In an effort to reduce harmful pollutants emitted by medium and heavy duty diesel engines, stringent emission regulations have been imposed by the Environmental Protection Agency (EPA) and the California Air Resources Board (CARB). Effective aftertreatment thermal management is critical for controlling tail pipe outlevels of NOx and soot, while improved fuel efficiency is also necessary to meet greenhouse gas emissions standards and customer expectations. Engine manufacturers have developed and implemented several engine and non-engine based techniques for emission reduction, a few examples being: exhaust gas recirculation (EGR), use of delayed in-cylinder injections, exhaust throttling, electric heaters and hydrocarbon dosers. This work elaborates the use of variable valve actuation strategies for improved aftertreatment system (ATS) thermal management of a modern medium-duty diesel engine while presenting opportunities for simplification of engine air handling architecture.<div><br></div><div>Experimental results at curb idle demonstrate that exhaust valve profile modulation enables effective ATS warm-up without requiring exhaust manifold pressure (EMP) control. Early exhaust valve opening with internal exhaust gas recirculation (EEVO+iEGR) resulted in 8% lower fuel consumption and reduction in engine out emissions. Late exhaust valve opening with internal EGR in the absence of EMP control was able to reach exhaust temperature of 287^◦C, without a penalty in fuel consumption or emissions compared to conventional thermal management. LEVO combined with EMP control could reach turbine outlet temperature of nearly 460^◦C at curb idle.<br></div><div><br></div><div>LEVO was studied at higher speeds and loads to assess thermal management benefits of LEVO in the absence of EMP control, with an observation that LEVO can maintain desirable thermal management performance up to certain speed/load conditions, and reduction in exhaust flow rate is observed at higher loads due to the inability of LEVO to compensate for loss of boost associated with absence of EMP control.<br></div><div><br></div><div>Cylinder deactivation (CDA) combined with additional valvetrain flexibility results in low emission, fuel-efficient solutions to maintain temperatures of a warmed-up ATS. Late intake valve closing, internal EGR and early exhaust valve opening were studied with both three cylinder and two cylinder operation. Some of these strategies showed additional benefits such as ability to use earlier injections, elimination of external EGR and operation in the absence of exhaust manifold pressure control. Three cylinder operation with LIVC and iEGR is capable of reaching exhaust temperatures in excess of 230^◦C with atleast 9% lower fuel consumption than three cylinder operation without VVA. Three cylinder operation with early exhaust valve opening resulted in exhaust temperature of nearly 340^◦C, suitable for extended idling operation. Two cylinder operation with and without the use of valve train flexibility also resulted in turbine outlet temperature relevant for extended idling (and low load operation), while reducing fuel consumption by 40% compared to the conventional thermal management strategy.<br></div><div><br></div><div>A study comparing the relative merits of internal EGR via reinduction and negative valve overlap (NVO) is presented in order to assess trade-offs between fuel efficient stay-warm operation and engine out emissions. This study develops an understanding of the optimal valve profiles for achieving reinduction/NVO and presents VVA strategies that are not cylinder deactivation based for fuel efficient stay-warm operation. Internal EGR via reinduction is demonstrated to be a more fuel efficient strategy for ATS stay-warm. An analysis of in-cylinder content shows that NOx emissions are more strongly affected by in-cylinder O2 content than by method of internal EGR.<br></div>

<div>The new technique of Vibration-Assisted 3D Printing (VAP) offers significant potential for leveraging the geometric flexibility of additive manufacturing (AM) into the realm of solid energetics. The first part of this work compares the print capabilities of a custom-made VAP printer to those of an established commercial direct-write printer using a polymer clay. Characterization tests were conducted and a variety of other shapes were printed comparing the two methods in their turning quality, feature resolution, unsupported overhang angle, negative space feature construction, and less-than-fully-dense self-supported 3D lattices. The porosity and regularity of the printed lattices were characterized using X-ray microtomography (MicroCT) scans. The quality of the shapes was compared using statistical methods and a MATLAB edge-finding code. The results show that the VAP printer can manufacture parts of superior resolution than the commercial printer, due to its ability to extrude highly viscous material through a smaller nozzle diameter. The VAP print speeds were also found to be as high as twenty times higher than those of the direct write printer.