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A detailed understanding of drop-wall interactions at high-temperature and high-pressure conditions can help optimize fuel injection, engine operation, and material design. The existing formulas developed for simulating drop-wall interactions are either valid only for a small range of operating conditions or based on the single-drop impact scenarios neglecting the effect of the non-stationary liquid film on the wall. The Leidenfrost temperature is a critical parameter in determining the impact outcome and needs to be considered in characterizing the impact behavior at extreme conditions. In this study, the Smoothed Particle Hydrodynamics (SPH) method, a Lagrangian-based method, is used to study the impact of an n-heptane droplet stream on a heated wall near and above the Leidenfrost temperature. The impingement frequency and wall temperature are varied to understand the impact dynamics and outcomes. Visualizations of the impact outcomes are provided to explain the interaction between the succeeding drops and the liquid film created by the preceding drops. To further characterize the shift in the Leidenfrost behaviors and the corresponding impact outcomes caused by the change in ambient pressure, simulations are also conducted at the corresponding fluid states for ambient pressures of 5 bar and 20 bar. Results show that the increase in ambient pressure impedes splashing and the film is concentrated inwards near the impingement point.

<div class="section abstract"><div class="htmlview paragraph">Understanding the fundamental details of drop/wall interactions is important to improving engine performance. Most of the drop-wall interactions studies are based on the impact of a single drop on the wall. To accurately mimic and model the real engine conditions, it is necessary to characterize spray/wall interactions with different impingement frequencies at a wide range of wall temperatures. In this study, a numerical method, based on Smoothed Particle Hydrodynamics (SPH), is used to simulate consecutive droplet impacts on a heated wall both below and above the Leidenfrost temperature. Impact regimes are identified for various impact conditions by analyzing the time evolution of the post-impingement process of n-heptane drops at different impingement frequencies and wall surface temperatures. For wall temperature below the Leidenfrost temperature, the recoiled film does not leave the surface. Recoiling of the film takes place at a rapid rate at wall temperature above the boiling point of the liquid. For the given impingement conditions, at low impingement frequency, the succeeding drops meet the secondary drop, coalescing into a large drop. An increase in the impingement frequency promotes splashing. For the same impinging conditions, with the wall temperature above the Leidenfrost temperature, at low impingement frequency, recoiling and rebounding of the secondary droplets is seen along with the secondary droplets above the heated wall. On the other hand, at higher impingement frequencies, the succeeding drops impinge on thin liquid films about to be raised above the wall by the vapor film on the wall and splash forming isolated chunks of secondary droplets. Results of this study can further lead to the development of spray/wall impingement models that consider the impact frequency and wall temperature at realistic engine conditions.</div></div>