Spray structures formed by a multi-nozzle injector during the injection of a multi-component surrogate synthetic fuel under flash-boiling conditions

Effect of water content in ethanol on spray formation at subcooled and flash-boiling conditions

This study aimed to investigate the influence of flash-boiling conditions on liquid propane sprays formed by a multi-hole injector at various injection pressures. The focus was on spray structures, which were analysed qualitatively and quantitatively by means of spray-tip penetration and global spray angle. The effect of flash boiling was evaluated in terms of trends observed for subcooled conditions. Propane was injected by a commercial gasoline direct injector into a constant volume vessel filled with nitrogen at pressures from 0.1 MPa up to 6 MPa. The temperature of the injected liquid was kept constant. The evolution of the spray penetration was observed by a high-speed camera with a Schlieren set-up. The obtained results provided information on the spray evolution in both regimes, above and below the saturation pressure of the propane. Based on the experimental results, an attempt to calibrate a simulation model has been made. The main advantage of the study is that the effects of injection pressure on the formation of propane sprays were investigated for both subcooled and flash-boiling conditions. Moreover, the impact of the changing viscosity and surface tension was limited, as the temperature of the injected liquid was kept at the same level. The results showed that despite very different spray behaviours in the subcooled and flash-boiling regimes, leading to different spray structures and a spray collapse for strong flash boiling, the influence of injection pressure on propane sprays in terms of spray-tip penetration and spray angle is very similar for both conditions, subcooled and flash boiling. As for the numerical model, there were no single model settings to simulate the flashing sprays properly. Moreover, the spray collapse was not represented very well, making the simulation set-up more suitable for less superheated sprays.

Experimental study of the spray collapse process of multi-hole gasoline fuel injection at flash boiling conditions

Local momentum flux measurement: An effective way for GDI spray targeting in flash boiling conditions

<div class="section abstract"><div class="htmlview paragraph">A novel one-dimensional multiphase and multicomponent spray model - hereafter referred to as the Kattke-Weigand model - has been developed to predict the penetration length of both vapor and liquid gasoline sprays under flash-boiling conditions, such as superheated injections. Its formulation is based on mass and momentum equations for unsteady jets and is therefore capable of capturing dynamic effects. Experiments were conducted in a constant volume chamber using various ambient and fuel temperature conditions and a six-hole GDI injector with a separated jet. Macroscopic spray parameters were extracted from the measurements to verify the model's ability to predict both liquid and vapor penetration length and the corresponding spray angles.</div><div class="htmlview paragraph">Apart from the separated jet of the injector used, the other five jets interact strongly with each other under flash boiling conditions, resulting in spray collapse, and thus affecting spray characteristics. The prediction of collapse is very sensitive to calculations of vaporization and air entrainment. Since these submodels cannot be validated directly, a calibration method was developed, that is based on a three-dimensional reconstruction of all fuel sprays of the injector used. For this purpose, all optical measurements performed in the constant volume chamber are utilized. As a result, a three-dimensional representation of the spray collapse can be calculated from the combination of the 3D spray reconstruction and the entrainment and vaporization submodels. The validation of the collapse leads indirectly to the calibration of the entrainment and vaporization submodels in the Kattke Weigand model. Latter is applied to gain a deeper understanding of the interaction between spray collapse and both liquid and vapor phase penetration.</div></div>

Flash-boiling of fuel sprays can occur when the fuel enters a metastable superheated state, which is common in direct-injection spark-ignition engines operating at low in-cylinder pressures and/or hot fuel temperatures. The effect of flash-boiling on the resultant spray formation can be both detrimental and advantageous to engine operation, hence numerical modelling capability is essential in future engine optimisation and design. A recently-developed new model by the current authors that can be applied as zero-dimensional boundary condition for multi-hole flash-boiling fuel spray predictions was investigated over a wide range of injection systems, focusing on the model’s ability to quantify in-nozzle phase change effects and automatically predict important global spray characteristics such as spray collapse, droplet recirculation and plume merging within a Lagrangian particle tracking framework. Mesh-type sensitivity was highlighted using a uniform Cartesian and a non-uniform polyhedral mesh. The model was also normalised through a dimensionless parameter for a wide range of single component fuels. The model was validated both qualitatively and, where possible, quantitatively against experimental data. The model’s ability to deal with a wide range of injection configurations and operating conditions was confirmed and a number of limitations are highlighted and discussed with respect to future work.