</div><div>Following up on this work, a second study explored the possibility of modifying grain geometry through variation of printed infill design using an ammonium perchlorate composite propellant (APCP). In the propellant formulation, a polymer that cures under ultra-violet (UV) light was used instead of the more common hydroxyl-terminated polybutadiene (HTPB). Although this formulation is a less-effective fuel than HTPB, its use enables layer-by-layer curing for improved structural strength during printing. Using VAP, cylindrical propellant charges were prepared using a gyroidal infill design with a range of internal porosities (infill amounts). Some additional propellant grains were prepared with both vertical and concentric layering of different infill amounts. These grains were then burned beginning at atmospheric pressure in a constant-volume Parr cell to measure the resulting pressure output. Analysis of the pressure trace data shows that a less-dense infill increases the maximum pressurization rate, due to the presence of small voids spaced roughly uniformly throughout the grain that increase the burning surface area. We show that additive manufacturing-based propellant grain modification can be used to tailor the pressure-time trace through adjustment of the number and size of small voids. Specifically, this study shows that, using a graded functional geometry, the duration of gas generation can be controlled. This work represents a preliminary effort to explore the possibilities to propellant</div><div>12</div><div>manufacture offered by additive manufacturing and to begin to address the challenges inherent in making it practical.</div>

<div>The aviation industry is continuously growing amid tight restrictions on global emission</div><div>reductions. Alternative aviation fuels have gained attention and developed to replace the</div><div>conventional petroleum-derived aviation fuels. The replacement of conventional fuels with</div><div>alternative fuels, which are composed solely of hydrocarbons (non-petroleum), can mitigate</div><div>impacts on the environment and diversify the energy supply, potentially reducing fuel costs.</div><div>To ensure the performance of alternative fuels, extensive laboratory and full-scale engine</div><div>testings are required, thereby a lengthy and expensive process. The National Jet Fuel Combustion</div><div>Program (NJFCP) proposed a plan to reduce this certification process time and</div><div>the cost dramatically by implementing a computational model in the process, which can be</div><div>replaced with some of the testings. This requires an understanding of the influence of chemical/</div><div>physical properties of alternative fuels on combustion performance. The main objective</div><div>of this work is to investigate the spray characteristics of alternative aviation fuels compared</div><div>to that of conventional aviation fuels, which have been characterized by different physical</div><div>liquid properties at different gas turbine-relevant conditions.</div><div>The experimental work focuses on the spray characteristics of standard and alternative</div><div>aviation fuels at three operating conditions such as near lean blowout (LBO), cold engine</div><div>start, and high ambient pressure conditions. The spray generated by a hybrid pressureswirl</div><div>airblast atomizer was investigated by measuring the drop size and drop velocity at</div><div>a different axial distance downstream of the injector using a phase Doppler anemometry</div><div>(PDA) measurement system. This provided an approximate trajectory of the largest droplet</div><div>as it traveled down from the injector. At LBO conditions, the trend of decreasing drop size</div><div>and increasing drop velocity with an increase in gas pressure drop was observed for both</div><div>conventional (A-2) and alternative aviation fuels (C-1, C-5, C-7, and C-8), while the effect of</div><div>fuel injection pressure on the mean drop size and drop velocity was observed to be limited.</div><div>Moreover, the high-speed shadowgraph images were also taken to investigate the effect of</div><div>the pressure drop and fuel injection pressures on the cone angles. Their effects were found</div><div>to be limited on the cone angle.</div><div><div>The spray characteristics of standard (A-2 and A-3) and alternative (C-3) fuels were</div><div>investigated at engine cold-start conditions. At such a crucial condition, sufficient atomization</div><div>needs to be maintained to operate the engine properly. The effect of fuel properties,</div><div>especially the viscosity, was investigated on spray drop size and drop velocity using both</div><div>conventional and alternative aviation fuels. The effect of fuel viscosity was found to be minimal</div><div>and dominated by the effect of the surface tension, even though it showed a weak trend</div><div>of increasing drop size with increasing surface tension. The higher swirler pressure drop</div><div>reduced the drop size and increased drop velocity due to greater inertial force of the gas for</div><div>both conventional and alternative aviation fuels at the cold start condition. However, the</div><div>effect of pressure drop was observed to be reduced at cold start condition compared to the</div><div>results from the LBO condition.