Applications & Pathways
HydroGenerally - Episode 5: Hydrogen for Glass Production
May 2022
Publication
In this fifth episode Steffan Eldred and Neelam Mughal from Innovate UK KTN discuss how the glass industry is driving new hydrogen developments and research and explore the hydrogen transition opportunities and challenges in this sector alongside their special guest Rob Ireson Innovation and Partnerships Manager at Glass Futures Ltd.
The podcast can be found on their website
The podcast can be found on their website
Electrification Versus Hydrogen for UK Road Freight: Conclusions from a Systems Analysis of Transport Energy Transitions
Mar 2022
Publication
Collectively the UK investment in transport decarbonisation is greater than £27B from government for incentivising zero-emission vehicles as part of an urgent response to decarbonise the transport sector. The investments made must facilitate a transition to a long-term solution. The success relies on coordinating and testing the evolution of both the energy and transport systems this avoids the risk of unforeseen consequences in both systems and therefore de-risks investment Here we present a semiquantitative energy and transport system analysis for UK road freight focusing on two primary investment areas for nation-wide decarbonisation namely electrification and hydrogen propulsion. Our study assembles and assesses the potential roadblocks of these energy systems into a concise record and considers the infrastructure in relation to all other components within the energy system. It highlights that for system-wide success and resilience a hydrogen system must overcome hydrogen production and distribution barriers whereas an electric system needs to optimise storage solutions and charging facilities. Without cohesive co-evolving energy networks the planning and operational modelling of transport decarbonisation may fall short of meaningful real-world results. A developed understanding of the dependencies between the energy and transport systems is a necessary step in the development of meaningful operational transport models that could de-risk investment in both the energy and transport systems.
Green Electricity and Medical Electrolytic Oxygen from Solar Energy - A Sustainable Solution for Rural Hospitals.
Oct 2022
Publication
The objective of this paper is to design and simulate for rural areas isolated from the electricity grid a system based on solar energy for the optimal supply of green electricity and medical oxygen to a hospital. The system sized to produce 20 Nm3 /day is constituted of a 37.46 kW photovoltaic farm a 15.47 kW electrolyzer and a 15.47 kW fuel cell. The simulation of the Photovoltaic system is performed using the single diode model solved with the Lambert function defined in MATLAB Software. The daily production of oxygen and hydrogen during the sunniest day of the month is respectively 20.81 Nm3 /day and 41.61 Nm3 /day. The daily energy that can be stored is relevant to the hydrogen production and an electricity storage capacity of 124.89 kWh is feasible. During the least sunny day of the least sunny month the daily production of oxygen and hydrogen is respectively 7.72 Nm3 /day and 15.44 Nm3 /day. The recorded values prove that the system sized can constitute a viable solution to ensure the permanent supply a green electricity and oxygen to the hospital with good energy storage capacity.
A Comprehensive Review of Electrochemical Hybrid Power Supply Systems and Intelligent Energy Managements for Unmanned Aerial Vehicles in Public Services
Jun 2022
Publication
The electric unmanned aerial vehicles (UAVs) are rapidly growing due to their abilities to perform some difficult or dangerous tasks as well as many public services including real-time monitoring wireless coverage search and rescue wildlife surveys and precision agriculture. However the electrochemical power supply system of UAV is a critical issue in terms of its energy/power densities and lifetime for service endurance. In this paper the current power supply systems used in UAVs are comprehensively reviewed and analyzed on the existing power configurations and the energy management systems. It is identified that a single type of electrochemical power source is not enough to support a UAV to achieve a long-haul flight; hence a hybrid power system architecture is necessary. To make use of the advantages of each type of power source to increase the endurance and achieve good performance of the UAVs the hybrid systems containing two or three types of power sources (fuel cell battery solar cell and supercapacitor) have to be developed. In this regard the selection of an appropriate hybrid power structure with the optimized energy management system is critical for the efficient operation of a UAV. It is found that the data-driven models with artificial intelligence (AI) are promising in intelligent energy management. This paper can provide insights and guidelines for future research and development into the design and fabrication of the advanced UAV power systems.
