Three Way Catalyst with Faster Light-Off Substrates – A Promising Approach to Reduce Tailpipe Emissions

Abstract

<div class="section abstract"><div class="htmlview paragraph">The ever-tightening regulation norms across the world emphasize the magnitude of the air pollution problem. The decision to leapfrog from BS4 to BS6 – with further reduction in emission limits -showed India’s commitment to clean up its atmosphere. The overall cycle emissions were reduced significantly to meet BS6 targets [<span class="xref">1</span>]. However, the introduction of RDE norms in BS6.2 [<span class="xref">1</span>] demanded further reduction in emissions under real time operating conditions – start-stop, hard acceleration, idling, cold start – which was possible only through strategies that demanded a cost effective yet robust solutions. The first few seconds of the engine operation after start contribute significantly to the cycle gaseous emissions. This is because the thermal inertia of the catalytic converter restricts the rate at which temperature of the catalyst increases and achieves the desired “light-off” temperature. The challenge becomes more prominent in the turbocharged engines (where some part of exhaust heat energy is used by the turbine to power the compressor) leading to lower exhaust gas temperatures, specifically at ambient/cold starts. In order to achieve better emission performance, an innovative approach is needed to attain quicker catalyst “light-off” as any change in only the PGM material content/composition may not yield an optimum solution. Though in-cylinder based strategies to increase EGT exist, they impose an additional fuel penalty along with issues like oil dilution. A much better way – avoiding the issues above - to improve the EGT profile is to reduce the thermal inertia of the catalytic converter. This is the idea behind introducing high-porosity substrates. A new Corning<sup>©</sup> FLORA<sup>©</sup> substrate with a higher porosity (55%) compared to the standard substrates (35%) was adopted as the primary substrate (CC1) in a twin brick catalyst design. Higher porosity reduces the thermal inertia of the substrate which in turn aids in rapid catalyst temperature rise and faster light-off. The advanced FLORA<sup>®</sup> substrate when combined with key contributor’s improvements on catalytic converter design and engine calibration strategy on 1.2 L MPFI Revotron<sup>TM</sup> engine, resulted in an improved emissions performance even with a lower PGM content. A reduction of 10 to 30% in regulated pollutants was demonstrated with an approximately 10% lower PGM material loading. The paper describes the multipronged approach taken here to tackle the cold start emissions - redesign of the close coupled catalyst, innovative calibration methodology & the introduction of the high porosity substrate popularly known as FLORA<sup>®</sup>. The work was conducted on a Tata Motors passenger car powered by a 1.2L MPFI Revotron<sup>TM</sup> gasoline engine that successfully met the BS6 Stage II emission norms.</div></div>