The automotive industry remains one of the most significant contributors to total global emissions worldwide. This growing challenge is primarily attributed to the high dependency on fossil fuel as ...its primary source of energy. This review highlights the current state of the application of fuel cells in the automotive industry, as well as the technological advances made in comparison to the early years of the automotive sector. Future prospects of these technologies are also thoroughly reviewed. Factors impeding the advancement of these technologies while also impeding their commercialization are presented, with possible solutions to this problem also suggested. In summary, this investigation seeks to explore pragamatic approach that can be adopted to reduce the overall cost of fuel cells and their possible integration in the automotive industry.
•Regulations on marine diesel engine emissions are listed and compared.•The contribution of marine diesel engine emissions to regional emissions is given.•The emission levels of marine diesel engines ...are reviewed.•Integrated multi-pollutant aftertreatment technologies are reviewed.
Marine diesel engines, which provide main power source for ships, mainly contribute to air pollution in ports and coastal areas. Thus there is an increasing demand on tightening the emission standards for marine diesel engines, which necessitates the research on various emission reduction strategies. This review covers emission regulations and emission factors (EFs), environmental effects and available emission reduction solutions for marine diesel engines. Not only the establishment of the emission control areas (ECAs) in the regulations but also many experiments show high concerns about the sulfur limits in fuels, sulfur oxides (SOx) and nitrogen oxides (NOx) emissions. Research results reveal that NOx emissions from marine diesel engines account for 50% of total NOx in harbors and coastal regions. Sulfur content in fuel oil is an important parameter index that determines the development direction of emission control technologies. Despites some issues, biodiesel, methanol and liquefied nature gas (LNG) play their important roles in reducing emissions as well as in replacing fossil energy, being promising fuels for marine diesel engines. Fuel-water emulsion (FWE) and exhaust gas recirculation (EGR) are effective treatment option for NOx emissions control. Common rail fuel injection is an effective fuel injection strategy to achieve simultaneous reductions in particulate matter (PM) and NOx. Selective catalytic reduction (SCR) and wet scrubbing are the most mature and effective exhaust aftertreatment methods for marine diesel engines, which show 90% De-NOx efficiency and 95% De-SOx efficiency. It can be concluded that the integrated multi-pollutant treatment for ship emissions holds great promise.
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•Waste cooking oil (WCO) recycling models and practices are reviewed.•The processing pathways of converting WCO into biofuels are examined.•Energy balance for biodiesel conversion ...using different techniques is analysed.•Conversion of WCO into biojet fuel is feasible using hydrogenation method.•Biofuel production using WCO is sustainable and reduces GHG emissions.
The increase in human consumption of plant and animal oils has led to the rise in waste cooking oil (WCO) production. Instead of disposing the used cooking oil as waste, recent technological advance has enabled the use of WCO as a sustainable feedstock for biofuels production, thereby maximising the value of biowastes via energy recovery while concomitantly solving the disposal issue. The current regulatory frameworks for WCO collection and recycling practices imposed by major WCO producing countries are reviewed, followed by the overview of the progress in biodiesel conversion techniques, along with novel methods to improve the feasibility for upscaling. The factors which influence the efficiency of the reactions such as properties of feedstock, heterogenous catalytic processes, cost effectiveness and selectivity of reaction product are discussed. Ultrasonic-assisted transesterification is found to be the least energy intensive method for producing biodiesel. The production of bio-jet fuels from WCO, while scarce, provide diversity in waste utilisation if problems such as carbon chain length, requirements of bio-jet fuel properties, extreme reaction conditions and effectiveness of selected catalyst-support system can be solved. Technoeconomic studies revealed that WCO biofuels is financially viable with benefit of mitigating carbon emissions, provided that the price gap between the produced fuel and commercial fuels, sufficient supply of WCO and variation in the oil properties are addressed. This review shows that WCO is a biowaste with high potential for advanced transportation fuel production for ground and aviation industries. The advancement in fuel production technology and relevant policies would accelerate the application of sustainable WCO biofuels.
Bio-based aviation fuels are considered as a promising alternative for conventional aviation fuels due to their sustainability and environmental friendliness. This review evaluated bio-jet fuels’ ...performance based on their physicochemical properties, including low-temperature fluidity, thermal oxidation stability, combustion property, fuel compatibility and volatility, and energy density. The objective is to understand the effects of the chemical compositions of bio-jet fuels on their performance characteristics. This is of particular importance in that bio-jet fuels are generally derived from a broad spectrum of feedstock and thus have very different composition. In general, bio-jet fuels exhibit satisfactory characteristics in compliance with the American Society for Testing and Materials D7566-18 standard. The aromatic content has a critical influence on the performance of bio-jet fuels. Research efforts are needed to study the characteristics of recently certified bio-based blending components such as synthesized iso-paraffins and alcohol-to-jet. Storage stability, a rarely reported property also deserves further investigation.