A Review on CO2 Mitigation in the Iron and Steel Industry through Power to X Processes
Feb 2021
Publication
In this paper we present the first systematic review of Power to X processes applied to the iron and steel industry. These processes convert renewable electricity into valuable chemicals through an electrolysis stage that produces the final product or a necessary intermediate. We have classified them in five categories (Power to Iron Power to Hydrogen Power to Syngas Power to Methane and Power to Methanol) to compare the results of the different studies published so far gathering specific energy consumption electrolysis power capacity CO2 emissions and technology readiness level. We also present for the first time novel concepts that integrate oxy-fuel ironmaking and Power to Gas. Lastly we round the review off with a summary of the most important research projects on the topic including relevant data on the largest pilot facilities (2–6 MW).
Optimization of Component Sizing for a Fuel Cell-Powered Truck to Minimize Ownership Cost
Mar 2019
Publication
In this study we consider fuel cell-powered electric trucks (FCETs) as an alternative to conventional medium- and heavy-duty vehicles. FCETs use a battery combined with onboard hydrogen storage for energy storage. The additional battery provides regenerative braking and better fuel economy but it will also increase the initial cost of the vehicle. Heavier reliance on stored hydrogen might be cheaper initially but operational costs will be higher because hydrogen is more expensive than electricity. Achieving the right tradeoff between these power and energy choices is necessary to reduce the ownership cost of the vehicle. This paper develops an optimum component sizing algorithm for FCETs. The truck vehicle model was developed in Autonomie a platform for modelling vehicle energy consumption and performance. The algorithm optimizes component sizes to minimize overall ownership cost while ensuring that the FCET matches or exceeds the performance and cargo capacity of a conventional vehicle. Class 4 delivery truck and class 8 linehaul trucks are shown as examples. We estimate the ownership cost for various hydrogen costs powertrain components ownership periods and annual vehicle miles travelled.
A General Vision for Reduction of Energy Consumption and CO2 Emissions from the Steel Industry
Aug 2020
Publication
The 2018 IPCC (The Intergovernmental Panel on Climate Change’s) report defined the goal to limit global warming to 1.5 ◦C by 2050. This will require “rapid and far-reaching transitions in land energy industry buildings transport and cities”. The challenge falls on all sectors especially energy production and industry. In this regard the recent progress and future challenges of greenhouse gas emissions and energy supply are first briefly introduced. Then the current situation of the steel industry is presented. Steel production is predicted to grow by 25–30% by 2050. The dominant iron-making route blast furnace (BF) especially is an energy-intensive process based on fossil fuel consumption; the steel sector is thus responsible for about 7% of all anthropogenic CO2 emissions. In order to take up the 2050 challenge emissions should see significant cuts. Correspondingly specific emissions (t CO2/t steel) should be radically decreased. Several large research programs in big steelmaking countries and the EU have been carried out over the last 10–15 years or are ongoing. All plausible measures to decrease CO2 emissions were explored here based on the published literature. The essential results are discussed and concluded. The specific emissions of “world steel” are currently at 1.8 t CO2/t steel. Improved energy efficiency by modernizing plants and adopting best available technologies in all process stages could decrease the emissions by 15–20%. Further reductions towards 1.0 t CO2/t steel level are achievable via novel technologies like top gas recycling in BF oxygen BF and maximal replacement of coke by biomass. These processes are however waiting for substantive industrialization. Generally substituting hydrogen for carbon in reductants and fuels like natural gas and coke gas can decrease CO2 emissions remarkably. The same holds for direct reduction processes (DR) which have spread recently exceeding 100 Mt annual capacity. More radical cut is possible via CO2 capture and storage (CCS). The technology is well-known in the oil industry; and potential applications in other sectors including the steel industry are being explored. While this might be a real solution in propitious circumstances it is hardly universally applicable in the long run. More auspicious is the concept that aims at utilizing captured carbon in the production of chemicals food or fuels e.g. methanol (CCU CCUS). The basic idea is smart but in the early phase of its application the high energy-consumption and costs are disincentives. The potential of hydrogen as a fuel and reductant is well-known but it has a supporting role in iron metallurgy. In the current fight against climate warming H2 has come into the “limelight” as a reductant fuel and energy storage. The hydrogen economy concept contains both production storage distribution and uses. In ironmaking several research programs have been launched for hydrogen production and reduction of iron oxides. Another global trend is the transfer from fossil fuel to electricity. “Green” electricity generation and hydrogen will be firmly linked together. The electrification of steel production is emphasized upon in this paper as the recycled scrap is estimated to grow from the 30% level to 50% by 2050. Finally in this review all means to reduce specific CO2 emissions have been summarized. By thorough modernization of production facilities and energy systems and by adopting new pioneering methods “world steel” could reach the level of 0.4–0.5 t CO2/t steel and thus reduce two-thirds of current annual emissions.
