Browse Publications Technical Papers 2004-28-0028
2004-01-16

ADVANCED CATALYSTS FOR CNG-ENGINES 2004-28-0028

Emission regulations of the fossil-fuel burning engines have been tightened throughout the world since the Clean Air Act was published at the beginning of 1970's in the US. After that designers of the engine and after-treatment systems have made big efforts to fulfil the demands of the tightening legislation in the whole world. In that work, the development of the fuels and the seeking of the alternative fuels have also had their own roles. In meeting that requirement one suitable alternative is natural gas (NG). To achieve emissions under prevailing tight emission standards, besides improving the motor technology, the after-treatment systems including catalytic converters are needed. The legislation is one of the major driving forces to develop more effective after-treatment systems for the new and improved engines.
Different catalyst systems are needed for various conditions like stoichiometric (▭ = 1.0) and lean-burn engines. Special cases are dual fuel engines, which can burn either natural gas or gasoline (or CNG-diesel dual fuels). In addition, stationary engines differ in demands for catalyst systems from automotive systems due to temperature, composition, and flow rate of the exhaust gases are different and the life expectancy period is longer. ECOCAT Oy (EO) has developed commercial products for different gas applications. In stoichiometric (▭ = 1.0) NG engines EO's solution is differentiated Pt-Pd chemistry, which can be produced only with the open foil coating technology, which enables loading of Pt on one and Pd on the other foil separately, along with, different optimized washcoats. Another type of solution, the double brick catalysts, with combination of Pt and Pd have been successful in meeting targets in stoichiometric operation. These designs enable a good ▭-window and light-off simultaneously. A special Pt-Pd concept was developed for lean NG emissions because a good sulphur resistance is needed in these conditions. Different applications, like dual fuel systems, demand their own solutions for after-treatment systems; then for example sulphur poisoning, particle formation and CO contributed light off have to be considered simultaneously. EO catalyst solutions for different gas applications and catalysts performances are introduced in this paper.

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