Conference Presentation Summary
Dinex outlines technology pathways for off-highway low NOx engines
Reference: Off-Highway Powertrains & Fuels, USA 2024
Following on the heels of the on-road heavy-duty low NOx rule, California is looking to implement a similar standard for off-highway machinery. We have previously summarized the current thinking from one of their recent workshops. Briefly, the standards, if finalized, would require a 90% reduction in NOx emissions and PM limit reduction by 75% for 56 – 560 kW engines.
Some of the regulatory and technical aspects of this rulemaking were discussed at the recent Off-Highway Powertrains & Fuels, USA 2024 conference, organized by EmissionsAnalytics.
Several advanced technologies are expected to find their way onto off-road agriculture and construction machinery to meet these requirements.
A good summary of the suite of technologies was presented by Dinex, shown in the picture here. These include:
- Low thermal mass components for faster heat-up
- Improved mixers for high ammonia utilization
- Improved diesel particulate filters (DPFs) with high filtration efficiency and low backpressure
- Optimized precious metal utilization on diesel oxidation catalyst (DOC)
- Dual SCR – one closer to engine and another downstream of the DPF in the conventional position.
- Combination of SCR catalysts – copper, iron, vanadia-based – for best deNOx performance, low N2O formation and high durability.
- Dual DEF dosing to feed the above SCRs.
- Electric heaters for active thermal management to raise SCR temperature quickly following a cold-start.
An example of the after-treatment layout is discussed, which includes the dual SCR and electric heater, as shown in this picture. The heater can be designed to deliver anywhere from 3.5 to 15 kW power, with the higher power associated with a 48V battery.
Note that space is especially limited on non-road engines so that packaging will be a key consideration. Also, this will be the first ever standard that will impose a CO2 reduction requirement, so that the additional backpressure and energy penalty of the electric heater must be managed.
The latest proposal envisions implementing the new Tier 5 standards in two stages – an intermediate one with a 45% reduction in NOx and the final one implementing the remaining 45% reduction. Simulations were done to show that an electric heater can help meet the first stage, but the combination of heater and dual SCR is likely needed to meet the final stringency.
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