Design of experiments optimized OMEx-diesel blends on a heavy-duty engine − Part 2: Engine performance and exhaust particle analysis with EGR variation

• OME x -diesel blends demonstrate stability across an environment temperature range of 5 to 30 ℃. • OME x addition enables diesel-like GIE with acceptable NO x levels at moderate EGR settings. • OME x is beneficial for limiting PN 23 within the nucleation-accumulation trade-off. • A comprehensive map suggests a clear operating window between engine performance and emissions for OME x -diesel blends. In previous work, oxymethylene dimethyl ether (OME x ) fuel blends have demonstrated their potential to achieve low engine-out emissions, complying with Euro V NO x and Euro VI PM regulations. In this subsequent study, further optimization of engine performance and exhaust particles reduction for OME x -diesel blends is conducted on the same single-cylinder heavy-duty research engine. The two factors, exhaust gas recirculation (EGR) and OME x ratios, were designed using the Design of Experiments (DOE) approach and applied with the same combustion phasing as diesel, under identical test conditions of 1425 RPM and 30 % load. The results indicate that OME x fuel enhances heat release at late combustion phase, effectively compensating for the longer injection duration. The gross indicated efficiency (GIE) increases with OME x addition, especially at low EGR regions, with up to a 3 % reduction for the equivalent fuel consumption. Optimizing GIE while adhering to acceptable NO x emission limits suggests that moderate EGR is advisable for all blends tested, with lower EGR is preferable for OME x ratios below 25 %. A trade-off relationship between particle numbers in nucleation and accumulation mode is observed, shifting towards the nucleation mode with OME x addition, especially at low EGR ratios. OME x is benefit for PN 23 (number of particles with diameter above 23 nm) reduction. Notably, a comprehensive global evaluation of engine performance confirms that combining an OME x ratio of approximately 24 % with moderate EGR levels achieves an equivalent GIE as diesel, while maintaining engine-out emissions within Euro VI PM and Euro V NO x regulations. And OME x fuel shows potential for higher GIE and compliance with Euro VI standards with aftertreatment systems support. Furthermore, a long-term stability test confirms OMEx blends remain stable between room temperature of 5 and 30 ℃.