</div><div>The final aspect of experimental work focuses on the effect of ambient pressures on the</div><div>spray characteristics for both conventional (A-2) and alternative (C-5) aviation fuels. Advanced</div><div>aviation technology, especially in turbomachinery, has resulted in a greater pressure</div><div>ratio in the compressor; therefore, greater pressure in combustors for better thermal efficiency.</div><div>The effect of ambient pressure on drop size, drop velocity, and spray cone angle was</div><div>investigated using the PDA system and simultaneous Planar Laser-Induced Fluorescence</div><div>(PLIF) and Mie scattering measurement. A significant reduction in mean drop size was</div><div>observed with increasing ambient pressure, up to 5 bar. However, the reduction in the mean</div><div>drop size was found to be limited with a further increase in the ambient pressure. The effect</div><div>of the pressure drop across the swirler was observed to be significant at ambient pressure of</div><div>5 bar. The spray cone angle estimation at near the swirler exit and at 25.4 mm downstream</div><div>from the swirler exit plane using instantaneous Mie images was found to be independent of</div><div>ambient pressure. However, the cone angle at measurement plane of 18 mm in the spray</div><div>was observed to increase with increasing ambient pressure due to entrainment of smaller</div><div>droplets at higher ambient pressure. Furthermore, the fuel droplet and vapor distribution in</div><div>the spray were imaged and identified by comparing instantaneous PLIF and Mie images.</div><div>Lastly, a semi-empirical model was also developed using a phenomenological three-step</div><div>approach for the atomization process of the hybrid pressure-swirl airblast atomizer. This</div><div>model includes three sub-models: pressure-swirl spray droplet formation, droplet impingement, and film formation, and aerodynamic breakup. The model predicted drop sizes as a</div><div>function of ALR, atomizing gas velocity, surface tension, density, and ligament length and</div><div>diameter and successfully demonstrated the drop size trend observed with fuel viscosity,</div><div>surface tension, pressure drop, and ambient pressure. The model provided insights into the</div><div>effect of fuel properties and engine operating parameters on the drop size. More experimental</div><div>work is required to validate the model over a wider range of operating conditions and</div><div>physical fuel properties.</div><div>Overall, this work provides valuable information to increase understanding of the spray</div><div>characteristics of conventional and alternative aviation fuels at various engine operating</div><div>conditions. This work can provide valuable data for developing an advanced computational</div><div>combustor model, ultimately expediting the certification of new alternative aviation fuels.</div></div>

Rocket combustors and other high-performance chemical propulsion systems are prone to combustion instability. Recent simulations of rocket combustors using detailed chemical kinetics show that the constant pressure assumption used in classical treatments may be suspect due to high rates of heat release. This study is a exploration on the effects of these extraordinary rates of heat addition on the local pressure field, and interactions between the heat release and an acoustic field. <br> <br>The full problem is decomposed into simpler unit problems focused on the particular interactions of physical phenomena involved in combustion instability. The overall strategy consists of analyzing fundamental problems with simplified scenarios and then build up the complexity by adding more phenomena to the analysis. Seven unit problems are proposed in this study. <br> <br>The first unit problem consists of the pressure response to an unsteady heat release source in an unconfined one-dimensional domain. An analytical model based on the acoustic wave equation with planar symmetry and an unsteady heat source is derived and then compared against results from highly-resolved numerical simulations. Two different heat release profiles, one a Gaussian spatial distribution with a step temporal profile, and the other a Gaussian spatial distribution with a Gaussian temporal distribution, are used to model the heat source. The analytical solutions predict two different regimes in the pressure response depending on the Helmholtz number, which is defined as the ratio of the acoustic time over the duration of the heat release pulse. A critical Helmholtz number is found to dictate the pressure response regime. For compact cases, in the subcritical regime, the amplitude of the pressure pulse remains constant in space. For noncompact cases, above the critical Helmholtz number, the pressure pulse reaches a maximum at the center of the heat source, and then decays in space converging to a lower far field amplitude. At the limits of very small and very large Helmholtz numbers, the heat release response tends to be a constant pressure process and a constant volume process, respectively. The parameters of the study are chosen to be