The Impact of Fuel Cell Electric Freight Vehicles on Fuel Consumption and CO2 Emissions: The Case of Italy
Oct 2022
Publication
The Italian Recovery and Resilience Plan promotes among its many actions the use of hydrogen by the deployment of refuelling stations for heavy-duty vehicles predicting a 5–7% penetration rate of fuel cell electric vehicles (FCEVs) for long-distance freight transport. In this work the impact of this action on the reduction of greenhouse gas emissions and consumption was estimated assuming the plan’s objectives are met. To achieve this aim a national simulation model of the road freight transport system was implemented consisting of a graph of the national road network and an inter-provincial origin-destination matrix; the graph was based on data available from OpenStreetMap while the interprovincial matrix was estimated from the interregional matrix with the use of two linear regression models one for emitted goods and one for attracted goods. The simulation of the system made it possible to estimate the impact of this action on CO2 emissions and fuel consumption under three different scenarios. From 2025 to 2040 a reduction in CO2 emissions ranging from around 9 to around 16.5 million tonnes was estimated and a reduction in consumption ranging from around 3 billion to around 5.6 billion litres of diesel. These results show how this action can be seen as one of the bricks contributing to the fight against global warming.
Economic Optima for Buffers in Direct Reduction Steelmaking Under Increasing Shares of Renewable Hydrogen
Oct 2021
Publication
While current climate targets demand substantial reductions in greenhouse gas (GHG) emissions the potentials to further reduce carbon dioxide emissions in traditional primary steel-making are limited. One possible solution that is receiving increasing attention is the direct reduction (DR) technology operated either with renewable hydrogen (H2) from electrolysis or with conventional natural gas (NG). DR technology makes it possible to decouple steel and hydrogen production by temporarily using overcapacities to produce and store intermediary products during periods of low renewable electricity prices or by switching between H2 and NG. This paper aims to explore the impact of this decoupling on overall costs and the corresponding dimensioning of production and storage capacities. An optimization model is developed to determine the least-cost operation based on perfect-foresight. This model can determine the minimum costs for optimal production and storage capacities under various assumptions considering fluctuating H2 and NG prices and increasing H2 shares. The model is applied to a case study for Germany and covers the current situation the medium term until 2030 and the long term until 2050. Under the assumptions made the role of using direct reduced iron (DRI) storage as a buffer seems less relevant. DRI mainly serves as long-term storage for several weeks similar to usual balancing storage capacities. Storing H2 on the contrary is used for short-term fluctuations and could balance H2 demand in the hourly range until 2050. From an economic perspective DRI production using NG tends to be cheaper than using H2 in the short term and potential savings from the flexible operation with storages are small at first. However in the long term until 2050 NG and H2 could achieve similar total costs if buffers are used. Otherwise temporarily occurring electricity price spikes imply substantial increases in total costs if high shares of H2 need to be achieved.
Integration of Hydrogen and Synthetic Natural Gas within Legacy Power Generation Facilities
Jun 2022
Publication
Whilst various new technologies for power generation are continuously being evaluated the owners of almost-new facilities such as combined-cycle gas turbine (CCGT) plants remain motivated to adapt these to new circumstances and avoid the balance-sheet financial impairments of underutilization. Not only are the owners reluctant to decommission the legacy CCGT assets but system operators value the inertia and flexibilities they contribute to a system becoming predominated with renewable generation. This analysis therefore focuses on the reinvestment cases for adapting CCGT to hydrogen (H2 ) synthetic natural gas (SNG) and/or retrofitted carbon capture and utilization systems (CCUS). Although H2 either by itself or as part of SNG has been evaluated attractively for longer-term electricity storage the business case for how it can be part of a hybrid legacy CCGT system has not been analyzed in a market context. This work compares the power to synthetic natural gas to power (PSNGP) adaptation with the simpler and less expensive power to hydrogen to power (P2HP) adaptation. Both the P2HP and PSNGP configurations are effective in terms of decarbonizations. The best results of the feasibility analysis for a UK application with low CCGT load factors (around 31%) were obtained for 100% H2 (P2HP) in the lower range of wholesale electricity prices (less than 178 GBP/MWh) but in the higher range of prices it would be preferable to use the PSNGP configuration with a low proportion of SNG (25%). If the CCGT load factor increased to 55% (the medium scenario) the breakeven profitability point between P2HP and PSNGP decreased to a market price of 145 GBP/MWh. Alternatively with the higher load factors (above 77%) satisfactory results were obtained for PSNGP using 50% SNG if with market prices above 185 GBP/MWh.