<div>Renewable synthetic fuels offer the opportunity to significantly reduce carbon dioxide (CO<sub>2</sub>) emissions worldwide if burned in the internal combustion engines of existing and future passenger car fleets. To evaluate this potential, two renewable synthetic gasoline fuels and alcohol blends that can be produced via the methanol-to-gasoline (MtG) synthesis process are evaluated in this study. The first synthetic gasoline, hereafter referred to as MtG, was developed by Chemieanlagenbau Chemnitz GmbH and Technische Universität Bergakademie Freiberg, produced within the closed carbon cycle mobility (C<sup>3</sup>-Mobility) project, and was blended with 10%(V/V) ethanol (MtG-E10), 20%(V/V) ethanol (MtG-E20), 15%(V/V) methanol (MtG-M15), and 15%(V/V) 2-butanol (MtG-2Bu15). The second synthetic fuel, named POSYN (POrsche SYNthetic fuel), was developed by Porsche. The suitability of the synthetic fuels was experimentally investigated in a spark-ignition (SI) single-cylinder research engine with a compression ratio (CR) of 10.8 and compared with conventional gasoline fuel with Research Octane Number 95 and 10%(V/V) ethanol (RON95 E10) gasoline fuel. Load variations at a constant engine speed of 2500 rpm showed no significant differences between Methanol-to-Gasoline with 10%(V/V) ethanol (MtG-E10) and RON95 E10 in terms of both combustion performance and emissions. Additionally, a load variation with MtG-E10 and RON95 E10 at an engine speed of 3000 rpm was performed on a commercially available BMW multi-cylinder engine (MCE), which confirmed that both these fuels show an almost identical combustion and emission behavior. However, the knock resistance improved with higher alcohol fractions. Because of the favorable anti-knock properties of methanol, Methanol-to-Gasoline with 15%(V/V) methanol (MtG-M15) showed the highest maximum net indicated efficiency of 39.33%. This is 2% more than with Methanol-to-Gasoline with 20%(V/V) ethanol (MtG-E20), despite the lower alcohol volume fraction. In contrast, Methanol-to-Gasoline with 15%(V/V) 2-butanol (MtG-2Bu15) showed no improvement. POSYN enabled a significant efficiency advantage over RON95 E10 because of its high knock resistance, however, achieved the same maximum engine load because of the reduced octane sensitivity. The variation of the relative air/fuel ratio at an engine speed of 2500 rpm and an engine load of 16 bar net indicated mean effective pressure confirmed these findings. The highest net indicated efficiency of 42.4% was achieved with POSYN at a relative air/fuel ratio of 1.6. The lean limit could not be increased with the synthetic fuels and alcohol blends albeit with an improved combustion stability.</div>

Investigation of two-hole flash-boiling plume-to-plume interaction and its impact on spray collapse

