Preventing harmful emissions is one of automobile manufacturers' major concerns have been focusing on. Convertors have been installed in cars to tackle this issue. Convertors use chemical reactions to transform various harmful gases like carbon monoxide and hydrocarbons into safer gases such as carbon dioxide and water vapor. Without these converters, the exhaust gases escape unchecked, harming the environment gravely. There are three major convertor technologies being used in the industry today.
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The first-ever model to the world by Eugene Houdry, a brilliant engineer. The converter is a device with a stainless-steel body. It consists of an inlet that receives raw gases and emissions from the engine and an outlet consisting of a tailpipe/particulate filter that filters out the gases.
These converters use a catalyst – a substance that reacts with the gases to produce less harmful emissions. There is a honeycomb-like structure that contains metals like palladium, rhodium, and platinum in low quantities.
A redox reaction occurs when these gases pass through the given metals. The catalyst reduces gases like nitrogen oxides to harmless nitrogen gases. This is a reduction reaction. A separate oxidation reaction occurs, which oxidizes the hydrocarbons and unburnt fuel into carbon dioxide and water vapors. One of the major conditions for these convertors to work is to operate at temperatures nearing 300-degree Celsius!
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SCR converters or Selective Catalytic Reduction convertors are majorly used with diesel engines. SCR is very effective against the deadly nitrogen oxide emissions of diesel engines.
There is a single catalytic convertor that is home to two separate processes. The oxidizing catalyst process is the first one that undertakes chemical reactions to oxidize the HCs and unburnt fuel into CO2 and water vapors.
The reduction process targets harmful nitrogen oxides and converts them into less harmful nitrogen compounds. The catalyst is known as a Diesel Exhaust Fluid and can be made of a solution of 32.5% urea in demineralized water. This mixture gives rise to ammonia gas at high temperatures, reducing nitrogen gases.
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Exhaust Gas Recirculation Convertors or EGRs contain EGR valves. These valves are controlled by the engine control unit and are placed in the combustion chamber. A particular amount of exhaust gas is recirculated into the chamber, reducing the amount of oxygen entering the chamber. This lowers the temperature inside the chamber significantly. A cooler chamber reduces the number of nitrogen oxides produced.
The modern EGR systems have been evolving over the decades. Now, these systems are equipped with an EGR cooler which significantly reduces the temperature in the exhaustion chamber. Thus, peak reduction can occur in the chamber, affecting the number of harmful gases being let out!
