One Box – A Modern Diesel Aftertreatment System

A One Box is a compact assembly that effectively packs all the machinery and exhaust pipes in a small box! 

 A truck with a One Box exhaust system.

Diesel-powered trucks have always functioned as the workhorses in our society for delivering massive amounts of goods between places. 


As emissions regulations have become stricter and the need for less downtime became continually greater several truck industries came up with a modern diesel aftertreatment system known as the ‘One-Box.’ While meeting the requirements of emissions regulators such as the EPA, the best thing about One Box is that it is a compact assembly that includes all the components in a small box efficiently!


One Box - Understanding the Workings of Exhaust System Components


To understand the functioning of One Box, you need to recognize its exhaust system’s internal workings. 

An exhaust system is made of four vital components, including:


DOC - Diesel Oxidation Catalyst

DPF - Diesel Particulate Filter

SCR -Diesel Particulate Filter/ Selective Catalytic Reduction

DEF – Diesel Exhaust Fluid, Adblue






A diesel oxidation catalyst (DOC) is a modern aftertreatment system component of the exhaust system designed to convert hydrocarbons and carbon monoxide (CO) into water vapors and carbon dioxide (CO2). This process is referred to as the oxidation reaction.

The DOC also breaks down the detrimental pollutants in the diesel engine’s exhaust stream to reduce particulate matter (PM), also known as particulates. Moreover, it oxidizes fuel to level the engine temperatures required for active regeneration.





After the exhaust stream has been treated by the DOC, it travels through the diesel particulate filter. The DPF’s primary purpose is to capture the soot (diesel particulates) exiting the engine. The DPF captures the soot and burns off the particulates through regeneration, which can happen in two ways, passive regeneration and active regeneration. This continuous process of baking soot (heavy and dense) into ash (low density and light) will lead to an accumulation of ash in the filter eventually. This can be removed and the DPF cleaned through DPF restoration processes.



DEF Dosing System


The next step in One Box is to inject diesel exhaust fluid (DEF) into the exhaust system. The purpose of this exhaust fluid is to decrease the NOX gases generated by the diesel engine. DEF is composed of urea, distilled water, and a small number of additives essential for the selective catalytic reduction (SCR) process.





Once DEF is injected into the exhaust, it travels through the SCR (Selective Catalytic Reduction) catalyst, an advanced emission control technology system. Here, the remaining nitric oxides or NOx are converted into nitrogen gas and water through a reduction reaction. This significantly reduces the active regeneration cycle


Passive regeneration can occur at any time when the engine is running and the exhaust gas temperature is high enough. Active regeneration is a forced regeneration process whereby sensors on the Onebox DPF sense that engine back pressure is reaching higher levels and a regeneration is required to maintain engine performance.


It is essential to understand that over time and the regular process of DPF regeneration a DPF filter will become full of ash and servicing of the DPF is required. There are several ways you can clean a DPF using liquid cleaning, air, or thermal processes. We suggest assigning this job to the professionals like The DPF Company, as other improper cleaning can often lead to one box overheating or performance loss. These damages are generally expensive to repair.