Our way of life is on a collision course with geological limitations. Ever since petroleum geologist M. King Hubbard correctly predicted in l956 that U.S. oil production would reach a peak in l973 and then decline (1), scientists and engineers have known that worldwide oil production would follow a similar trend. Today, the only question is when the world peak will occur.The U.S. transportation system depends almost entirely (∼97%) on oil (2), and foreign imports have risen steadily since l973 as the demand increased and domestic supplies decreased. Today, more than 60% of U.S. oil consumption is imported and the dependence on foreign oil is bound to increase. There is no question that once the world peak is reached and oil production begins to drop, either alternative fuels will have to be supplied to make up the difference between demand and supply, or the cost of fuel will increase precipitously and create an unprecedented social and economic crisis for our entire transportation system.Among energy analysts the above scenario is not in dispute. There is, however, uncertainty about the timing. Bartlett (3) has developed a predictive model based on a Gaussian curve similar in shape to the data used by Hubbard as shown in Fig. 1. The predictive peak in world oil production depends only on the assumed total amount of recoverable reserves. According to a recent analysis by the Energy Information Agency (4), world ultimately recoverable oil reserves are between 2.2×1012 barrels (bbl) and 3.9×1012bbl with a mean estimate of the USGS at 3×1012bbl. But changing the total available reserve from 3×1012bbl to 4×1012bbl increases the predicted time of peak production by merely 11yr, from 2019 to 2030. The present trend of yearly increases in oil consumption, especially in China and India, shortens the window of opportunity for a managed transition to alternative fuels even further. Hence, irrespective of the actual amount of oil remaining in the ground, peak production will occur soon and the need for starting to supplement oil as the primary transportation fuel is urgent because an orderly transition to develop petroleum substitutes will take time and careful planning.Some analysts claim that hydrogen can take the place of petroleum in a future transportation system (56). But in previous publications, the authors have shown that hydrogen is inferior as an energy carrier to electricity (7) and that the energy efficiency of hydrogen vehicles, especially if the hydrogen were produced by the electrolysis of water, is considerably less than the efficiency of hybrid electric vehicles or fully electric battery vehicles (7). The results of these analyses have subsequently been confirmed by other studies, particularly those by Hammererschlag and Mazza (8) and Mazza and Hammerschlag (9).Before hydrogen could become a useful automotive fuel, an entirely new system of energy production and distribution on twice the scale of today’s electric power generating stations and distribution grid would have to be built. It has been estimated that a hydrogen transmission and storage system to fuel only 50% of the automotive fleet by the year 2020 would cost at least $600 billion (10) and that to make the hydrogen by electrolysis would require doubling the electric power generation rate (11). There is no question that a paradigm shift in fuel for worldwide transportation is imperative, and before embarking on such a huge investment, it is prudent to compare the hydrogen option with alternative ways to provide the energy and/or fuel needed by the transportation system.This paper presents and analyzes two generic approaches to meet the future demand of the U.S. ground transportation systems that do not require hydrogen, can use existing transmission infrastructure, and can eventually reduce CO2 emission drastically with a renewable energy system. Both these pathways are examined from an energetic and environmental perspective and are shown to be superior to the hydrogen economy on both these criteria. The first approach is a demand-side strategy based on the use of electric hybrid vehicles, an energy-efficient vehicle configuration, combined with a liquid fuel. This approach could use the existing liquid-fuel distribution system, but would need an expanded and robust electric-transmission system, albeit on a smaller and much more economical scale than a hydrogen fuel-cell infrastructure. The second approach is a supply-side strategy, based on synthetic fuel generation that can use initially coal or natural gas as the energy source, but can eventually transition to renewable biomass sources. The two pathways are not mutually exclusive, but can be combined into a secure and efficient future transportation system as will be shown in this paper.Cradle-to-grave energy efficiency is an important criterion for comparing energy-source utilization pathways because if a pathway is less efficient than another pathway that accomplishes the same final goal from the same amount of primary energy, then the less efficient pathway requires more primary energy to accomplish the same end. Hence, if the primary energy source is nonrenewable, then the less efficient pathway leaves less of the energy source for the future. It also means that more pollution is produced and the cost for the final end use is likely higher. However, if the primary energy source is renewable, then the efficiency does not change the amount of primary energy available in the future and energy efficiency does not have the same significance for renewable energy sources as for nonrenewable sources. Efficiency is, of course, important because the cost of delivering the energy is usually strongly influenced by the system efficiency. But a comparison between renewable and nonrenewable pathways should be based on economic and environmental criteria, such as cost and CO2 generation.In order to demonstrate the urgency for initiating a plan to supplement oil as soon as possible, we have made calculations to predict the potential gasoline savings based on the very optimistic scenario that, at an arbitrary starting time, all new light vehicles sold in the U.S. would be either hybrid or electric vehicles. The term “light vehicles” as used here includes all automobiles, family vans, sports utility vehicles, motorcycles, and pickup trucks. This scenario is an extreme case to show that because of the slow turnover of the light-vehicle fleet, it takes a long time for a significant impact on gasoline consumption to occur. The following cases are considered: (i) All new vehicles sold are gasoline-electric hybrid vehicles (HEV); (ii) all new vehicles sold are plug-in, gasoline-electric hybrids with a 20mil electric-only range (PHEV20); (iii) all new vehicles are diesel-electric hybrids (DHEV) with diesel fuel from coal or biomass; (iv) all new vehicles are plug-in, diesel hybrids with a 20mil all-electric range (PDHEV20); or (v) all new vehicles are all-electric vehicles (EV).The calculations use a rate of new vehicle sales of 7% of the fleet per year, a retirement rate of 5%/y, and a resulting net increase in total vehicles of 2%/y. These numbers represent an approximate fit to the light-vehicle sales and total number data for the years 1966 to 2003 reported by the U.S. government (12). All calculated results are presented in percentages and are therefore independent of the time at which all new vehicle sales switch to hybrids or EVs. When new car sales begin to be all hybrids or all EVs, it is assumed that the future rate of retirement of vehicles from the all-gasoline fleet is 5%/y of the remaining gasoline vehicles. The all-gasoline fleet is therefore completely retired 20 years later. The yearly rate of retirement of hybrid or EV vehicles is then 5% of the total number of vehicles at the beginning of that year, less 5% of the number of gasoline vehicles at the beginning of year zero. Thus, in year zero, no hybrid or EVs are retired.The following average vehicle mileage values were used: gasoline fleet, 21mpg (miles per gallon); gasoline HEV, 41mpg; gasoline PHEV 20, 56mpg of gasoline (13). A mileage is not needed for the EVs, or the diesels, since neither use gasoline, and we assume that the diesel fuel will be derived from nonpetroleum sources, as discussed in Secs. 34.The results of these calculations are presented in Figs. 234. Figure 2 shows the ratio of the total number of vehicles in the fleet, the number of all-gasoline vehicles in the fleet, and the number of hybrid or EV vehicles in the fleet to the total number in the fleet as a function of time. The total number of vehicles increases by over 60% in 25 years at the assumed 2%/y net increase while the number of all-gasoline vehicles decreases linearly from 100% initially to 0% after 20y. The number of hybrid or EV vehicles increases from 0% initially to 58% in 10y and 100% in 20y. This graph emphasizes how long it takes for the introduction of a new vehicle type to show a significant impact on the composition of the vehicle fleet, even when only the new vehicle types are sold after a starting point. This slow turnover of the fleet is the fundamental reason that the effects on gasoline consumption show up so slowly.Figure 3 shows the annual reduction in gasoline consumption as a function of time. Note that for HEVs the annual savings in gas consumption is 29% of the gasoline consumption for a conventional fleet in the tenth year and becomes constant at 49% in the twentieth year. Figure 3 also shows that the plug-in gasoline hybrid scenario saves 41% of the usage in the tenth year and increasing to 64% in the twentieth year and thereafter. Clearly, 10y after starting to sell only hybrid or EV vehicles, the impact of the HEV or PHEV20 scenarios on gasoline consumption is still rather small. After 20yr, the impact becomes significant, but gasoline consumption still remains high for gasoline hybrids. The total number of vehicles and the consumption (with the assumption of no efficiency improvement) by an all-gasoline fleet will have increased by more than 60%, but even the PHEV20 savings is only 40% of the zero-time annual-rate of gasoline consumption. The DHEV, DPHEV20, and EV scenarios show 59% annual savings in the tenth year and 100% in the twentieth year and thereafter. As would be expected, the nongasoline vehicles have a much greater impact on gasoline usage than gasoline-using HEVs, and the impact occurs more rapidly.Figure 4 gives the cumulative gasoline savings for the various scenarios compared to an all-gasoline fleet. HEVs save cumulatively 16% after 10yr and 20% after 20 years. Because of the cumulative savings, HEVs would use in 28yr the same amount of gasoline as an all-gasoline fleet would use in 20yr. PHEV20s save 21% after 10yr and 38% after 20yr. These results emphasize the relatively small effect on gasoline consumption that these highly optimistic scenarios have in the first decade after implementation. DHEVs, DPHEV20s, and EVs, the options without any gasoline use, save cumulatively as much as 32% after 10yr and 59% after 20yr.A 2004 report of the Committee on Alternatives and Strategies for Future Hydrogen Production and Use (14), prepared under the auspices of the National Research Council (NRC), concluded that the vision of a hydrogen economy is based on the expectation that hydrogen can be produced from domestic energy sources in a manner that is “both affordable and environmentally benign.” An analysis of currently available technologies for achieving this goal (7) showed that irrespective of whether fossil fuels, nuclear fuels or renewable technologies are used as the primary energy source, hydrogen is inefficient compared to using the electric power or heat from any of these sources directly. Given these facts, it is important to note that the NRC report also stated that “If battery technology improves dramatically, all-electric vehicles might become the preferred alternative (to fuel cell electric vehicles).” The report also noted that “Hybrid vehicle technology is commercially available today and can therefore be realized immediately.” If synthetic fuels made from coal, natural gas, or biomass were used in place of gasoline in hybrid vehicles, the consumption of oil could be reduced immediately and eventually eliminated. In the light of these observations, it is therefore important to examine what the current state of battery technology is, what can be expected in the near future, and how these developments affect the potential of hybrid vehicle performance and economics.To assess the performance of a battery for electric vehicles, the following characteristics have to be considered: Specific energy, a measure of the battery weight in units of watt hours per kilogramEnergy density, a measure of the space the battery occupies in watt hours per cubic meterCapacity, the total quantity of energy a battery can store and later deliver in watt hoursEfficiency, the