OCTOBER 19-20, 2012 - YMCA University of Science & Technology

Proceedings of the National Conference on
Trends and Advances in Mechanical Engineering,
YMCA University of Science & Technology, Faridabad, Haryana, Oct 19-20, 2012
4.2 Catalytic converter for diesel engines
For compression-ignition (i.e., diesel engines), the most-commonly-used catalytic converter is the Diesel
Oxidation Catalyst (DOC). This catalyst uses O 2 (oxygen) in the exhaust gas stream to convert CO (carbon
monoxide) to CO 2 (carbon dioxide) and HC (hydrocarbons) to H 2 O (water) and CO 2 . These converters often
operate at 90 percent efficiency, virtually eliminating diesel odor and helping to reduce visible particulates
(soot). These catalysts are not active for NO x reduction because any reductant present would react first with the
high concentration of O 2 in diesel exhaust gas.
Reduction in NO x emissions from compression-ignition engine has previously been addressed by the addition of
exhaust gas to incoming air charge, known as exhaust gas recirculation (EGR). In 2010, most light-duty diesel
manufactures in the U.S. added catalytic systems to their vehicles to meet new federal emissions requirements.
There are two techniques that have been developed for the catalytic reduction of NO x emissions under lean
exhaust condition - selective catalytic reduction (SCR) and the lean NO x trap or NO x adsorber. Instead of
precious metal-containing NO x adsorbers, most manufacturers selected base-metal SCR systems that use a
reagent such as ammonia to reduce the NO x into nitrogen. Ammonia is supplied to the catalyst system by the
injection of urea into the exhaust, which then undergoes thermal decomposition and hydrolysis into ammonia.
One trademark product of urea solution, also referred to as Diesel Emission Fluid (DEF), is AdBlue.
Diesel exhaust contains relatively high levels of particulate matter (soot), consisting in large part of elemental
carbon. Catalytic converters cannot clean up elemental carbon, though they do remove up to 90 percent of the
soluble organic fraction, Diesel exhaust contains relatively high levels of particulate matter (soot), consisting in
large part of elemental carbon. Catalytic converters cannot clean up elemental carbon, though they do remove up
to 90 percent of the soluble organic fraction.
5. Performance Analysis of Catalytic Converter
The experimental methodology consists of two different parts. The first one is the emission test and the other one
is microstructure and materials composition analysis. The emission test was conducted by multi-gas analyzer for
emission measurements. After completing the test, the converters were cut to extract the substrate or
‘honeycomb’ inside the housing and being analyzed for microstructure and materials composition using
Scanning Electron Microscopy (SEM) and Energy Dispersive Analysis (EDX) [7].
Fig 4: Experimental Setup [7]
Two ceramic catalytic converters (underbody type) of different vehicle models were evaluated. The first one is
extracted from PROTON Wira 1.3L and another one from FIAT Punto Selecta 1.2L. Both converters had same
substrate material, synthetic cordierite ceramic and substrate shape, square cell except they differ in size,
chemical properties and geometrical attributes. Double substrate systems are as thermal mass, geometric surface
area, and washcoat distribution (Presti et. al 2002). Per Marsh et. al (2001) have shown that less favorable mass
transfer and higher flow velocity can be found as a results of the reduction of diameter, however, compensated
with the cases of lower cell densities implemented on both converters for separate reduction and oxidation
purposes.
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