Facts on Selective Catalytic Reduction of NOX for Truck Owners

Diesel engines are considered as a better alternative to gasoline engines due to fuel economy. Diesel-powered vehicles have demonstrated a 30 to 40% fuel economy advantage over its gasoline-powered counterparts. At the same time, diesel is preferred over gasoline due to the 20% reduction in carbon dioxide emissions; however diesel engines have their drawbacks with the significant emissions of particulate matter and nitrogen oxide which are considered hazardous pollutants. Technology on the other hand has endeavored to create a solution to minimize these emissions through selective catalytic reduction of NOX, which is both a cost effective and fuel efficient solution.

What is selective catalytic reduction of NOX?

Selective catalytic reduction (SCR) is an exhaust after-treatment for the control of NOX emissions downstream from the diesel engine. SCR takes place after the combustion process and utilizes diesel exhaust fluid (DEF) to reduce nitrogen oxide levels. DEF is injected into the exhaust stream to react with NOX in the SCR catalyst to form harmless nitrogen and water vapor. In order to achieve extremely low levels of NOX emissions required by EPA 2010, most machine manufacturers uses both SCR and EGR and applies the advantages of both technologies to reduce hazardous emissions and provide better engine performance.

What is EGR technology?

Exhaust gas recirculation works by cooling exhaust gas and recycling it back through the engine. This reduces the amount of oxygen available for combustion which in turn reduces the combustion temperature in the cylinder. A cooler combustion reduces NOX emissions however; the lower temperature diesel combustion creates more particulate matter and burns more fuel. The costs of in-cylinder EGR involves additional vehicle cooling and air handling system with potential for additional turbo charging capability and decreased engine life. There is a significant loss of performance for engines using in-cylinder EGR by as much as 50 to 100% horsepower depending on the platform. It will also take a larger displacement in-cylinder EGR engine to do the same job as an SCR engine.

Why selective catalytic reduction of NOX is is highly considered by the trucking industry

SCR is cost effective

The costs are associated with compliance to EPA standards no matter what solution is taken. The initial investment on the selective catalytic reduction of NOX will be recovered over the life of the vehicle in terms of fuel economy, improved reliability, and improved regeneration cycles not to mention less downtime and maintenance costs.

SCR has fewer regeneration cycles

SCR will have fewer regeneration cycles with less manual stationary regenerations required. Improved regeneration rates means less fuel burned and more time on the road

SCR requires minimal maintenance

With selective catalytic reduction of NOX, engine maintenance intervals remain the same with one service point added, the DEF filter which should be changed every 200,000 miles. With SCR there are no issues over driver training and understanding of how a DEF gauge works and how to fill a tank. With SCR, engine components last longer because there is less heat generated and fewer contaminants. The overall result is a longer engine life.