I remember years ago, I could not, for the life of me, get my little Honda Civic wagon to pass a Massachusetts emission test. These nitrogen-based toxic gases have been one of the worst problems of diesel emissions, but the selective catalytic reduction system, including DEF, takes care of it. They transform toxic nitrogen dioxide and nitrogen monoxide into harmless pure nitrogen and water. Why spray urea into the exhaust stream? The compounds in urea react chemically with exhaust gases and the catalytic converter. Yes, that’s the same compound found in urine (go ahead, laugh), but this is a much stronger, more potent version of it. DEF is made of two-thirds deionized water and one-third urea. The new selective catalytic reduction systems inject a small amount of DEF into the exhaust stream, after the particulate filter, and before the catalytic converter. This is why DEF has recently become a thing, even though diesel engines have been around forever without it. They require the use of diesel exhaust fluid in the emissions system. Then, in 2010, the Environmental Protection Agency mandated the use of selective catalytic reduction systems in diesel engines to reduce their emissions. For 120 years, there was no such thing as diesel exhaust fluid, also known as DEF. This, plus the type of fuel they use, is the main difference between gas and diesel engines. Instead, the air/fuel mixture inside the cylinder spontaneously ignites from compression alone. Unlike gasoline engines, they don’t have spark plugs. What is it? Why do we need it now when we never did before? Read on for the answers to these questions and more.ĭiesel engines have been around since the 1890s, when the man for which they are named, Rudolf Diesel, invented them. Most of us, including people who have extensive experience with diesel engines, have never heard of this before. In recent years, something called “diesel exhaust fluid” has become a new addition to diesel vehicles. The same advantage applies to smaller trucks that we can buy for personal use, with most major manufacturers offering diesel engines as well as gasoline. Big rigs have always used diesel engines since they’re better for hauling and towing heavy loads, and more fuel-efficient for such use. Not many cars in the United States use diesel engines, but they’ve always been useful in trucks. The DEF is injected into the diesel exhaust stream where it reacts with a chemical catalyst to convert NOx into a harmless gas.What’s this new-fangled fluid that diesel trucks use these days? SCR converts NOx to nitrogen and water vapor using a catalyst, exhaust heat, and Diesel Exhaust Fluid (DEF). SCR technology isn’t new-its been in use for many years in Europe and since the late 1950’s on large commercial boilers. It’s a neutral solid that doesn’t have color or odor and dissolves in water. Commonly known as a major component in mammal urine, it was the first organic chemical to be artificially produced in a lab. To do so, many diesel engine manufacturers (OEM’s) decided to use Selective Catalytic Reduction (SCR), which is emissions after-treatment technology that converts nitrogen oxides (NOx) in the diesel-engine exhaust stream into nitrogen and water vapor…two natural components in the air we breathe. NOx emissions need to be removed from the air because they contribute to global warming, acid rain, and atmospheric particles that cause visual impairment. The 2010 Emissions standards in North America have mandated that all on-road diesel vehicles manufactured in 2010 or later must be equipped with technology to reduce NOx emissions. In 2010, cars and trucks with diesel engines that were sold in the United States had to meet new American EPA emissions requirements.
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