Decarbonizing combustion: Tier 4, Stage V and beyond

First published by Global Mining Review, May 2025

The mining industry is confronted with myriad opportunities and challenges in its energy transition.   Mining equipment operates in the harshest of environments the world has to offer. In mining equipment of the size and scale, physical demands of the machines are tremendous, and reliability is paramount. Combine emissions compliance, robust demands of the products, and an ever-changing market landscape with an imperative need to balance Total Cost of Ownership (TCO), and it is easy to see why many across the industry are asking important questions about what will be powering equipment in years to come. 

There are many potential power solutions in varying stages of development that could meet the outputs needed for the future of mining, each with different surrounding infrastructure requirements and installation complexities. While there is a long-term future for many of these solutions, the timeframe and validation of when these technologies will be readily available, as well as able to meet the power demands and reliability requirements of miners while balancing TCO, is currently unknown. 
What solutions therefore can we look at today that can generate valuable and required emissions reductions, while balancing robustness, TCO and performance? For Cummins, these conditions point towards a strong case for the future of combustion.   

Why combustion? 

Internal combustion engines (ICE) play a crucial role in powering mining operations today and are likely to continue to do so for many years to come. While zero emission technologies and accompanying infrastructure are advancing, combustion engines are also evolving to be more efficient and cleaner than ever before. The ongoing development of these technologies creates a promising pathway for the mining industry to reduce emissions while delivering dependable performance. 

Latest generation combustion technology offer major benefits to miners without requiring OEMs to entirely redesign existing equipment. For example, the Cummins QSK60 is a familiar design for OEMs that delivers up to 2,850 hp and 8,274 lb-ft of torque at Tier 4 and Stage V compliant levels of emissions. It can run for over 40,000 hours without an engine overhaul and can be rebuilt more than three times. This long lifespan and commonality with previous generations reduces installation costs and total cost of ownership (TCO), while also lowering supply chain emissions associated with the development and transportation of brand new engines.

Tier 4 and Stage V 

Tier 4 and Stage V legislation was introduced with the primary goal of reducing NOx and particulate matter emissions from engines, but there are also wider benefits to be had.  

Cummins Tier 4/Stage V compliant engines operate with an average 5% reduction in fuel consumption compared to previous generations while still meeting aggressive emission regulations and providing significant gains in TCO to add substantial value to miners and their operations.

One of the ways in which Cummins has met these challenges is through the optimization of combustion technology, combustion hardware and systems to reduce particulate matter and improve fuel consumption efficiency.

Tier 4 requires reducing Oxides of Nitrogen (NOx) by 45% and Particulate Matter (PM) by 80% compared to Tier 2, driving the most significant change to date in mining power technology. 

Aftertreatment and SCR 

Meeting emissions in mining is a challenge that has brought forth multiple solutions to provide robust and cost-effective products to market.  Varying solutions bring about opportunities and challenges for mining customers that they have never experienced before. Vastly different means and mechanisms to achieve Tier 4 and Stage V regulations have proven to vary greatly, with each requiring new levels of integration between engine manufacturers and OEMs. In order to meet Tier 4 and Stage V, Cummins evaluated multiple architectures for developing a product that would ensure delivery of dependable power, minimal TCO implications and, crucially, reliable reduction of emissions from the tailpipe in application.  

The two dominant architecture choices for meeting Tier 4 and Stage V are Cooled Exhaust Gas Recirculation (cEGR) and Selective Catalytic Reduction (SCR). These architectures are widely used below 751 horsepower today.  In-depth evaluation of these technologies was conducted by Cummins for engines above 751 horsepower.  Both architectures were thoroughly evaluated. Following this testing, Cummins believes that the implementation of SCR technology provides that best systemic combination of low TCO and maximum robustness for the mining sector.

To explain the key differences, Cooled Exhaust Gas Recirculation (cEGR) is often used in on-highway applications and recirculates a portion of spent exhaust gas, cooling it, before mixing it with fresh air. This process lowers the charge temperature, effectively reducing NOx formation.  

The heat rejection required for higher displacement engines is significant, as diesel engines have high cEGR recirculation volumes. Many times, cEGR engines require the addition of a Diesel Particulate filters and, or Diesel Oxidation catalyst to meet the required emission limits.  

