Kaushik Saha

Direct-injection spark-ignition (DISI) engines enhance fuel efficiency and reduce emissions, but spray-wall impingement poses challenges, especially during cold start conditions. This study examines E85 (85% ethanol, 15% gasoline) spray morphology versus gasoline (G100) under controlled impingement using a single-hole injector at 5–7 MPa injection pressure in a constant-volume chamber at 0.03–0.5 MPa. A flat wall was placed 16.8 mm (suction stroke) and 32 mm (compression stroke) downstream. High-speed diffused backlight imaging was used to measure liquid penetration, cone angle, and spray width pre- and post-impingement. Before impingement at 16.8 mm, E85 showed greater liquid penetration and wider spray than G100, especially at low chamber pressure and high injection pressure, due to higher density, momentum, and Ohnesorge number. At 32 mm, G100 developed a wider spray after 0.4–0.5 ms ASOI from better atomization and radial dispersion. Spray cone angle varied little with injection pressure but strongly with chamber pressure and fuel volatility. Post-impingement at both distances, spray height followed hyperbolic relaxation at low chamber pressures (inertia-dominated) and exponential at high pressures (gas-damping). E85 rebounded higher than G100, forming vortex-driven, disk-like structures with less peripheral wall contact at low pressures. G100 initially spread more on the wall due to superior atomization, but widths converged later as gasoline lost liquid phase faster peripherally. These behaviors stem from Spalding-type mass-transfer-controlled evaporation, modulated by fuel-specific momentum and atomization under cold-start conditions.