تحقیق و توسعه

The four main and very harmful by-products of combustion engines are: unburned hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NOx) and particulate matter (PM or soot). Depending on the type of fuel and the design of combustion engine performance, different emission catalysts can be used to purify these harmful by-products and prevent them from entering the environment. Ignition engines typically use gasoline or natural gas as fuel for combustion, and require a Three Way Catalyst (TWC) to purify emissions from the process. Compression combustion engines often use diesel or diesel fuel as fuel and may require four separate catalysts to purify pollutants. These catalysts typically include Diesel Oxidation Catalyst (DOC), Diesel Particulate Filter (DPF), Selective Catalytic Reduction (SCR), and Catr. -ASC).

A three-purpose catalyst oxidizes exhaust gases including hydrocarbons (HC) and carbon monoxide (CO) as well as reducing nitrogen oxides (NOx). Therefore, these highly harmful by-products are converted to harmless compounds such as water (H2O), nitrogen (N2) and carbon dioxide (CO2). Depending on the operating conditions of the engine and the composition of its exhaust gases, conversion rates higher than 98% can be achieved in conditions close to stoichiometry (λ = 1). Necessary conditions for the progress of the reaction can be provided after less than one minute by performing various measures, especially rapid heating of the engine exhaust gas. This is especially important for city driving when the engine is frequently switched on and off. In three-purpose catalysts controlled by the mass-to-fuel ratio (λ) during combustion, the following three basic reactions are catalyzed in parallel:

2CO + O2 → 2CO2

CXH2X + 2 + [(3X + 1) / 2] O2 → XCO2 + (X + 1) H2O

2NOX → X N2 + X O2

A high conversion rate can be achieved for all three reactions at the stoichiometric ratio of the exhaust gas at which the air-to-fuel mass ratio (λ) is in the range of 1. This ratio is slightly dependent on the fuel composition / octane number (ON). It is important to note that lean operating conditions (λ> 1, excess oxygen) rapidly reduce nitrogen oxide (NOx) conversion rates. Therefore, the balance between the catalyst and the λ ratio is absolutely essential to ensure a high conversion rate over the life of the vehicle. The diagram below shows the narrow range of air-to-fuel mass ratio in which the conversion rate of all gaseous components is at its highest.

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