Alternative Transportation Fuels Research Articles

Comprehensive Multipath Variational Kinetics Study on Hydrogen Abstraction Reactions from Three Typical Dimethylcyclohexane Isomers by Hydroxyl Radicals: from the Electronic Structure to Model Applications.

Cycloalkanes serve as an important class of chemical components in both fossil and alternative transportation fuels and have attracted considerable attention from the combustion community. Hydrogen abstractions from cycloalkanes by hydroxyl radicals initiate the fuel decomposition process and trigger off the subsequent chain reactions and thus play an important role in both combustion and atmospheric chemistry. The target of this study is to fill the vacancy in kinetics data toward the H-abstraction reactions by hydroxyl radical from three typical dimethylcyclohexane isomers through first-principles and direct dynamics. The rate constants involving 18 elementary reactions in total were accurately determined by the multipath canonical variational transition state theory with the multidimensional small-curvature correction for tunneling (MP-CVT/SCT), over a broad temperature range of 200-2000 K. The significant roles of multistructural torsional anharmonicity and recrossing effects were stressed per abstraction site, while the quantum tunneling effect was found to be slight at temperatures of interest in combustion. The discrepancies observed among different reaction systems at a similar abstraction site highlight the fuel molecular effects on site-specific rate constants. The comparison results of total rate constants given by different dynamics approaches prove the importance of considering the torsional anharmonicity, recrossing, and tunneling effects, and the robust feature of the simplified MS-CVT/SCT. The calculated total constants for dimethylcyclohexane isomers by OH are consistent with those measured for methylcyclohexane and 1,4-dimethylcyclohexane at low temperatures. The branching ratio analysis confirms the predominant role of the tertiary abstraction at low-to-intermediate temperatures and its growing competition with distinct secondary abstractions as temperature increases. The calculated rate constants were eventually fitted into the analytical expressions and incorporated into the kinetic models to learn about the influences on modeling performance.

Exploring the potential of ammonia and hydrogen as alternative fuels for transportation

Abstract This study investigates the potential of hydrogen and ammonia, as alternatives for transportation fuels to tackle urgent issues concerning greenhouse gas emissions and air quality in the worldwide transportation sector. By examining studies and technological progresses, we evaluate the feasibility of transitioning to these energy options. Through an investigation of production methods, energy efficiency, environmental consequences, and infrastructure requirements, we present both the advantages and disadvantages of using hydrogen and ammonia as fuel substitutes. We spotlight production techniques such as electrolysis and renewable energy sources that could significantly decrease carbon emissions and air pollutants. Nonetheless, key challenges such as expanding infrastructure, cost-effectiveness, and safety considerations need to be resolved for adoption. Drawing on findings from research and industry developments, this article contributes to publications on transportation solutions while proposing avenues for research efforts and policy initiatives. Existing challenges and limitations are also discussed in details. In conclusion, this research underscores the significance of research endeavors and policy backing to unlock the potential of hydrogen and ammonia as sustainable transportation fuels underscoring their role in mitigating environmental impacts and promoting global sustainability objectives.

Autoignition of cyclohexane at low-to-intermediate temperatures: Rapid compression machine experiments and improved comprehensive chemical kinetic model

Cycloalkanes are an important class of hydrocarbons found in conventional and alternative transportation fuels. Being one of the simplest practical cycloalkanes, cyclohexane is often used as a surrogate in studies to understand the oxidation, ignition, and sooting characteristics of cycloalkanes more broadly. Although cyclohexane has been extensively studied, very limited datasets for cyclohexane oxidation at low-to-intermediate temperatures are available in the literature. Moreover, the literature autoignition data from rapid compression machines (RCMs) did not provide information on volume histories or experimental heat transfer characteristics which can significantly impact model predictions, thereby hindering the detailed validation of chemical kinetic models. It has also been observed that the cyclohexane kinetic models developed so far are not able to predict the literature data across a wide range of operating and mixture conditions. Hence, further studies are recommended to understand and improve model predictions for cyclohexane oxidation. In this study, RCM experiments were conducted using cyclohexane/air mixtures at varying compressed pressures (PC =15, 20, and 30 bar), equivalence ratios (ϕ=0.5, 1.0, and 2.0), and compressed temperatures (TC=670–960 K). The current RCM results of cyclohexane were found to complement well with the literature data, with the first-stage IDTs at high pressures and volume histories at all test conditions being first reported for better development and validation of chemical kinetic models. In addition, a detailed chemical kinetic model for the cyclohexane oxidation has been developed and validated using both newly acquired experimental IDTs in this study and literature experimental studies (IDTs in RCMs and STs, species profiles in jet-stirred reactors, and laminar burning velocities). Unlike literature models, the proposed model was observed to provide an overall better prediction for experimental results over a wide range of conditions. Chemical kinetic analysis of the developed model was further conducted to identify the reaction pathways controlling the autoignition of cyclohexane.