Cradle-grave Energy Consumption, Greenhouse Gas and Acidification Emissions in Current and Future Fuel Cell Vehicles: Study Based on Five Hydrogen Production Methods in China
Jun 2022
Publication
Hydrogen fuel cell vehicles (FCVs) are regarded as a promising solution to the problems of energy security and environmental pollution. However the technology is under development and the hydrogen consumption is uncertain. The quantitative evaluation of life cycle energy consumption pollution emissions of current and future FCVs in China involves complex processes and parameters. Therefore this study addresses Life Cycle Assessment (LCA) of FCV and focuses on the key parameters of FCV production and different hydrogen production methods which include steam methane reforming catalysis decomposition methanol steam reforming electrolysis–photovoltaic (PV) and electrolysis Chinese electricity grid mix (CN). Sensitivity analysis of bipolar plate glider mass power density fuel cell system efficiency and energy control strategy are performed whilst accounting for different assumption scenarios. The results show that all impact assessment indicators will decrease by 28.8– 44.3% under the 2030 positive scenario for the production of FCVs. For cradle-grave FCVs the use of hydrogen from electrolysis operated with photovoltaic power reduces global warming potential (GWP) by almost 76.4% relative to steam methane reforming. By contrast the use of hydrogen from electrolysis operated with the Chinese electricity grid mix results in an increase in GWP of almost 158.3%.
Experimental Study on Tri-fuel Combustion Using Premixed Methane-hydrogen Mixtures Ignited by a Diesel Pilot
Apr 2021
Publication
A comprehensive investigation on diesel pilot spray ignited methane-hydrogen (CH4–H2) combustion tri-fuel combustion (TF) is performed in a single-cylinder compression ignition (CI) engine. The experiments provide a detailed analysis of the effect of H2 concentration (based on mole fraction MH2) and charge-air temperature (Tair) on the ignition behavior combustion stability cycle-to-cycle (CCV) and engine performance. The results indicate that adding H2 from 0 to 60% shortens the ignition delay time (IDT) and combustion duration (based on CA90) up to 33% and 45% respectively. Thereby H2 helps to increase the indicated thermal efficiency (ITE) by as much as 10%. Furthermore to gain an insight into the combustion stability and CCV the short-time Fourier transform (STFT) and continuous wavelet transform (CWT) methodologies are applied to estimate the combustion stability and CCV of the TF combustion process. The results reveal that the pressure oscillation can be reduced up to 4 dB/Hz and the CCV by 50% when MH2 < 60% and Tair < 55 °C. However when MH2 > 60% and Tair > 40 °C abnormal combustion and knocking are observed.
Sustainable Synthetic Carbon Based Fuels for Transport
Sep 2019
Publication
The report considers two types of sustainable synthetic fuels: electro fuels (efuels) and synthetic biofuels. Efuels are made by combining hydrogen (from for example the electrolysis of water) with carbon dioxide (from direct air capture or a point source). Synthetic biofuels can be made from biological material (for example waste from forestry) or from further processing biofuels (for example ethanol).<br/>Whilst synthetic fuels can be “dropped in” to existing engines they are currently more expensive than fossil fuels and in the case of efuels could be thought of as an inefficient use of renewable electricity. However where renewable electricity is cheap and plentiful the manufacture and export of bulk efuels might make economic sense.<br/>Key research challenges identified include improving the fundamental understanding of catalysis; the need to produce cheap low-carbon hydrogen at scale; and developing sources of competitively priced low carbon energy are key to the development of synthetic efuels and biofuels. The UK has the research skills and capacity to improve many of these process steps such as in catalysis and biotechnology and to provide a further area of UK leadership in low-carbon energy.
The Path to Net Zero and Progress on Reducing Emissions in Wales
Dec 2020
Publication
These two joint reports required under the Environment (Wales) Act 2016 provide ministers with advice on Wales’ climate targets between now and 2050 and assess progress on reducing emissions to date. Our advice to the Welsh Government is set out in two parts:
Advice Report: The path to a Net Zero Wales provides recommendations on the actions that are needed in Wales including the legislation of a Net Zero target and package of policies to deliver it.