•Adding primary alcohol fuels increased the ignition delay and reduced the combustion duration.•BTE was decreased, CO and PM emissions were reduced, and THC and NOX emissions were increased by adding ...primary alcohol fuel.•For a fixed ASP, methanol has the lowest COVIMEP and ringing intensity, and the highest BTE among the three alcohol fuels.•Adding methanol produces the highest THC emission and the lowest CO, NOX and soot emissions among the three alcohol fuels.
Primary alcohol fuels are the most promising fuels for diesel engines, thanks to their low emissions and easy adaptability to engine technologies. In this paper, the effects of the addition of methanol, ethanol, and n-butanol on the combustion characteristics and performance of a common rail dual fuel engine with diesel direct injection and alcohol fuel port injection are examined, followed by a comparative analysis of the test results.The test engine was operated at the maximum torque speed of 2500 rpm, and with a mean effective pressure (IMEP) of 0.75 MPa. The engine performance was analyzed for different alcohol/diesel fuel mixtures by using five alcohol substitute percentages (ASPs): 0% (pure diesel), 10%, 20%, 30%, and 40%. The experimental results demonstrate that slower flame development and faster flame propagation can be obtained by mixing any of the three alcohol fuels with diesel, compared with the pure diesel. With an increased ASP, the coefficient of variation of IMEP (COVIMEP) and the brake thermal efficiency (BTE) decreased, and the ringing intensity (RI) first increased and then dropped. The addition of primary alcohol fuels in the dual-fuel mode can also increase the total hydrocarbon (THC) and nitrogen oxide (NOX) emissions, but the carbon monoxide (CO) and soot emissions decrease. The comparative analysis indicated that the addition of methanol has the lowest COVIMEP and RI and the highest BTE among the three alcohol fuels. Adding methanol produces the lowest CO, NOX, and soot emissions and the highest THC emissions among the three alcohol fuels.
•Gasoline/diesel/hydrogenated catalytic biodiesel blends are used.•String cavitation which is incepted by vortex is researched with a real-size optical nozzle.•The addition of gasoline into diesel ...and HCB enhanced cavitation and make the weaker vortex in the sac visible.•Increasing temperature enhanced cavitation and enlarged sprayangle but affects gasoline/HCB blends a few.
Renewable clean fuel such as biodiesel, alcohol-based fuel blended with fossil fuel has been widely studied for applications in engines aiming at partial solution of fuel consumption and environment emission issues. These blending fuels have also shown advantages in new combustion modes like GCI and LTC. However, the fuel injector nozzle internal flow and spray behaviors of these blending fuels are still not well understood, which may largely influence the subsequent fuel–air mixture, combustion, and emission characteristics. The investigation of cavitation flow in the high-pressure common-rail injector nozzle and spray characteristics with blending fuels of gasoline, diesel, and hydrogenated catalytic biodiesel (HCB) was conducted in the present work. The real-size optical nozzle was used to visualize the nozzle internal cavitating flow and spray. It was found that, by adding gasoline into diesel and HCB, the string cavitation increased significantly, and the spray cone angle expanded, especially under low needle lift. This behavior can be interpreted as the lower viscosity and higher saturation vapor pressure of gasoline enhanced vortex and cavitation. It can be concluded that increasing fuel temperature significantly impacted the cavitation and affected the vortex lightly, suggesting that with higher temperatures, blended fuels show better performance. As the fraction of HCB of gasoline/HCB blends increased, the cavitation inside nozzles was restrained due to its high viscosity. String cavitation can be interrupted by the needle tip, and the spray cone angle fluctuated enormously under this situation, which may cause uneven mixing of fuels and air.
