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Getting a handle on DEF for 2010 engines


In accordance with government-mandated on-highway engine emission limits, MCI is introducing the use of urea-based DEF (Diesel Exhaust Fluid) for use in its 2011-model coaches equipped with 2010 EPA-compliant engines. While this technology is new to North America, it has been used for years in Europe, where the fluid is also known as AdBlue. More than half a million diesel trucks in Europe now use urea SCR (Selected Catalytic Reduction), with the fleet growing by about 25,000 per month.

Urea SCR systems reduce NOx by as much as 90% alone, and with DPF technology can take NOx to near-zero levels. Urea SCR, with its superior economic and environmental returns, is being recognized as the preferred method to control and reduce NOx emissions. Urea SCR systems are being adopted by many makers of heavy-duty engines, including Cummins and Detroit Diesel, and many truck stops are stocking DEF for 2010 truck engines.

What is NOx?

We know that the air we breathe is about 78% nitrogen, usually drawn as N2, or two nitrogen molecules bonded together. Nitrogen is normally an inert gas and is very stable. But under the rigors of combustion, it is forced to combine with the oxygen in the air. This leaves us with different combinations of "Oxides of Nitrogen" represented by NO, NO2, NO3, with all of the different oxygen levels represented by the variable "X", so we get NOx. These gases react with ultra-violet in sunlight and are a major producer of the hazy fog that hangs in the atmosphere and commonly known as smog.

What is Urea?

Urea has been known to us since 1773, when it was discovered in biological liquid waste. In 1828, it was synthesized, and between 1950 and 1970 it was found to be very useful in agriculture as a convenient source of nitrogen in fertilizer. Urea is made by dehydrating ammonia carbonate at high pressure and temperature. The urea that is used to lower the NOx is a much higher grade of urea than the urea used in fertilizers, consisting of a 32.5% nitrogen solution of high-purity urea in demineralized water, than the urea used in fertilizers.


SCR (Selective Catalytic Reduction)

A catalyst is a substance that promotes a chemical reaction. Since the NOx was created by a chemical reaction (combustion), it is only natural that we can reduce it with a chemical reaction, breaking it back down into its simplest components. SCR is a means of converting NOx with the aid of a catalyst (urea) into nitrogen and water. The heat of the SCR breaks the urea into ammonia, the actual NOx-reducing agent, turning exhaust pollutant into simple nitrogen and water. Through the further use of DPF filter technology, NOx can be reduced to near-zero levels, and the exhaust may even be cleaner that the air around it.

Handling with care

Urea is considered to be a nonhazardous material, but it can be corrosive to aluminum, so protective measures should always be observed as when handling any chemical substance. It is recommended that urea be stored at 80° Fahrenheit for best shelf life. It can be handled safely at 122° Fahrenheit, but can become volatile and can ignite at higher temperatures. Urea will freeze at 12° Fahrenheit, so care should be used in cold storage areas as well.

Gauging use

MCI coaches will have two fuel gauges: one for diesel fuel and a new one for DEF (urea) level. The DEF gauge will resemble this example. With urea consumption at about 3% of fuel used, the 15-gallon urea tank will need to be refilled about every 3,000 to 4,500 miles. It is estimated that only one tank of urea will be required for every two tanks of ULSD fuel.

There will be additional lights that will turn on to inform the driver of low fuel and DEF. While the two DPF lights we have become familiar with will not change, there is a new light for the DEF. It will illuminate when the DEF tank is below approximately 25% of volume. If the coach runs out of urea, the engine will still operate, but at reduced power until the tank can be refilled. DEF may not be mixed with diesel fuel.

The new "Water In Fuel" (WIF) sensor detects the presence of water in the fuel filter. When the conductivity probe indicates a change consistent with water, the warning lamp flashes after the key switch is turned on.

On Detroit Diesel DD13 engines and Cummins ISL-hybrid engines, a new "Wait To Start" lamp will illuminate at the KEY ON cycle. The driver must wait until the light goes out before cranking the engine. An intake air heater, or grid heater, comes standard to preheat the engine's incoming air on these select engines.

With the new DEF-related lights have also come some updates to the existing driver alert lights you already know:

The long-used CHECK ENGINE and STOP ENGINE lights have received an EPA-required makeover as well. Instead of a sideways look at an engine, they are now more of a "head-on" look, but you will still see AMBER for CHECK ENGINE and RED for STOP ENGINE.

The MALFUNCTION INDICATOR LAMP (MIL) previously used by Detroit Diesel is now universally used. Notice that it has adopted the previous "side view" engine diagram, but has no check mark in it.

Good news for fuel economy

It has been reported that SCR and DPF technology may even increase fuel economy by up to 4% over engines with only DPF Technology, while still reducing NOx emissions. And cleaner air and reduced fuel consumption is to everyone's benefit.

The FYI from MCI editorial staff values your feedback. Please e-mail any suggestions, comments, or ideas for future articles to fyi@mcicoach.com.

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