Progress Report: Reducing emissions in Wales looks back at the progress made in Wales since the 2016 Environment (Wales) Act was passed and assesses whether Wales is on track to meet its currently legislated emissions reductions targets.
This work is based on an extensive programme of analysis consultation and consideration by the Committee and its staff building on the evidence published last year for our Net Zero report. It is compatible with our advice on the UK’s Sixth Carbon Budget. In support of the advice in this report we have also published:
Advice Report: The path to a Net Zero Wales provides recommendations on the actions that are needed in Wales including the legislation of a Net Zero target and package of policies to deliver it.
Progress Report: Reducing emissions in Wales looks back at the progress made in Wales since the 2016 Environment (Wales) Act was passed and assesses whether Wales is on track to meet its currently legislated emissions reductions targets.
This work is based on an extensive programme of analysis consultation and consideration by the Committee and its staff building on the evidence published last year for our Net Zero report. It is compatible with our advice on the UK’s Sixth Carbon Budget. In support of the advice in this report we have also published:
- All the charts and data behind the report as well as a separate dataset for the scenarios which sets out more details and data on the pathways than can be included in this report.
- A public Call for Evidence several new research projects three expert advisory groups and deep dives into the roles of local authorities and businesses.
Improve Hydrogen Economy for Vehicular Fuel Cell System via Investigation and Control of Optimal Operating Oxygen Excess Ratio
Apr 2022
Publication
This study investigates and controls the optimal operating oxygen excess ratio (OER) for PEMFC which effectively prevents oxygen starvation and improves the hydrogen economy of proton exchange membrane fuel cells (PEMFC). Firstly the PEMFC output characteristic model and the five-order nonlinear air supply system model are established. Moreover an adaptive algebraic observer was developed to observe the partial pressure of gas in PEMFC and further reconstruct OER. Secondly to achieve the minimum hydrogen consumption under the required power the reference OER is determined by analyzing the PEMFC system output power with its minimum current. Finally the super-twisting algorithm is adopted to track reference OER. Simulation results show that the average absolute observation errors of oxygen nitrogen and cathode pressures under the Highway Fuel Economy Test are 1351.1 Pa (5.1%) 1724.2 Pa (0.9%) and 409.9 Pa (1.6%) respectively. The OER adjust average absolute error is 0.03. Compared with the commonly used fixed OER (e.g. OER of 1.5 and 2.3) the optimal OER strategy can reduce the hydrogen consumption of the PEMFC system by 5.2% and 1.8% respectively. Besides a DSP hardware in loop test is conducted to show the real-time performance of the proposed optimal method.
Boosting Carbon Efficiency of the Biomass to Liquid Process with Hydrogen from Power: The Effect of H2/CO Ratio to the Fischer-Tropsch Reactors on the Production and Power Consumption
Jun 2019
Publication
Carbon efficiency of a biomass to liquid process can be increased from ca. 30 to more than 90% by adding hydrogen generated from renewable power. The main reason is that in order to increase the H2/CO ratio after gasification to the value required for Fischer-Tropsch (FT) synthesis the water gas shift reaction step can be avoided; instead a reversed water gas shift reactor is introduced to convert produced CO2 to CO. Process simulations are done for a 46 t/h FT biofuel production unit. Previous results are confirmed and it is shown how the process can be further improved. The effect of changing the H2/CO ratio to the Fischer-Tropsch synthesis reactors is studied with the use of three different kinetic models. Keeping the CO conversion in the reactors constant at 55% the volume of the reactors decreases with increasing H2/CO ratio because the reaction rates increase with the partial pressure of hydrogen. Concurrently the production of C5+ products and the consumption of hydrogen increases. However the power required per extra produced liter fuel also increases pointing at optimum conditions at a H2/CO feed ratio significantly lower than 2. The trends are the same for all three kinetic models although one of the models is less sensitive to the hydrogen partial pressure. Finally excess renewable energy can be transformed to FT syncrude with an efficiency of 0.8–0.88 on energy basis.
Flexible Electricity Use for Heating in Markets with Renewable Energy
Mar 2020
Publication
Using electricity for heating can contribute to decarbonization and provide flexibility to integrate variable renewable energy. We analyze the case of electric storage heaters in German 2030 scenarios with an open-source electricity sector model. We find that flexible electric heaters generally increase the use of generation technologies with low variable costs which are not necessarily renewables. Yet making customary night-time storage heaters temporally more flexible offers only moderate benefits because renewable availability during daytime is limited in the heating season. Respective investment costs accordingly have to be very low in order to realize total system cost benefits. As storage heaters feature only short-term heat storage they also cannot reconcile the seasonal mismatch of heat demand in winter and high renewable availability in summer. Future research should evaluate the benefits of longer-term heat storage.