Pathways to net-zero emissions from China's transportation industry: Considering alternative fuels

In the context of the national ‘dual carbon’ strategy, expediting the green and low-carbon transformation has become a focal point across various industries. The challenge of reducing carbon dioxide (CO2) emissions in the transportation sector is exceptionally formidable, given its heavy reliance on energy. Swift progress within this industry unavoidably entails heightened energy consumption, consequently exacerbating CO2 emissions within the sector. This article aims to identify an attainable, comprehensive pathway towards achieving net-zero emissions within the industry. The study reveals that strict control over the growth rate of the transportation industry's total output value and significant promotion of energy intensity decline can lead to a substantial 44% reduction in CO2 emissions by 2050, equivalent to approximately 2.17 Gt and 2.15 Gt of CO2eq. Successfully achieving net-zero emissions necessitates the replacement of fossil fuels with alternative transportation fuels in the range of 3.34 EJ to 15.22 EJ, accompanied by technological advancements to drive cost reductions. Additionally, considering non-CO2 radiation forcing, each scenario requires carbon dioxide removal (CDR) ranging from 0.17 Gt to 2.67 Gt for achieving net-zero emissions. This article comprehensively examines key factors including economy, energy, and technology, conducting an in-depth investigation into the viable pathway to achieve net-zero emissions within the industry. The findings presented herein offer valuable insights into facilitating the industry's low-carbon development and supporting the attainment of the national ‘dual carbon’ goal.

Comparing Life-Cycle Emissions of Biofuels for Marine Applications: Hydrothermal Liquefaction of Wet Wastes, Pyrolysis of Wood, Fischer-Tropsch Synthesis of Landfill Gas, and Solvolysis of Wood.

Recent restrictions on marine fuel sulfur content and a heightened regulatory focus on maritime decarbonization are driving the deployment of low-carbon and low-sulfur alternative fuels for maritime transport. In this study, we quantified the life-cycle greenhouse gas and sulfur oxide emissions of several novel marine biofuel candidates and benchmarked the results against the emissions reduction targets set by the International Maritime Organization. A total of 11 biofuel pathways via four conversion processes are considered, including (1) biocrudes derived from hydrothermal liquefaction of wastewater sludge and manure, (2) bio-oils from catalytic fast pyrolysis of woody biomass, (3) diesel via Fischer-Tropsch synthesis of landfill gas, and (4) lignin ethanol oil from reductive catalytic fractionation of poplar. Our analysis reveals that marine biofuels' life-cycle greenhouse gas emissions range from -60 to 56 gCO2e MJ-1, representing a 41-163% reduction compared with conventional low-sulfur fuel oil, thus demonstrating a considerable potential for decarbonizing the maritime sector. Due to the net-negative carbon emissions from their life cycles, all waste-based pathways showed over 100% greenhouse gas reduction potential with respect to low-sulfur fuel oil. However, while most biofuel feedstocks have a naturally occurring low-sulfur content, the waste feedstocks considered here have higher sulfur content, requiring hydrotreating prior to use as a marine fuel. Combining the break-even price estimates from a published techno-economic analysis, which was performed concurrently with this study, the marginal greenhouse gas abatement cost was estimated to range from -$120 to $370 tCO2e-1 across the pathways considered. Lower marginal greenhouse gas abatement costs were associated with waste-based pathways, while higher marginal greenhouse gas abatement costs were associated with the other biomass-based pathways. Except for lignin ethanol oil, all candidates show the potential to be competitive with a carbon credit of $200 tCO2e-1 in 2016 dollars, which is within the range of prices recently received in connection with California's low-carbon fuel standard.

