Publications

The first part of the present work is to validate a detailed kinetic mechanism for the oxidation of hydrogen – methane – air mixtures in a detonation waves. A series of experiments on auto-ignition delay times have been performed by shock tube technique coupled with emission spectrometry for H2 / CH4 / O2 mixtures highly diluted in argon. The CH4/H2 ratio was varied from 0 to 4 and the equivalence ratio from 0.4 up to 1. The temperature range was from 1250 K to 2000 K and the pressure behind reflected shock waves was between 0.15 and 1.6 MPa. A correlation was proposed between temperature (K) concentration of chemical species (mol m-3) and ignition delay times. The experimental auto-ignition delay times were compared to the modelled ones using four different mechanisms from the literature: GRI [22] Marinov et al. [23] Hughes et al. [24] Konnov [25]. A large discrepancy was generally found between the different models. The Konnov’s model that predicted auto-ignition delay times close to the measured ones has been selected to calculate the ignition delay time in the detonation waves. The second part of the study concerned the experimental determination of the detonation properties namely the detonation velocity and the cell size. The effect of the initial composition hydrogen to methane ratio and the amount of oxygen in the mixture as well as the initial pressure on the detonation velocity and on the cell size were investigated. The ratio of methane / (methane + hydrogen) varied between 0 and 0.6 for 2 different equivalence ratio (0.75 and 1) while the initial pressure was fixed to 10 kPa. A correlation was established between the characteristic cell size and the ignition delay time behind the leading shock of the detonation. It was clearly showed that methane has an important inhibitor effect on the detonation of these combustible mixtures.

When looking out to 2050 there is huge uncertainty surrounding how gas will be consumed transported and sourced in Great Britain (GB). The extent of the climate change challenge is now widely accepted and the UK Government has introduced a legislative requirement for aggressive reductions in carbon dioxide (CO2) emissions out to 2050. In addition at European Union (EU) level a package of measures has been implemented to reduce greenhouse gas emissions improve energy efficiency and significantly increase the share of energy produced from renewable sources by 2020. These policy developments naturally raise the question of what role gas has to play in the future energy mix.



To help inform this debate the Energy Networks Association Gas Futures Group (ENA GFG) commissioned Redpoint and Trilemma to undertake a long-range scenario-based modelling study of the future utilisation of gas out to 2050 and the consequential impacts of this for gas networks. Our modelling assumptions draw heavily on the Department of Energy and Climate Change (DECC) 2050 Pathways analysis and we consider that our conclusions are fully compatible with both DECC‟s work and current EU policy objectives.



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Climate change and air quality concerns have pushed clean energy up the global agenda. As we switch over to new cleaner technologies and fuels our experience of using power heat and transport are going to change transforming the way we live work and get from A to B. Explore this guide to find out what hydrogen is how it is made transported and used what the experience would be like in the home for transport and for businesses and discover what the future of hydrogen might be.  

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This paper shows the experimental results and findings of field explosion tests conducted to obtain fundamental data concerning the explosion of hydrogen-air mixtures. A tent covered with thin plastic sheets was filled with hydrogen/air mixed gas and subsequently ignited by an electric-spark or explosives to induce deflagration and/or detonation. Several experiments with different concentrations and/or volumes of mixture were carried out. The static overpressure of blast waves was measured using piezoelectric pressure sensors. The recorded data show that the shape of the pressure-time histories of the resulting blast waves depends on the difference in the ignition method used. The pictures of the explosion phenomenon (deflagration and/or detonation) were taken by high-speed cameras.

Hydrogen is not more dangerous than current fossil energy carriers but it behaves differently. Therefore hydrogen specific analyses and countermeasures will be needed to support the development of safe hydrogen technologies. A systematic step-by-step procedure for the mechanistic analysis of hydrogen behaviour and mitigation in accidents is presented. The procedure can be subdivided into four main parts:<br/>1) 3D modelling of the H2-air mixture generation<br/>2) hazard evaluation for this mixture based on specifically developed criteria for flammability flame acceleration and detonation on-set<br/>3) numerical simulation of the appropriate combustion regime using verified 3D-CFD codes and<br/>4) consequence analysis based on the calculated pressure and temperature loads.

A phenomenological approach is developed to calculate the velocity of flame propagation and to estimate the value of pressure peak when igniting gaseous combustible mixtures in a congested space. The basic idea of this model is afterburning of the remanent fuel in pockets of congested space behind the flame front. The estimation of probable overpressure peak is based on solution of one-dimensional problem of the piston (having corresponding symmetry) moving with given velocity in polytropic gas. Submitted work is the first representation of such phenomenological approach and is realized for the simplest situation close to one-dimensional.

