Date of Award

2016

Document Type

Open Access Master's Report

Degree Name

Master of Science in Mechanical Engineering (MS)

Administrative Home Department

Department of Mechanical Engineering-Engineering Mechanics

Advisor 1

Jeffrey Naber

Advisor 2

John Johnson

Committee Member 1

David Shonnard

Abstract

The study of NOx reduction across the SCRF® is presented in this report to understand the inlet and outlet NO, NO2, NH3 species from the SCRF®. The SCRF® is a prototype SCR catalyst on a Diesel Particulate Filter (DPF) that reduces NOx and PM at the downstream location. The SCRF® reduces the packaging volume of the aftertreatment components in order to reduce the cost, volume and weight of the aftertreatment system. A total of 12 experiments were performed on a Cummins ISB 2013 280 hp engine and the aftertreatment system. The tests were performed to investigate the NOx reduction performance of the SCRF® under various Particulate Matter loading.

The loading phase has been divided into two stages: Stage 1 and Stage 2. Stage 1 begins after all the PM has been removed from the SCRF®, which is then followed by Stage 2 loading. The engine is run at 2400 rpm and 200 Nm load with different fuel rail pressures for a duration to achieve PM loadings of 0, 2, and 4 g/L (grams of PM per volume of the SCRF®) in the SCRF®.

For the testing of the SCRF® without PM loading, a Catalyzed Particulate Filter (CPF) was placed before the SCRF®. After the loading phase, NOx reduction stage was run at different engine conditions. The engine speed and load conditions were selected for the NOx reduction stage, named as test points 1, 3, 6, and 8, in order to attain a wide range in space velocities, inlet temperatures and NO2/NOx ratios in the SCRF®, which are the major parameters determining NOx reduction efficiency in the SCRF®. The exhaust temperature varied from 206 to 443 °C, inlet NO2/ NOx ratio varied from 0.22 to 0.46, and space velocity varied from 13.5 to 48.2 k/hr. Urea was dosed in the decomposition tube before the SCRF® to determine the NOx conversion efficiency at different ammonia to NOx ratio (ANR) values. The ANR values considered for the NOx reduction and NH3 slip were 0, 0.8, 1, 1.2, and 1.2 repeat. The ANR of 1.2 was repeated in the urea dosing cycle.

It was found that the NOx conversion efficiency across the SCRF® is maximum for test points 3 and 6 i.e. for the temperature range of 300-350 °C. The NO2/NOx ratio at those points was around 0.42-0.46. It is observed that the loading in the SCRF® does not affect the NOx conversion efficiency at low (205 °C) and high (440 °C) temperature points but affects in between. The NOx conversion efficiency improved with PM loading until 300°C SCRF® inlet temperature and decreased (with PM loading) after 350 °C. There is noticeable ammonia oxidation at temperatures above 400 °C in the SCRF® that affects NOx conversion efficiency [1]. At higher temperature of about 440 °C, NH3 slip is observed varying with PM loading in the SCRF®. With PM loading, NO2 assisted oxidation increases the concentration of NO [2] and affects the NOx conversion efficiency.

It is concluded from the results that the NO2 concentration across the SCRF® decreased with PM loading and SCRF® temperature due to NO2 assisted PM oxidation. The impact of PM loading on NOx reduction in the SCRF® was insignificant below 300 °C. NOx conversion decreased by 3 – 5 % above 350 °C with increase in PM loading from 0 to 2 and 4 g/L, due to consumption of NO2 via passive oxidation of PM. The NOx concentration is not completely converted across the SCRF® at temperatures above 350 °C even if dosed with an ANR value of 1.2.

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