Production of transportation fuels via hydrotreating of scrap tires pyrolysis oil

The hydrotreating of scrap tires pyrolysis oil over commercial Ni-Mo/Al2O3 catalyst was researched for the best processing scheme allowing the production of high-quality alternative transportation fuels components of gasoline, jet, diesel, and marine fuel. Despite the initial high content of olefins, aromatics, sulfur, and nitrogen in pyrolysis oil, fuel components obtained by redistillation after the hydrotreating at 360 °C and 10 MPa met the majority of standard fuel specifications. Although the octane number of the naphtha fraction was lower, this fraction can be used as acomponent of the gasoline pool directly or after the catalytic reforming. Kerosene fraction can be utilized as jet fuel after the additional mild hydrotreatment or blending with hydroprocessed esters and fatty acids (HEFA) to decrease aromatics content. Diesel fraction can be blended with hydrotreated vegetable oils (HVO) to fulfill the density and cetane index specification. The bottom residue can be utilized as a low-sulfur fuel oil component in marine transportation.

Alternative Transportation Fuels

Energy is a necessity for economic development. Energy is used extensively in transportation and power generation. Human civilization would not have advanced to modern living standards without the transportation of millions of personalized and mass transport vehicles and the availability of 24x7 power. The global economy and society are heavily reliant on energy availability because it touches every aspect of human life and activity. Because of the rising population and urbanization, energy demand has skyrocketed. Thus, growing energy consumption has resulted in the world becoming increasingly reliant on fossil fuels such as coal, oil, and gas. Therefore, a sustainable energy path must be developed. Fossil fuels provide more than 80% of global consumption and more than 95% of global transportation energy. While global fossil fuel reserves are depleting, global energy demand is rising due to the evolution of energy-intensive lifestyles. To improve energy security and reduce greenhouse gas emissions, it is critical to investigate alternative fuels for the transportation sector. This paper summarizes the information on current transportation fuels and the potential use case of alternative transportation fuels.

An analysis of trends and policies supporting alternative fuels for road freight transport in Europe

A significant proportion of transport greenhouse gas emissions originates from the activity of light-duty trucks and heavy-duty vehicles. The overarching aim of this study is to assess road freight transport decarbonization in Europe by analyzing relevant trends (recent developments and future estimates) and policies. Specifically, the paper investigates the policy measures in place or introduced in the European Union Member States plus the United Kingdom between 2016 and 2018, as reported in their submissions to the European Commission, the market progress and status until 2020/1 and the techno-economic barriers that slow down further emissions mitigation. The study focuses on electric vehicles (battery electric and plug-in hybrid), fuel cell electric vehicles and natural gas-powered vehicles. We find wide differences in the strength of policy support by country, mode and fuel. Our analysis is constrained by data availability and we highlight the need for improvements in data reporting by countries, including the communication of future vehicle estimates and infrastructure targets. We reach the conclusion that, despite some progress, stronger action is needed to timely decarbonize road freight transport in Europe.

Combined effects of biodiesel − ULSD blends and EGR on performance and emissions of diesel engine using Response surface methodology (RSM)

Diesel engines are commonly employed in transportation and power generation. Due to the fast usage of fossil fuels such as diesel, alternative fuels for transportation and power generation are required. In present study, waste soybean cooking oil (WSCO) biodiesel is used as an alternative fuel in an agriculture-based diesel engine. The investigation has been done with blends of WSCO biodiesel-ultra-low sulfur diesel (ULSD) at different EGR rates using Response surface methodology (RSM). Binary blends were prepared by adding 20–35% v/v of WSCO biodiesel with ULSD. The results show that blend 35% v/v WSCO biodiesel-ULSD at 15% EGR (B35EGR15) has found maximum desirability. There is a significant reduction in NOx and smoke emissions by 59.04% and 17.46% respectively for B35EGR15 as compared to ULSDEGR0 with tolerable limit of BTE. The cost analysis shows that B35EGR15 is more economical than ULSDEGR0. It is concluded that all WSCO biodiesel-ULSD blends are shown to be effective in decreasing emissions in diesel engines.

