Applications & Pathways

While electrification of light duty vehicles is becoming a real solution to abate local pollutant as well as greenhouse gases emission heavy duty applications (such as long distance freight and maritime transport) will keep requiring fuel-based propulsion systems. In these sectors dominated by compression ignition engines research on alternative biofuels and new combustion modes is still highly necessary. Dual-fuel combustion appears as a very promising concept to replace conventional diesel fuel by sustainable ones. Among the latter hydrogen-derived fuels (the so-called electrofuels or e-fuels) are maybe the most interesting. This work addresses the effect of partial substitution of diesel fuel by hydrogen and hydrogen-carriers (ammonia and methane) on the autoignition process under low temperature conditions. Tests were carried out in a constant volume combustion chamber at different temperatures (535 600 and 650 ◦C) and pressures (11 16 and 21 bar). While the cool flames timing and intensity was only slightly affected by the low reactivity fuel energy content the main ignition was delayed this effect being much more noticeable for ammonia followed by hydrogen and finally methane. Kinetic simulations showed a clear competition for active radicals between both fuels (diesel and low reactivity fuel). The combustion duration also increased with the hydrogen or hydrogen-carrier content which greatly points to the need of modifications in the injection strategy of compression ignition engines operating under dual mode. A correlation was proposed for estimating the autoignition delay time for dual-fuel lean combustion at low temperature.

A thermochemical recuperation (TCR) reactor was developed and experimentally evaluated with the objective to improve dual-fuel diesel–ammonia compression ignition engines. The novel system simultaneously decomposed ammonia into a hydrogen-containing mixture to allow high diesel fuel replacement ratios and oxidized unburned ammonia emissions in the exhaust overcoming two key shortcomings of ammonia combustion in engines from the previous literature. In the experimental work a multi-cylinder compression ignition engine was operated in dual-fuel mode using intake-fumigated ammonia and hydrogen mixtures as the secondary fuel. A full-scale catalytic TCR reactor was constructed and generated the fuel used in the engine experiments. The results show that up to 55% of the total fuel energy was provided by ammonia on a lower heating value basis. Overall engine brake thermal efficiency increased for modes with a high exhaust temperature where ammonia decomposition conversion in the TCR reactor was high but decreased for all other modes due to poor combustion efficiency. Hydrocarbon and soot emissions were shown to increase with the replacement ratio for all modes due to lower combustion temperatures and in-cylinder oxidation processes in the late part of heat release. Engine-out oxides of nitrogen (NOx) emissions decreased with increasing diesel replacement levels for all engine modes. A higher concentration of unburned ammonia was measured in the exhaust with increasing replacement ratios. This unburned ammonia predominantly oxidized to NOx species over the oxidation catalyst used within the TCR reactor. Ammonia substitution thus increased post-TCR reactor ammonia and NOx emissions in this work. The results show however that engine-out NH3 -to-NOx ratios were suitable for passive selective catalytic reduction thus demonstrating that both ammonia and NOx from the engine could be readily converted to N2 if the appropriate catalyst were used in the TCR reactor.

This paper aims to present a pre-feasibility study of a power-to-fuel plant configuration designed for the production of 500 kg/h of renewable methanol (e-methanol) from green hydrogen and captured carbon dioxide. Hydrogen is obtained by water electrolysis employing the overproduction of renewable electricity. Carbon dioxide is assumed to be separated from the flue gas of a conventional power station by means of an amine-based CO2 absorption system. A comprehensive process model has been developed with the support of Aspen Plus tool to simulate all the plant sections and the overall system. After the process optimization a detailed economic analysis – based on capital and operating costs derived from commercial-scale experience and assuming a 20- year lifetime – has been performed to calculate a levelized cost of methanol (LCoM) of 960 €/t (about 175 €/MWh). The analysis confirms that today the technology is still not competitive from the economic point of view being LCoM more than double than the current methanol price in the international market (450 €/t). However it indicates that the process is expected to become competitive in a mid-term future as a consequence of the new European policies. The study also reveals that LCoM is mainly affected by the electricity price and the electrolyser capital cost as well as the capacity factor of the plant.

