Macroscopic spray characteristics of a fuel injection system in an internal combustion (IC) engine have a direct impact on engine performance, emissions, and combustion characteristics. Nonintrusive in-cylinder measurements provide insights into the spray formation process for greater understanding of fuel-air mixing and combustion processes in an IC engine. In this paper, there are two parts: (a) procedure and methodology to configure the Artium phase Doppler interferometer (PDI) for in situ measurements through a cylindrical window and (b) comparative macroscopic spray characteristics in a firing Gasoline Direct Injection (GDI) optical engine to a constant volume spray chamber (CVSC) for spray droplet size-velocity distributions. Binned average velocity and average Sauter mean diameter of spray droplets in a firing engine were compared with that of a CVSC. Probability density function of droplet diameters in the CVSC under ambient conditions and in the engine combustion chamber provides an insight into the comparative droplet size distributions and droplet dynamics. Discussion on challenges encountered during PDI measurements in the firing engine environment, safety protocols, and tools required is also included. In addition, shadowgraphy images have been used to discuss the details on spray boundaries and spray evolution. The droplet size distribution inside the engine combustion chamber was found to be significantly different from the one observed in the CVSC. An engine simulation model can be developed/validated by using the data reported in this manuscript for attaining superior accuracy in the model. This paper describes the comparisons of the spray droplet size and velocity distributions in a CVSC and in situ for a working GDI engine. Maximum spray droplet velocity components (Vx, Vy) under engine combustion chamber conditions were 29.8 m/s, 14.2 m/s whereas the corresponding velocities in the CVSC under ambient conditions they were 78.41 m/s, 23.92 m/s, respectively, showing a large difference between the traditional measurements in the CVSC simulating engine conditions, and actual firing engine conditions. This study also reports the very first attempt in the open literature to measure spray droplet size and velocity distribution measurements in a firing IC engine.

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