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

In previous work, oxymethylene dimethyl ether (OMEx) fuel blends have demonstrated their potential to achieve low engine-out emissions, complying with Euro V NOx and Euro VI PM regulations. In this subsequent study, further optimization of engine performance and exhaust particles reduction for OMEx-diesel blends is conducted on the same single-cylinder heavy-duty research engine. The two factors, exhaust gas recirculation (EGR) and OMEx 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 OMEx fuel enhances heat release at late combustion phase, effectively compensating for the longer injection duration. The gross indicated efficiency (GIE) increases with OMEx addition, especially at low EGR regions, with up to a 3 % reduction for the equivalent fuel consumption. Optimizing GIE while adhering to acceptable NOx emission limits suggests that moderate EGR is advisable for all blends tested, with lower EGR is preferable for OMEx ratios below 25 %. A trade-off relationship between particle numbers in nucleation and accumulation mode is observed, shifting towards the nucleation mode with OMEx addition, especially at low EGR ratios. OMEx is benefit for PN23 (number of particles with diameter above 23 nm) reduction. Notably, a comprehensive global evaluation of engine performance confirms that combining an OMEx 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 NOx regulations. And OMEx 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 ℃.