ratio of energy that can be extracted from the battery to the initial energy input to change the batterySpecific power, the rate at which the battery can deliver the stored energy per unit weight of battery in watts per kilogramBattery lifecycle, the number of charge and discharge cycles that a battery can sustain during its lifeA significant effort to replace oil as a transportation fuel was undertaken ten years ago in California, when the California Air Resources Board [CARB] mandated that a certain percentage of all vehicles sold in California had to have zero tailpipe emissions (15). At that time the only technology available to meet the mandate was the all battery electric vehicle [BEV], which required no gasoline for its operation. The experiment to mandate the use of BEVs in California failed because the technology was not ready for commercialization. The best battery available in 1995 (fluted-tubular lead acid) had an energy storage density of 35Wh∕kg, a specific power of 100W∕kg, and a life cycle of 600-1000cycles. With these battery characteristics, the maximum range of a BEV was only 50mil, and the battery pack required replacement every 25,000mil at a cost of between $7000 and $8000 for an average BEV (16). Since that time, new batteries have been developed by Panasonic, VARTA, and SAFT, that have twice the energy-storage density, three times the specific power, and two or three times the cycle life of the lead acid batteries sold in California, as shown in Table 1 (13).In addition to the advanced batteries, a new concept has been developed that combines the best qualities of hybrid and battery vehicle technologies. This “plug-in hybrid vehicle” can recharge vehicle batteries during off-peak hours, and since most cars are parked 90% of the time, there are plenty of charging opportunities at both home and the workplace. Furthermore, a large portion of the electric generation infrastructure is only needed for peak demands and lays idle much of the time. Hence, if charging automobile batteries occurred during off-peak hours, they would level out the load of the electric production system and reduce the average cost of electricity (17). Moreover, plug-in hybrid vehicles are not range limited because they have an engine that can refuel at existing gas stations to use when the batteries are low.The efficiency of a PHEV depends on the number of miles the vehicle travels on liquid fuel and electricity, respectively, as well as on the efficiency of the prime movers according to1η=energytowheelsenergyfromprimarysource=f1η1η2+f2η3η4where η1 is the efficiency of the primary source of electricity, η2 is the efficiency of transmitting electricity to the wheels, f1 is the fraction of energy supplied by electricity, f2 is the fraction of energy supplied by fuel =(1−f1), η3 is the efficiency of primary source to fuel, and η4 is the efficiency of fuel to wheels.PHEVs can be designed with different all-electric ranges. The distance, in miles, that a PHEV can travel on batteries alone is denoted by a number after PHEV. Thus, a PHEV20 can travel 20mil on fully charged batteries without using the gasoline engine. According to a study by EPRI (13), on average 1/3 of the annual mileage of a PHEV20 is supplied by electricity and 2/3 by gasoline. The percentage depends, of course, on the vehicle design and the capacity of the batteries on the vehicle. A PHEV60 can travel 60mil on batteries alone, and the percentage of electric miles will be greater as will the battery capacity.The tank-to-wheel (more appropriately, battery-to-wheel) efficiency for a battery all-electric vehicle according to EPRI (13) is 0.82. In a previous analysis by the authors (18), the efficiency in 1993 was only 0.49. Comparing these results shows the enormous improvements in the electric component efficiency (controller 87%, battery 90%, charger 90%, drivetrain 90%;). When these numbers are multiplied by a hybrid-weight-times-idle factor of 1.3 (19), the overall efficiency of an electric hybrid is 82%, the same as that used in the EPRI study (13). It is important to note that currently all-electric vehicles can be nearly twice as efficient as when (18) was published.Given the potentials for plug-in hybrid vehicles, the Electric Power Research Institute (13) conducted a large-scale analysis of the cost, the battery requirements, and the economic competitiveness of plug in vehicles today and within the near term future. Table 2 presents the net present value of life-cycle costs over ten years for a midsized combustion vehicle [CV], hybrid vehicle [HEV] and a plug in electric vehicle with a 20mil electric-only range [PHEV20]. The battery module cost in dollars per kilowatt is the cost at which the total life-cycle costs of all three vehicles would be the Figure presents cost for battery as a function of number of units produced per year. According to this a production of about units per year units would the cost reduction to make both hybrid electric vehicles and plug in electric vehicles 3 presents the electric and plug-in hybrid vehicle battery that would be to make electric vehicles cost for vehicles according to EPRI (13). As shown in Table the characteristics of batteries, and batteries are to meet the required cost and performance The battery characteristics shown in Table 1 and Fig. are years and it is likely that more from would show Furthermore, the EPRI study assumed a current gasoline cost of A of the analysis based on a gasoline cost of that the battery at which the net present values of conventional combustion vehicles and battery vehicles are would up from to for an HEV and from to for a PHEV Figure shows the cost for batteries production for Hence, it that the cost of HEVs and with available batteries is with that of engine The EPRI analysis is because it compared the performance of all battery electric and plug in hybrid vehicles only to currently available combustion as shown in the use of diesel in a hybrid would increase the efficiency of compared to a hybrid with engine and the amount of fuel Hence, it be concluded that the EPRI analysis is it includes advanced batteries, it does not the increased efficiency by using diesel of combustion Furthermore, diesel fuel, as will be shown in can be produced from coal or renewable sources as can the electric power required for charging the The introduction of to the energy is the of this it is and can be as renewable technologies become more cost and fossil fuels more natural gas and biomass can be into liquid the most fossil fuel in the is used almost to In order to make coal into a vehicle fuel, it first be to a gas by a of The of this then be to of that can be used as vehicle fuel. biomass and natural gas can be used of coal or combined with coal to make these and are discussed gas can be used as a vehicle fuel, or it can be with to make gas, which can be used to fuels in the same manner as for The technology is well developed as shown by the recent of of which will natural gas, which is currently to liquid fuel. These and a in of which is diesel in With a with an estimated billion and a diesel with the of with an estimated at The of natural gas to make vehicle fuels was discussed in an paper by the authors (18), and of those results are presented later for comparison with coal as the fuel It should also be noted that biomass can be either alone or in with coal and to liquid fuels by the same as coal, or it can also be and then into vehicle fuels as in is a that is a in the production of synthetic liquid fuels from coal for transportation The coal is shown in Fig. It a such as coal or with to and This gas can be to hydrogen or to make or can be used as a transportation fuel in but this study on diesel fuel because are more the first of the coal is with limited to and The in the coal is to hydrogen gas, and are as In the shift is with to and The and hydrogen are from the and to the or into The that is in this is from the in a for Thus, it can be from the and are the costs when liquid fuel is produced from The estimated time of for a is to years. The depends on the production capacity of the the cost of a with a capacity to barrels of liquid fuel per is estimated to be of the order billion of coal claim that there will be gas pollution from the However, in the future vehicle emissions of can be reduced those of vehicles, by the use of plug-in hybrid electric vehicles and by of the from the fuel production is a synthetic diesel fuel that can be made from coal by of The is first to make which can then be to The is to the and the gas is to electricity for the as shown in Fig. is a gas at but can be under and then can be to other liquid of make it an fuel for It is similar to but has a number The number to the of a fuel to With combustion of the fuel occurs after and emissions are as a of combustion The combustion also in by the need for to the shown in Fig. coal into liquid fuel. The was by scientists before and is used today in by to make diesel fuel gas to make a liquid fuel of synthetic diesel fuel, which is similar to and which is used to make synthetic gasoline (7). The is from the liquid diesel and to the The gas resulting from is to electricity for the can be made from coal by by gas After the hydrogen gas and are from the gas, and hydrogen are The hydrogen can be stored and the can be for electricity and/or to the shift as shown in Fig. store and the hydrogen, it is either to it to or to it at a The efficiency of the first option is while the second is efficient (7). Both and hydrogen have been for fuel storage in a of hydrogen fuel-cell vehicles is in the of coal or natural gas into a vehicle fuel. The energy efficiency of these is important in the overall well to efficiency of these alternative Table 4 presents or efficiency for various fuels from coal or natural and have reported the and energy for with of the and values are used (18) presented for natural gas without and estimated that of CO2 the efficiency of by about two percentage Since natural gas only about as much per unit of energy as coal, it has been assumed that will reduce the efficiency of to fuels by percentage point. Thus, percentage has been from values reported by (18) to the values shown in Table In the of data for the of natural gas to the authors assumed that the ratio of the for natural gas is the same as that for coal to estimate this efficiency as shown in Table 4 that the production of liquid fuels from natural gas is more efficient than from But is in and the technology is not a It is however, for the that is currently into the in gasoline The of of these has been But production is the more for the term and does not require hydrogen as a fuel or energy Today, the of fuel from coal, at the only in The of supplies of such fuels as gasoline, and The economic and of coal have been U.S. and for a fuel in using technology and are to the that will have a capacity to of diesel fuel. has in recent NRC study other technologies that could synthetic fuels from biomass and presents a comparison of the energy on energy for production from and These significant in synthetic But the for synthetic fuel production need to be multiplied before synthetic fuels can make up for the between demand and of gasoline after the peak in oil production is on the analysis presented in this we the following and oil production is expected to peak within the and as is liquid fuel are expected to increase This could lead to a crisis in the U.S. transportation system that on 60% of which is options for a transportation crisis by and/or liquid fuels derived from petroleum with synthetic fuels from natural gas, or coal and by demand by increasing the efficiency and mileage of options to have impact they be at least before hybrid vehicles are a option to reduce the liquid fuel consumption of future transportation hybrid vehicles can the existing infrastructure for electric power transmission by charging batteries during peak hours and use liquid fuels only for a fraction of overall power hybrid vehicles can diesel that can be by synthetic fuels derived from coal, natural gas, or use efficiency is increased efficiency alone will not be to the transportation without the production of large of synthetic liquid number of technologies for synthetic diesel that can be used in diesel and reduce emission of that lead to scale of effort required to provide synthetic fuels will require years to and should therefore be as soon as hybrid or all-electric vehicles with available battery technology in an are compared to gasoline of the of the transportation it is that be by government such as for the of synthetic fuels and CO2 high liquid fuel mileage for automobiles, and for efficient plug-in hybrid scenario in this paper for a secure transportation system can be immediately with available technologies and without hydrogen or authors to for as of an independent study for the of at the of

