Katsufumi Kondo

A Progress Review on Soot Experiments and Modeling in the Engine Combustion Network (ECN)

The following individuals and funding agencies are acknowledged for their support. The authors from DTU acknowledge the Technical University of Denmark, Danish Strategic Research Council, and MAN Diesel & Turbo University of Wisconsin: Financial support provided by the Princeton Combustion Energy Frontier Research Center. ETH Zurich: Financial support from the Swiss Federal Office of Energy (grant no. SI/500818-01) and the Swiss Competence Center for Energy and Mobility (CCEM project “In-cylinder emission reduction”) is gratefully acknowledged. Argonne National Labs: Work was funded by U.S. DOE Office of Vehicle Technologies, Office of Energy Efficiency and Renewable Energy under Contract No. DE-AC02-06CH11357. We also gratefully acknowledge the computing resources provided on Fusion, a computing cluster operated by the Laboratory Computing Resource Center at Argonne National Laboratory. Sandia National Labs, Combustion Research Facility: Work was supported by the U.S. Department of Energy, Office of Vehicle Technologies. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under contract DEAC04-94AL85000. Chris Carlen and Dave Cicone are gratefully acknowledged for technical assistance. The authors from ANL and SNL also wish to thank Gurpreet Singh and Leo Breton, program managers at U.S. DOE, for their support.

Diesel flame imaging and quantitative analysis of in-cylinder soot oxidation

This study concerns a quantitative analysis of late-cycle soot oxidation in diesel engines that focuses on two-dimensional KL factor images obtained by the two-color method. The spatially integrated KL factor was converted into the in-cylinder soot mass using a new formula of diesel soot emissivity. This methodology was applied to two combustion systems: a heavy-duty optical engine which was tuned for a higher fuel–air mixing capability and a rapid compression and expansion machine which had a lower mixing performance. The in-cylinder soot mass history during the last stage of soot oxidation phase was converted into a normalized soot mass history and was used for comparison with simulated soot mass history. A model calculation of in-cylinder soot mass history which was based on oxidation of a primary soot particle was performed with the surface-specific soot oxidation rate as a parameter. A value of the surface-specific soot oxidation rate was specified from the curve fitting approach between the experimental and simulated in-cylinder soot mass traces. The resultant soot oxidation rates plotted on the Arrhenius diagram were found to lie in domains with different oxidation mechanisms. The reason for the scattered plots was discussed referring to model predictions of soot oxidation in the literature, and it was concluded that the higher oxidation rates could be attributed to well-mixed soot oxidizer structure.

Thermocouple temperature measurements in diesel spray flame for validation of in-flame soot formation dynamics

It is well known that the soot formation is governed by equivalence ratio and temperature. However, there are only few examples of temperature measurements in the soot formation region of diesel spray flame, which has been impeding better understanding and model validation. In this study, the time histories of temperature at different axial locations in a single-shot diesel spray flame were measured in a constant volume vessel using a 50-µm-thin wire type R thermocouple and used to demonstrate their usefulness for the model validation of in-flame soot formation dynamics. The measured temperature was (1) compared and cross-checked with two-color temperatures of diesel flame periphery and core, (2) compared with predicted temperature from large eddy simulation of the diesel flame for validation and (3) contrasted with previous laser spectroscopic measurements of soot precursors (polycyclic aromatic hydrocarbons) in diesel spray flame and predicted soot processes from the large eddy simulation of diesel spray flame employing detailed chemical kinetics. The measured steady-state temperature increased from upstream to downstream in diesel spray flame corresponding to the progress of mixing and combustion. The measured temporal histories of temperature exhibited notable increase after the end of injection duration considered due to entrainment of ambient gases and resulting heat release in the wake of the injection pulse. The thermocouple-measured “core” temperatures and two-color “peripheral” temperatures of diesel flame were significantly different as up to 700 K in the upstream and gradually converged to around 2000 K in the downstream. The thermocouple-measured and large eddy simulation–predicted temperature histories showed similar general trends; however, 500 K as significant discrepancy was observed between the measured and predicted temperatures of the polycyclic aromatic hydrocarbon onset locations in diesel spray flame, suspected partially due to deficiency in the current polycyclic aromatic hydrocarbon formation model employed in the simulation.

High-speed ultraviolet chemiluminescence imaging of late combustion in diesel spray flame

For modern diesel engines employing relatively small injector nozzle holes, reduction of late combustion in high load operation is an attractive potential strategy to shorten the combustion period and thus thermal efficiency. However, the governing mechanism of the late combustion has not intensively been studied. This study aims to experimentally investigate where in the diesel spray flame the late combustion heat release is occurring and what governs the phenomenon. As a practical and qualitative marker of local heat release location and existence, which is applicable not only to idealized vessel experiments but also to future production engine experiments, ultraviolet emission from diesel spray flame during the late combustion was examined. First, the ultraviolet emission spectra of diesel spray flame during the late combustion were measured and found to mainly consist of OH* chemiluminescence with some background due to broadband CO2* chemiluminescence and soot luminosity ultraviolet components. Second, simultaneous high-speed imaging of 310 nm ultraviolet emission and visible soot luminosity from flame were performed to distinguish the OH* chemiluminescence from the soot luminosity. Third, simultaneous high-speed imaging of 310 nm ultraviolet emission, visible soot luminosity, and 266 nm ultraviolet absorption in diesel spray flame were performed, showing similar spatial and temporal distributions of heat release locations and combustible mixtures during the late combustion. The observation results suggest that the late combustion heat release occurs in the mixtures losing momentum and accumulated at the spray tip region.