An experimental and numerical investigation of HD diesel engine DOC efficiency in oxidizing NO to NO2

Almoutazbellah Kutkut; Zhiming Gao; Todd Toops; Hailin Li

doi:10.1016/j.fuel.2025.137784

An experimental and numerical investigation of HD diesel engine DOC efficiency in oxidizing NO to NO₂

Almoutazbellah Kutkut
, Zhiming Gao
, Todd Toops
, Hailin Li

Research output: Contribution to journal › Article › peer-review

Abstract

Reducing pollutant emissions from heavy-duty (HD) diesel engines is critical due to their significant environmental impact, particularly concerning NO_x emissions. Understanding and optimizing modern diesel oxidation catalyst (DOC) and selective catalytic reduction (SCR) performance is essential for improving exhaust aftertreatment (EAT) system efficiency to meet stringent emissions regulations. The oxidation of nitric oxide (NO) to nitrogen dioxide (NO₂) in DOC plays a key role in improving SCR efficiency in reducing NO_x. This study investigates the DOC performance in oxidizing NO to NO₂ and its impact on the SCR efficiency of a 2021 MY Navistar E39 HD diesel engine. The influence of engine speed, load, exhaust gas temperature, and composition on DOC efficiency is experimentally investigated. The relationships between DOC inlet temperature, oxygen availability and NO₂/NO_x ratio at the DOC inlet are examined to better understand their effects on the overall DOC efficiency. The results indicate that DOC NO oxidation efficiency is highly dependent on exhaust temperature, with optimal oxidation occurring within a specific temperature range (275–350 °C). Below this threshold, the chemical reactions are kinetically limited, while at higher temperatures, thermodynamic constraints reduce the efficiency of DOC in oxidizing NO to NO₂. The experimental data further reveal that the NO₂/NO_x ratio peaks at medium loads before declining at higher loads due to reduced residence time and mass transfer effects. Additionally, the SCR NO_x conversion efficiency is significantly influenced by the NO₂/NO_x ratio, achieving peak performance when the NO₂/NO_x ratio approaches 0.5. A DOC chemistry model was developed and validated against the experimental data to predict DOC oxidation behavior under various operating conditions. The findings of this study provide insights into the interdependencies between DOC and SCR performance, contributing to the optimization of SCR systems for optimized NO_x reduction.

Original language	English
Article number	137784
Journal	Fuel
Volume	409
DOIs	https://doi.org/10.1016/j.fuel.2025.137784
State	Published - Apr 1 2026

Funding

This research is funded by US DOE DE-EE0009654 “Fast Simulation of Real Driving Emissions from Heavy-duty Diesel Vehicle Integrated with Advanced Aftertreatment System”. The hardware, software and technical support from Navistar and Bosch, USA to this project are gratefully appreciated. The contribution of the staff in EEA and especially the testing engineer Brad Ralston, to conduct the engine test work should also be acknowledged.

Keywords

DOC Efficiency
HD Diesel Engine
NO Emissions
NO/NO ratio
SCR Efficiency

Access to Document

10.1016/j.fuel.2025.137784

Cite this

@article{85899ea906974450860d499dbd3ea20b,

title = "An experimental and numerical investigation of HD diesel engine DOC efficiency in oxidizing NO to NO2",

abstract = "Reducing pollutant emissions from heavy-duty (HD) diesel engines is critical due to their significant environmental impact, particularly concerning NOx emissions. Understanding and optimizing modern diesel oxidation catalyst (DOC) and selective catalytic reduction (SCR) performance is essential for improving exhaust aftertreatment (EAT) system efficiency to meet stringent emissions regulations. The oxidation of nitric oxide (NO) to nitrogen dioxide (NO2) in DOC plays a key role in improving SCR efficiency in reducing NOx. This study investigates the DOC performance in oxidizing NO to NO2 and its impact on the SCR efficiency of a 2021 MY Navistar E39 HD diesel engine. The influence of engine speed, load, exhaust gas temperature, and composition on DOC efficiency is experimentally investigated. The relationships between DOC inlet temperature, oxygen availability and NO2/NOx ratio at the DOC inlet are examined to better understand their effects on the overall DOC efficiency. The results indicate that DOC NO oxidation efficiency is highly dependent on exhaust temperature, with optimal oxidation occurring within a specific temperature range (275–350 °C). Below this threshold, the chemical reactions are kinetically limited, while at higher temperatures, thermodynamic constraints reduce the efficiency of DOC in oxidizing NO to NO2. The experimental data further reveal that the NO2/NOx ratio peaks at medium loads before declining at higher loads due to reduced residence time and mass transfer effects. Additionally, the SCR NOx conversion efficiency is significantly influenced by the NO2/NOx ratio, achieving peak performance when the NO2/NOx ratio approaches 0.5. A DOC chemistry model was developed and validated against the experimental data to predict DOC oxidation behavior under various operating conditions. The findings of this study provide insights into the interdependencies between DOC and SCR performance, contributing to the optimization of SCR systems for optimized NOx reduction.",