Cost assessment of alternative fuels for maritime transportation in Ireland

In this study, we investigated the cost-effectiveness of four alternatives: Liquified Natural Gas (LNG), methanol, green hydrogen, and green ammonia, for the case of top 20 most frequently calling ships to Irish ports in 2019, through the Net Present Value (NPV) methodology, incorporating the benefits incurred through saved external, carbon tax and conventional fuel costs. LNG had the highest NPV (€6,166 million), followed by methanol (€1,705 million) and green hydrogen (€319 million). Green ammonia utilisation (as a hydrogen carrier) looks inviable due to higher operational costs, resulting from its excessive consumption (i.e., losses) during the cracking and purifying processes and its lower net calorific value. Green hydrogen remains the best option to meet future decarbonisation targets, although, a further reduction in its current fuel price (by 60%) or a significant increment in the proposed carbon tax rate (by 275%) will be required to improve its cost-competitiveness over LNG and methanol.

Membrane-assisted reactor for the direct conversion of CO2 to DME/MeOH

Several strategies are currently underway to investigate alternative routes to efficiently use CO2 as a carbon source for the production of alternative fuels for energy end transportation [1,2].

Conventional and Intensified Transesterification Process of Biodiesel Production: A Review

The dependency on fossil fuels is growing day by day with the need of drastic energy demand. Due to concern over diminution of fossil fuels, many researchers have focused on the renewable and unconventional sources of energy in the last decades. Alternative Fuels for transportation are one of those areas of research. In this paper, a concise review of various biodiesel production methods have been presented. First of all, conventional method is presented based on the transesterification reaction and later, a few novel techniques such as microwave irradiation aided, solar energy assisted, ultrasonic cavitation etc. have been depicted and the later part of this paper is an effort to discuss the use of solar energy in the biodiesel production to make it a feasible option for future research in the field of biodiesel production on a larger scale in a cost-effective manner

An Overview of Promising Alternative Fuels for Road, Rail, Air, and Inland Waterway Transport in Germany

To solve the challenge of decarbonizing the transport sector, a broad variety of alternative fuels based on different concepts, including Power-to-Gas and Power-to-Liquid, and propulsion systems, have been developed. The current research landscape is investigating either a selection of fuel options or a selection of criteria, a comprehensive overview is missing so far. This study aims to close this gap by providing a holistic analysis of existing fuel and drivetrain options, spanning production to utilization. For this purpose, a case study for Germany is performed considering different vehicle classes in road, rail, inland waterway, and air transport. The evaluated criteria on the production side include technical maturity, costs, as well as environmental impacts, whereas, on the utilization side, possible blending with existing fossil fuels and the satisfaction of the required mission ranges are evaluated. Overall, the fuels and propulsion systems, Methanol-to-Gasoline, Fischer–Tropsch diesel and kerosene, hydrogen, battery-electric propulsion, HVO, DME, and natural gas are identified as promising future options. All of these promising fuels could reach near-zero greenhouse gas emissions bounded to some mandatory preconditions. However, the current research landscape is characterized by high insecurity with regard to fuel costs, depending on the predicted range and length of value chains.

Non-detoxified acid hydrolysate of de-oiled Pongamia seed cake as a low-cost solution to microbial oil synthesis

• A lignocellulose residue, derived as a biodiesel byproduct, was used for microbial oil synthesis. • Acid pretreated biomass was used for lipid fermentation without detoxification. • The biomass and lipids in detoxified and non-detoxified media did not significantly differ. • A. ochraceus was resistant to inhibitors in the non-detoxified medium. • Avoiding the detoxification step may improve process economics. With rising energy demands, alternative transportation fuels are continually sought. The most recent advances in this area have been in the use of microorganisms to produce oils for biodiesel. When pretreated with dilute acid and used for microbial fermentation, the lignocellulosic sources currently preferred for microbial oil production require an additional detoxification step. In this work, microbial oil was produced from de-oiled Pongamia cake, a low-value residue from the biodiesel industry, to evaluate whether the detoxification step might be omitted during raw material processing. Non-detoxified acid hydrolysate (NDAH) and detoxified acid hydrolysate (DAH), when subjected to fermentation with Aspergillus ochraceus , produced comparable biomass and lipid concentrations, with a maximum biomass of 22.249 g/L and 21.445 g/L, and maximum lipid of 4.463 g/L and 4.106 g/L, in NDAH and DAH media, respectively, thus indicating that detoxification might be avoided. Detoxifying the medium decreased the concentrations of the fermentation inhibitors furfural, 5-hydroxymethyl furfural (HMF), and acetic acid; however, the microorganism was resistant to the inhibitors, thus demonstrating that bio-oil can be produced from acid-pretreated Pongamia cake without any detoxification procedure. Overall, these results may enable the elimination of additional process and operating costs.