In recent years, renewable energy resources have become more important due to the limited number of regions for production of petroleum-based fuels, which are continuously depleting. The aviation ...sector in terms of commercial and cargo transportation has an increasing need for conventional, as well as, alternative fuels. Derivatives of petroleum fuels used in aviation have negative impacts on air quality. Factors causing greenhouse gas emissions (GHG) in the aviation sector must be reduced. However, such fuels used in the aviation sector are not sustainable. Biofuels which have the potential to replace petroleum fuels and help with emissions are heavily investigated in developed countries for independency, creating a better environment and sustainability. Biofuels which are already used for ground vehicles could also be implemented in the aviation sector to reduce fuel cost and emissions. Overall, aviation fuels made of sustainable resources would also support social and economic development. Numerous industrial initiatives have emerged to find alternative ways to attain bio-aviation fuels. Therefore, there is an increasing level of research with regards to alternative aviation fuels made of biomass in recent years. It is important to obtain basic feedstocks and to develop biofuel production processes in a cost-effective way. This study examines the necessity and the types of biofuels in the aviation sector. By designing unique fuel systems for air vehicles, it is possible to formulate biofuels which can be used for both air and ground vehicle applications. This type of consensus would help with sustainability and a better environment.
•Potential use of alternative fuels in aviation is discussed.•Environmental benefits are summarized.•Future of sustainable aviation fuels has proven to have a good trend.
To improve the sustainability of transportation, a major goal is the replacement of conventional petroleum-based fuels with more sustainable fuels that can be used in the existing infrastructure ...(fuel distribution and vehicles). While fossil-derived synthetic fuels (e.g. coal derived liquid fuels) and biofuels have received the most attention, similar hydrocarbons can be produced without using fossil fuels or biomass. Using renewable and/or nuclear energy, carbon dioxide and water can be recycled into liquid hydrocarbon fuels in non-biological processes which remove oxygen from CO2 and H2O (the reverse of fuel combustion). Capture of CO2 from the atmosphere would enable a closed-loop carbon-neutral fuel cycle.
This article critically reviews the many possible technological pathways for recycling CO2 into fuels using renewable or nuclear energy, considering three stages—CO2 capture, H2O and CO2 dissociation, and fuel synthesis. Dissociation methods include thermolysis, thermochemical cycles, electrolysis, and photoelectrolysis of CO2 and/or H2O. High temperature co-electrolysis of H2O and CO2 makes very efficient use of electricity and heat (near-100% electricity-to-syngas efficiency), provides high reaction rates, and directly produces syngas (CO/H2 mixture) for use in conventional catalytic fuel synthesis reactors. Capturing CO2 from the atmosphere using a solid sorbent, electrolyzing H2O and CO2 in solid oxide electrolysis cells to yield syngas, and converting the syngas to gasoline or diesel by Fischer–Tropsch synthesis is identified as one of the most promising, feasible routes.
An analysis of the energy balance and economics of this CO2 recycling process is presented. We estimate that the full system can feasibly operate at 70% electricity-to-liquid fuel efficiency (higher heating value basis) and the price of electricity needed to produce synthetic gasoline at U.S.D$ 2/gal ($ 0.53/L) is 2–3U.S. cents/kWh. For $ 3/gal ($ 0.78/L) gasoline, electricity at 4–5cents/kWh is needed. In some regions that have inexpensive renewable electricity, such as Iceland, fuel production may already be economical. The dominant costs of the process are the electricity cost and the capital cost of the electrolyzer, and this capital cost is significantly increased when operating intermittently (on renewable power sources such as solar and wind). The potential of this CO2 recycling process is assessed, in terms of what technological progress is needed to achieve large-scale, economically competitive production of sustainable fuels by this method.
Natural gas has been proposed as a possible “bridge” fuel to eventual use of hydrogen in zero emission fuel cell vehicles. This literature review explores whether the natural gas system might help ...enable a transition to longer-term use of hydrogen in transportation. Two transition strategies are reviewed: adapting natural gas refueling infrastructure for future use with H2 and blending renewable hydrogen into the NG system.
Our review suggests it is not attractive to re-purpose or overbuild NG fueling station equipment for future hydrogen service. Transporting H2/NG blends in the NG pipeline grid appears technically possible at modest fractions of 5–15% hydrogen by volume, but requires careful case by case assessment and could be expensive. Blending does not enable major reductions in GHG emissions from transport, unless “green” hydrogen can be cost effectively separated from the blend and delivered to highly efficient fuel cell vehicles. Ultimately, blend limits could make it difficult to utilize the existing NG system to deliver hydrogen at the scale needed to achieve deep cuts in transportation related GHGs. A dedicated renewable hydrogen system would be needed, if zero emission fuel cell vehicles play a major role in a future low carbon world.
•NG/H2 synergies constrained by market, technical, economic, network design factors.•Costs unattractive to overbuild natural gas stations for hydrogen compatibility.•Using hydrogen in natural gas grid is complex, renewable methane may be easier fit.•Long term H2 demand might exceed capacity of NG grid to deliver H2 in blend.•In 2 degree world, a dedicated H2 refueling infrastructure would be needed.
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