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Title: Fuel Stratification for Low-Load HCCI Combustion: Performance and Fuel-PLIF Measurements.

Abstract

Abstract not provided.

Authors:
; ;
Publication Date:
Research Org.:
Sandia National Lab. (SNL-CA), Livermore, CA (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1148121
Report Number(s):
SAND2007-3258C
523035
DOE Contract Number:
AC04-94AL85000
Resource Type:
Conference
Resource Relation:
Conference: Proposed for presentation at the SAE Powertrain and Fuids Systems Conference held October 29 - November 1, 2007 in Chicago, IL.
Country of Publication:
United States
Language:
English

Citation Formats

Hwang, Wontae, Dec, John E., and Sjoberg, Carl-Magnus G. Fuel Stratification for Low-Load HCCI Combustion: Performance and Fuel-PLIF Measurements.. United States: N. p., 2007. Web.
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Hwang, Wontae, Dec, John E., & Sjoberg, Carl-Magnus G. Fuel Stratification for Low-Load HCCI Combustion: Performance and Fuel-PLIF Measurements.. United States.
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Hwang, Wontae, Dec, John E., and Sjoberg, Carl-Magnus G. Tue . "Fuel Stratification for Low-Load HCCI Combustion: Performance and Fuel-PLIF Measurements.". United States. doi:. https://www.osti.gov/servlets/purl/1148121.
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@article{osti_1148121,
title = {Fuel Stratification for Low-Load HCCI Combustion: Performance and Fuel-PLIF Measurements.},
author = {Hwang, Wontae and Dec, John E. and Sjoberg, Carl-Magnus G},
abstractNote = {Abstract not provided.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Tue May 01 00:00:00 EDT 2007},
month = {Tue May 01 00:00:00 EDT 2007}
}
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Conference:
View Conference (9.29 MB)
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    In recent years a number of studies have demonstrated that boosted operation combined with external EGR is a path forward for expanding the high load limit of homogeneous charge compression ignition (HCCI) operation with the negative valve overlap (NVO) valve strategy. However, the effects of fuel composition with this strategy have not been fully explored. In this study boosted HCCI combustion is investigated in a single-cylinder research engine equipped with direct injection (DI) fueling, cooled external exhaust gas recirculation (EGR), laboratory pressurized intake air, and a fully-variable hydraulic valve actuation (HVA) valve train. Three fuels with significant compositional differences aremore » investigated: regular grade gasoline (RON = 90.2), 30% ethanol-gasoline blend (E30, RON = 100.3), and 24% iso-butanol-gasoline blend (IB24, RON = 96.6). Results include engine loads from 350 to 800 kPa IMEPg for all fuels at three engine speeds 1600, 2000, and 2500 rpm. All operating conditions achieved thermal efficiency (gross indicated efficiency) between 38 and 47%, low NOX emissions ( 0.1 g/kWh), and high combustion efficiency ( 96.5%). Detailed sweeps of intake manifold pressure (atmospheric to 250 kPaa), EGR (0 25% EGR), and injection timing are conducted to identify fuel-specific effects. The major finding of this study is that while significant fuel compositional differences exist, in boosted HCCI operation only minor changes in operational conditions are required to achieve comparable operation for all fuels. In boosted HCCI operation all fuels were able to achieve matched load-speed operation, whereas in conventional SI operation the fuel-specific knock differences resulted in significant differences in the operable load-speed space. Although all fuels were operable in boosted HCCI, the respective air handling requirements are also discussed, including an analysis of the demanded turbocharger efficiency.« less

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    Thermal stratification has the potential to reduce pressure-rise rates and allow increased power output for HCCI engines. This paper systematically examines how the amount of thermal stratification of the core of the charge has to be adjusted to avoid excessive knock as the engine speed and fueling rate are increased. This is accomplished by a combination of multi-zone chemical-kinetics modeling and engine experiments, using iso-octane as the fuel. The experiments show that, for a low-residual engine configuration, the pressure traces are self-similar during changes to the engine speed when CA50 is maintained by adjusting the intake temperature. Consequently, the absolutemore » pressure-rise rate measured as bar/ms increases proportionally with the engine speed. As a result, the knocking (ringing) intensity increases drastically with engine speed, unless counteracted by some means. This paper describes how adjustments of the thermal width of the in-cylinder charge can be used to limit the ringing intensity to 5 MW/m2 as both engine speed and fueling are increased. If the thermal width can be tailored without constraints, this enables smooth operation even for combinations of high speed, high load, and combustion phasing close to TDC. Since large alterations of the thermal width of the charge are not always possible, combustion retard is considered to reduce the requirement on the thermal stratification. The results show that combustion retard carries significant potential since it amplifies the benefit of a fixed thermal width. Therefore, the thermal stratification required for operation with an acceptable knocking intensity can be decreased substantially by the use of combustion retard. This enables combinations of high engine speed and high fueling rate even for operation with the naturally occurring thermal stratification. However, very precise control of the combustion phasing will likely be required for such operation.« less