Characterization of the ECN spray A in different facilities. Part 1: boundary conditions characterization

Abstract

The Engine Combustion Network (ECN) community has greatly contributed to improve the fundamental understanding of spray atomization and combustion at conditions relevant to internal combustion engines. In this context, standardized spray experiments have been defined to facilitate the comparison of experimental and simulation studies performed in different facilities and with different models. This operating mode promotes collaborations among research groups and accelerates the advancement of research on spray. In efforts to improve the comparability of the ECN spray A experiments, it is of high importance to review the boundary conditions of different devices used in the community. This work is issued from the collaboration in the ECN France project, where two new experimental facilities from PPRIME (Poitiers) and PRISME (Orleans) institutes are validated to perform spray A experiments. The two facilities, based on Rapid Compression Machine (RCM) design, have been investigated to characterize their boundary conditions (e.g., flow velocity as well as fuel and gas temperatures). A set of standardized spray experiments were performed to compare their results with those obtained in other facilities, in particular the Constant Volume Pre-burn (CVP) vessel at IFPEN. It is noteworthy that it is the first time that RCM type facilities are used in such a way within the ECN. This paper (part 1) focuses on the facilities description and the fine characterization of their boundary conditions. A further paper (part 2) will present the results obtained with the same facilities performing ECN standard spray A characterizations. The reported review of thermocouple thermometry highlights that it is necessary to use thin-wires and bare-bead junction as small as possible. This would help to measure the temperature fluctuations with a minimal need for error corrections, which are highly dependent on the proper estimation of the velocity through the junction, and therefore it may introduce important uncertainties. Temperature heterogeneities are observed in all spray A devices. The standard deviation of the temperature distribution at the time of injection is approximately 5%. We report time-resolved temperature measurement from PPRIME RCM, performed in the near nozzle area during the injection. In inert condition, colder gases from the boundary layer are entrained toward the mixing area of the spray causing a further deviation from the target temperature. This emphasizes the importance of the temperature in the boundary (wall) layer. In reacting condition, the temperature of these entrained gases increases by the effect of the increased pressure, as the RCM has a relatively small volume. Generally, the velocity and turbulence levels are an order of magnitude higher in RCM and constant pressure flow compared to CVP vessels. The boundary characterization presented here will be the base for discussing spray behavior in the part 2 of this paper.

Analysis of ECN spray A ignition in a Rapid Compression Machine using simultaneous OH* chemiluminescence and formaldehyde PLIF

“…In the RCM, the RMS field also reveals a very few ignition events occur closer to the injector, at 15 mm from the tip. It is worth noticing the residual flow is very weak (average velocity U < 0.3 m/s) in the RCM at SOI [6]. Consequently, it does not induce any additional fluctuation to the ignition process, which would not be the case in a diesel engine [9].…”

“…The spray is injected on the cylinder axis. The RCM and its qualification for ECN spray A is described in Hespel et al [5], and boundary conditions and their influence were characterized in detail in Ben Houidi et al [6].…”

“…Figure 2 reports the corresponding pressure traces in the reactive case and in inert conditions, with and without injection. They highlight the effects of vaporization and heat release in this confined environment, the reader is referred to Ben Houidi et al [6] for more information. Two different temperatures at the Start Of Injection (SOI) are targeted herein: 850 K and 900 K. Initial temperature and volumetric compression ratio are kept constant, and temperature at injection timing is varied by changing the diluent gas composition (see Tab.…”

“…The data obtained from optical Rapid Compression Machines (RCM) and from more classical devices like Constant Volume Preburn (CVP) vessels were successfully compared in this work. The effect of boundary conditions for the different devices was analyzed with special care in Ben Houidi et al [6]. The Pprime Institute optical RCM [5,6] is also employed in the present work: the objective is to characterize and analyze the first instants of the spray A ignition, and in particular the ignition dynamics and its topology.…”

“…The effect of boundary conditions for the different devices was analyzed with special care in Ben Houidi et al [6]. The Pprime Institute optical RCM [5,6] is also employed in the present work: the objective is to characterize and analyze the first instants of the spray A ignition, and in particular the ignition dynamics and its topology. Indeed, despite the large number of studies devoted to the spray A, additional experimental data are still needed to analyze and to better understand the phenomena involved at the early stages of ignition.…”