Combustion, knock, and emissions of ethanol–iso-butanol–gasoline blends in a DISI engine: The role of ignition timing

This study investigates the influence of ignition timing and high-volume alcohol gasoline blends on the performance, combustion, knock, and emission characteristics of a direct-injection spark-ignition (DISI) engine. Experiments were conducted at 5000 rpm under full-load and slightly rich conditions (λ ≈ 0.91) using neat gasoline and alcohol–gasoline blends containing 30% alcohol and 70% gasoline by volume, including ethanol–gasoline, iso-butanol–gasoline, and ethanol–iso-butanol–gasoline blends, at three ignition-timing settings. Results indicate that maximum work output and the highest mechanical efficiency (82.6%) were achieved by the E15ISB15 ternary blend at advanced ignition timings, whereas it reached its peak brake thermal efficiency (30.2%) under the baseline (MAIN) timing condition. Although oxygenated blends increased brake specific fuel consumption, E30 yielded the highest indicated mean effective pressure. Combustion analysis revealed that advancing spark timing increased the maximum in-cylinder pressure and shifted its occurrence closer to top dead center. Moreover, binary blends (E30, ISB30) exhibited higher in-cylinder pressure values and more advanced combustion phasing than baseline gasoline (G100), while maintaining high combustion stability (CoV IMEP < 1.1%). Retarding ignition effectively suppressed knocks, stabilizing maximum amplitude of pressure oscillations below 1.0 bar. Conversely, under knock-prone advanced timing, E15ISB15 demonstrated superior auto-ignition resistance over G100 and E30. Environmentally, high-alcohol blends reduced soot formation by over 90%, with E15ISB15 achieving a 97.5% reduction at baseline timing. Their oxygenated structure enhanced carbon oxidation, lowering CO and THC emissions, while E30 exhibited the lowest CO 2 and NO emissions. Overall, coupling the E15ISB15 blend with optimized ignition timing offers an effective strategy for maximizing DISI engine efficiency while mitigating knock and emissions.