representative of the extreme conditions in a rocket combustor. The analytical models for both heat source profiles closely match the simulations with a slight overprediction. The differences observed in the analytical solutions are due to neglecting mean flow property variations and the absence of loss mechanisms. The numerical simulations also reveal the presence of nonlinear effects such as weak shocks that cannot be captured by the linear acoustic wave equation. <br> <br>The second unit problem extends the analysis of the pressure response of an unsteady heat release source to an unconfined three-dimensional domain. An analytical model based on the spherical acoustic wave equation with an unsteady heat source is derived and then compared against results from highly-resolved three-dimensional numerical simulations. Two different heat release profiles, a three-dimensional Gaussian spherical distribution with either a step or a Gaussian temporal distribution, are used to model the heat source. Two different regimes in the pressure response depending on the Helmholtz number are found. This analysis also reveals that whereas for the one-dimensional case the pressure amplitude is constant over the distance, for the three-dimensional case it decays with the radial distance from the heat source. In addition, although for moderate heat release values the analytical solution is able to capture the dynamics of the fluid response, for large heat release values the nonlinear effects deviate the highly-resolved numerical solution from the analytical model. <br> <br>The third unit problem studies the pressure response of a fluctuating unsteady heat release source to an unconfined one-dimensional domain. An analytical model based on the acoustic wave equation with planar symmetry and an unsteady heat source is derived and then compared against results from highly-resolved numerical simulations. Two different heat release profiles, a flat spatial distribution with sinusoidal temporal profile and a Gaussian spatial distribution and sinusoidal temporal profile, are used to model the heat source. For both cases, the acoustically compact and noncompact regimes depending on the Helmholtz number are analyzed. While in the compact regime the amplitude of the pressure is constant over the distance, in the noncompact regime the amplitude of the pressure fluctuation is larger within the heat source area of application, and once outside the heat source decays to a far field pressure value. In addition, the analytical model does not capture the nonlinear effects present in the highly-resolved numerical simulations for large rates of heat release such as the ones present in rocket combustors.<br> <br>Finally, the last four unit problems focus on the interaction between unsteady heat release and the longitudinal acoustic modes of a combustor. The goal is to assess and quantify how pressure fluctuations due to unsteady heat release amplify a longitudinal acoustic mode. To investigate the nonlinear effects and the limitations based on the acoustic wave equation, the analytical models are compared against highly-resolved numerical simulations. The fourth unit problem consists of the pressure response to a moving rigid surface that generates a forced sinusoidal velocity fluctuation in a one-dimensional open-ended cavity. The fifth unit problem combines an analytical solution from the velocity harmonic fluctuation with an unsteady heat pulse with Gaussian spatial and temporal distribution developed in the first unit problem. The choice of an open-ended cavity simplifies the analysis and serves as a stepping stone to the sixth unit problem, which also includes the pressure reflections provoked by the acoustic boundaries of the duct. This sixth unit problem describes the establishment of a 1L acoustic longitudinal mode inside a closed duct using the harmonic velocity fluctuations from the fourth unit problem. A wall on the left end of the duct is only moved for one cycle at the 1L mode frequency to establish a 1L mode in the initially quiescent fluid. The last unit problem combines the analytical solution of the 1L mode acoustic field developed in the sixth unit problem with an unsteady heat pulse with Gaussian spatial and temporal distribution, and also accounts for pressure reflections. The derivation of the present analytical models includes the identification of relevant length and time scales that are condensed into the Helmholtz number, the phase shift between the longitudinal fluctuating pressure field and the heat source, and ratio of the fluctuating periods. The analytical solution is able to capture with an acceptable degree of accuracy the pressure trace of the numerical solution during the fist few cycles of the 1L mode, but it quickly deviates very significantly from the numerical solution due to wave steepening and the formation of weak shocks. Therefore, models based on the acoustic wave equation can provide a good understanding of the combustion instability behavior, but not accurately predict the evolution of the pressure fluctuations as the nonlinear effects play a major role in the combustion dynamics of liquid rocket engines.