Green ammonia has received increasing interest for its potential as an energy carrier in the international trade of renewable power. This paper considers the factors that contribute to producing cost-competitive green ammonia from an exporter’s perspective. These factors include renewable resource quality across potential sites operating modes for off-grid plants and seasonal complementarity with trade buyers. The study applies a mixed-integer programming model and uses Australia as a case study because of its excellent solar and wind resources and the potential for synergy between Southern Hemisphere supply and Northern Hemisphere demand. Although renewable resources are unevenly distributed across Australia and present distinct diurnal and seasonal variability modelling shows that most of the pre-identified hydrogen hubs in each state and territory of Australia can produce cost-competitive green ammonia providing the electrolysis and Haber-Bosch processes are partially flexible to cope with the variability of renewables. Flexible operation reduces energy curtailment and leads to lower storage capacity requirements using batteries or hydrogen storage which would otherwise increase system costs. In addition an optimised combination of wind and solar can reduce the magnitude of storage required. Providing that a partially flexible Haber Bosch plant is commercially available the modelling shows a levelised cost of ammonia (LCOA) of AU$756/tonne and AU$659/tonne in 2025 and 2030 respectively. Based on these results green ammonia would be cost-competitive with grey ammonia in 2030 given a feedstock natural gas price higher than AU$14/MBtu. For green ammonia to be cost-competitive with grey ammonia assuming a lower gas price of AU$6/MBtu a carbon price would need to be in place of at least AU$123/tonne. Given that there is a greater demand for energy in winter concurrent with lower solar power production there may be opportunities for solar-based Southern Hemisphere suppliers to supply the major industrial regions most of which are located in the Northern Hemisphere.

Hydrogen is a promising future fuel to enable the transition of transportation sector toward carbon neutrality. The direct utilization of H2 in internal combustion engines (ICEs) faces three major challenges: high NOx emissions severe pressure rise rates and pre-ignition at mid to high loads. In this study the potential of H2 combustion in a truck-size engine operated in spark ignition (SI) and pre-chamber (PC) mode was investigated. To mitigate the high pressure rise rate with the SI configuration the effects of three primary parameters on the engine combustion performance and NOx emissions were evaluated including the compression ratio (CR) the air–fuel ratio and the spark timing. In the simulations the severity of the pressure rise was evaluated based on the maximum pressure rise rate (MPRR). Lower compression ratios were assessed as a means to mitigate the auto-ignition while enabling a wider range of engine operation. The study showed that by lowering CR from 16.5:1 to 12.5:1 an indicated thermal efficiency of 47.5% can be achieved at 9.4 bar indicated mean effective pressure (IMEP) conditions. Aiming to restrain the auto-ignition while maintaining good efficiency growth in λ was examined under different CRs. The simulated data suggested that higher CRs require a higher λ and due to practical limitations of the boosting system λ at 4.0 was set as the limit. At a fixed spark timing using a CR of 13.5 combined with λ at 3.33 resulted in an indicated thermal efficiency of 48.6%. It was found that under such lean conditions the exhaust losses were high. Thus advancing the spark time was assessed as a possible solution. The results demonstrated the advantages of advancing the spark time where an indicated thermal efficiency exceeding 50% was achieved while maintaining a very low NOx level. Finally the optimized case in the SI mode was used to investigate the effect of using the PC. For the current design of the PC the results indicated that even though the mixture is lean the flame speed of H2 is sufficiently high to burn the lean charge without using a PC. In addition the PC design used in the current work induced a high MPRR inside the PC and MC leading to an increased tendency to engine knock. The operation with PC also increased the heat transfer losses in the MC leading to lower thermal efficiency compared to the SI mode. Consequently the PC combustion mode needs further optimizations to be employed in hydrogen engine applications.

Alternatives to cope with the challenges of high shares of renewable electricity in power systems have been addressed from different approaches such as energy storage and low-carbon technologies. However no model has previously considered integrating these technologies under stability requirements and different climate conditions. In this study we include this approach to analyse the role of new technologies to decarbonise the power system. The Spanish power system is modelled to provide insights for future applications in other regions. After including storage and low-carbon technologies (currently available and under development) batteries and hydrogen fuel cells have low penetration and the derived emission reduction is negligible in all scenarios. Compressed air storage would have a limited role in the short term but its performance improves in the long term. Flexible generation technologies based on hydrogen turbines and long-duration storage would allow the greatest decarbonisation providing stability and covering up to 11–14 % of demand in the short and long term. The hydrogen storage requirement is equivalent to 18 days of average demand (well below the theoretical storage potential in the region). When these solutions are considered decarbonising the electricity system (achieving Paris targets) is possible without a significant increase in system costs (< € 114/MWh).