Dynamic Modeling of a PEM Fuel Cell Power Plant for Flexibility Optimization and Grid Support
Jun 2022
Publication
The transition toward high shares of non-programmable renewable energy sources in the power grid requires an increase in the grid flexibility to guarantee grid reliability and stability. This work developed within the EU project Grasshopper identifies hydrogen Fuel Cell (FC) power plants based on low temperature PEM cells as a source of flexibility for the power grid. A dynamic numerical model of the flexible FC system is developed and tested against experimental data from a 100-kW pilot plant built within the Grasshopper project. The model is then applied to assess the flexible performance of a 1 MW system in order to optimize the scale-up of the pilot plant to the MW-size. Simulations of load-following operation show the flexibility of the plant which can ramp up and down with a ramp rate depending only on an externally imposed limit. Warm-up simulations allow proposing solutions to limit the warm-up time. Of main importance are the minimization of the water inventory in the system and the construction of a compact system which minimizes the distance between the components.
An Adaptive Renewable Energy Plant (AREP) - To Power Local Premises and Vehicles with 100% Renewables
Aug 2021
Publication
An adaptive response renewable energy plant (AREP) that provides grid balancing services and XeV station fuelling services (where “X” is any type) using renewable energy located in urban centres is described. The AREP has its own primary renewable energy sources and adapts operation in the short term to changing levels of excess or deficient energy on LV and MV electricity grids. The AREP adaptively responds by (1) storing excess energy in batteries for the short term and in hydrogen tanks after energy conversion by electrolysers for the long term; (2) returning power to the grid from either the AREP’s own primary (electron-based) energy sources or batteries and/or from hydrogen via conversion in fuel cells; (3) providing electricity for fast charging BeVs and PHeVs and hydrogen for FCeVs; and (4) exporting excess stored energy as hydrogen to domestic markets. The AREP also adapts over the long term by predictive planning of charging capacity such that the type and capacity of renewable energy equipment is optimised for future operations. A key advantage of this AREP configuration is a flexible “plug and play” capability with modular extension of energy assets. If the AREP footprint is constrained interaction with neighbouring AREPs as a mini-VPP-AREP network can assist in balancing short-term operating requirements. The benefits of this grid balancing and XeV renewable energy filling station or AREP are environmental social and economic through efficient functionality of appropriately sized components. AREPs provide a net zero emissions electricity solution to an existing network with short and long-term storage options as well as a net zero emissions fuel alternative to the transport sector while leveraging existing infrastructure with minimal upfront CAPEX. AREPs can give the flexibility a grid needs to enable high levels of renewable installations while developing green hydrogen production.
Controlled Autoignition of Hydrogen in a Direct-injection Optical Engine
Mar 2021
Publication
Research into novel internal combustion engines requires consideration of the diversity in future fuels in an attempt to reduce drastically CO2 emissions from vehicles and promote energy sustainability. Hydrogen has been proposed as a possible fuel for future internal combustion engines and can be produced from renewable sources. Hydrogen’s wide flammability range allows higher engine efficiency than conventional fuels with both reduced toxic emissions and no CO2 gases. Most previous work on hydrogen engines has focused on spark-ignition operation. The current paper presents results from an optical study of controlled autoignition (or homogeneous charge compression ignition) of hydrogen in an engine of latest spark-ignition pentroof combustion chamber geometry with direct injection of hydrogen (100 bar). This was achieved by a combination of inlet air preheating in the range 200–400 C and residual gas recirculated internally by negative valve overlap. Hydrogen fuelling was set to various values of equivalence ratio typically in the range / = 0.40–0.63. Crank-angle resolved flame chemiluminescence images were acquired for a series of consecutive cycles at 1000 RPM in order to calculate in-cylinder rates of flame expansion and motion. Planar Laser Induced Fluorescence (LIF) of OH was also applied to record more detailed features of the autoignition pattern. Single and double (i.e. ‘split’ per cycle) hydrogen injection strategies were employed in order to identify the effect of mixture preparation on autoignition’s timing and spatial development. An attempt was also made to review relevant in-cylinder phenomena from the limited literature on hydrogen-fuelled spark-ignition optical engines and make comparisons were appropriate.
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