuel but rather injected into the exhaust stream.

Handling

Contaminated DEF can cause an SCR system to malfunction. This means pumps and containers used for DEF must not be used for any other fluids. It is important that tanks, pumps, hoses and nozzles previously used for other products like diesel or lube oil are not used for DEF.

When DEF is stored outside in bulk tanks or totes, heating and cooling solutions can keep it within the desirable temperature range. Cooling is usually achieved by insulation and ventilation. Air conditioning is not required.

Certain stainless steels and various plastic materials are suitable for storing DEF. Carbon steels, copper, copper-containing alloys and zinc-coated steels should be avoided.

According to Jean Van Wyk, marketing specialist for Thunder Creek Equipment, taking the following steps will prevent contamination of DEF in off-road environments:

1. Make sure your fluid is made in accordance with the ISO (International Organization for Standardization) standard by looking for the American Petroleum Institute (API) Diesel Exhaust Fluid Certification Mark.

2. Use a container made for DEF. It should be constructed with materials approved in the ISO standard and rinsed and sealed properly.

3. Maintain a clean, closed fluid path. The standard does allow for open systems, but systems must be cleaned between each use. This isn’t practical in off-road environments, so closed-loop systems are best here.

4. Keep your workspace clean. Dirt and debris near the DEF fill port can also lead to contamination.

DEF’s origins

EPA’s tiered emissions program reduced emissions of particulate matter and NOx by 99 percent from Tier 1 (1996) through Tier 4 Final (2014). It would take 100 of today’s diesel engines to emit the same amount of particulate matter and NOx as just one diesel engine prior to the program.

NOx and particulate matter emissions are associated with a wide range of health problems, including respiratory and cardiovascular diseases, aggravation of asthma, acute respiratory symptoms, chronic bronchitis and decreased lung function. EPA estimates that the new standards will prevent 8,300 premature deaths, more than 9,500 hospitalizations and 1.5 million workdays lost due to illness, saving about $70.3 billion by 2030.

SCR is an after-treatment technology because it destroys harmful emissions after combustion, allowing manufacturers to tune engines for improved fuel efficiency and more power. Vehicles equipped with SCR require fewer oil changes.

To meet 2010 emissions standards for heavy-duty trucks, SCR is the technology of choice for the majority of truck and engine manufacturers. For example, Detroit Diesel’s BlueTec technology claims up to 5 percent better fuel economy, and Cummins has said its EPA 2010 technology delivers 5 to 7 percent better fuel efficiency compared with EPA 2007 technology.

Nissan Diesel first used SCR technology in 2004. Since then, SCR has been widely used on diesel vehicles, and by the end of 2010 more than 1 million trucks and buses in Europe alone were equipped with the technology.

One of the most common configurations for SCR includes four steps:

1. Reaction of the exhaust gas with an oxidation catalyst to remove hydrocarbons and convert some nitric oxide to nitrogen dioxide.

2. Conversion of urea from DEF to ammonia on a hydrolysis catalyst. This requires injection of the urea solution into the exhaust stream at the correct dosing rate, which avoids buildup of urea on the walls of the exhaust or on the injector itself.

3. Reaction of ammonia with NOx on an SCR catalyst to produce nitrogen and water.

4. A final oxidation catalyst is often installed after the SCR catalyst to destroy any remaining ammonia. This is sometimes called an ammonia slip catalyst.

Emissions regulations

Source: Thunder Creek Equipment

Source: Thunder Creek Equipment

The reduction of NOx and particulate matter is central to the EPA strategy for cleaner air. Since passing the Clean Air Act in the 1970s, the EPA has taken steps to lower emissions of NOx, particulate matter and other pollutants from on-road vehicles, electric utilities and off-road equipment.

The EPA is responsible for managing and enforcing emissions limits at the federal level. It sets the limits for emissions standards for diesel engines and takes actions against manufacturers who do not meet the standards. It also takes an active interest in the technology choices that are made by the manufacturers and evaluates their progress.

EPA standards for emissions from heavy-duty diesel trucks have been lowered dramatically since 2001. The EPA’s 2001 guidelines stipulated that models manufactured from January 2010 onward must reduce particulate matter emissions to 0.01 per brake horsepower hour and NOx emissions to 0.20 per brake horsepower hour. A phase-in period allowed NOx emissions of 1.2 per brake horsepower hour by 2007.

EPA implemented a bank-and-trade system for NOx, which meant manufacturers who exceeded the requirements before 2010 (such as Cummins and Navistar) could accrue NOx credits. The credits could be used to sell models producing emissions above the standard after the deadline. There was no banking and trading of particulate matter emissions.

In 2004, the EPA issued its final program to reduce emissions from off-road diesel engines, to be phased in from 2008 to 2015. The Tier 4 off-road rule established new emissions standards and test procedures, and led to the implementation of SCR technology by a number of manufacturers. The standards require a further reduction of emissions of particulate matter and NOx by about 90 percent from Tier 1 to 3 standards.

Tier 4 Final standards will be implemented for all engine power categories by 2015. Manufacturers can use the banking and trading program for Tier 4 engines up to 75 hp. Each of the major off-road engine manufacturers has confirmed the use of SCR for engines above 75 hp in their product range for Tier 4 Final.

DEF’s guiding force

The ISO (International Organization for Standardization) 22241 standard governs the production, handling and transportation of DEF. The standard covers five key points:

1. Urea concentration. DEF must have a urea concentration of 32.5 percent by weight. This concentration was selected because it has the lowest freezing temperature, at 12 degrees.

2. Contamination. Contaminated fluid can damage SCR injectors and catalysts, resulting in system malfunction or failure. Therefore, the maximum level of impurities permitted in DEF, such as calcium and metals like iron, copper, zinc and aluminum, is clearly specified. The limits are set very low. For example, a spoonful of table salt in a DEF tote would push the sodium content far above the ISO 22241 limit of 0.5 ppm.

3. Quality. ISO 22241 excludes the use of urea granules used as fertilizer in agriculture and requires water purified by distillation or deionization.

4. Materials. Only certain materials are permitted for the storage and handling of DEF, which is corrosive to many materials, including carbon steel, copper and aluminum.

5. Handling guidelines. Guidelines require manufacturers to follow clear procedures for the manufacture and distribution of DEF, ensuring that the product meets the requirements of vehicle manufacturers.

Take note

Contaminated DEF can cause an SCR system to malfunction. This means pumps and containers used for DEF must not be used for any other fluids.

Patrick G. Mahoney, a freelance writer based in Cleveland, writes extensively on engineering and other technical topics.

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