Status,challenges and opportunities of dual fuel hybrid approaches-a review

Consumers conventionally adopt diesel generation to meet the energy needs where the grid connection is unreliable or unavailable. While electrification has provided these communities a variety of economic and social opportunities, diesel consumption has resulted in adverse costs and environmental pollution. Two technologies available to reduce the expense and emissions of diesel fuel reliance include dual fuel or hybrid diesel applications. The dual-fuel approach involves a supplementary gas fuel charge in support of reduced diesel fuel consumption. Hybrid applications involve the integration of renewable generation to displace diesel fuel consumption. This paper reviews the potential for hybrid dual-fuel applications, identifying engine flexibility as a major integration barrier. In comparing the flexibility of various dual-fuel technologies to operate dynamically, this paper presents a critical review across hydrogen, liquified petroleum gas (LPG), natural gas (NG) and blended hydrogen and NG derivatives. The results identify a range of approaches able to improve engine flexibility and thus reduce the cost and carbon intensity of diesel-fired internal combustion engines. At low load conditions, while NG and LPG exhibit similar performance, the use of hydrogen and hydrogen blends provide improved engine performance and response. Unfortunately, given the current cost of hydrogen fuel, significant commercial barriers exist to the adoption of hydrogen or hydrogen blended fuels. Despite this, this review indicates the potential of hydrogen-NG blends to offer additional flexibility in comparison to alternative dual-fuel technologies. This position is furthered considering near term cost targets associated with the development of a global green hydrogen industry, coupled with its ability to serve as a demand-side management approach within isolated power systems, one of the multiple future research themes.     

Electric and plug-in hybrid vehicles influence on CO2 and water vapour emissions

The main objective of this research is to quantify the impact of introducing electric vehicles and plug-in hybrid vehicles, including fuel cell on conventional fleets. The impact is estimated in terms of local pollutants, HC, CO, NO_x, PM, and in terms of CO₂ and water vapour global emissions. The specific fleet of Portugal, roughly 6 million light-duty vehicles (30% diesel, 70% gasoline) is considered, and the mobility indicator of the fleet, 90 thousand million p × km, is kept constant throughout the analysis. Probability density functions for energy consumption and emissions are derived for conventional, electric and plug-in hybrid vehicles, in charge depleting and charge sustaining modes. The Monte Carlo method is used to obtain average distribution estimates for discounting values of “old vehicles” that are removed from the fleet, and to add average distribution estimates for the “new vehicles” entering the fleet. Considering the actual Portuguese fleet as the reference case, local pollutant emissions decrease by a factor of 10-53%, for 50% fleet replacement. A potential 23% decrease of CO₂ is foreseen, and a potential 31% increase of H₂O emissions is forecasted. Life cycle water vapour emissions tend to rise and are, typically, 2-4 times higher than CO₂ values at the upstream stage, due to its release in the cooling towers of thermal power plants. It is interesting to note that considering 1 MJ of energy required at vehicle wheels, in an overall life cycle context, both fuel cell and electric modes have nearly twice as much H₂O emissions than internal combustion vehicles. CO₂ emissions tend to decrease with electric drive vehicles penetration due to the higher fleet life cycle efficiency.     

Life cycle cost analysis to examine the economical feasibility of hydrogen as an alternative fuel

This study uses a life cycle costing (LCC) methodology to identify when hydrogen can become economically feasible compared to the conventional fuels and which energy policy is the most effective at fostering the penetration of hydrogen in the competitive fuel market. The target hydrogen pathways in this study are H₂ via natural gas steam reforming (NG SR), H₂ via naphtha steam reforming (Naphtha SR), H₂ via liquefied petroleum gas steam reforming (LPG SR), and H₂ via water electrolysis (WE). In addition, the conventional fuels (gasoline, diesel) are also included for the comparison with the H₂ pathways.     

Are HFC buses a feasible alternative for urban transportation in Paraguay?

Paraguay is very rich in hydropower and a net importer of fossil fuels. Besides, in Paraguay, the transportation sector counts for a big share of the total energy demand. So if this sector would be changed to clean fuel, imported oil dependence and air pollution will be reduced dramatically. This paper assesses the feasibility of HFC urban buses implementation in the transportation sector in Paraguay. In general, annual transportation cost for a fleet of 55 HFC urban buses is estimated in US$ 33,682,581 compared with US$ 40,612,741.84 for diesel urban buses, which indicates that this technology could be an economical and environmentally clean alternative to substitute diesel urban buses in the Paraguayan transportation sector. These results are strongly linked to the chosen boundary conditions, such as electricity price and availability, the electrolytic hydrogen demand and the basic electrolyser's management.     

