An engine’s power level determines the allowable emissions for off-road vehicles.
Researchers in the United States have demonstrated a diesel engine system that can meet Tier 5 emissions standards proposed by the California Air Resources Board (CARB).
Developed by researchers from Southwest Research Institute (SwRI), the diesel engine system is designed to help off-highway diesel vehicles.
“CARB’s Tier 5 rules aim to reduce nitrogen oxides (NOx) and particulate matter (PM) emissions by a significant margin,” said Alex Michlberger, a lead engineer in SwRI’s Powertrain Engineering Division. “However, the industry doesn’t currently have a cost-effective solution to meet Tier 5. Our project is meant to help provide that solution.”
Optimized calibration strategies
SwRI-developed hardware modifications and optimized calibration strategies that allowed an off-road vehicle with a commercially available diesel engine to meet the standards without negatively affecting performance.
Researchers also revealed an engine’s power level determines the allowable emissions for off-road vehicles. Most off-road engines operating between 19 and 56-kilowatts (kW) do not have a clear technical path for compliance with the new standards. Engines above the 56-kW threshold are expected to use emissions control technologies resembling those used by on-road vehicles, while applications currently using engines below 19 kW are expected to electrify.
SwRI conducted extensive laboratory testing
It’s also revealed that SwRI conducted extensive laboratory testing on a commercially available 55-kW, four-cylinder diesel engine to identify potential Tier 5 solutions.
The project utilized exhaust gas recirculation (EGR) to mitigate NOx and other calibration strategies to control PM. This approach required both hardware and calibration modifications. To enable a higher EGR rate, the team modified the turbocharger waste gate control to increase boost, and they installed a higher capacity EGR cooler. The hardware and calibration changes together demonstrated low emissions while maintaining engine performance, according to a press release.
The team also revealed that SwRI’s improved system achieved the Tier 5 targets in both ramped modal cycle (RMC) and non-road transient cycle (NRTC) certification tests. The researchers compared NOx, non-methane hydrocarbon (NMHC) and PM emissions with the Tier 5 targets.
“In the RMC demonstrations, we saw NOx emissions reduced by 22%and NMHC by 56%, compared to the Tier 5 target. For the NRTC, we found NOx emissions reduced by 28%and NMHC by 50%, compared to the Tier 5 target,” Michlberger said. “In short, we achieved significant reductions in emissions with an innovative engine calibration and minimal hardware changes.”
The successful demonstration suggests that off-road vehicle manufacturers may not need to rely solely on costly new technologies or full electrification to meet future emissions requirements. Instead, carefully engineered hardware upgrades combined with advanced calibration techniques could provide a realistic pathway toward cleaner and more sustainable off-road transportation.
As emissions regulations continue to tighten worldwide, SwRI’s work highlights the important role of engineering innovation in helping industries reduce environmental impact while preserving performance, reliability, and economic feasibility.
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Prabhat, an alumnus of the Indian Institute of Mass Communication, is a tech and defense journalist. While he enjoys writing on modern weapons and emerging tech, he has also reported on global politics and business. He has been previously associated with well-known media houses, including the International Business Times (Singapore Edition) and ANI.