In recent decades, stringent emission norms have been enforced upon the engine research community and OEMs to encourage them to develop new spark ignition engine technologies, such as variable valve lifts, turbocharging, and direct injection spark ignition (DISI) engines. For further development, greater control of parameters such as in-cylinder air motion, spray characteristics, injection, and ignition events is required. Spray characterizations are crucial for understanding the mixing phenomena in heated and pressurized engine combustion chamber conditions. Spray pattern, fuel injection pressure (FIP), rate shape, and thermodynamic conditions of the combustion chamber play a vital role in the mixture preparation. The present study uses Mie-Scattering techniques to examine spray structures of fuels like methanol and ethanol and compare them to gasoline, which is of great interest to DISI engines. Three different temperatures of 50, 100, and 200°C and two chamber pressures, 4 and 8 bar, are considered to simulate typical engine-cylinder conditions. It is observed that the initial chamber conditions greatly influence the spray structure. Spray collapse is lesser for alcohol than gasoline. Three semi-empirical models for predicting spray penetration are analyzed: Dent, Hiroyasu and Arai, and Arrègle. These models could not differentiate between the test fuels, particularly methanol and ethanol, for predicting spray penetration length. The degree of deviation in predictions is the lowest in the Hiroyasu and Arai model and the highest in the Dent model. Spray penetration length increased with an increasing FIP regardless of ambient conditions; however, the spray penetration length decreased with increasing chamber pressure.