Alternative fuel buses currently in use in China: Life-cycle fossil energy use,GHG emissions and policy recommendations

The Chinese government has enacted policies to promote alternative vehicle fuels (AVFs) and alternative fuel vehicles (AFVs), including city bus fleets. The life cycle (LC), energy savings (ES) and GHG reduction (GR) profiles of AVFs/AFVs are critical to those policy decisions. The well-to-wheels module of the Tsinghua-CA3EM model is employed to investigate actual performance data. Compared with conventional buses, AFVs offer differences in performance in terms of both ES and GR. Only half of the AFVs analyzed demonstrate dual benefits. However, all non-oil/gas pathways can substitute oil/gas with coal. Current policies seek to promote technology improvements and market creation initiatives within the guiding framework of national-level diversification and district-level uniformity. Combined with their actual LC behavior and in keeping with near- and long-term strategies, integrated policies should seek to (1) apply hybrid electric technology to diesel buses; (2) encourage NG/LPG buses in gas-abundant cities; (3) promote commercialize electric buses or plug-in capable vehicles through battery technology innovation; (4) support fuel cell buses and hydrogen technology R&D for future potential applications; and (5) conduct further research on boosting vehicle fuel efficiency, applying low-carbon transportation technologies, and addressing all resultant implications of coal-based transportation solutions to human health and natural resources.     

Coal-based synthetic natural gas (SNG): A solution to China’s energy security and CO2 reduction?

Considering natural gas (NG) to be the most promising low-carbon option for the energy industry, large state owned companies in China have established numerous coal-based synthetic natural gas (SNG) projects. The objective of this paper is to use a system approach to evaluate coal-derived SNG in terms of life-cycle energy efficiency and CO₂ emissions. This project examined main applications of the SNG and developed a model that can be used for evaluating energy efficiency and CO₂ emissions of various fuel pathway systems. The model development started with the GREET model, and added the SNG module and an end-use equipment module. The database was constructed with Chinese data. The analyses show when the SNG are used for cooking, power generation, steam production for heating and industry, life-cycle energies are 20–108% higher than all competitive pathways, with a similar rate of increase in life-cycle CO₂ emissions. When a compressed natural gas (CNG) car uses the SNG, life-cycle CO₂ emission will increase by 150–190% compared to the baseline gasoline car and by 140–210% compared to an electric car powered by electricity from coal-fired power plants. The life-cycle CO₂ emission of SNG-powered city bus will be 220–270% higher than that of traditional diesel city bus. The gap between SNG-powered buses and new hybrid diesel buses will be even larger—life-cycle CO₂ emission of the former being around 4 times of that of the latter. It is concluded that the SNG will not accomplish the tasks of both energy conservation and CO₂ reduction.     

A study on the environmental aspects of hydrogen pathways in Korea

In this study, the environmental aspects of H₂ pathways are analyzed according to plausible H₂ production methods, production capacity, and distribution options in Korea, using life cycle assessment (LCA) methodology. The target H₂ pathways analyzed are H₂ via naphtha steam reforming (Naphtha SR), H₂ via natural gas steam reforming (NG SR), H₂ via liquefied petroleum gas steam reforming (LPG SR), H₂ via water electrolysis with wind power (WE[Wind]), and H₂ via water electrolysis with Korea electricity mix (WE[KEM]). The results are then compared with those of conventional fuels (gasoline, diesel, and LPG) to identify which H₂ pathway has less environmental impact than the conventional fuels.     

A correct perspective for hydrogen from engineered diagenesis

Wind and solar photovoltaic electricity production have already reached very low levels of levelized cost of energy (LCOE). Electrolyzers have already reached high efficiencies which are further improving, while costs are dramatically reducing. They are commercial products. Green hydrogen (H₂) is the product of excess wind and solar electricity, specifically electricity that will be otherwise wasted, without the huge energy storage needed presently almost completely missing. By growing the installed capacity of wind and solar power plants, there will be a non-dispatchable production by wind and solar more often in excess, but sometimes also in defect, of the grid demand, in presence of limited energy storage. H₂ is one of the key energy storage technologies needed to ensure grid stability. Production of H₂ above what is needed to stabilize the grid significantly helps in applications such as land, and sea but especially air transport where the storage of energy onboard in a fuel is preferable to the storage of energy as electricity into a battery. The engineered diagenesis for H₂ is unlikely better than green hH₂. Apart from being a nice idea to be proven workable, with a technology readiness level (TRL) presently of zero, and thus impossible to be objectively compared with commercial products, the engineered diagenesis for H₂, even if possible, also does not help with non-dispatchable renewable energy production. The concept may also have negative environmental aspects similar to fracking which have not been considered yet, and also bear huge economic costs in addition to environmental. Here we review the pros and cons of this novel technology, which once proven workable, which is not the case yet, should be considered as a possible way to complement rather than replace green H₂ production.     

