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SwRI demonstrates 0.02 g/bhp-hr NOx diesel engine

26 May 2020

Southwest Research Institute (SwRI) announced it has demonstrated a diesel engine technology that can reduce NOx emissions to below 0.02 g/bhp-hr (FTP), while minimizing fuel consumption and CO2 emissions. Working with regulatory agencies, vehicle manufacturers and suppliers, SwRI combined engine modifications with integrated aftertreatment and control strategies. SwRI developed the technology for the California Air Resources Board (CARB), under stage 3 of the ongoing program to demonstrate heavy-duty engine technology to meet the lower NOx emission standards, a.k.a. Cleaner Trucks Initiative (CTI), planned by CARB and the US EPA.

SwRI engineers modified a 2017 Cummins X15 engine architecture, integrated aftertreatment technology and enhanced controls to produce the desired results [4752][4753]. A dual SCR system, with a close-coupled SCR catalyst was used to reduce NOx during cold-start and low load operation, Figure 1. As reported earlier, the engine has been fitted with cylinder deactivation (CDA) and an EGR cooler bypass [4140]. For the cold start FTP, a modified cold start strategy was developed, which included elevated idle speed combined with EGR, VGT and multiple fuel injections.

Figure 1. SwRI stage 3 final aftertreatment configuration

Before testing, the aftertreatment system was subjected to hydrothermal aging using a burner-based engine simulator. The aging target of 435,000 miles represented the current US EPA emission useful life period for heavy heavy-duty diesel engines (GVWR > 33,000 lbs). However, the upcoming lower NOx standards are expected to strengthen the useful life requirements for this engine category to as much as 800,000 - 1,000,000 miles.

In 2013, CARB contracted SwRI to investigate potential approaches for achieving an ultra-low NOx target in three stages. Stage 1 assessed the feasibility of lowering engine NOx emissions to 0.02 g/bhp-hr from a diesel and natural gas heavy-duty engine. While the 0.02 g NOx emissions were demonstrated in the natural gas engine [3685], the diesel engine fell short of the target at that time [3809]. In stage 2, SwRI developed a new emission certification test, the low-load cycle (LLC), intended to evaluate engine emissions in low-load operation.

Under the ongoing stage 3, SwRI continues to evaluate the system and its NOx reduction performance under realistic operating conditions such as hydrothermal stress and catalyst contamination to validate real-world performance. Final results are expected in summer 2020.

The CARB/EPA lower NOx emission standards are expected to include NOx limits over both the FTP and the LLC cycles. California-only limits of 0.05 g/bhp-hr (FTP) and 0.20 g/bhp-hr (LLC) are envisioned from 2024. US federal limits in the range of 0.015-0.030 g/bhp-hr (FTP) and (1-3) × FTP (LLC) could become effective from 2027.

Source: SwRI