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Advantages of fuels with high resistance to auto-ignition in late-injection, lowtemperature, compression ignition combustion
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.ORCID iD: 0000-0002-4243-7134
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
2006 (English)In: Submitted to SAE Powertrain & Fluid Systems Conference & Exhibition, heldOctober 2006, in Toronto, Ontario, Canada. SAE 2006-01-xxxx, 2006Conference 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.

Place, publisher, year, edition, pages
National Category
Other Materials Engineering
URN: urn:nbn:se:kth:diva-5662DOI: 10.4271/2006-01-3385ScopusID: 2-s2.0-80054811178OAI: diva2:10101
QC 20100917Available from: 2006-05-08 Created: 2006-05-08 Last updated: 2010-09-17Bibliographically 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.
Trita-MMK, ISSN 1400-1179 ; 2006:07
Auto-Ignition Quality, RON, MON, Cetane Number, HCCI, CAI and Fuels
National Category
Other Materials Engineering
urn:nbn:se:kth:diva-3938 (URN)
Public defence
2006-05-22, Sal M2, Brinellvägen 64, Stockholm, 10:00
QC 20100917Available from: 2006-05-08 Created: 2006-05-08 Last updated: 2011-07-06Bibliographically approved

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