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Title: RCCI Combustion Regime Transitions in a Single-Cylinder Optical Engine and a Multi-Cylinder Metal Engine

Abstract

We present that Reactivity Controlled Compression Ignition (RCCI) is an approach to increase engine efficiency and lower engine-out emissions by using in-cylinder stratification of fuels with differing reactivity (i.e., autoignition characteristics) to control combustion phasing. Stratification can be altered by varying the injection timing of the high-reactivity fuel, causing transitions across multiple regimes of combustion. When injection is sufficiently early, combustion approaches a highly-premixed autoignition regime, and when it is sufficiently late it approaches more mixing-controlled, diesel-like conditions. Engine performance, emissions, and control authority over combustion phasing with injection timing are most favorable in between, within the RCCI regime.To study charge preparation phenomena that dictate regime transitions, two different optical diagnostics are applied in a single-cylinder heavy-duty optical engine, and conventional engine diagnostics are applied in a multi-cylinder, light-duty all-metal engine. Both engines are operated with iso-octane and n-heptane as the low- and high-reactivity fuels, respectively. The iso-octane fuel fraction delivers 80% of the total fuel energy, the global equivalence ratio is 0.35, and no exhaust gas recirculation is used. In the optical engine, single-shot, band-pass infrared (IR) imaging of emission near 3.3 microns measures thermal C-H stretch-band emission of hot fuel vapor and intermediate combustion products, providing qualitative informationmore » about the fuel-vapor distribution and ignition locations during low-temperature heat release. Additionally, high-speed 7.2 kHz visible-light imaging of natural luminosity, optimized to detect chemiluminescence, indicates the spatial and temporal evolution of high-temperature heat release and combustion. Similar combustion regimes are observed for both engine platforms, allowing an opportunity for optical engine data to provide insight into fundamental phenomena affecting regime ranges and transitions in production engines. Key findings from imaging diagnostics indicate that at the late-injection limit of RCCI control authority, low-temperature ignition occurs when clearly identifiable jet structures are still intact, and during high-temperature combustion there is prevalent and persistent soot incandescence representative of locally mixing-limited (i.e., fuel-rich) combustion. Finally, at the early-injection limit of RCCI control, observed stratification during low-temperature ignition is subtle; however, high-temperature combustion still occurs sequentially from the bowl rim radially inwards.« less

Authors:
 [1];  [2];  [1];  [3];  [3];  [4]
  1. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
  2. University of Orleans (France)
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  4. Wayne State University, Detroit, MI (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1394308
DOE Contract Number:  
AC05-00OR22725
Resource Type:
Journal Article
Journal Name:
SAE International Journal of Engines (Online)
Additional Journal Information:
Journal Volume: 10; Journal Issue: 5; Journal ID: ISSN 1946-3944
Publisher:
SAE International
Country of Publication:
United States
Language:
English
Subject:
33 ADVANCED PROPULSION SYSTEMS; 32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION

Citation Formats

Roberts, Gregory, Rousselle, Christine Mounaim, Musculus, Mark, Wissink, Martin, Curran, Scott, and Eagle, Ethan. RCCI Combustion Regime Transitions in a Single-Cylinder Optical Engine and a Multi-Cylinder Metal Engine. United States: N. p., 2017. Web. doi:10.4271/2017-24-0088.
Roberts, Gregory, Rousselle, Christine Mounaim, Musculus, Mark, Wissink, Martin, Curran, Scott, & Eagle, Ethan. RCCI Combustion Regime Transitions in a Single-Cylinder Optical Engine and a Multi-Cylinder Metal Engine. United States. doi:10.4271/2017-24-0088.
Roberts, Gregory, Rousselle, Christine Mounaim, Musculus, Mark, Wissink, Martin, Curran, Scott, and Eagle, Ethan. Mon . "RCCI Combustion Regime Transitions in a Single-Cylinder Optical Engine and a Multi-Cylinder Metal Engine". United States. doi:10.4271/2017-24-0088.
@article{osti_1394308,
title = {RCCI Combustion Regime Transitions in a Single-Cylinder Optical Engine and a Multi-Cylinder Metal Engine},
author = {Roberts, Gregory and Rousselle, Christine Mounaim and Musculus, Mark and Wissink, Martin and Curran, Scott and Eagle, Ethan},
abstractNote = {We present that Reactivity Controlled Compression Ignition (RCCI) is an approach to increase engine efficiency and lower engine-out emissions by using in-cylinder stratification of fuels with differing reactivity (i.e., autoignition characteristics) to control combustion phasing. Stratification can be altered by varying the injection timing of the high-reactivity fuel, causing transitions across multiple regimes of combustion. When injection is sufficiently early, combustion approaches a highly-premixed autoignition regime, and when it is sufficiently late it approaches more mixing-controlled, diesel-like conditions. Engine performance, emissions, and control authority over combustion phasing with injection timing are most favorable in between, within the RCCI regime.To study charge preparation phenomena that dictate regime transitions, two different optical diagnostics are applied in a single-cylinder heavy-duty optical engine, and conventional engine diagnostics are applied in a multi-cylinder, light-duty all-metal engine. Both engines are operated with iso-octane and n-heptane as the low- and high-reactivity fuels, respectively. The iso-octane fuel fraction delivers 80% of the total fuel energy, the global equivalence ratio is 0.35, and no exhaust gas recirculation is used. In the optical engine, single-shot, band-pass infrared (IR) imaging of emission near 3.3 microns measures thermal C-H stretch-band emission of hot fuel vapor and intermediate combustion products, providing qualitative information about the fuel-vapor distribution and ignition locations during low-temperature heat release. Additionally, high-speed 7.2 kHz visible-light imaging of natural luminosity, optimized to detect chemiluminescence, indicates the spatial and temporal evolution of high-temperature heat release and combustion. Similar combustion regimes are observed for both engine platforms, allowing an opportunity for optical engine data to provide insight into fundamental phenomena affecting regime ranges and transitions in production engines. Key findings from imaging diagnostics indicate that at the late-injection limit of RCCI control authority, low-temperature ignition occurs when clearly identifiable jet structures are still intact, and during high-temperature combustion there is prevalent and persistent soot incandescence representative of locally mixing-limited (i.e., fuel-rich) combustion. Finally, at the early-injection limit of RCCI control, observed stratification during low-temperature ignition is subtle; however, high-temperature combustion still occurs sequentially from the bowl rim radially inwards.},
doi = {10.4271/2017-24-0088},
journal = {SAE International Journal of Engines (Online)},
issn = {1946-3944},
number = 5,
volume = 10,
place = {United States},
year = {2017},
month = {9}
}