A Qualitative Comparison of the Macroscopic Spray Characteristics of Gasoline Mixtures and their Multi-Component Surrogates Using a Rapid Compression Machine

Rapid Compression Machines (RCM) offer the ability to easily change the compression ratio and the pressure/mixture composition/temperature to gather ignition delay data at various engine relevant conditions. Therefore, RCMs with optical access to the combustion chamber can provide an effective way to analyze macroscopic spray characteristics needed to understand the spray injection process and for spray model development, validation and calibration at conditions that are suitable for engines. Fuel surrogates can help control fuel parameters, develop models for spray and combustion, and perform laser diagnostics with known fluorescence characteristics. This study quantifies and evaluates the macroscopic spray characteristics of multicomponent gasoline surrogates in comparison to their gasoline counterparts, under gasoline direct injection (GDI) engine conditions. Using a RCM to compress air and injecting fuel with no tracer doping, 5 ms after TDC helps emulate engine like conditions and studying the development of spray in such conditions can provide insights that other systems typically used for spray studies cannot. Experiments were carried out at 10 bar and 20 bar compressed pressures, over a temperature range of 650 K-825 K and at 2 injection pressures of 30 bar and 100 bar. A 7-hole production GDI injector was used for both gasoline fuels, which differed in their mixture composition and RON rating, namely Low RON fuel and High RON fuel, and their corresponding multi-component surrogates. A Photron SA4 high speed camera along with a 105 mm, 1:2.8G, AF-S Micro Nikkor lens was used for the high-speed imaging of the injection process and no wavelength filter or laser excitation was used. The high-speed images were analyzed to determine the spray tip penetration lengths, spray tip velocities and projected areas of the sprays with the results indicating that the fuel surrogates were representative of their equivalent target fuels at various operating conditions.