Modern Diesel Engine Exhaust System

Modern Diesel Engine Exhaust System.

 Selective Catalytic Reduction (SCR) System

According to Bharat Stage- VI (BS-VI) emissions norm, all the Indian automaker companies taking place major steps for their engine exhaust system and adopting advanced engines technology which were already adopted in western countries vehicles for their Euro Norm. Now, in the Bharat stage vehicles, emissions norm implemented BS6 on last year 1 April 2020. 

This norm mainly focuses on very harmful toxic gases to reduces Nitrogen oxide (NOx) and Particulate Matter (PM) especially in all diesel vehicles which emits more NOx pollutants gases from the engines as compared to petrol vehicles. In petrol engines not much problem to switch on BS4 to BS6 because petrol engines emit a lower label of Nitrogen oxide (NOx) emission gases. So that, petrol engine replaced port injection into the direct fuel injection is called Gasoline direct injection or GDI technology introduced with installed threeway catalytic converter on the engine exhaust system. It works as catalysts to reduces Hydrocarbon (HC), Carbon monoxide It directly affects cars prices at least 20 to 40 thousand cost hikes.

But, In all diesel engine vehicles had great challenges to switch on from BS4 to BS6 norm. To reduce Nitrogen oxide (NOx) and Particulate Matter (PM) (also called carbon soot particles). It is very taught adopting advanced technology for the increased cost of diesel engine vehicles particularly in light passenger cars and SUVs car prices hikes almost 80 to1 lakh Rupees in the Indian auto market.

The advanced technology system installed in the diesel engines exhaust system is a urea-based  Selective Catalytic Reduction (SCR) technology system and Lean NOx Trap (LNT) technologies assumed. 

 Selective Catalytic Reduction (SCR) Technology.

Selective Catalytic Reduction (SCR) system most effective solution reducing nitrogen oxides (NOx) and Particulate Matter (PM) or soot carbon particles emissions leaves during the combustion process of in modern diesel engine vehicles. SCR system can achieve up to 85 to 90 % of nitrogen oxides (NOx) reduction. It is located in the exhaust system.

 It works catalyst with chemicals reaction in ureas injected in exhaust gases it mixes and reacts in the SCR catalytic converter with Nitrogen oxides (NOx) converting Nitrogen (N2), water (H20) and very fewer amount of Carbon dioxide (CO2), after treatment of SCR system.

Diesel Exhaust Fluid (DEF) / Adblue 

Diesel exhaust fluid (DEF) also known as Adblue, Diesel exhaust fluid/liquid is a reducing agent for Nitrogen oxides (NOx)for SCR system, it aqueous urea 32.5% ureas and 67.5% dissolved in deionized water. This added to the engine leaves exhaust gases before the SCR catalyst treatment. This additive solution helped to convert harmful gases nitrogen oxides (NOx)  into harmless gases nitrogen (N2). 

Diesel Particulate Filter (PDF)

A Diesel Particulate Filter (PDF) is a filter device, designed to removed diesel Particulate Matter (PM) or (carbon soot particles), Which is emits from the engine Particulate Matter (PM) exhaust gas, PDF catalyst made by ceramic honeycomb filter with tiny channels or pores catalysts. This structure helps good thermal durability. It is located downstream of the exhaust system fitted with an in-between exhaust manifold and SCR catalysts, uses all modern diesel engine vehicles.  

Diesel particulate filters (PDF) have become the most effective technology for the control diesel particulate (PM) emissions. Due to an excess of particulate matter (PM) or soot particles accumulated inside the filter. This PDF filter is different from conventional types, it is not a removing type of filter from the assembly. PDF catalysts, the accumulated exhaust soot particle burnt itself, during the driven engine operation on the road but some certain speeds as required to burn off or soots particles is called filter regeneration. In other words to said that the process of burning soot particles in the PDF system is known as filtration regeneration or also called PDF regeneration. 

PDF Regeneration process

Generally, three types of the PDF regeneration process is done by all modern diesel engine vehicles.

• Passive regeneration process
• Active regeneration process and
• Service / parked regeneration process

The passive PDF regeneration process is done by the heat generated from exhaust heat used to burn the soot particles. You need to raise a high combustion chamber and oxidize in the presence of excess oxygen in the exhaust gas. In Regeneration, the process is done automatically without knowing the driver taking place in the PDF catalyst.

The active PDF regeneration process is self-activated by electronic control module or control unit (ECU) with the help of various sensors, mainly exhaust temperature and oxygen sensors, then the control unit or ECU received the input and command to output devices in the form of pressure, signal and voltages for proper oxidise and filtration in the PDF regeneration process.

Another one is Service or Parked PDF regeneration when the vehicles blinking frequently, PDF regeneration warning lights or messages on the cluster meter while vehicles drive due to filter clog or choked. In that case, the vehicle immediately sends to authorise dealer service centre. They have done a regeneration process in parked in the workshop using On-board Diagnosis (OBD), a process that occurs at the required temperature around 600°C the filter must operate at a sufficient temperature and the oxidation and heating process burn the soot. 

 Diesel Oxidation Catalyst (DOC)

This is an oxidation device used for all diesel engine exhaust systems. It is similar construction of catalytic converter of the vehicles. DOC locates in-between the exhaust manifold and Diesel Particulate Filter (PDF). When the exhaust gases passed through Diesel Oxidation Catalyst (DOC), exhaust gases break down with the excess presence of oxygen and reaction in the pollutant gases Carbon monoxide (CO) and Hydrocarbon (HC) converted into carbon dioxide (CO2) and water vapour (H2O).

DOC system requires high temperature for oxidised into fraction reaction. It also oxidised NO to NO2 and helping to reduce particulate matter (PM) emission at certain levels and diesel exhaust odor by converting them to H2O and CO2.