As with any vehicle operated in the United States today, the Everett Porsche Catalytic Convertor Service must be monitored to assure it is operating properly. In counties that require emissions testing, the performance of your vehicle’s catalytic convertor is monitored on a regular basis. For counties that do not require admissions testing, you can have your Porsche Catalytic Convertor performance monitored by requesting either an On Board Diagnotic (OBD) or a tailpipe emissions test.
Your Vehicle’s Emissions
In a perfect world, every car’s engine burns fuel at 100% efficiency. This perfect combustion with regard to gasoline means that the stoichiometric ratio of air to fuel is 14.7:1; meaning that 14.7 pounds of air is required to burn 1-pound of gasoline.
- Lean Mixture: more than 14.7 pounds of air to each pound of gasoline; the term “lean” refers to the mixture being a low or “lean” concentration of fuel
- Rich Mixture: less than 14.7 pounds of air to each pound of gasoline; referring to the mixture being heavy or “rich” concentration of fuel. When the ratio is rich, not all the fuel is burned, as there is not enough air present for combustion.
- Nitrogen Gas (N2) – with a concentration of 78% N2 present in air, most passes through the engine
- Carbon Dioxide (CO2) – formed when carbon in the fuel combines with oxygen in air
- Water Vapor (H2O) – formed when hydrogen in fuel combines with oxygen in air
Nitrogen and water are benign and not harmful to the environment. Carbon dioxide (CO2) contributes to global warming (it is thought that CO2 is harmful to the ozone layer). In addition to the prevalent yet benign exhaust, there are 3-hazardous emissions resulting from incomplete combustion:
- Carbon Monoxide (CO) – odorless, colorless, poisonous gas
- Hydrocarbons or Volatile Organic Compounds (VOCs) – unburned fuel that has evaporated; most prevalent component of smog
- Nitrogen Oxides (NO & NO2) – the combination is termed NOx, contributes to acid rain and smog
cat·a·lyst /’katl-ist/ (noun): 1. A substance that increases the rate of a chemical reaction without itself undergoing any permanent change (Merriam-Webster)
A catalytic convertor uses 2-types of catalysts:
- Oxydation Catalyst – oxidizes the emissions by reacting with oxygen
- Reduction Catalyst – reduces (chemically) emissions by reacting with hydrogen
ox·i·da·tion /ok’si-da’shen/ (verb): 1. The chemical combination of a substance with oxygen.2. A chemical reaction in which an atom or ion loses electrons, thus undergoing an increase in valence.re·duc·tion /ri-duk-shen/ (verb): 1. A reaction in which hydrogen is combined with a compound. 2. A reaction in which oxygen is removed from a compound. 3. A decrease in positive valence or an increase in negative valence by gaining of electrons.
The Process of Catalytic Conversion
The engine’s exhaust first passes through the reduction catalyst. Using platinum and rhodium, reduces the NOx emissions. Coming in contact with the catalyst, separates Nitrogen from the NO and NO2 molecules; the Nitrogen is retained while the Oxygen is emitted as O2:
2NO => N2 + O2 and 2NO2 => N2 + 2O2
The second stage of the catalytic converter is the oxidation catalyst. Hydrocarbons and Carbon Monoxide (CO) are oxidized as they pass across the platinum and palladium catalyst, reducing the amount of the harmful emissions:
2CO + O2 => 2CO2
The final stage of the catalytic converter is the control system that monitors the final exhaust. The information from the control system is relayed to the fuel injection system, regulating the amount of fuel passed into the combustion chamber. Additionally, there is an O2 sensor between the engine and the catalytic converter that measures the amount of O2 in the pre-treated exhaust; relaying the information to the air-fuel ratio meter, adjusting the amount of O2 as indicated.
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