Catching the hydrogen train: economics-driven green hydrogen adoption potential in the United Arab Emirates

The establishment of a hydrogen economy for domestic use and energy exports is increasingly attractive to fossil fuel exporting countries. This paper quantifies the potential of green hydrogen in the United Arab Emirates, using an integrated adoption model based on global technoeconomic trends and local costs. We consider the impact of varying hydrogen, oil, natural gas, and carbon prices on the economics of green H₂ adoption. In our Business-As-Usual (BAU) scenario, we observe economic viability in UAE industries between 2032 and 2038 at H₂ prices between $0.95/kg and $1.35/kg based on electrolyzer cost assumptions, solar forecasts and learning rates. We also note rapid scale-up to large export-oriented production capacities across our scenarios. However, if cost reductions slow or gas prices return to historical lows, additional interventions such as carbon pricing would be required to fully decarbonize in alignment with the 2050 net-zero target.     

Performance comparison of autothermal reforming for liquid hydrocarbons,gasoline and diesel for fuel cell applications

This paper discusses the reforming of liquid hydrocarbons to produce hydrogen for fuel cell applications, focusing on gasoline and diesel due to their high hydrogen density and well-established infrastructures. Gasoline and diesel are composed of numerous hydrocarbon species including paraffins, olefins, cycloparaffins, and aromatics. We have investigated the reforming characteristics of several representative liquid hydrocarbons. In the case of paraffin reforming, H₂ yield and reforming efficiency were close to thermodynamic equilibrium status (TES), although heavier hydrocarbons required slightly higher temperatures than lighter hydrocarbons. However, the conversion efficiency was much lower for aromatics than paraffins with similar carbon number. We have also investigated the reforming performance of simulated commercial diesel and gasoline using simple synthetic diesel and gasoline compositions. Reforming performances of our formulations were in good agreement with those of commercial fuels. In addition, the reforming of gas to liquid (GTL) resulted in high H₂ yield and reforming efficiency showing promise for possible fuel cell applications.     

Comparison of fuel economies of high efficiency diesel and hydrogen engines powering a compact car with a flywheel based kinetic energy recovery systems

Coupling of small turbocharged high efficiency diesel engines with flywheel based kinetic energy recovery systems is the best option now available to reduce fuel energy usage and reduce green house gas (GHG) emissions. The paper describes engine and vehicle models to generate engine brake specific fuel consumption maps and compute vehicle fuel economies over driving cycles, and applies these models to evaluate the benefits of a H₂ICEs developed with the direct injection jet ignition engine concept to further reduce the fuel energy usage of a compact car equipped with a with a flywheel based kinetic energy recovery systems. The car equipped with a 1.2 L TDI Diesel engine and KERS consumes 25 g/km of fuel producing 79.2 g/km of CO₂ using 1.09 MJ/km of fuel energy. These CO₂ and fuel energy values are more than 10% better than those of today’s best hybrid electric vehicle. The car equipped with a 1.6 L DI-JI H₂ICE engine consumes 8.3 g/km of fuel, corresponding to only 0.99 MJ/km of fuel energy.     

Life cycle assessment of alternative energy types – including hydrogen – for public city buses in Taiwan

Human activities have exacerbated the global greenhouse effect, resulting in extreme climate changes that have caused disasters and food and water shortages in recent years. Transportation is one of the main causes of global greenhouse gas (GHG) emission. Therefore, policy makers must develop feasible strategies to reduce GHG emission. One of Taiwan's policy is to replace traditional diesel fuel urban buses with alternative energy buses. This paper uses a case study of city bus route No. 2 in Tainan City following the international standard ISO/TS 14067:2013 to measure the carbon footprint of different energy buses. The bus carbon footprints measured from high to low as: LNG buses, 63.14 g CO2e/pkm; traditional diesel buses, 54.6 g CO2e/pkm; liquefied petroleum gas (LPG) buses, 47.4 g CO2e/pkm; plug-in electric buses, 37.82 g CO2e/pkm, and hydrogen fuel cell buses, 29.17 g CO2e/pkm. If all urban area public buses in Taiwan were switched to hydrogen fuel cell buses, this would reduce CO2e footprint by 227,832.39 t annually. This reduction is equivalent to planting 22.78 million trees.     