keywords = "DOC Efficiency, HD Diesel Engine, NO Emissions, NO/NO ratio, SCR Efficiency",

author = "Almoutazbellah Kutkut and Zhiming Gao and Todd Toops and Hailin Li",

note = "Publisher Copyright: {\textcopyright} 2025 Elsevier Ltd.",

year = "2026",

month = apr,

day = "1",

doi = "10.1016/j.fuel.2025.137784",

language = "English",

volume = "409",

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T1 - An experimental and numerical investigation of HD diesel engine DOC efficiency in oxidizing NO to NO2

AU - Kutkut, Almoutazbellah

AU - Gao, Zhiming

AU - Toops, Todd

AU - Li, Hailin

PY - 2026/4/1

Y1 - 2026/4/1

N2 - Reducing pollutant emissions from heavy-duty (HD) diesel engines is critical due to their significant environmental impact, particularly concerning NOx emissions. Understanding and optimizing modern diesel oxidation catalyst (DOC) and selective catalytic reduction (SCR) performance is essential for improving exhaust aftertreatment (EAT) system efficiency to meet stringent emissions regulations. The oxidation of nitric oxide (NO) to nitrogen dioxide (NO2) in DOC plays a key role in improving SCR efficiency in reducing NOx. This study investigates the DOC performance in oxidizing NO to NO2 and its impact on the SCR efficiency of a 2021 MY Navistar E39 HD diesel engine. The influence of engine speed, load, exhaust gas temperature, and composition on DOC efficiency is experimentally investigated. The relationships between DOC inlet temperature, oxygen availability and NO2/NOx ratio at the DOC inlet are examined to better understand their effects on the overall DOC efficiency. The results indicate that DOC NO oxidation efficiency is highly dependent on exhaust temperature, with optimal oxidation occurring within a specific temperature range (275–350 °C). Below this threshold, the chemical reactions are kinetically limited, while at higher temperatures, thermodynamic constraints reduce the efficiency of DOC in oxidizing NO to NO2. The experimental data further reveal that the NO2/NOx ratio peaks at medium loads before declining at higher loads due to reduced residence time and mass transfer effects. Additionally, the SCR NOx conversion efficiency is significantly influenced by the NO2/NOx ratio, achieving peak performance when the NO2/NOx ratio approaches 0.5. A DOC chemistry model was developed and validated against the experimental data to predict DOC oxidation behavior under various operating conditions. The findings of this study provide insights into the interdependencies between DOC and SCR performance, contributing to the optimization of SCR systems for optimized NOx reduction.

AB - Reducing pollutant emissions from heavy-duty (HD) diesel engines is critical due to their significant environmental impact, particularly concerning NOx emissions. Understanding and optimizing modern diesel oxidation catalyst (DOC) and selective catalytic reduction (SCR) performance is essential for improving exhaust aftertreatment (EAT) system efficiency to meet stringent emissions regulations. The oxidation of nitric oxide (NO) to nitrogen dioxide (NO2) in DOC plays a key role in improving SCR efficiency in reducing NOx. This study investigates the DOC performance in oxidizing NO to NO2 and its impact on the SCR efficiency of a 2021 MY Navistar E39 HD diesel engine. The influence of engine speed, load, exhaust gas temperature, and composition on DOC efficiency is experimentally investigated. The relationships between DOC inlet temperature, oxygen availability and NO2/NOx ratio at the DOC inlet are examined to better understand their effects on the overall DOC efficiency. The results indicate that DOC NO oxidation efficiency is highly dependent on exhaust temperature, with optimal oxidation occurring within a specific temperature range (275–350 °C). Below this threshold, the chemical reactions are kinetically limited, while at higher temperatures, thermodynamic constraints reduce the efficiency of DOC in oxidizing NO to NO2. The experimental data further reveal that the NO2/NOx ratio peaks at medium loads before declining at higher loads due to reduced residence time and mass transfer effects. Additionally, the SCR NOx conversion efficiency is significantly influenced by the NO2/NOx ratio, achieving peak performance when the NO2/NOx ratio approaches 0.5. A DOC chemistry model was developed and validated against the experimental data to predict DOC oxidation behavior under various operating conditions. The findings of this study provide insights into the interdependencies between DOC and SCR performance, contributing to the optimization of SCR systems for optimized NOx reduction.

KW - DOC Efficiency

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KW - NO/NO ratio

KW - SCR Efficiency

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