While cEGR has been successful in below 751 hp installations, many later systems include cEGR along with SCR and other components. This is the differentiator between Cummins Tier 4 strategy for below and above 751 hp.  For applications above 751 hp, Cummins has chosen an SCR only architecture. This choice simplified the systemic architecture by eliminating the need for a DPF and a DOC. Cummins has enabled the particulate matter (PM) reduction to take place in cylinder and has chosen to treat the handling of NOx to the SCR. By choosing this architecture, the robustness and proven reliability of the base engine has been built upon.  

The SCR only approach also ensured that the need for additional increased heat load due to cEGR was not impacted, as increasing heat load for the large volume exhaust gas recirculation has to be absorbed by a cooling system, either in increased cooling capacity or feature reduction.

Cummins Tier 4 solutions utilize purpose designed and built SCR canisters that are scalable for varying engine displacements. These canisters incorporate integrated dosing reactor features to greatly simplify installation. They are also sized to fit into existing silencer space claims for ease of integration and adaptation into OEM equipment. SCR works through a chemical reaction, in which Diesel Exhaust Fluid (DEF) is injected into the exhaust stream. This fluid mixes with hot exhaust gases and reacts with specifically formulated catalyst coatings.  This chemical reaction results in up to 90% reduction in NOx molecules out the tailpipe while being a passive and non-serviceable component of the certified system.  The SCR has limited impact on engine performance and system tuned diagnostics to ensure proper system function.

SCR is a tried and tested technology that has won in the on-highway sector and paved the way for adoption into the off-road and mining markets. Understanding the advantages and drawback of both systems and evaluating the solutions in a databased fashion has allowed for a clear choice in durability and reliability.

Looking ahead: how to decarbonize beyond ICE  

As the mining industry moves beyond reducing NOx and particulate matter emissions, the focus will shift to achieving lower and even zero carbon emissions. This requires an open-minded approach to consider a variety of technologies rather than a one-size-fits-all alternative to diesel, with internal combustion engines remaining a strong foundation for carbon reduction. One route miners can take is hybridization, which offers a practical and less-disruptive transition in comparison to full electrification or battery only,  while significant reducing carbon reduction.  

Retrofitting existing trucks with hybrid power systems extends duty cycles and enhances efficiency while maintaining operational familiarity. Because hybrid systems share much of their structure with traditional ICEs, it’s a cost-effective way to decarbonize, decreasing TCO for operators. Additionally, given the infrastructure challenges in remote locations, hybrids provide a compelling solution as they deliver optimal power and transient load capacities without the requirement of extensive modifications. Research and field data shows that the savings in both fuels and GHG emissions with a hybrid system are substantial. Hybrids operating a haul route with an average gradient between 6-9% grade can expect a 20% carbon reduction in carbon savings compared to those with diesel engines. 

Beyond hybrids, alternative clean fuels offer another pathway to low or zero-emissions. Many of these fuels, such as hydrotreated vegetable oil (HVO), biodiesel, ethanol and methanol are already in use, with varying levels of adoption. Cummins’ high-horsepower engines are approved for unblended HVO and various blends of biodiesel fuels, and ongoing projects are exploring dual fuel kits that integrate methanol or ethanol with diesel.  

It has also been found by Cummins that when supplementing the fuel of a hybrid system engine with 55% HVO, a total CO₂ reduction of up to 50% is possible. As the combination of these technologies progresses, miners that are actively utilizing this technology will see the benefits, from the dual perspective of total cost of ownership and emissions reduction. 

A balanced path to decarbonization 

ICE technology remains a crucial foundation towards decarbonization, particularly given the large existing asset base and the current infrastructure limitations in the mining industry. As electric, hybrid, hydrogen and clean fuel alternative solutions continue to develop, ICE provides a reliable and proven power source that can drive emission reductions until emerging technologies mature.  

Advanced component development, such as SCR, reduce NOx and particulate matter while maintaining the performance and reliability of ICE that miners depend on. Meanwhile, long-term solutions like hybrid and clean fuels are being advanced, positioning the industry for greater emissions reductions in years to come.  

To achieve meaningful progress toward zero-emissions, miners must embrace these technologies and collaborate on solutions that balance sustainability with operational demands. Cummins is confident that these advancements will drive environmental benefits across the sector while balancing performance and TCO for miners.