<p>A variety of methods have been developed to enhance solid propellant burning rates, including adjusting oxidizer particle size, modifying metal additives, tailoring the propellant core geometry, and adding catalysts or wires. Fully consumable reactive wires embedded in propellant have been used to increase the burning rate by increasing the surface area; however, the manufacture of propellant grains and the observation of geometric effects with reactive components has been restricted by traditional manufacturing and viewing methods. In this work, a printable reactive filament was developed that is tailorable to a number of use cases spanning reactive fibers to photosensitive igniters. The filament employs aluminum fuel within a printable polyvinylidene fluoride matrix that can be tailored to a desired burning rate through stoichiometry or aluminum fuel configuration such as particle size and modified aluminum composites. The material is printable with fused filament fabrication, enabling access to more complex geometries such as spirals and branches that are inaccessible to traditionally cast reactive materials. However, additively manufacturing the reactive fluoropolymer and propellant together comes attendant with many challenges given the significantly different physical properties, particularly regarding adhesion. To circumvent the challenges posed by multiple printing techniques required for such dissimilar materials, the reactive fluoropolymer was included within a solid propellant carrier matrix as small fibers. The fibers were varied in aspect ratio (AR) and orientation, with aspect ratios greater than one exhibiting a self-alignment behavior in concordance with the prescribed extrusion direction. The effective burning rate of the propellant was improved nearly twofold with 10 wt.% reactive fibers with an AR of 7 and vertical orientation. </p> <p>The reactive wires and fibers in propellant proved difficult to image in realistic sample designs, given that traditional visible imaging techniques restrict the location and dimensions of the reactive wire due to the necessity of an intrusive window next to the wire, a single-view dynamic X-ray imaging technique was employed to analyze the evolution of the internal burning profile of propellant cast with embedded additively manufacture reactive components. To image complex branching geometries and propellant with multiple reactive components stacked within the same line of sight, the dynamic X-ray imaging technique was expanded to two views. Topographic reconstructions of propellants with multiple reactive fibers showed the evolution of the burning surface enhanced by the geometric effects caused by the faster burning fibers. These dual-view reconstructions provide a method for accurate quantitative analysis of volumetric burning rates that can improve the accessibility and viability of novel propellant grain designs.</p>

Today’s society is adapting to reduce the climate footprint which is why the Swedish Armed Forces is expected to revise its use of fossil fuel. The choice of fuel is not obvious, and this report aims to examine the possibilities and limitations for a few renewable fuel’simplementation in the Swedish Armed Forces. Based on Moche Kress logistics concept an analyzing tool were created. The analyzing tool is based on the category’s economy, industry/engine technology, technology/characteristics, inventory, storage facilities and transports. Methods used is a mixture of document collection and interviews with an expert in the area of alternative fuels and combustion engines. The renewable fuels analyzed are FAME, HVO, biogas and DME. Results of the analysis show that FAME has