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As 2010 draws closer, there is ever more discussion about the issues, technology and products coming into the marketplace to meet the U.S. Environmental Protection Agency’s more stringent diesel emission standards. These new regulations will dramatically reduce discharges of both particulate matter (soot and ash) and nitrogen oxide (NOx).
Particulate matter is formed by the incomplete combustions of fuel in diesel engines. Nitrogen oxide is the generic term for a group of highly reactive gases, all of which contain nitrogen and oxygen in varying amounts. NOx is formed in small amounts when fuel is burned at high temperatures and pressures during an engine’s combustion process.
Meeting reduced pollutant standards has already required a change to ultra low sulfur diesel fuel and a reformulation of engine oils, designated CJ-4.
The 2010 diesels will have near zero emissions of both particulate matter and NOx. Engine manufacturers will achieve this through a variety of means, so we are faced with a number of new and confusing terms. They are fast becoming a part of the language of trucking. Here’s a quick guide to the terms you will want to know:
Selective Catalytic Reduction (SCR) is the process that most of the major engine manufacturers chose to tackle 2010 emissions requirements for nitrogen oxide (NOx). It employs a chemical reaction triggered by heat. A fine mist of urea (diesel exhaust fluid, or DEF) is injected into the exhaust stream. The reaction converts nitrogen oxide levels into harmless levels of nitrogen and water vapor and eliminates the diesel smell.
Exhaust Gas Recirculation (EGR) is the second technology being used to control NOx. In simple terms, exhaust gas recirculation, also referred to as cooled EGR, captures a small portion of exhaust gas and injects into the engine’s combustion cycle, along with fresh air and fuel. This lowers the temperature of the combustion, resulting in a lower level of nitrogen oxide emissions. Unlike SCR, EGR does not require an additive. International has made the decision to go with EGR for its 2010-compliant engines.
Term: Urea or DEF
Diesel exhaust fluid, also known as urea, is a man-made, organic compound that is harmless to the environment. Urea is already widely distributed for many other industrial and agricultural needs. Urea consumption varies with duty cycle and other factors, but is not expected to exceed 5 percent of fuel consumption. It also costs less than diesel.
SCR systems require a separate container for the urea, along with extra wiring, hoses and sensors to manage the injection flow of urea into the truck’s exhaust stream.
Installed in place of mufflers, diesel particulate filters (DPF) typically contain a porous ceramic to strain and catch the particulate matter from the exhaust stream and prevent these particles from reaching the atmosphere. Over time, these traps fill up and need to be periodically cleaned, otherwise the filter can plug up and adversely affect the engine’s performance and fuel economy.
DPF cleansing is done by passive or active regeneration. Passive regeneration uses the heat from the normal engine cycle while a vehicle is being driven to create a catalytic reaction that burns away the soot built up in the DPF. It uses no additional fuel in the process.
When the engine runs cool, exhaust heat is increased by active regeneration. The system achieves the same cleansing result by adding a small amount of diesel into the exhaust gas. This starts a process that raises the DPF temperature enough to get rid of the soot. Active regenerations typically won’t be necessary for highway applications where engines work hard enough to generate the heat necessary to continually burn off the trapped particulate matter. They may be required for city or suburban operations where engines don’t generate enough heat for regeneration.
Term: Onboard Diagnostic System (OBD)
EPA regulations mandate that the emission control systems of highway diesel truck engines be monitored similarly to passenger cars via onboard diagnostic systems. These regulations, applying to vehicles more than 14,000 pounds, begin in 2010 and will be phased in over a number of years.
Engine manufacturers are required to install OBD systems that monitor the function of specific major emission control systems and components. These systems must alert the vehicle operator, through indicator lamps, to any need for emission-related repair.
In addition, all emissions-related electronic sensors and actuators will have to be monitored for proper operation. When a malfunction occurs, diagnostic information must be stored in the engine’s computer to assist in diagnosis and repair of the problem, condition or malfunction. The regulations define a “failure” as any change from as-built conditions that can raise the engine emissions beyond the regulated level.
Term: Tier 3, Tier 4
On the federal level, the EPA has regulated on-highway diesel engine emissions standards through the Clean Air Act since 1970. Emission regulations are phased in over a number of years, gradually reducing the legal levels of emissions for various sizes of diesel engines. These phases are identified as Tiers.
There are no heavy-duty emission regulations beyond 2010. For light duty diesel vehicles, Tier 3 emission standards will take effect in 2011/2012, followed by Tier 4 in 2015. The EPA estimates that Tier 3 standards will reduce NOx emissions from diesel engines by about 1 million tons per year. Tier 4 standards are even more rigorous, reducing NOx emissions by 90 percent beyond Tier 3.