Spray/wall interaction analysis on an ECN single-hole injector at diesel-like conditions through Schlieren visualization.

Abstract

To continuously improve CFD models which simulate spray evolution, breakup and evaporation mechanisms, it is helpful to validate them with results obtained by experimental research. In the present study, a mono-orifice target nozzle from Engine Combustion Network, referred to as Spray D, was investigated at conditions of spray-wall interaction, which actually is a real situation in internal combustion engines that is not frequently analyzed by visualization. A Photron SA-X2 high-speed camera was employed to record the vapor phase development of the spray in an inert atmosphere using a Schlieren imaging single-pass setup. The experiments show that the spreading of the spray along the wall has a behavior fairly similar to penetration at free-jet situations, especially regarding to its susceptibility to the operating conditions and its proportionality to the square root of time once the spray reaches a steady regime interacting with the wall. Furthermore, the spray film thickness was measured at three distances from the spray-wall impact point during the injection event, thereby characterizing that parameter both spatially and temporally. The tests were carried out in a constant pressure-flow facility able to reproduce pressure and temperature conditions, similar to those seen into a diesel engine. In order to observe the behavior of the spray colliding with a wall within this test rig, a system capable to being fitted into it and to holding a fused quartz wall at different injector tip-wall distances and impingement angle configurations, was designed and employed. IntroductionAt present, the study of the spray-wall interactions into the field of transportation systems is increasingly relevant in a world aimed at reducing the displacement per cylinder of the internal combustion engines. This phenomenon plays a fundamental role in the mixing and evaporation of fuel , the impact of spray with a wall is a subject of difficult analysis both theoretically and experimentally due to the highly transient nature of the spray and the high spatio-temporal variability of the event. Because of this, its effects on the engine performance are not entirely known. On the one hand, the incidence and accumulation of fuel in the cylinder walls can lead to the formation of a fuel film that worsens combustion, promotes the emission of carbon monoxide and unburned hydrocarbons and involves energy losses given the increase of heat transfer [7]. On the other hand, the impact of the spray with a surface tends to improve the mixing of the fuel in the air due to both the impact and the subsequent expansion of the front of the jet. The complexity of the jet-wall impact phenomenon has to be added to the overall complexity of the injection-combustion processes, which, although they have been extensively studied in 'free jet' conditions [7]-[9] remain an active area of research.

ECN Spray D visualization of the spray interaction with a transparent wall under engine-like conditions. Part I: Non-reactive impinging spray

“…• R-parameter for penetration and spreading (R S and R Y ): In accordance with several models from spray theory [44,45], under the assumption of a cone-shaped spray, at the steady part of its evolution it can be considered that penetration is proportional to the time rised to the power of 0.5, which makes its derivative respect to the square root of time to be a nearly constant value, as shown in the sample of Figure 7, where both penetration (le ) and its derivative respect to the square root of time (right) are shown for a di erent ECN injector [35]. is constant parameter to study penetration has shown to be particularly useful since it can be analyzed regardless of the considered temporal reference [35,3,6]. : Sample of spray penetration and its R-parameter at free-jet non-reactive conditions for an ECN Spray C injector (plot adapted from [35]).…”

“…On the one hand, the jet-wall interaction may improve the air-fuel mixing, by generating secondary atomization and enhancing the gas entrainment into the spray. Nevertheless, a fuel lm can be formed on the walls a er the impingement, rising the formation of soot and unburned hydrocarbons, besides a reduction of the engine e ciency produced by a worsening in the combustion and the heat transfer from the reactive spray to the walls [4][5][6]. Related to the wall Some experimental researches have been proposed to characterize the spray-wall interaction phenomenon, being possible to divide them into two main categories similar to what is stated by several authors [7,8]: e study of the impact of single drops, and the analysis of wall impingement of sprays.…”

“…Akop et al [19] carried out a series experiments in an environment at atmospheric pressure, taking into account the plate angle, observing that a pronounced inclination decreases the adhered fuel mass ratio. Another experiments [6,20,21] indicate that the spray momentum has an important e ect on the spray expansion along the wall and gas entrainment. Arcoumanis and Chang [22] employed fast response thermocouples to determine that the pre-impingement spray velocities play a key role on the local heat transfer rates.…”

ECN Spray D visualization of the spray interaction with a transparent wall under engine-like conditions, Part II: Impinging spray combustion

“…e ambient gas, initially stored in reservoirs from a compressor, is introduced into the test rig through a 30 kW electric heaters system that is in the bo om of the vessel in order to control ambient gas temperature. A er the gas is exhausted from the chamber, it is cooled down and recirculated to the compressor again or thrown to the atmosphere depending on the desired concentration of oxygen [27,25]. In this experiment, the air is introduced from the atmosphere in an open loop con guration in order to have a standard air oxygen concentration around 21%.…”

Analysis of the Influence of Diesel Spray Injection on the Ignition and Soot Formation in Multiple Injection Strategy

“…Consequently, the effectiveness of the post injection on reducing soot emissions is closely linked to a restrained engine bowl-shaped combustion chamber. As a matter of fact, Payri et al [41] and Zhao et al [42] concluded that spray-wall interactions enhance soot oxidation due to higher mixing with ambient air caused by wall impingement. Further, they found that the heat exchanged with the walls cooled down the jet, slowing the rate of soot formation.…”