a relative low cost for production, only requires small-scale modifications in engines, the domestic production is expected to expand and is interoperable with the current supply chain. The biggest limitations are the bad qualities regarding cold temperatures and can’t be stored longer periods of time. HVO has a bit higher production cost but has good qualities even in colder temperatures, high energy density, can beused in all diesel engines after an approval from the manufacturer and can be implemented incurrent infrastructure as well as supply chain. Raw materials consist on the other hand largely from palm oil production. Biogas has a relatively high production cost, low energy density, requires extensive renovations/installations of engines/fuel systems and can neither be implemented in current infrastructure nor supply chain. Positive features are its good qualities in cold temperatures and big part domestic production. DME also has good qualities in cold temperatures but requires a new injection system and a new tank, can’t be implemented in neither current infrastructure nor supply chain and is not produced anywhere globally today. Based on the results from the analysis HVO were concluded as the most realistic alternative for the Swedish Armed Forces. Further conclusions were that FAME is not the best alternative and neither biogas nor DME were estimated as a realistic choice today. The last conclusion of the analysis is that none of the alternatives had possible self-sufficiency in Sweden as of now. / Mot bakgrund av att samhället ställer om till att bli mer klimatpolitiskt hållbart förväntas ett drivmedelsbyte vara aktuellt för Försvarsmakten. Vilket drivmedel som är aktuellt för detta är inte självklart och detta arbete syftar till att undersöka vilka förutsättningar ett antal förnybara drivmedelsalternativ har för implementering i Försvarsmakten. Utifrån Moche Kress logistikkoncept togs ett analysverktyg fram som utgår från kategorierna ekonomi, industri/motorteknik, teknologi/egenskaper, lagerhållning/tillgänglighet, infrastruktur för lagerhållning och transporter. Empiri samlades därefter in via en dokumentinsamling samt intervjuer med en expert inom alternativa drivmedel och förbränningsmotorer. Alternativen som analyserats är FAME, HVO, biogas och DME. Resultat av analysen var att FAME har en relativt låg produktionskostnad, enbart kräver mindre anpassningar i motorer, har inhemsk produktion som förväntas expandera och kan implementeras i befintlig försörjningskedja. Största begränsningarna är att det har begränsade köldegenskaper samt låg lagringsbeständighet. HVO har en något högre produktionskostnad men goda köldegenskaper, högt energiinnehåll, kan nyttjas i samtliga dieselmotorer efter tillverkarens godkännande och kan implementeras i befintlig försörjningskedja respektive infrastruktur. Råvaror kommer dock till stor del från palmoljeproduktion. Biogas har en relativt hög produktionskostnad, lågt energiinnehåll, kräver omfattande renoveringar/installationer av motorer/bränslesystem och kan inte implementeras i varken befintlig försörjningskedja eller infrastruktur. Det har dock bra köldegenskaper och hög andel inhemsk produktion. DME har bra köldegenskaper, men kräver nytt insprutningssystem och ny tank, kan inte implementeras i dagens försörjningskedja eller infrastruktur och produceras ingenstans i världen idag. Utifrån analysens resultat bedömdes HVO som det mest realistiska alternativet för Försvarsmakten. Utöver det bedöms inte FAME som mindre fördelaktigt, och biogas respektive DME som orealistiska alternativ i dagsläget. Den sista slutsatsen av analysen var att inget alternativ medger självförsörjning i Sverige idag.

