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The ACME experiments will be conducted with a single modular set of hardware in the Combustion Integrated Rack (CIR) on the International Space Station (ISS), where the CIR is depicted below.

From left to right, the Combustion Integrated Rack (CIR) with the Multi-user Droplet Combustion Apparatus (MDCA) removed from the chamber for servicing by Expedition 34 Commander Kevin Ford. ACME will be conducted in the CIR with a chamber insert similar to the MDCA.

The three main elements of the ACME-unique hardware are the chamber insert (shown below), a high-definition color camera, and an avionics package (for data acquisition and control and also depicted below).

ACME chamber insert
ACME chamber insert design.
Engineering model of the ACME avionics package, with the internal card stack shown at the right (where the two photographs are at different scales).

Burners and Igniter

Initial ACME burner
The initial ACME burners include, from left to right, gas-jet burners (with inner diameters ranging from 0.4 to 3.2 mm), porous spherical burners (with diameters ranging from 6.35 to 12.7 mm), a small co-flow burner (where the two concentric tubes have inner diameters of 2.1 and 25 mm), and two flat porous burners for the BRE experiment (with inner diameters of 25 and 50 mm).

Gas Delivery

ACME manifold assembly
High-fidelity engineering hardware of the manifold assembly for the gas delivery system on the ACME chamber insert.

Imaging Overview

  • ACME’s primary flame diagnostics are a suite of imaging systems including five video cameras and two illumination systems. Three of the cameras and one illumination system are part of the CIR facility and are already in use on orbit.
  • Collectively, the imaging systems will enable color, CH*, and OH* imaging; pyrometry; measurement of the soot volume fraction; and/or operational support.
  • All but one of the cameras is mounted outside of the chamber.

Color Imaging

ACME analog camera
Engineering model of ACME’s analog camera (with lens) and turning mirror.
ACME digital camera
Engineering model of ACME’s digital camera including the motorized zoom lens.
rotating filter assembly
Engineering model of the rotating filter assembly for ACME’s digital camera. The camera is mounted facing downward to the top (in this image) of the filter assembly, which includes a turning mirror.

OH* Imaging

  • OH* is an excited (radical) molecule that emits light at 310 nm, which is in the ultraviolet, when it drops to a lower energy state in a process known as chemiluminescence.
  • ACME will carry out OH* imaging using CIR’s Low-Light-Level Ultraviolet (LLL-UV) package, which is a monochrome camera with an intensifier (for 280-700 nm) and a 310-nm bandpass filter (with a 10-nm FWHM) for OH* imaging.
  • As a result of the signal loss through the narrow bandpass filter, binning is employed such that the OH* images are recorded at 512×512 and 30 fps.

Color Ratio Pyrometry

Temperature Measurement

  • As a supplement to the pyrometry, the ACME chamber insert can accommodate six far-field thermocouples to measure the spread of the thermal field in the spherical flame experiments.
  • The thermocouples are of limited utility for the other experiments because they are positioned upstream of the burner tip. Therefore, they will generally not be installed by the crew to reduce the chance of accidental damage.
  • There will be two versions of a four-thermocouple rake to allow a choice of near and far measurements. Other arrays could be designed to support future experiments, but they cannot extend downstream of the burner tip without interfering with other (e.g., optical) measurements.

Soot Volume Fraction

  • The amount of soot particulate in a flame can be determined via an extinction technique, where the camera and the collimated light source are positioned at opposite windows.
  • For ACME, the extinction measurement will be made with a second High-Bit Depth Multispectral (HiBMs) camera, without a filter, in combination with CIR’s illumination package (with its two fiber-coupled laser diodes). The images are recorded at 1024×1024 and 30 frames per second.
  • Alternatively, the soot volume fraction can be determined directly from the digital color camera, where an alternate Thin Filament Pyrometry (TFP) fiber array including a platinum wire will be used for inflight characterization for that measurement.

Thermal Radiation

engineering model
Engineering model of the standard (ACME) array of radiometers.
radiometer arrays
The standard ACME array is equipped with a single wide-view radiometer with two narrow-view radiometers that are downstream and two more that are upstream, where all views are orthogonal to the chamber axis. The narrow-view radiometers are intended to support studies of gas-jet flames, where ACME can accommodate shorter burners, making the “lower” detectors useful. The other array provides for three wide-view measurements of the flame, where one view is masked to nominally block radiant emission from the burner. It was specifically designed for the BRE experiment but will be a resource available to other ACME experiments.

Chemiluminescent Emission

  • To detect the quenching of dim flames, the chamber insert will be equipped with a set of three Photomultiplier Tube (PMT) modules.
  • Each PMT will have a wide-angle view, a sight line that is orthogonal to the chamber axis, and will be centered (along the chamber length) relative to the chamber windows so that it is aligned with most of the other instrumentation.
  • The PMTs’ spectral range will be 230-700 nm, i.e., visible and near ultraviolet, but one will have a 310-nm bandpass filter and another will have a 430-nm bandpass filter (where both are with a 10-nm FWHM). The filtered pair of detectors will enable measurement of OH* and CH* emission, respectively. The third PMT will be equipped with a neutral density filter to prevent saturation. Like many other ACME components, the PMT array can be removed from the chamber insert by the crew.

Other Measurements

  • Additional supporting measurements will be made for the ACME experiments, where the chamber pressure is a simple example.
  • The ACME experiments will use the CIR’s gas chromatograph for pre- and post-test analysis of the chamber atmosphere, e.g., for oxygen, nitrogen, carbon dioxide, carbon monoxide, and fuel gases.
  • Acceleration measurements will be provided by the Space Acceleration Measurement System II (SAMS-II), which is the primary instrument for such measurements on ISS. Its predecessor previously served that role for the space shuttle.

Experiment-Unique Equipment

ACME Operations

  • All ACME experiments will be constant volume (i.e., rather than constant pressure) studies, where the chamber’s free volume will be about 90 liters. Burner flows will generally be constrained to limit the pressure rise, and tests will typically be 0.5-2 minutes in duration.
  • The ACME experiments will be configured, but not conducted, by the ISS crew. Instead, the experiments will be commanded from the ground, specifically from the Telescience Support Center (TSC) at the NASA Glenn Research Center.
  • The ACME tests can be conducted in a nominally automated mode using pre-programmed scripts or in a “manual” mode where changes can be made (e.g., in the burner flow) in response to the analog video downlink and/or the numerical data available in the telemetry stream. The latter mode can facilitate the conduct of tests at or near limit conditions, e.g., for soot or stability.

Project Management

Project Manager: Lauren M. Brown, NASA Glenn Research Center

Project Scientists: Dennis Stocker, NASA Glenn Research Center

Engineering Team: ZIN Technologies, Inc.

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