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A Method of Defining Ignition Quality of Fuels in HCCI Engines
KTH, Superseded Departments, Machine Design.ORCID iD: 0000-0002-4243-7134
KTH, Superseded Departments, Machine Design.
2003 (English)Conference paper, Published paper (Refereed)
Abstract [en]

A homogeneous charge compression ignition (HCCI) engine has been run at different operating conditions with fuels of different RON and MON and different chemistries. The ignition quality of the fuel at a given operating condition is characterized by CA50, the crank angle at which the cumulative heat released reaches 50% of the maximum value for the cycle. It is found that CA50 might show no correlation with either RON or MON but correlates very well with the Octane Index, OI defined as OI = (1-K)RON + KMON = RON - KS, where K is a constant depending on the engine operating condition and S is the fuel sensitivity, (RON - MON). The higher the OI, the more the resistance to autoignition and the later is the heat release in the HCCI engine at a given condition. When the engine is run with a boost pressure of 1 bar and with the intake air temperature maintained at 40° C, K is highly negative and fuels of low MON, such as those containing aromatics, olefins or ethanol, have a higher OI and ignite later than paraffinic fuels of comparable RON. When the engine is run with no intake boost and the intake air is heated to 120° C, the value of K becomes slightly greater than zero so that the autoignition quality of the fuel is determined mostly by its RON. Thus K decreases as the engine is run relatively cooler and at higher pressures and MON contributes less to the measure of resistance to autoignition. This trend is in line with earlier studies of autoignition in knocking engines.

Place, publisher, year, edition, pages
2003.
National Category
Other Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-5657DOI: 10.4271/2003-01-1816OAI: oai:DiVA.org:kth-5657DiVA: diva2:10096
Conference
Presented at the SAE Fuels & Lubricants Meeting, held May 19-22, 2003, in Yokohama, Japan, SAE 2003-01-1816
Note
QC 20100917 Available from: 2006-05-08 Created: 2006-05-08 Last updated: 2010-12-20Bibliographically approved
In thesis
1. Discribing the Auto-Ignition Quality of Fuels in HCCI Engines
Open this publication in new window or tab >>Discribing the Auto-Ignition Quality of Fuels in HCCI Engines
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The Homogeneous Charge Compression Ignition (HCCI) engine is a promising engine concept that emits low concentrations of NOx and particulates and still has a high efficiency. Since the charge is auto-ignited, the auto-ignition quality of the fuel is of major importance.

It has been shown in several studies that neither of the classical measures of auto-ignition quality of gasoline-like fuels, RON and MON, can alone describe this in all conditions in HCCI combustion. However, even in such cases it is possible to combine RON and MON into an octane index, OI, that describes the auto-ignition quality well in most conditions. The octane numbers are combined into the OI with the variable K according to the following equation:

OI = (1-K)RON + K MON = RON – K S

The OI of a sensitive fuel is the equivalent of the octane number of a primary reference fuel with the same resistance to auto-ignition in the tested condition. The K-value is dependent on the temperature and pressure history. A generic parameter Tcomp15, the temperature at 15 bar during the compression, was introduced to describe the temperature and pressure history. It was found that the K-value increases with increasing Tcomp15 and two linear equations have been suggested to describe this relationship.

At high or low Tcomp15 it has been found that the sensitivity of the fuel octane quality on combustion phasing is small and the auto-ignition quality defined by the OI scale does no longer play a big role.

NO affects the combustion phasing of gasoline-like fuels. This effect is most significant at low concentration where it advances the combustion phasing considerably. At higher conditions its influence is different for different fuels.

A sensitive fuel is considered a good HCCI fuel since its OI changes in the same direction as the octane requirement of the engine, which would make the engine management easier. It is also likely that a sensitive fuel will enable a wider operating range.

The auto-ignition quality of diesel-like fuels was studied in tests with three different strategies of mixture formation. In these tests it was found that the ignition delay increased with lower cetane number and that the cetane number described the auto-ignition quality well, even for fuels of significantly different physical properties. The experiments were, however, made at a limited range of operating conditions and low load.

A good diesel-like HCCI fuel should be easy to vaporize to facilitate homogeneity. It should have a high resistance to auto-ignition, not necessarily the highest, one that allows both high and low loads at a given compression ratio. Finally, it should also function well with the injection system without a significant decrease in injection system life length.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. 95 p.
Series
Trita-MMK, ISSN 1400-1179 ; 2006:07
Keyword
Auto-Ignition Quality, RON, MON, Cetane Number, HCCI, CAI and Fuels
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-3938 (URN)
Public defence
2006-05-22, Sal M2, Brinellvägen 64, Stockholm, 10:00
Opponent
Note
QC 20100917Available from: 2006-05-08 Created: 2006-05-08 Last updated: 2011-07-06Bibliographically approved
2. A method of defining the auto-ignition quality of gasoline-like fuels in HCCI engines
Open this publication in new window or tab >>A method of defining the auto-ignition quality of gasoline-like fuels in HCCI engines
2005 (English)Licentiate thesis, comprehensive summary (Other scientific)
Place, publisher, year, edition, pages
Stockholm: KTH, 2005. 74 p.
Series
Trita-MMK, ISSN 1400-1179 ; 2005:10
Keyword
Engineering design, auto-ignition quality, HCCI, CAI and fuels, Konstruktionsteknik
National Category
Reliability and Maintenance
Identifiers
urn:nbn:se:kth:diva-343 (URN)
Presentation
2005-04-29, M3, Brinellv 64, Stockholm, 10:00
Supervisors
Note
QC 20101220Available from: 2005-08-01 Created: 2005-08-01 Last updated: 2010-12-20Bibliographically approved

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