Among the alternative fuels enabling the energy transition hydrogen-based transportation is a sustainable and efficient choice. It finds application both in light-duty and heavy-duty mobility. However hydrogen gas has unique qualities that must be taken into account when employed in such vehicles: high-pressure levels up to 900 bar storage in composite tanks with a temperature limit of 85 ◦C and a negative Joule–Thomson coefficient throughout a wide range of operational parameters. Moreover to perform a refueling procedure that is closer to the driver’s expectations a fast process that requires pre-cooling the gas to −40 ◦C is necessary. The purpose of this work is to examine the major phenomena that occur during the hydrogen refueling process by analyzing the relevant theory and existing modeling methodologies.

This paper addresses the energy management of a standalone renewable energy system. The system is configured as a microgrid including photovoltaic generation a lead-acid battery as a short term energy storage system hydrogen production and several loads. In this microgrid an energy management strategy has been incorporated that pursues several objectives. On the one hand it aims to minimize the amount of energy cycled in the battery in order to reduce the associated losses and battery size. On the other hand it seeks to take advantage of the long-term surplus energy producing hydrogen and extracting it from the system to be used in a fuel cell hybrid electric vehicle. A crucial factor in this approach is to accommodate the energy consumption to the energy demand and to achieve this a model predictive control (MPC) scheme is proposed. In this context proper models for solar estimation hydrogen production and battery energy storage will be presented. Moreover the controller is capable of advancing or delaying the deferrable loads from its prescheduled time. As a result a stable and efficient supply with a relatively small battery is obtained. Finally the proposed control scheme has been validated on a real case scenario.

Hydrogen may represents a good alternative fuel that can be used to fuel internal combustion engines in order to ameliorate energetic and emissions performance. The paper presents some experimental aspects registered at hydrogen use to fuel a diesel engine different substitute ratios being use in the area of 18–34% at 40% engine load and speed of 2000 rev/min. The engine is equipped with an open ECU and the control of the cyclic dosses of diesel fuel and hydrogen are adjusted in order to maintain the engine power performance. The in-cylinder pressure diagrams show the increase of the maximum pressure with 17% from 78.5 bar to 91.8 bar for the maximum substitute ratio. Also values of maximum pressure rise rate start to increase for hydrogen addition in correlation with the increase of fuel amount burned into the premixed stage without exceed the normal values with assure the normal and reliable engine operation. Higher Lower Heating Value and combustion speed of hydrogen assure the increase in thermal efficiency the brake specific energy consumption decreases with 5.4%–7.8% at substitute ratios of 20–27%. The CO2 emission level decreases with 20% for maximum hydrogen cyclic dose. In terms of pollutant emission level at hydrogen use the emission level of the NOx decreases with 50% and the smoke number decreases with 73.8% comparative to classic fuelling at the maximum hydrogen cyclic dose.

Rapid depletion of conventional fossil fuels and increasing environmental concern are demanding an urgent carry out for research to find an alternate fuel which meets the fuel demand with minimum environmental impacts. Hydrogen is considered as one of the important fuel in the near future which meets the above alarming problems. Hydrogen–gasoline dual fuel engines use hydrogen as primary fuel and gasoline as secondary fuel. In this review paper the combustion performance emission and cyclic variation characteristics of a hydrogen–gasoline dual fuel engine have been critically analyzed. According to scientific literature hydrogen–gasoline dual fuel engines have a good thermal efficiency at low and partial loads but the performance deteriorates at high loads. Hydrogen direct injection with gasoline port fuel injection is the optimum configuration for dual fuel engine operating on hydrogen and gasoline. This configuration shows superior result in mitigating the abnormal combustion but experiences high NOx emission. Employing EGR showed a maximum reduction of 77.8% of NOx emission with a EGR flowrate of 18% further increment in flowrate leads to combustion instability. An overview on hydrogen production and carbon footprint related with hydrogen production is also included. This review paper aims to provide comprehensive findings from past works associated with hydrogen–gasoline dual fuel approach in a spark ignition engine