Combined influence of hydrogen enrichment and exhaust gas recirculation in dual-fuel mode on the combustion, performance, and emission characteristics of a B20-fueled compression ignition engine

Abstract

The increasing environmental burden caused by diesel engines, characterized by high exhaust emissions and gradual performance limitations, necessitates the development of cleaner and more efficient combustion strategies. Conventional biodiesel blends such as B20 often experience a slight reduction in efficiency due to their higher viscosity and lower calorific value when compared with neat diesel fuel. Earlier investigations have explored biodiesel–diesel blending to improve soot oxidation, hydrogen enrichment to promote premixed combustion, compression ratio modification to influence ignition behavior, and exhaust gas recirculation to suppress nitrogen oxide formation. Despite their benefits, these techniques involve trade-offs, as hydrogen addition can increase NO_x emissions, while excessive EGR may deteriorate combustion stability and promote incomplete oxidation. To address these limitations, the present work proposes an integrated strategy combining B20 biodiesel, hydrogen enrichment, reduced compression ratio, and controlled EGR operation. Experimental results reveal that hydrogen induction at a compression ratio of 18:1 enhanced brake thermal efficiency by 2.5%, increased peak cylinder pressure by 9%, and improved cumulative heat release by 8% compared with baseline B20 at 18:1 CR. At the same condition, carbon monoxide, hydrocarbon, and smoke emissions were reduced by 30%, 33%, and 32%, respectively. Reducing the compression ratio to 17:1 effectively moderated the NO_x rise associated with hydrogen addition without imposing a noticeable efficiency penalty. Furthermore, hydrogen-enriched B20 operation paired with EGR rates of 4–10% showed that moderate levels of 4–6% provided the most balanced performance and emission characteristics. Overall, the combined application establishes a viable pathway forward.