Laminar burning velocities of lean hydrogen–air mixtures at pressures up to 1.0 MPa

Bradley, D.; Lawes, M.; Liu, K; Verhelst, Sebastian; Woolley, Robert

doi:10.1016/j.combustflame.2006.12.002

Cited by 226 publications

(109 citation statements)

References 26 publications

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“…In this case, the value of u l L/n was estimated to be approximately 2000 and of Ma sr as approximately −7 [36]. For these values, figure 10 suggests values of (u t /u l ) m greater than 140, well in excess of the actual approximate value of u t /u l of 15.…”

Section: Values Of the Turbulent Burning Velocitymentioning

confidence: 81%

Autoignitions and detonations in engines and ducts

Bradley

2012

Phil. Trans. R. Soc. A.

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The origins of autoignition at hot spots are analysed and the pressure pulses that arise from them are related to knock in gasoline engines and to developing detonations in ducts. In controlled autoignition engines, autoignition is benign with little knock. There are several modes of autoignition and the existence of an operational peninsula, within which detonations can develop at a hot spot, helps to explain the performance of various engines. Earlier studies by Urtiew and Oppenheim of the development of autoignitions and detonations ahead of a deflagration in ducts are interpreted further, using a simple one-dimensional theory of the generation of shock waves ahead of a turbulent flame. The theory is able to indicate entry into the domain of autoignition in an 'explosion in the explosion'. Importantly, it shows the influence of the turbulent burning velocity, and particularly its maximum attainable value, upon autoignition. This value is governed by localized flame extinctions for both turbulent and laminar flames. The theory cannot show any details of the transition to a detonation, but regimes of eventually stable or unstable detonations can be identified on the operational peninsula. Both regimes exhibit transverse waves, triple points and a cellular structure. In the case of unstable detonations, transverse waves are essential to the continuing propagation. For hazard assessment, more needs to be known about the survival, or otherwise, of detonations that emerge from a duct into the same mixture at atmospheric pressure.

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Section: Values Of the Turbulent Burning Velocitymentioning

confidence: 81%

Autoignitions and detonations in engines and ducts

Bradley

2012

Phil. Trans. R. Soc. A.

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“…Hydrogen also has some very high values of key transport properties, such as kinematic viscosity, thermal conductivity and diffusion coefficient. These differences lead to a Lewis number that is lower than that of most common fuels and contribute substantially to the unique combustion characteristics of hydrogen [17][18].…”

Section: Introductionmentioning

confidence: 99%

Hydrogen SI and HCCI Combustion in a Direct-Injection Optical Engine

Rosati¹,

Aleiferis²

2009

SAE Int. J. Engines

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The Engineering Meetings Board has approved this paper for publication. It has successfully completed SAE's peer review process under the supervision of the session organizer. This process requires a minimum of three (3) reviews by industry experts. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of SAE. ISSN 0148-7191 Positions and opinions advanced in this paper are those of the author(s) and not necessarily those of SAE. The author is solely responsible for the content of the paper. SAE ABSTRACTHydrogen has been largely proposed as a possible alternative fuel for internal combustion engines. Its wide flammability range allows higher engine efficiency with leaner operation than conventional fuels, for both reduced toxic emissions and no CO 2 gases. Independently, Homogenous Charge Compression Ignition (HCCI) also allows higher thermal efficiency and lower fuel consumption with reduced NO X emissions when compared to Spark-Ignition (SI) engine operation. For HCCI combustion, a mixture of air and fuel is supplied to the cylinder and autoignition occurs from compression; engine is operated throttle-less and load is controlled by the quality of the mixture, avoiding the large fluid-dynamic losses in the intake manifold of SI engines. HCCI can be induced and controlled by varying the mixture temperature, either by Exhaust Gas Recirculation (EGR) or intake air pre-heating. A combination of HCCI combustion with hydrogen fuelling has great potential for virtually zero CO 2 and NO X emissions. Nevertheless, combustion on such a fast burning fuel with wide flammability limits and high octane number implies many disadvantages, such as control of backfiring and speed of autoignition and there is almost no literature on the subject, particularly in optical engines. Experiments were conducted in a singlecylinder research engine equipped with both Port Fuel Injection (PFI) and Direct Injection (DI) systems running at 1000 RPM. Optical access to in-cylinder phenomena was enabled through an extended piston and optical crown. Combustion images were acquired by a highspeed camera at 1° or 2° crank angle resolution for a series of engine cycles. Spark-ignition tests were initially carried out to benchmark the operation of the engine with hydrogen against gasoline. DI of hydrogen after intake valve closure was found to be preferable in order to overcome problems related to backfiring and air displacement from hydrogen's low density. HCCI combustion of hydrogen was initially enabled by means of a pilot port injection of n-heptane preceding the main direct injection of hydrogen, along with intake air preheating. Sole hydrogen fuelling HCCI was finally achieved and made sustainable, even at the low compression ratio of the optical engine by means of closed-valve DI, in synergy with air-pre-heating and negative valve overlap to promote intern...

