Supercritical water injection in a single cylinder research engine: a PIV study

This work presents the experimental results of a fluid dynamic investigation to characterize the injection of supercritical water in the combustion chamber of an internal combustion engine. Particle Image Velocimetry (PIV) analysis is carried out in an optically accessible 2-stroke Diesel engine. A prechamber, equipped with two optical accesses is connected to the main cylinder through a tangential duct so that the piston stroke induces a swirled motion field with angular velocities typical of light duty engines for automotive application. The engine is equipped with an injection system for the production and injection of supercritical water, with the possibility to independently regulate the injection pressure, temperature, duration, and timing. Tests have then been carried out under different operating conditions to evaluate the impact of the fluid dynamics in the combustion chamber on the water spray. First, the airflow velocity field has been characterized at different engine crank train angles. The water spray has been macroscopically characterized for an injection temperature of 300°C and pressure of 30Mpa. Then, the supercritical water/air interaction has been explored, at different injection pressure, temperature, and Start of Injection (SOI) to provide global information in terms of spray morphology, tip penetration, and velocity vector distribution of the water droplets within the combustion chamber for different injection strategies.