<div class="section abstract"><div class="htmlview paragraph">The continuous improvement of spark-ignition direct-injection (SIDI) engines is largely attributed to the enhanced understanding of air-fuel mixing and combustion processes. The intricate interaction between transient spray behavior and the ambient flow field is important to unveil the airflow dynamics during the spray injection process. This study investigates the fuel-spray boundary interactions under different superheated conditions by analyzing the ambient flow field pattern with constraint-based modeling (CBM). In the experimental setup, superheated conditions are facilitated by adjusting different fuel temperatures and ambient pressures. By adding the tracer particles containing Rhodamine 6G to the ambient air, the combined diagnostic of fluorescent particle image velocimetry (FPIV) and Mie-scattering is implemented to measure the velocity distribution and flow trajectory of the air surrounding the spray formation and propagation. For analytical analysis, a data-driven approximation method is developed by utilizing the spatiotemporal characteristics of spray-air boundary interaction. Specifically, a piecewise exponential regression model is proposed with 6 model coefficients and three segment boundaries. The segment boundaries of the piecewise expression align well with the boundary position between the entrainment, recirculation, and spray-tip regions. Further analysis of the coefficients of the regression model reveals different time-evolving flow field patterns under sub-cooled and flash-boiling conditions. For most non and transitional flash-boiling conditions, the model reaches over 90% reconstruction accuracy compared to the experimental result. Moreover, detailed model coefficient analysis suggests that the temporal development of ambient flow field pattern could be accurately captured from an explicit exponential expression. For flare flash-boiling conditions, more intense atomization near the injector would result in more intense entrainment velocity near the injection region. Besides, flare flash-boiling would increase the area of the recirculation region and subsequently decrease entrainment and spray-tip area. Furthermore, the momentum of the ambient flow is primarily aggregated within the recirculation region, resulting in lower entrainment and diffusion intensity at the other two regions. In conclusion, this work proposes an innovative CBM approach to investigate the spatiotemporal flow field patterns and sheds light on the potentials of low-latency time-series flow field prediction.</div></div>