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“…As of today, there are insufficient data on stretch-free burning velocities at engine conditions, for any fuel. Stretch and instabilities hamper the experimental determination of stretch-free data at higher (engine-like) pressures [20].…”

Section: Simulation Programmentioning

confidence: 99%

Development and Validation of a Quasi-Dimensional Model for (M)Ethanol-Fuelled SI Engines

Vancoillie

Sileghem

Demuynck

et al. 2012

Lecture Notes in Electrical Engineering

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-Methanol and ethanol are interesting spark-ignition engine fuels, both from a production and an end-use point of view. Despite promising experimental results, the full potential of these fuels remain to be explored. In this respect, quasi-dimensional engine simulation codes are especially useful as they allow cheap and fast optimization of engines. The aim of the current work was to develop and validate such a model for methanol-fuelled engines. Several laminar burning velocity correlations and turbulent burning velocity models were implemented in a QD code and their predictive performance was assessed for a wide range of engine operating conditions.The effects of compression ratio and ignition timing on the in-cylinder combustion were well reproduced irrespective of the employed correlation or model. However, to predict the effect of changes in mixture composition, the correlation and model selection proved crucial. Compared to existing correlations, a new correlation developed by the current authors led to better reproduction of the effects of equivalence ratio and residual gas content and the combustion duration.For the turbulent burning velocity, the models of Damköhler and Peters consistently underestimated the influence of equivalence ratio and residual gas content on the combustion duration, while the Gülder, Leeds, Zimont and Fractals model corresponded well with the experiments. The combination of one of these models with the new correlation can be used with confidence to simulate the performance and efficiency of methanol-fuelled engines.INTRODUCTION -The use of sustainable liquid alcohols in spark-ignition engines offers the potential of decarbonizing transport and securing domestic energy supply while increasing engine performance and efficiency compared to fossil fuels thanks to a number of interesting properties [1,2]. The most significant interesting properties of light alcohols include:-High heat of vaporization, which causes considerable charge cooling as the injected fuel evaporates -Elevated knock resistance, which allows to apply higher compression ratios (CR), optimal spark timing and aggressive downsizing. -High flame speeds, enabling qualitative load control using mixture richness or varying amounts of exhaust gas recirculation (EGR). The potential of neat light alcohol fuels (methanol and ethanol) has been demonstrated experimentally in both dedicated and flex-fuel alcohol engines [1]. In dedicated alcohol engines high compression ratios enable peak brake thermal efficiencies up to 42%, while throttleless load control using EGR allows to spread the high efficiencies to the part load regions [1,3]. In flex-fuel engines the CR is limited due to knock constraints associated with gasoline operation, but still relative power and efficiency benefits of about 10% and NO x reductions of 5-10 g/kWh can be obtained over the entire load range thanks to more isochoric combustion, optimal ignition timing and reduced flow and dissociation losses [1].

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Laminar burning velocities of lean hydrogen–air mixtures at pressures up to 1.0 MPa

Cited by 226 publications

References 26 publications

Autoignitions and detonations in engines and ducts

Autoignitions and detonations in engines and ducts

Hydrogen SI and HCCI Combustion in a Direct-Injection Optical Engine

Development and Validation of a Quasi-Dimensional Model for (M)Ethanol-Fuelled SI Engines

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