Predictability of Biodiesel Fuel Properties from the Fatty Acid Composition of the Feedstock Oils

Among alternative transport fuels, biodiesel is an eco-friendly substitute for petrodiesel. The quality of biodiesel is dependent on the composition of feedstock oils used for its preparation. The mathematical/statistical tools are used to determine the biodiesel properties, and their outputs are further compared with experimental results for their consistency and reliability. To reduce the cost, efforts and resources, the current study aims to evaluate the predicting ability of the standalone software BiodieselAnalyzer. In the present study, properties of 45 biodiesels are predicted using BiodieselAnalyzer software and the obtained results are compared with earlier published literature. The % absolute relative deviation was found as 4.47% and 5.31% for density and higher heating value, respectively, but the highest deviation was found for kinematic viscosity (70.19%), oxidation stability (131.19%), cloud point (118.57%) and cold filter plugging point (234.17%). The results indicate that the software shows a good performance in predicting the density and higher heating value; however, the software shows poor reliability in predicting kinematic viscosity, oxidation stability, cloud point and cold filter plugging point. This inconsistency might be due to the non-inclusion of factors such as minor oil components, natural antioxidant in oil, oil extraction process, storage conditions of oil, impurities in oil, production processes, oil and biodiesel clean-up process. Based on this work, it is recommended to improve/develop the software in terms of accuracy and precision for predicting the biodiesel properties or adopt experimentation to determine biofuel properties.

A review of bio-oil upgrading by catalytic hydrotreatment: Advances, challenges, and prospects

• Two most common biofuels production techniques including fast pyrolysis and HTL arecovered. • The proposed crude bio-oil upgrading approaches are discussed. • Effects of various upgrading parameters on bio-oil HDO are described. • The mechanism for catalyst deactivation and possible solutions are provided. • Chemistry of major bio-oil model compounds during HDO is thoroughly reviewed. Fast pyrolysis and hydrothermal liquefaction (HTL) have been regarded as the most promising thermochemical conversion technologies for liquid bio-fuels production. However, the poor quality of generated crude bio-oils, such as high O and water contents, low thermal stability, and high corrosivity, limits their direct applications as the alternative transportation fuels. Thus, a number of upgrading techniques mainly including chemical and physical methods have been developed. Among them, hydrotreatment like hydrodeoxygenation (HDO) as a well-established technology at petroleum refinery plants has been widely adopted for upgrading of the crude oil obtained from pyrolysis or HTL. In this review, the effects of various upgrading reaction conditions (temperature, H 2 pressure, solvents, residence time, and catalyst) of HDO treatment of real bio-oil and its mode compounds are thoroughly reviewed. In which, the underlying mechanisms for bio-oil HDO are elucidated with a wide range of its model compounds (lignin-derived oxygenates and carbohydrates-derived oxygenates) and the interaction between these model compounds. Moreover, a discussion regarding the HDO of real bio-oil from pyrolysis and HTL is provided, and the technical/operating problems for the catalytic HDO and the possible solutions are presented. Finally, the important knowledge gaps and future directions are addressed for further investigations.

Use of hydrogen as a source of clean energy

The increase in energy consumption is closely correlated with the continuous evolution of human society, which implies both the depletion of fossil fuels and the increase in pollution levels. One solution to these problems is to obtain electricity from renewable sources but also to use alternative fuels for car transportation. Within the paper, there are presented the necessary conditions for the design of hydrogen gas stations in accordance with the legal requirements in force regarding the protection to explosion.

