Effects of active energy intervention timing on combustion and emissions in high-compression-ratio natural gas/diesel dual-fuel engines

Abstract

Natural gas/diesel dual-fuel engines demonstrate superior thermal efficiency and emissions performance, with increased compression ratios serving as a key strategy for further enhancing efficiency. Within high compression ratio systems, the timing of active energy intervention plays a critical role in shaping the combustion process. Using a combination of experimental and simulation methods, this study investigates the effects of varying active energy intervention timings on the combustion and emissions characteristics of dual-fuel engines. The findings reveal that optimal timing is essential for maintaining engine efficiency, power output, and operational stability. Deviations from the optimal timing—either too early or too late—detrimentally impact engine performance. Under the tested conditions, an intervention timing of −15°CA ATDC achieves the highest thermal efficiency and an ideal combustion phase distribution. Furthermore, the timing significantly influences the formation, reaction rates, and spatial distribution of key free radicals, including OH, CH₂O, and H₂O₂. The formation of NOx, HC and CO emissions is strongly influenced by in-cylinder temperature and, at the microscopic level, is governed by the cumulative evolution of various reactive radical species. These results underscore the importance of regulating free radical dynamics through precise timing to achieve both high thermal efficiency and low emissions.