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Discribing the Auto-Ignition Quality of Fuels in HCCI Engines
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.ORCID iD: 0000-0002-4243-7134
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 [en]
Auto-Ignition Quality, RON, MON, Cetane Number, HCCI, CAI and Fuels
National Category
Other Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-3938OAI: oai:DiVA.org:kth-3938DiVA: diva2:10102
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
List of papers
1. A Method of Defining Ignition Quality of Fuels in HCCI Engines
Open this publication in new window or tab >>A Method of Defining Ignition Quality of Fuels in HCCI Engines
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.

National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-5657 (URN)10.4271/2003-01-1816 (DOI)
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
2. Auto-ignition quality of gasoline-like fuels in HCCI engines
Open this publication in new window or tab >>Auto-ignition quality of gasoline-like fuels in HCCI engines
2003 (English)Conference paper, Published paper (Refereed)
Abstract [en]

The auto-ignition quality of a fuel of any chemistry at a given engine condition is described by an octane index defined as, OI = (1-K) RON + K MON, where RON and MON are the Research and Motor Octane numbers respectively and K depends only on the engine design and operating conditions. The higher the OI value, the greater is the resistance to auto-ignition. A single cylinder homogeneous charge compression ignition (HCCI) engine has been run at thirty seven different operating conditions using fuels of different chemistries and different known RON and MON values. At each operating condition CA50, the crank angle for 50% of the total heat release, is established for different fuels and from this the value of K is determined. We take T comp15 , the temperature when the pressure reaches 15 bar during the compression stroke, as a generic engine parameter. K is strongly dependent on and increases with T comp15 and is less strongly dependent on the mixture strength. Surprisingly, there was no significant effect of engine speed on K. A predictive equation for K as a function of T comp15 and the normalized air/fuel ratio, λ is found. At each operating condition there is an ideal fuel with OI = OI 0 such that heat release occurs at top dead center (TDC). OI 0 increases with increasing P maxcomp and T maxcomp the compression pressure and temperature at TDC, and decreases with increasing λ and engine speed. An empirical equation relating OI 0 to these generic engine parameters is found. These predictive equations could also be used to explore control strategies for an HCCI engine running on a fuel of known RON and MON.

National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-5658 (URN)10.4271/2003-01-3215 (DOI)
Conference
Presented at the SAE Powertrain & Fluid Systems Conference & Exhibition,held October 2003, in Pittsburgh, PA, USA. SAE 2003-01-3215
Note
QC 20100917Available from: 2006-05-08 Created: 2006-05-08 Last updated: 2010-12-20Bibliographically approved
3. The influence of EGR on auto-ignition quality of gasoline-like fuels in HCCI engines
Open this publication in new window or tab >>The influence of EGR on auto-ignition quality of gasoline-like fuels in HCCI engines
2004 (English)In: SP-1896, 2004Conference paper, Published paper (Refereed)
Abstract [en]

In previous studies it has been shown that the auto-ignition quality of a fuel at a given engine condition can be described by an octane index defined as, OI=(1-K) RON + K MON, where RON and MON characterize the fuel and the K-value depends only on the engine design and operating conditions. It has been shown that the K-value is highly dependent on the pressure and temperature history. Another important parameter is OI 0 , the OI of the fuel which gives heat release centred at top dead center; OI 0 can be considered to be the requirement of the engine. In previous work, empirical relations for both K and OI 0 in terms of in-cylinder pressure and temperature and engine speed and mixture strength were found but the influence of EGR was not considered. Therefore experiments have been done in a single cylinder engine, working in HCCI mode, at different operating conditions including various internal and external EGR rates, using fuels of different chemistries and different known RON and MON values.

National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-5659 (URN)10.4271/2004-01-2952 (DOI)
Conference
Presented at SAE Powertrain & Fluid Systems Conference & Exhibition, heldOctober 2004, in Tampa, FL, USA. SAE 2004-01-2952, SAE Transactions
Note
QC 20100917Available from: 2006-05-08 Created: 2006-05-08 Last updated: 2010-12-20Bibliographically approved
4. Auto-ignition quality of Diesel-like fuels in HCCI engines
Open this publication in new window or tab >>Auto-ignition quality of Diesel-like fuels in HCCI engines
2005 (English)In: Presented at SAE Brazil Fuels & Lubricants Meeting, held May 2005, in Rio DeJaneiro, Brazil. SAE 2005-01-2127, SAE Transactions, 2005Conference paper, Published paper (Refereed)
Abstract [en]

In Homogeneous Charge Compression Ignition (HCCI) engines heat release occurs by auto-ignition and hence the fuel auto-ignition quality is very important. The auto-ignition quality of Diesel fuels is conventionally described by the cetane number. Conventional Diesel fuels are involatile compared to gasoline fuels and mixture preparation becomes far more critical in assessing their behaviour in HCCI engines. This paper considers the relationship between auto-ignition behaviour of Diesel-like fuels in a single-cylinder HCCI engine and the fuel cetane number under different mixture preparation strategies.