Cost and CO2 aspects of future vehicle options in Europe under new energy policy scenarios

New electrified vehicle concepts are about to enter the market in Europe. The expected gains in environmental performance for these new vehicle types are associated with higher technology costs. In parallel, the fuel efficiency of internal combustion engine vehicles and hybrids is continuously improved, which in turn advances their environmental performance but also leads to additional technology costs versus today’s vehicles. The present study compares the well-to-wheel CO₂ emissions, costs and CO₂ abatement costs of generic European cars, including a gasoline vehicle, diesel vehicle, gasoline hybrid, diesel hybrid, plug in hybrid and battery electric vehicle. The predictive comparison is done for the snapshots 2010, 2020 and 2030 under a new energy policy scenario for Europe. The results of the study show clearly that the electrification of vehicles offer significant possibilities to reduce specific CO₂ emissions in road transport, when supported by adequate policies to decarbonise the electricity generation. Additional technology costs for electrified vehicle types are an issue in the beginning, but can go down to enable payback periods of less than 5 years and very competitive CO₂ abatement costs, provided that market barriers can be overcome through targeted policy support that mainly addresses their initial cost penalty.     

Comparative analysis of performance and techno-economics for a H2O–NH3–H2 absorption refrigerator driven by different energy sources

The objectives of the present work are of two-folds. First, it evaluates the transient temperature performance of the H₂O–NH₃–H₂ absorption cooling machine system’s components under two types of energy sources, i.e. the conventional electric energy from grid (electric) and fuel energy from liquid petroleum gas (LPG). Results obtained have shown that performance of various components under different type of energy sources is almost coherent. For the evaporator, the system with electric supply has shorter starting time, around 6 min earlier than the system run with LPG. Meanwhile, the system powered by LPG produced a lower cooling temperature around −9 °C, compared to the system run with electric which produced temperature at around −7 °C. Economical study had been carried out subsequently, for three different energy sources, i.e. electric, LPG and solar energy (photovoltaic). From the techno-economical analyzes, it was found that the conventional electric from grid is still the best form of energy source for short-term application, as far as the present location and conditions are concerned. LPG is the next attractive energy source, especially at locations with constant LPG supply; the photovoltaic energy from solar is attractive for long term consideration since it has zero fuel cost and environmentally-friendly, but with the highest initial cost.     

Enhancement of biological hydrogen production using green alga Chlorococcum minutum

It is estimated that the fossil fuel reserves are going to deplete continuously due to extensive usage. In order to cope with this crisis, it is necessary to increase the efforts towards production of biofuels such as biological hydrogen (H₂). It is well-known fact that the biological hydrogen is a clean and ideal energy and liberates high amount of energy per unit mass. Several groups are working for the large scale production of H₂ chemically and also using photosynthetic organisms, but output is not satisfactory. The best way to achieve enhancement of H₂ is through altering the photosynthetic process by applying various stress conditions or by natural selection. In the process of selection, Chlorococcum minutum was found with improved H₂ output when compared to model green alga Chlamydomonas reinhardtii in a massively parallel and competitive high-throughput screen of different green algae. Both the species belongs to class chlorophyceae of green algae and live in fresh water conditions. In extent various light, pH and temperature conditions were applied and achieved the enhancement of H₂ production in this species under in vitro settings. Augmented hydrogenase activity was found in Chlorococcum minutum when compared to model alga and this may be one of the reason behind improved H₂ output. Hence this species may be considered as one of the best species with respect to H₂ production and also this work may be useful for future renewable energy research.     

Diesel vehicles and sustainable mobility in the U.S.

Concerns regarding global warming and energy security have increased the importance of decreasing emissions of CO₂ from vehicles. Diesel vehicles have higher fuel economy and lower CO₂ emissions than their gasoline counterparts. On a well-to-wheels per vehicle per km basis it has been estimated that diesel light-duty vehicles in 2015 will emit 14–27% less CO₂ than their gasoline counterparts. We estimate here that on a gCO₂/kWh at peak torque, diesel medium-duty vehicles currently have an approximately 10% CO₂ advantage over their gasoline counterparts. At light and moderate loads the CO₂ advantage for medium-duty diesels with SCR after-treatment will be greater than 10% (reflecting pumping losses when gasoline engines are operated at low and moderate loads). Emission of NO_x, HCs, and PM from diesel (and gasoline) vehicles has decreased substantially over the past decade and further reductions are anticipated in the future. In addition to the heavy-duty segment, which diesels currently dominate, modern diesel engines are likely to continue to play an important role in the medium-duty segment, and perhaps also in the light-duty segment in a transition to more sustainable mobility.     