During certain operating conditions in spark-ignited direct injection engines (GDI), the injected fuel will be superheated and begin to rapidly vaporize. Fast vaporization can be beneficial for fuel–oxidizer mixing and subsequent combustion, but it poses the risk of spray collapse. In this work, spray collapse is numerically investigated for a single hole and the spray G eight-hole injector of an engine combustion network (ECN). Results from a new OpenFOAM solver are first compared against results of the commercial CONVERGE software for single-hole injectors and validated. The results corroborate the perception that the superheat ratio Rp, which is typically used for the classification of flashing regimes, cannot describe spray collapse behavior. Three cases using the eight-hole spray G injector geometry are compared with experimental data. The first case is the standard G2 test case, with iso-octane as an injected fluid, which is only slightly superheated, whereas the two other cases use propane and show spray collapse behavior in the experiment. The numerical results support the assumption that the interaction of shocks due to the underexpanded vapor jet causes spray collapse. Further, the spray structures match well with experimental data, and shock interactions that provide an explanation for the observed phenomenon are discussed.

<div class="htmlview paragraph">A previously developed injection system model has been enhanced including a quasi-dimensional, multi-zone, direct injection (DI) diesel combustion model, with the aim of taking into account the actual injection process, the spray formation and the droplet heating-vaporization processes. Such a goal is obtained by means of the integration of different modeling approaches. In a commercial simulation environment, a lumped parameter mechanical-hydraulic scheme is used to model the injection process, in terms of fuel flow rate and injection pressure. The spray formation processes and the droplet vaporization phenomena are then implemented in a self developed computation code, accounting for finite thermal conductibility of the liquid phase fuel. The coupling among the models allows for a detailed representation of the involved phenomena at each simulation step (e.g. fuel time pressure history, fuel properties, atomization, evaporation ambient condition); at the same time, it is possible to evaluate the operation of the injection system on the basis of atomization, vaporization and combustion behavior. The results of the numerical prediction are compared to experimental data referred to a DI diesel engine.</div>