Long-term production technology mix of alternative fuels for road transport: A focus on Spain

Road transport is one of the main sources of greenhouse gas emissions due to the current dependence on fossil fuels such as diesel and gasoline. This situation needs to be changed through the retirement of fossil fuels and the implementation of alternative fuels and vehicles such as biofuels, battery electric vehicles, and fuel cell electric vehicles fuelled by hydrogen. Nevertheless, the environmental suitability of alternative fuels is conditioned by how they are produced. Through the case study of Spain, this article prospectively assesses – from a techno-economic and carbon footprint perspective– the production technology mix of alternative fuels from 2020 to 2050. The proposed energy systems optimisation model includes a large number of production technologies regarding biofuels (bioethanol, biodiesel, synthetic diesel/gasoline, and hydrotreated vegetable oil), electricity, and hydrogen. The combined study of these fuels provides a relevant framework to discuss the targets established for the road transport sector with a high level of detail not only regarding fuel type but also technology breakdown. The results show the relevance of second-generation biofuel production technologies in fulfilling the future biofuel demand. Regarding the extra electricity demand associated with the penetration of electric vehicles, the results suggest a key role of wind- and solar-based technologies in meeting such a need. Concerning hydrogen as an option to decarbonise the transport system, even though steam methane reforming is the most mature and cost-competitive production technology, hydrogen production would be satisfied through electrolysis in order to avoid relying on fossil resources as the main feedstock. Overall, this integrated approach to the long-term production technology mix of alternative fuels for road transport is expected to be relevant to a wide range of decision-makers willing to prospectively assess road transport systems from a technology perspective.

Modeling Viscosity and Density of Ethanol-Diesel-Biodiesel Ternary Blends for Sustainable Environment

Rapid depletion in fossil fuels, inflation in petroleum prices, and rising energy demand have forced towards alternative transport fuels. Among these alternative fuels, diesel-ethanol and diesel-biodiesel blends gain the most attention due to their quality characteristics and environmentally friendly nature. The viscosity and density of these biodiesel blends are slightly higher than diesel, which is a significant barrier to the commercialization of biodiesel. In this study, the density and viscosity of 30 different ternary biodiesel blends was investigated at 15 °С and 40 °С, respectively. Different density and viscosity models were developed and tested on biodiesel blends soured from different feedstock’s including palm, coconut, soybean, mustard, and calophyllum oils. The prognostic ability and precisions of these developed models was assessed statistically using Absolute Percentage Error (APE) and Mean Absolute Percentage Error (MAPE). The MAPE of 0.045% and 0.085% for density model and 1.85%, 1.41%, 3.48% and 2.27%, 1.85%, 3.50% for viscosity models were obtained on % volume and % mass basis. These developed correlations are useful for ternary biodiesel blends where alcohols are the part of biodiesel blends. The modeled values of densities and viscosities of ternary blends were significantly comparable with the measured densities and viscosities, which are feasible to avoid the harm of vehicles’ operability.

Experimental investigation of compressed natural gas using in an indirect injection diesel engine at different conditions

Because of deficiency of fossil fuels and stringent emission legislations of environmental pollutants, many researches have been done on the sustainable fuel resources. Natural gas ranks as one of the most popular alternative fuels for public transportation due to its lower impact on human health and air quality, low cost, and appropriate availability. The novelty of this experimental work is replacing different mass fractions of diesel fuel with natural gas in an indirect injection diesel engine and evaluating its effect on the emissions of soot and nitrogen oxides, and brake specific fuel consumption in the presence of cold exhaust gas recirculation. The test bed is provided in the internal combustion engine laboratory of the Ferdowsi University of Mashhad by modifications on a naturally aspirated indirect injection diesel engine. Experiments were done at different equivalence ratios with 1200, 2000, and 3000 rpm and at 25, 50, and 75% of the full load in each speed. Replacing 40% mass fraction of input diesel fuel by adding natural gas resulted in a maximum 74% reduction of soot; the reason is a decrease in carbon to hydrogen ratio in the mixture. Also adding 40% natural gas made a maximum 54% reduction in nitrogen oxides mainly because of more homogeneity in the fuel mixture which reduces hot spots in the combustion chamber, and lower nitrogen content in the fuel. Moreover, maximum decrease in brake specific fuel consumption was 15%, due to increase in power output meanwhile lubricated engine friction remains unchanged in each speed. These research engine improvements in average are 62% for NOx and 35% for soot emission indicating acceptable decrease in exhaust emissions in comparison with allowable decrease in Euro emission standards.