<div>The commercial vehicle sector is an important enabler of the economy and is heavily dependent on fossil fuels. In the fight against climate change, reduction of emissions by improving fuel economy is a key step for the commercial vehicle sector. Improving fuel economy deals with reducing energy losses from fuel to the wheels. This study aims to analyze efficiency improvements for two systems that are important in reducing CO2 emissions - hybrid powertrains and natural gas engines. At first, a prototype series hybrid powertrain was analyzed based on on-highway data collected from its powertrain components. Work done per mile by the electrical components of the powertrain showed inefficient battery operation. The net energy delivery of the battery was close to zero at the end of the runs. This indicated battery was majorly used as an energy storage device. Roughly 15% of losses were observed in the power electronics to supply power from battery and generator to the motor. Ability of the hybrid system to capture regenerative energy and utilize it to propel the vehicle is a primary cause for fuel savings. The ability of this system to capture the regenerative energy was studied by modeling the system. The vehicle model demonstrated that the system was capturing most of the theoretically available regenerative energy. The thesis also demonstrates the possibility of reduction of vehicular level losses for the prototype truck. Drag and rolling resistance coefficients were estimated based on two coast down tests conducted. The ratio of captured regenerative to the drive energy energy for estimated drag and rolling resistant coefficients showed that the current system utilizes 4%-9% of its drive energy from the captured regenerative energy. Whereas a low mileage Peterbilt 579 truck could increase the energy capture ratio to 8%-18% for the same drive profile and route. Decrease in the truck’s aerodynamic drag and rolling resistance can potentially improve the fuel benefits.</div><div>The second study aimed to reduce the engine level pumping losses for a natural gas spark ignition engine by cylinder deactivation (CDA). Spark ignited stoichiometric engines with an intake throttle valve encounter pumping/throttling losses at low speed, low loads due to the restriction of intake air by the throttle body. A simulation study for CDA on a six cylinder natural gas engine model was performed in GT- Power. The simulations were ran for steady state operating points with a torque range 25-560 ftlbs and 1600 rpm. Two , three and four cylinders were deactivated in the simulation study. CDA showed significant fuel benefits with increase in brake thermal efficiency and reduction in brake specific fuel consumption depending on the number of deactivated cylinders. The fuel benefits tend to decrease with increase in torque. Engine cycle efficiencies were analyzed to investigate the efficiency improvements. The open cycle efficiency is the main contributor to the overall increase in the brake thermal efficiency. The work done by the engine to overcome the gas exchange during the intake and exhaust stroke is referred to the pumping losses. The reduction in pumping losses cause an improvement in the open cycle efficiency. By deactivating cylinders, the engine meets its low torque requirements by increase in the intake manifold pressure. Increased intake manifold pressure also resulted in reduction of the pumping loop indicating reduced pumping losses. A major limitation of the CDA strategy was ability to meet EGR fraction requirements. The increase in intake manifold pressure also caused a reduction in the delta pressure across the EGR valve. At higher torques with high EGR requirements CDA strategy was unable to meet the required EGR fraction targets. This limited the benefits of CDA to a specific torque range based on the number of deactivated cylinders. Some variable valve actuation strategies were suggested to overcome this challenge and extend the benefits of CDA for a greater torque range.</div><div><br></div>

<p>The main accomplishments of this research are </p> <p>(1) developed a high fidelity computational methodology based on large eddy simulation to capture lean blowout (LBO) behaviors of different fuels; </p> <p>(2) developed fundamental insights into the combustion processes leading to the flame blowout and fuel composition effects on the lean blowout limits; </p> <p>(3) developed artificial intelligence-based models for early detection of the onset of the lean blowout in a realistic complex combustor. </p> <p>The methodologies are demonstrated by performing the lean blowout (LBO) calculations and statistical analysis for a conventional (A-2) and an alternative bio-jet fuel (C-1).