It is claimed by many manufacturers that odour additive compounds can reduce odour intensity. However, it is observed that by using additives, there is hardly any effect on odour formation and is carried by exhaust gases.
The control of odours by using catalysts are under development and experiments have revealed that a few oxidation catalysts reduce odour intensity.
Unfortunately, the study of exhaust odour is hampered by lack of standard tests and standard units to measure the intensity of odour and the type of odour.
Several nations have been undertaking studies on suppressing odours by different methods.
Cleaning Up Diesel Emissions with Plasma and a Converter
While diesel engines are more economical, they produce NOx during combustion and put engine designers in a catch-22 situation. Presently, the permitted emission of NOx in Europe is 0.7 g /km and it will be further reduced to 0.57 g /km. This limit is already in force in USA.
The major problem faced to reduce NOx by catalytic converter which has proved successful in conventional engines cannot be applied to lean burn S.I. engines or diesel engines because these engines burn their fuel with high excess air (A:F = 30:1) and O2 in the exhaust prevents the catalytic decomposition of NOx.
Siemens and Partners have developed an efficient exhaust gas purification process for diesel engine (SINOx). This system comprises a catalytic converter, a control system, and a dosing device for urea. The urea undergoes hydrolysis into CO2 and NH3, which act as a reducing agent, transforming NOx into environmentally compatible N2 and water. However, in order to chemically reduce NOx effectively in a catalytic converter, a minimum temperature of 200°C is essential—a condition that is usually met in trucks. In passenger cars, on other hand, the low efficiency of the process at temperatures below 200°C causes problems typical of urban driving and cold start phase.
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