Emissions control systems for today’s air quality standards
FAQs: Three-Way Catalyst Technology and the CleanAIR ASSURE™ TWC
Meets NSPS Regulations with Three-Way Catalyst
Section 1 - Why do you need a Three-Way Catalyst?
- Why do you need a three-way catalyst?
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- compliance with EPA NSPS air quality regulations
- provides a safer working/living environment through reduced emissions
- lessens the impact on human health by reducing toxic air pollutants, particularly in the immediate area that a spark-ignited engine is operating
- provides a cleaner environment by dramatically reducing engine emissions
- What is the New Source Performance Standards (NSPS) and what does this regulation have to do with three-way catalysts?
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The NSPS, regulated by the Environmental Protection Agency, is a set of air quality standards of performance for stationary, spark ignited internal combustion engines and national emission standards for hazardous air pollutants for reciprocating internal combustion engines.
The regulation sets new engine emissions standards for NOx, CO, VOCs and HC. To view the final ruling go to: http://www.epa.gov/ttn/atw/area/fr18ja08.pdf.
- When a spark-ignited, rich-burn engine is retrofitted with a three-way catalyst that is correctly sized for that engine, it will meet the NSPS regulations bringing the engine into compliance with EPA standards.
- Owners who do not bring their engines into compliance using retrofit technology (such as a TWC) in accordance with NSPS regulations, may face fines and/or not be allowed to operate their engines.
- When did the NSPS regulations go into affect for new engines?
- The final rule was passed on January 18, 20008 and affected new small natural gas and lean burn LPG engines with a manufacturer’s date of July 2008 and later. Other engines must meet NSPS standards within the next few years with manufacturer’s dates between 2009 and 2011. Some re-manufactured engines must also comply with NSPS. Rulings concerning retrofitting older spark-ignited engines are expected to be discussed in 2009. To find the emission standards that apply to your specific engine, refer to the NSPS final ruling at: http://www.epa.gov/ttn/atw/area/fr18ja08.pdf.
Section 2 - What does a Three-Way Catalyst do?
- What does a three-way catalyst do?
- A TWC reduces emissions in the exhaust stream of a spark-ignited, rich-burn engine in order to bring it into compliance with NSPS air quality regulations.
- What emissions are reduced using a three-way catalyst?
- Nitrogen Oxides (NOx)
- Hydrocarbons (HC) or Volatile Organic Compounds (VOC)
- Carbon Monoxide (CO)
- What is the reduction summary for a three-way catalyst:
- NOx – reductions up to 95%
- HC – reductions up to 95%
- CO – reductions up to 95%
Results are fuel dependent and may vary with application.
Section 3 - What is a Three-Way Catalyst?
- What is a three-way catalyst?
- Utilizing a flow-through substrate coated with a precious metal catalyst, a three-way catalyst is an emissions reduction technology used on rich-burn spark-ignited engines that performs three simultaneous chemical reactions:
- reduction of nitrogen oxides
- oxidation of carbon monoxide
- oxidation of unburnt hydrocarbons and volatile organic compounds
The result being toxic emissions from the engine are changed into nitrogen, carbon dioxide and water vapor as they pass through the three-way catalyst.
- What engines use a three-way catalyst?
- Spark-ignited engines such as natural gas and propane engines. Three-way catalytic Catalysts can be used on vehicles and stationary engines.
- What does “stoichiometric” mean?
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“Stoichiometric” is the exact air-to-fuel ratio where precisely enough oxygen is supplied for the complete combustion of fuel. Engines running slightly rich of stoichiometric are referred to as rich-burn.
- How does a three-way catalyst work?
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A three-way catalyst promotes the chemical reduction of NOx in the presence of CO and VOC to produce nitrogen. At the same time it oxidizes VOC and CO into carbon dioxide and water vapor. In order to do this simultaneously, a three-way catalyst operates in a narrow air-to-fuel ratio where the oxygen content is theoretically zero.
- What fuel is compatible with a TWC?
- Natural Gas
- Propane
- Liquefied petroleum gas (LPG)
- What is the recommended temperature range for exhaust being supplied to a TWC?
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TWCs manufactured by CleanAIR Systems begin operating efficiently with exhaust temperatures as low as 650 degrees F. Insulation of the exhaust system may be considered to minimize heat loss if the TWC is not placed directly after the engine exhaust outlet, making it difficult to reach a minimum operating temperature. Some natural gas (NG) engines can have exhaust temperatures exceeding 1200 degrees F. These higher temperatures can result in the deterioration of the catalyst materials and supporting substrates. Consult with CleanAIR Systems for additional options when considering a TWC for use with engine temperatures exceeding 1200 degrees F.
- In a three-way catalyst, what is the reduction process?
- Reduction is the process of removing oxygen from compounds. During three-way conversion, nitrogen oxides (NOx) formed during the combustion process, are reduced by removing oxygen to form nitrogen and carbon dioxide (CO2). The process is promoted by the catalyst.
- What does “rich-burn” mean? Why does a TWC work with a rich-burn engine?
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Rich-burn means an air-to-fuel ratio that is less than stoichiometric or more fuel to oxygen. Rich-burn is a term used in conjunction with spark-ignited engines. In order to perform simultaneous oxidation and reduction processes and not have excess concentrations of VOC and CO, a TWC operating on a natural gas engine must stay in a narrow air/fuel ratio band.
- What does “lean-burn” mean? Why doesn’t a TWC work with a lean-burn engine?
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Lean-burn is an air-to-fuel ratio that is more than stoichiometric or more oxygen to fuel. A lean-burn engine tends to produce a high concentration of NOx, with an excess of oxygen. If excess oxygen is in the exhaust stream, CO and HC will preferentially react with oxygen, and NOx will not be reduced. Therefore, a TWC can not operate on a lean-burn engine.
Section 4 - Other FAQs about TWCs
- What is an Air-to-Fuel Ratio Controller (AFRC) and why do I need to use one with a TWC?
- An AFRC is an electronic controller that maintains the correct air-to-fuel ratio to help a three-way catalyst perform oxidation and reduction. An AFRC includes an oxygen sensor as a feedback mechanism and a fuel control valve. CleanAIR Systems offers several different controllers. Engine specifications and application needs are taken into account when recommending the correct AFRC for the job. A TWC depends on an AFRC to maintain the proper balance of air-to-fuel. Without an AFRC, a three-way catalyst may not achieve desired reductions.
- What is involved in the installation of a TWC with an AFRC?
- This is a simple process of connecting a flow control valve to the fuel supply system and an oxygen sensor to the supplied test port on the TWC. CleanAIR Systems supplies a comprehensive installation manual outlining the details along with the AFRC manufacturer’s manual.
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