SCR’s Total Value Proposition Outweighs Initial Acquisition Cost

Technology November 2019 SCR Selective Catalytic Reduction Total Value Proposition Outweighs Initial Acquisition Cost Nitrogen Oxide NOx Emissions Diesel-Powered Vehicles

The Selective Catalytic Reduction (SCR) technology enables the reduction of nitrogen oxide (NOx) emissions from the tailpipe of diesel-powered vehicles

SCR technology controls emissions by injecting a urea-based reducing agent through a catalyst into the exhaust system in a diesel engine. This reducing agent comprises automotive-specification urea, which is known as Diesel Exhaust Fluid (DEF), or more commonly as ‘AdBlue.’ The DEF creates a reaction in the exhaust chamber, chemically breaks down the NOx emissions mainly into nitrogen and water, along with a small amount of carbon dioxide (CO2). The SCR technology ensures around 90 % NOx emission reduction.

As a technology, SCR is widely spoken about in the commercial vehicle space, while it is also adopted in diesel passenger vehicles to maintain emission levels. However, since the passenger vehicle space is less cost-sensitive and more technology-oriented, it is easier to educate customers and increase its adoption. Meanwhile, the commercial vehicle segment still needs a nudge in the direction of SCR technology for increased adoption as well as understanding of the overall value proposition.

Indian manufacturers have already showcased their BS VI-compliant diesel engines that feature SCR technology


The SCR technology allows diesel engines to operate at optimal combustion temperatures, resulting in improved power delivery, better fuel efficiency as well as lower NOx and particulate matter generation. However, SCR is a more expensive technology than Exhaust Gas Recirculation (EGR), but also comes with more benefits. EGR is simple and easy to integrate, but does not offer the ability to be scaled up for more stringent emission standards like that of SCR. Since EGR and SCR technologies offer varied benefits, their adoption is also split between price-sensitive and technology-heavy segments, respectively.

Commercial vehicles in the mid and lower segments adopt the EGR technology, while premium commercial vehicles and passenger vehicles adopt SCR. Therefore, automotive manufacturers have diesel vehicle models in their line-up featuring both these emission check systems, depending on the type of vehicle and the segment it has been positioned in. In the Indian context, it is clear that EGR might be an obvious choice in meeting BS VI regulations, due to the advantages of low-cost, simplicity and easy integration. The selection of SCR technology will also be made for both current and future models to conform to more stringent norms as well as for vehicles exported to markets, where it is mandatorily required.


The SCR technology uses less fuel since all emission control processes are carried out separately in the exhaust system, and the engine can be set up for performance and economy. Additionally, fewer active ‘regenerations’ of diesel particulate filters are required to burn off the soot, which also facilitates lower fuel utilisation. To ensure further gain in emission reduction of particulate matter, the SCR technology is combined with diesel particulate filters. Such a technology becomes extremely important in industry requirements that will only become more stringent in coming times.

This technology is also seeing a new form of development, which is making these systems more feasible in a market like India that has a tight control over prices. One form of such development is the airless SCR technology from Mahindra, which is claimed to meet global standards to control emissions from heavy commercial vehicles. It also achieves this with a simple layout and lesser number of parts, allowing drivers and engineers to reap maximum benefits with minimal specialised training, the company noted. Under Mahindra’s SmartSCR system, AdBlue dosing takes place through the ECU input, thereby reducing maintenance since only one filter is required, when compared to three in a regular SCR, and also precise dosing of AdBlue is enabled. Mahindra observed that this technology has led to around
30 % reduced consumption of AdBlue.

It is clear that the acquisition cost and cost of ownership increase with the SCR technology, which explains why its adoption in the industry has been relatively slow. However, the returns in the form of lower emissions and consequently increased fuel economy pose a better value proposition in the long run. Therefore, OEMs are of the view that sooner customers understand the value proposition offered by SCR, it will be easier for them to switch to this technology, when BS VI norms are implemented in April 2020.

The DEF tank needs to be a separate unit that needs to be monitored regularly, since the liquid is required constantly to break down NOx emissions into safer gases


The challenges posed by the SCR technology are temporary in nature, since increased adoption of this emission control system pares off these deficiencies over time. The main requirement for an SCR system is the need to replenish the DEF on a periodic basis. Additionally, the vehicle needs to be designed with space to accommodate a separate on-board tank for this liquid, which must also be monitored and refilled based on vehicle operation. DEF refill intervals may occur around the time of a recommended oil change in the case of light-duty vehicles, but may vary depending on the operating conditions, hours used, mileage, load factors and other parameters in case of heavy load engines.

At present, mainly due to the low adoption of the technology, along with a few suppliers of DEF, the cost of SCR technology is higher than EGR. Although the initial cost and DEF refill costs are paid off with vehicle usage, they are parameters that potential customers take into consideration before confirming their purchase. Therefore, OEMs need to adopt an educative approach, in terms of educating customers about the benefits of the total cost of ownership this technology offers across the vehicle’s lifecycle.

The diesel engine becomes more complex with stringent emission norms due to the addition of critical components that maintain low output of gases and particulate matters


The SCR is a proven technology, which almost every diesel engine manufacturer has adopted globally. Major international commercial vehicle OEMs have adopted SCR to comply with new and upcoming emission standards. In India, companies are offering both SCR as well as EGR technologies in their vehicle portfolios, to address their customer requirements. However, these OEMs are of the opinion that SCR will be the emission control technology that diesel engines will need to adopt if they want to offer lower levels of NOx emissions along with improved fuel economy.

Furthermore, the ever-increasing integration of electronic systems within the powertrain enables the self-tuning of engines in order to run optimally. As a technology, SCR can be easily integrated with ECUs in the vehicle for improved vehicle performance capabilities.

(Inputs from VE Commercial Vehicles; Daimler India Commercial Vehicles; Tata Motors; Diesel Technology Forum)

TEXT: Naveen Arul