Large-scale deflagration and detonation experiments of hydrogen and air mixtures provide fundamental data needed to address accident scenarios and to help in the evaluation and validation of numerical models. Several different experiments of this type were performed. Measurements included flame front time of arrival (TOA) using ionization probes blast pressure heat flux high-speed video standard video and infrared video. The large-scale open-space tests used a hemispherical 300-m3 facility that confined the mixture within a thin plastic tent that was cut prior to initiating a deflagration. Initial homogeneous hydrogen concentrations varied from 15% to 30%. An array of large cylindrical obstacles was placed within the mixture for some experiments to explore turbulent enhancement of the combustion. All tests were ignited at the bottom center of the facility using either a spark or in one case a small quantity of high explosive to generate a detonation. Spark-initiated deflagration tests were performed within the tunnel using homogeneous hydrogen mixtures. Several experiments were performed in which 0.1 kg and 2.2 kg of hydrogen were released into the tunnel with and without ventilation. For some tunnel tests obstacles representing vehicles were used to investigate turbulent enhancement. A test was performed to investigate any enhancement of the deflagration due to partial confinement produced by a narrow gap between aluminium plates. The attenuation of a blast wave was investigated using a 4-m-tall protective blast wall. Finally a large-scale hydrogen jet experiment was performed in which 27 kg of hydrogen was released vertically into the open atmosphere in a period of about 30 seconds. The hydrogen plume spontaneously ignited early in the release.

Hydrogen embrittlement which severely affects structural materials such as steel comprises several mechanisms at the atomic level. One of them is hydrogen enhanced decohesion (HEDE) the phenomenon of H accumulation between cleavage planes where it reduces the interplanar cohesion. Grain boundaries are expected to play a significant role for HEDE since they act as trapping sites for hydrogen. To elucidate this mechanism we present the results of first-principles studies of the H effect on the cohesive strength of α-Fe single crystal (001) and (111) cleavage planes as well as on the Σ5(310)[001] and Σ3(112)[11¯0] symmetrical tilt grain boundaries. The calculated results show that within the studied range of concentrations the single crystal cleavage planes are much more sensitive to a change in H concentration than the grain boundaries. Since there are two main types of procedures to perform ab initio tensile tests different in whether or not to allow the relaxation of atomic positions which can affect the quantitative and qualitative results these methods are revisited to determine their effect on the predicted cohesive strength of segregated interfaces

About 20 years ago Fraunhofer ICT has performed large scale experiments with premixed hydrogen air mixtures [1]. A special feature has been the investigation of the combustion of the mixture within a partial confinement simulating some sort of a “lane” which may exist in reality within a hydrogen production or storage plant for example. Essentially three different types of tests have been performed: combustion of quiescent mixtures combustion of mixtures with artificially generated turbulence by means of a fan and combustion of mixtures with high speed flame jet ignition. The observed phenomena will be discussed on the basis of measured turbulence levels flame speeds and overpressures. Conditions for DDT concerning critical turbulence levels and flame speeds as well as a scaling rule for DDT related to the detonation cell size of the mixture can be derived from the experiments for this special test setup. The relevance of the results with respect to safety aspects of future hydrogen technology is assessed. Combustion phenomena will be highlighted by the presentation of impressive high speed film videos.

The CCC has established a variety of viable scenarios in which UK decarbonisation targets can be met. Each has consequences for the way in which the UK’s gas network infrastructure is utilised. This report considers the implications of decarbonisation for the future regulation of the gas grid.<br/>The CCC’s 5th Carbon Budget envisaged different scenarios that would enable the UK to meet its emissions targets for 2050. These scenarios represent holistic analyses based on internally consistent combinations of different technologies which could deliver carbon reductions across different sectors of the economy.<br/>The CCC’s scenarios incorporate projections of the demand for natural gas to 2050. The scenarios imply that the volume of throughput on the gas networks1 and the nature and location of network usage is likely to change significantly to meet emissions targets. They are also characterised by significant uncertainty.<br/>Under some decarbonisation scenarios gas networks could be re-purposed to supply hydrogen instead of natural gas meaning there would be ongoing need for network infrastructure.<br/>In other scenarios gas demand in buildings is largely replaced by electric alternatives meaning portions of the low pressure gas distribution networks could be decommissioned.<br/>Patchwork scenarios are also possible in which there is a mixture of these outcomes across the country.<br/>In this project the CCC wished to assess the potential implications for gas networks under these different demand scenarios; and evaluate the associated challenges for Government and regulatory policy. The challenge for BEIS and Ofgem is how to regulate in a way that keeps options open while uncertainty persists about the best solution for the UK; and at the same time how best to make policy and regulatory decisions which would serve to reduce this uncertainty. Both Government and Ofgem have policy and regulatory levers that they can use – and we identify and evaluate such levers in this report.