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The Influence of NO on the Combustion Phasing in an HCCI Engine
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.ORCID iD: 0000-0002-4243-7134
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
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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.

Place, publisher, year, edition, pages
2006. no 2006-01-0416
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-7572DOI: 10.4271/2006-01-0416Scopus ID: 2-s2.0-84864407492OAI: oai:DiVA.org:kth-7572DiVA: diva2:12639
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
In thesis
1. Kinetic modelling of autoignition phenomena
Open this publication in new window or tab >>Kinetic modelling of autoignition phenomena
2007 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

To fully understand the elementary reactions behind the ignition of automotive fuels the interaction between the fuel components must be known. The ignition initiation is most often caused by loss of an H radical from a reactive fuel molecule, for example n-heptane. The formed alkyl radical is prone to react with oxygen under lean conditions. However, it can also abstract hydrogen from other fuel molecules, hence activating more unreactive species. This type of reactions is called cooxidation reactions and including it in combustion mechanisms improve ignition delay predictions in a wide range of experiments, for Primary Reference Fuel mixtures and toluene/heptane mixtures. Example of such reactions are

C7H15• + C8H18 = C7H16+ C8H17•

C7H15OO• + C8H18 = C7H15OOH+ C8H17•

Adding cooxidation reactions also significantly improves prediction of the general trend of auto-ignition phasing as function of operating conditions in Homogeneous Charge Compression Ignition, HCCI, engine combustion.

The effect of NO addition on engine combustion has also been studied in this work. A novel strategy to control ignition onset in HCCI engines is to retain exhaust gases in the cylinder to control the cylinder temperature. While this not only controls the engine temperature it also introduces NOx in the cylinder. The NO will advance ignition onset by several crank angle degrees at concentrations below 10 ppm. This is because NO activates HO2 in the reaction: HO2• + NO = OH• + NO2. At higher concentrations the ignition onset is not as advanced and in the PRF case even retarded. This is because NO has cool flame-inhibiting effects.

Kinetic modelling can also be used to predict combustion efficiency in catalytic combustors for power generation. It was shown that at high pressures the number of free sites decreases which limits the combustion efficiency. Thus a hybrid concept could be used where only a fraction of the air and fuel is burned catalytically.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. 53 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2007:65
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-4516 (URN)978-91-7178-778-1 (ISBN)
Presentation
2007-11-15, 591, KTH, Teknikringen 42, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20101109Available from: 2007-11-06 Created: 2007-11-06 Last updated: 2010-11-09Bibliographically approved
2. 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

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Risberg, Per

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