Experimental investigations of fuel breakup very close to nozzle of practical high-pressure swirl injector, which is used in direct injection spark ignition (DISI) engine, were carried out. In DISI engines, fuel is directly injected into cylinder therefore the spray characteristics and mixture formation are of primary importance. Many experimental investigations using several measurement techniques like laser sheet method with high-speed camera, LIF or PDA have been carried out for better understandings of spray and combustion characteristics. However, experimental investigations of atomization process were restricted due to very high-speed and very small region phenomena. Although scale-up models have been used to study the primary spray structure, it is impossible to match Reynolds, Weber, and cavitation numbers and time scales in practical high-pressure swirl injector. Microscopic investigation of primary spray structure of practical swirl injector is needed. On the other hand, numerical simulations have been conducted for better understanding of spray formation process. These researches indicated qualitatively good agreement, but the initial conditions, such as liquid sheet thickness and break-up length, were not accurately since break-up process of the liquid sheet from swirl injector has not been examined. In numerical simulation of spray behavior, a sub-model for atomization phenomena is very important. Therefore the primary atomization process and the break-up process of liquid sheet play an important role. In this research, visualizations of primary spray formation process were demonstrated using a high-speed video camera (maximum speed: Imfps) with a long-distance microscope. Initial state and development of the spray were discussed under the different ambient (back) pressure condition. During the injection period, the length and thickness of the liquid sheet, which is produced from the nozzle exit, were measured using Ar-ion laser sheet and high-speed camera. Moreover, fluctuations of the length and thickness of liquid sheet were discussed. Three main conclusions were drawn from this study. (1) It has been shown that the liquid fuel column without swirl motion was injected as a compact jet at the beginning of the injection. During the injection period, the spray indicates the quasi-steady state mode. (2) Liquid film sheet has a ligament structure. Using Ar-ion laser sheet and high-speed camera, length and thickness of the liquid sheet can be measured. (3) Surface waves of liquid sheet can be recognized. Higher ambient (back) pressure makes shorter wavelength of surface waves of liquid sheet of swirl injector.

<div>In the last years, new stringent emission legislation in terms of nitrogen oxides (NO<sub>x</sub>) has been leading to a massive development of advanced after-treatment systems for diesel engines. Among them, selective catalytic reduction (SCR) technology has proved to be an effective approach for NO<sub>x</sub> reduction in a wide range of engine operating conditions. In SCR systems, the interaction between diesel exhaust fluid (DEF) and hot exhaust gas is crucial to promote the chemical reactions through which ammonia is produced. Hence, a proper matching between the exhaust pipe architecture and the DEF spray is mandatory for obtaining an adequate SCR efficiency, especially in close-coupled configurations and moderate exhaust gas temperature conditions. To this end, significant benefits could be derived via appropriate SCR injector thermal management, as the spray structure is significantly influenced by the DEF temperature upstream of the injector nozzle.</div> <div>In this article, the results of a spray analysis campaign carried out on a prototype DEF dosing system are presented. The goal of this research is to investigate the influence of both air and DEF temperature upon spray structure and atomization. In a previous investigation, preliminary tests were carried out using a hot flow bench (HFB) in order to perform spray evolution and SCR system efficiency analyses in realistic flow rate and temperature conditions. In the current investigation, a deeper analysis was carried out individually controlling DEF and test vessel air temperature, with the spray evolving in quiescent hot conditions. Mie scattering and Schlieren spray images were simultaneously acquired in order to investigate both liquid and vapor spray phase evolution, in order to perform a characterization of spray global structure. In the same conditions, a dedicated test campaign was carried out to perform drop sizing analysis. Some of the most significant results are discussed, along with their possible effects in real exhaust system applications.</div>