In-situ hydrogen generation from 1,2,3,4-tetrahydronaphthalene for catalytic conversion of oleic acid to diesel fuel hydrocarbons: Parametric studies using Response Surface Methodology approach

This work reported a new strategy in producing synthetic diesel hydrocarbons from a mono-unsaturated fatty acid model compound, oleic acid and replacing high pressure molecular hydrogen with a hydrogen-rich donor solvent, 1,2,3,4–tetrahydronaphthalene for the first time. Under the absence of an external H₂ supply, oleic acid was dispersed in 1,2,3,4-tetrahydronaphthalene and hydrotreated over commercially available 5 wt% Pd/C in a fed-batch reactor to obtain diesel range fuel products. A maximum oleic acid conversion of 92.4% and highest diesel hydrocarbon selectivity of 67.4% were achieved at 330 °C with a solvent to fatty acid mass ratio of 1 for 3 h under autogenous pressure. In-situ H₂ produced from 1,2,3,4-tetrahydronaphthalene operated as an effective hydrogen donor vehicle that continuously transported active hydrogen species from gas phase to reactant acid molecules and radical fragments. It minimized polymerization of reaction intermediate and suppressed coke formation, which subsequently improved catalyst resistance toward deactivation.     

Dazzled by diesel? The impact on carbon dioxide emissions of the shift to diesels in Europe through 2009

This paper identifies trends in new gasoline and diesel passenger car characteristics in the European Union between 1995 and 2009. By 2009 diesels had captured over 55% of the new vehicle market. While the diesel version of a given car model may have as much as 35% lower fuel use/km and 25% lower CO₂ emissions than its gasoline equivalent, diesel buyers have chosen increasingly large and more powerful cars than the gasoline market. As a result, new diesels bought in 2009 had only 2% lower average CO₂ emissions than new gasoline cars, a smaller advantage than in 1995. A Laspeyres decomposition investigates which factors were important contributors to the observed emission reductions and which factors offset savings in other areas. More than 95% of the reduction in CO₂ emissions per km from new vehicles arose because both diesel and gasoline new vehicle emissions/km fell, and only 5% arose because of the shift from gasoline to diesel technology. Increases in vehicle mass and power for both gasoline and diesel absorbed much of the technological efficiency improvements offered by both technologies. We also observe changes in the gasoline and diesel fleets in eight EU countries and find changes in fuel and emissions intensities consistent with the changes in new vehicles reported. While diesel cars continue to be driven far farther than gasoline cars, we attribute only some of this difference to a “rebound effect”. We conclude that while diesel technology has permitted significant fuel savings, the switch from gasoline to diesel in the new vehicle market contributed little itself to the observed reductions in CO₂ emissions from new vehicles.     

在用柴油客车的柴油/LPG双燃料改装技术

介绍了一种将在用柴油公共汽车改装成柴油 /LPG双燃料车的切实可行的方法。道路试验结果表明 :相对原型车而言 ,改装后的双燃料车的自由加速烟度下降 5 0 %以上 ,百公里当量油耗下降 3% ,最高车速基本不变。     

Can hydrogen be the sustainable fuel for mobility in India in the global context?

This article provides a critical assessment of H₂ from the standpoint of more widespread use as a sustainable fuel for Indian mobility applications in the global context. The potential techno-economic advantages of utilizing H₂ for automobiles rather than battery electric vehicles or conventional internal combustion engine vehicles are emphasized. The present assessment demonstrates that H₂ production, storage, and distribution costs are the primary challenges, and a significant improvement is still necessary for H₂ to compete either against the internal combustion engine vehicle or the battery electric vehicle to win the race, arguably. The secondary challenges have also been demonstrated, which include the cost of the fuel cell stack and the modifications associated with internal combustion engine vehicles, as well as regulatory and safety concerns, which impede the widespread usage of H₂. It is critical that policy-making for sustainable mobility in India is possible with the aid of a National H₂ Energy Road-Map. This in turn can achieve a cost target of $0.5/kg for H₂.