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Research Papers: Experimental Techniques

Development of a Device for the Nondestructive Thermal Diffusivity Determination of Combustion Chamber Deposits and Thin Coatings

[+] Author and Article Information
Mark A. Hoffman

Department of Automotive Engineering,
International Center for Automotive Research,
Clemson University,
4 Research Drive,
Greenville, SC 29607
e-mail: mhoffm4@clemson.edu

Benjamin J. Lawler

W. E. Lay Automotive Laboratory,
Department of Mechanical Engineering,
University of Michigan,
1231 Beal Avenue,
Ann Arbor, MI 48109

Zoran S. Filipi

Department of Automotive Engineering,
International Center for Automotive Research,
Clemson University,
4 Research Drive,
Greenville, SC 29607

Orgun A. Güralp, Paul M. Najt

General Motors R&D,
30500 Mound Road,
Warren, MI 48090

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received April 15, 2013; final manuscript received February 17, 2014; published online March 17, 2014. Assoc. Editor: William P. Klinzing.

J. Heat Transfer 136(7), 071601 (Mar 17, 2014) (10 pages) Paper No: HT-13-1204; doi: 10.1115/1.4026908 History: Received April 15, 2013; Revised February 17, 2014

An experimental radiation chamber has been developed to nondestructively measure the thermal diffusivity of a combustion chamber deposit (CCD) layer. The accumulation of CCD shifts the operability range of homogeneous charge compression ignition (HCCI) to lower loads where the fuel economy benefit of HCCI over a traditional spark ignition strategy is at a maximum. The formation and burn-off of CCD introduce operational variability, which increases the control system burden of a practical HCCI engine. To fully characterize the impact of CCD on HCCI combustion and develop strategies which limit the CCD imposed variability, the thermal and physical properties of HCCI CCD must be determined without destroying the morphology of the CCD layer. The radiation chamber device provides a controlled, inert atmosphere absent of cyclical pressure oscillations and fuel/air interactions found within an engine. The device exposes temperature probes coated with CCD to controlled heat flux pulses generated by a graphite emitter and a rotating disk. CCD layer thermal diffusivity is then calculated based on the phase delay of the sub-CCD temperature response relative to the response of the temperature probe when clean. This work validates the accuracy of the radiation chamber's diffusivity determination methodology by testing materials of known properties. Wafers of three different materials, whose thermal diffusivities span two orders of magnitude centered on predicted CCD diffusivity values, are installed over the temperature probes to act as CCD surrogates. Multiple thicknesses of each material are tested over a range of heat flux pulse durations. Diffusivity values determined from radiation chamber testing are independent of sample thickness with each of the three calibration materials. The radiation chamber diffusivity values exhibit a slight, but consistent underprediction for all wafers due to residual contact resistance at the wafer–probe interface. Overall, the validation studies establish the radiation chamber as an effective device for the nondestructive thermal diffusivity determination of thin insulative coatings. The similarity of expected CCD diffusivity values to those of the validation specimens instills confidence that the methodology and device presented herein can be successfully utilized in the characterization of HCCI CCD layers.

Copyright © 2014 by ASME
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References

Figures

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Fig. 1

Evolution of measured temperature profile at CCD/metal interface. Change in peak temperature phasing, ΔΘTmax, for the first 10 h of operation is indicated. This figure has been reproduced from Ref. [2].

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Fig. 2

Calculated thermal diffusivity of CCD accumulated on head and piston surfaces during HCCI operation as a function of thickness. This figure has been reproduced from Ref. [2].

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Fig. 3

Creation of a pulsed heat flux source via a chopping wheel

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Fig. 4

Sectional schematic of the radiation chamber

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Fig. 5

Conceptual response of the probe surface temperature to a pulsed heat flux source when clean and coated with CCD

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Fig. 6

Normalized residual sum of squares for a temperature trace reconstructed with various harmonic numbers illustrating the automatic harmonic selection process

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Fig. 7

The overall shape of the Fourier temperature reconstruction can look similar for many harmonic numbers

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Fig. 8

Peak portion of a temperature trace reconstructed with various harmonic numbers, where a harmonic number of four was automatically selected

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Fig. 9

Photograph of a zirconium wafer poised for installation over the heat flux probe and via screws on the probe mounting sleeve

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Fig. 10

Normalized temperature traces of a clean probe and a probe covered with a 500 μm aluminum wafer at various chopping disk speeds

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Fig. 11

Normalized temperature trace for a clean probe and subwafer temperature traces for various aluminum wafer thicknesses at a constant chopping disk speed of 600 rpm exhibiting the loss of temperature swing amplitude as thickness increases

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Fig. 12

Temperature profiles of a clean probe and a probe covered with a ceramic wafer exhibiting transparency to the radiation source and minimization of that transparency via the application of aerosol graphite

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Fig. 13

Heat flux profiles of a clean probe and a probe covered with a ceramic wafer exhibiting transparency to the radiation source and minimization of that transparency via the application of aerosol graphite

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Fig. 14

Normalized temperature profiles depicting the influence of graphite aerosol on the response of a clean heat flux probe

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Fig. 15

Diffusivities for aluminum wafers of various thicknesses at different chopping disk speeds

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Fig. 16

Diffusivities for all thicknesses of the three wafer materials and their sample averages (black dashed lines) relative to the mean of the expected diffusivity range for each material (solid green lines)

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Fig. 17

Ex-situ diffusivities and their sample standard deviations compared with the mean expected values and the range of expected values as provided by various texts

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