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2010 Emissions

In order to meet the 2010 emissions requirement of reduced NOx, truck manufacturers will have to chose from two alternatives.  These two alternatives are Exhaust Gas Recirculation (EGR) and Selective Catalytic Reduction

EGR vs. SCR

Which solution is better for me?

There are clearly negatives and positives for each alternative, the following will provide a general overview of the two alternatives.

EGR

This technology is currently in place on the majority of 2007 emission engines. NOx is formed as a result of excess, unburned, oxygen in the combustion process.  A small portion of the exhaust gas is cooled, recirculated into the engine and mixed with oxygen rich air from the intake.  Due to the lower level of oxygen found in the exhaust gas, fewer oxygen molecules are found in the combustible air and combustion temperature is reduced.  Therefore NOx gases are reduced.  The downside to this technology is that the lower combustion temperature results in a less efficient combustion process.

SRC

Selective catalytic reduction is a new technology that is being developed in order to help engine manufactures meet the 2010 emissions.  This alternative allows the engine to operate under the optimized combustion conditions which produces an unacceptable amount of NOx.  It is then up to an intricate exhaust system to get rid of the NOx.  Because of the difficulty breaking down NOx, SCR requires Urea to be injected into the exhaust stream. 

The difficulty with this solution is the Urea that needs to be injected.  Currently their is no distribution channel for urea in the United Sates.  The amount of urea used will be approximately 5% of diesel used.  This means that if a 30 gallon tank of urea is installed, it would have to be filled every third time the truck is fueled.  Also, urea is not stable, it's freeze point is -11°F and it starts to decompose at 105°F.

The next issue is actually storing the urea on the vehicle and adding the additional catalyst and injector.  The process takes up valuable real estate behind the cab of the vehicle.  It also adds several hundred pounds of additional weight.

SUMMARY

The EGR solution is a business as usual solotion.  No additional technology, catalysts, or fluids are required.  SCR Requires additional weight to be added to the vehicle, new technology that must be implemented, and availability of urea.  What little fuel mileage increase (1-3%) is expected from the SCR solution should be derogated by the cost of urea which would have to filled every 3 fill ups at an estimated cost of $130.