National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-5660 (URN)10.4271/2005-01-2127 (DOI)2-s2.0-84877161797 (Scopus ID)
Note
QC 20100917Available from: 2006-05-08 Created: 2006-05-08 Last updated: 2010-09-17Bibliographically approved
5. The Influence of NO on the Combustion Phasing in an HCCI Engine
Open this publication in new window or tab >>The Influence of NO on the Combustion Phasing in an HCCI Engine
Show others...
2006 (English)In: SAE 2006 World Congress & Exhibition Technical Papers, 2006, no 2006-01-0416Conference paper, Published paper (Refereed)
Abstract [en]

In this work the influence of NO on combustion phasing has been studied experimentally in a single cylinder HCCI engine. A isooctane/n-heptane blend (PRF), a toluene/n-heptane mixture (TRF) and a full boiling range gasoline were tested at two different operating conditions with NO concentrations ranging from 4 up to 476 ppm in the fresh intake air. All three fuels had the same RON of 84. The first operating condition had a high intake pressure (2 bar absolute) and low intake temperature (40 °C), where low temperature chemistry is relatively prominent. The other operating condition had a high intake temperature (100 °C) and atmospheric intake pressure with significantly lower cool flame reactivity. Additionally the effect of NO at two different engine speeds, 900 and 1200 rpm were studied.

The combustion phasing, represented by CA50 was advanced up to 12.5 CAD by the influence of NO. In the cases with the TRF and the full boiling range gasoline the combustion phasing advanced with an increasing NO concentration. The combustion phasing in the PRF case also advanced at low concentrations of NO, but retarded beyond the baseline case at high concentrations in the high-pressure case. Such effects on combustion phasing are explained in terms of reaction kinetic theory from the literature. At low concentrations NO provides extra branching pathways, but as NO concentration increases termination reactions take over. The interaction of NO and aromatic fuels has not been theoretically examined to the same extent in the literature and more work in this area is needed.

National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-7572 (URN)10.4271/2006-01-0416 (DOI)2-s2.0-84864407492 (Scopus ID)
Conference
SAE 2006 World Congress & Exhibition, April 2006, Detroit, MI, USA,
Note
QC 20101109Available from: 2007-11-06 Created: 2007-11-06 Last updated: 2011-07-06Bibliographically approved
6. Advantages of fuels with high resistance to auto-ignition in late-injection, lowtemperature, compression ignition combustion
Open this publication in new window or tab >>Advantages of fuels with high resistance to auto-ignition in late-injection, lowtemperature, compression ignition combustion
2006 (English)In: Submitted to SAE Powertrain & Fluid Systems Conference & Exhibition, heldOctober 2006, in Toronto, Ontario, Canada. SAE 2006-01-xxxx, 2006Conference paper, Published paper (Refereed)
Abstract [en]

Oxides of nitrogen (NOx) and smoke can be simultaneously reduced in compression ignition engines by getting combustion to occur at low temperatures and by delaying the heat release till after the fuel and air have been sufficiently mixed. One of the ways to obtain such combustion in modern engines using common-rail direct injection is to inject the fuel near top dead centre with high levels of exhaust gas recirculation (EGR) - Nissan MK style combustion. In this work we study the effect of fuel auto-ignition quality, using four fuels ranging from diesel to gasoline, on such combustion at two inlet pressures and different EGR levels. The experiments are done in a 2 litre single-cylinder engine with a compression ratio of 14 at an engine speed of 1200 RPM. The engine can be easily run on gasoline with a single injection near TDC, even though it cannot be run with very early injection, in the HCCI mode. Moreover for any given condition, gasoline has a significantly higher ignition delay for the same combustion phasing and hence results in very much lower NOx and smoke for a given load compared to diesel fuels. Using gasoline, an IMEP of 14.86 bar could be reached with ISFC of 178 g/kWh, smoke < 0.4 FSN, peak pressure of 133 bar, ISNOx of 1.21 g/kWh, and ISHC and ISCO < 4 g/kWh. It was not possible to get comparable performance with diesel fuels with low smoke at the same operating conditions. Further improvements in all these parameters using gasoline should be possible by optimising injector and engine design and operating conditions and bringing in other strategies such as multiple injections.

National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-5662 (URN)10.4271/2006-01-3385 (DOI)2-s2.0-80054811178 (Scopus ID)
Note
QC 20100917Available from: 2006-05-08 Created: 2006-05-08 Last updated: 2010-09-17Bibliographically approved

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Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
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  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
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  • asciidoc
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