Comprehensive experimental study on spray dynamics, combustion performance, and emission profiles of ethanol-gasoline and butanol-gasoline mixtures in a constant volume combustion chamber under cold start GDI conditions

Adoption of low-carbon renewable fuels like ethanol and butanol in gasoline direct injection (GDI) engines is critical for global decarbonization goals, yet hindered by poor cold-start performance, excessive emissions, and atomization challenges. While flash boiling injection could mitigate these issues, prior studies neglect its synergy with 50%-50% biofuel-gasoline blends under cold-start, a critical gap given that cold starts account for 60-80% of urban driving emissions. This study pioneers the co-optimization of 50% ethanol/butanol blends with flash boiling in a constant volume combustion chamber (CVCC). Experiments under cold-start GDI conditions analyzed spray dynamics (Mie scattering), flame propagation (high-speed imaging), combustion pressure, emissions (FTIR for 15 species), soot nanostructure (TEM), and volatility (TGA). Results show flash boiling enhances fuel-air mixing, reducing ignition delay by 77.2% for gasoline (G100) and boosting heat release rates by 75% (E50) and 57.8% (B50). E50 outperformed B50, achieving 43.4% smaller soot aggregates, 38.5% lower aromatics, and 37.5% NOx reduction under flash boiling, with higher soot oxidation reactivity. E50 balanced efficiency and emissions, cutting HC by 42% and demonstrating superior cold-start adaptability. This work validates flash boiling as a pathway to deploy 50% low-carbon renewable fuels in GDI engines, addressing cold-start inefficiencies critical for urban PHEV emission reduction.