</p> <p>High-performance computing methodology is developed based on the large eddy simulation (LES) turbulence models, detailed chemistry and flamelet based combustion models. This methodology is employed for predicting the combustion characteristics of the conventional fuels and bio-derived alternative jet fuels in a realistic gas turbine engine. The uniqueness of this methodology is the inclusion of as-it-is combustor hardware details such as complex hybrid-airblast fuel injector, thousands of tiny effusion holes, primary and secondary dilution holes on the liners, and the use of highly automated on the fly meshing with adaptive mesh refinement. The flow split and mesh sensitivity study are performed under non-reacting conditions. The reacting LES simulations are performed with two combustion models (finite rate chemistry and flamelet generated manifold models) and four different chemical kinetic mechanisms. The reacting spray characteristics and flame shape are compared with the experiment at the near lean blowout stable condition for both the combustion models. The LES simulations are performed by a gradual reduction in the fuel flow rate in a stepwise manner until a lean blowout is reached. The computational methodology has predicted the fuel sensitivity to lean blowout accurately with correct trends between the conventional and alternative bio-jet fuels. The flamelet generated manifold (FGM) model showed 60% reduction in the computational time compared to the finite rate chemistry model. </p> <p>The statistical analyses of the results from the high fidelity LES simulations are performed to gain fundamental insights into the LBO process and identify the key markers to predict the incipient LBO condition in swirl-stabilized spray combustion. The bio-jet fuel (C-1) exhibits significantly larger CH₂O concentrations in the fuel-rich regions compared to the conventional petroleum fuel (A-2) at the same equivalence ratio. It is observed from the analysis that the concentration of formaldehyde increases significantly in the primary zone indicating partial oxidation as we approach the LBO limit. The analysis also showed that the temperature of the recirculating hot gases is also an important parameter for maintaining a stable flame. If this temperature falls below a certain threshold value for a given fuel, the evaporation rates and heat release rated decreases significantly and consequently leading to the global extinction phenomena called lean blowout. The present study established the minimum recirculating gas temperature needed to maintain a stable flame for the A-2 and C-1 fuels. </p> The artificial intelligence (AI) models are developed based on high fidelity LES data for early identification of the incipient LBO condition in a realistic gas turbine combustor under engine relevant conditions. The first approach is based on the sensor-based monitoring at the optimal probe locations within a realistic gas turbine engine combustor for quantities of interest using the Support Vector Machine (SVM). Optimal sensor locations are found to be in the flame root region and were effective in detecting the onset of LBO ~20ms ahead of the event. The second approach is based on the spatiotemporal features in the primary zone of the combustor. A convolutional autoencoder is trained for feature extraction from the mass fraction of the OH ( data for all time-steps resulting in significant dimensionality reduction. The extracted features along with the ground truth labels are used to train the support vector machine (SVM) model for binary classification. The LBO indicator is defined as the output of the SVM model, 1 for unstable and 0 for stable. The LBO indicator stabilized to the value of 1 approximately 30 ms before complete blowout.

Fossila drivmedel står idag för en överlägsen majoritet av den totala användningen av drivmedel som dagligen förburkas. Alternativ till de fossila drivmedlen krävs för att säkerställa tillgång i framtiden. Försvarsmakten har fått uppdrag från regeringen att utforska möjligheten att övergå till att driva sina fordon på förnyelsebara bränslen.Militära organisationer strävar efter ett enhetsdrivmedel, alltså ett gemensamt drivmedel som driver samtliga fordon och enheter. Största anledningen är den förenklade logistik som kan uppnås om endast ett drivmedel används.Detta arbete har sökt efter ett alternativt drivmedel som skulle kunna användas som enhetsdrivmedel inom Försvarsmakten. Detta för att lösa problematiken med att både byta till ett förnyelsebart drivmedel och ett enhetsdrivmedel i samma fas.Slutsatserna som dragit i detta arbete är att FT-bränslen har potential att användas som enhetsdrivmedel ur ett tekniskt perspektiv. Den höga flampunkt som FT-bränslen har skulle kunna innebära att även sjöfarkoster kan använda samma drivmedel som mark- och luftfarkoster. Dock saknas i dagsläget tillräcklig tillgänglighet och framställningen är i utvecklingsfasen. / Fossil fuels currently account for the vast majority of the total amount of fuel that isconsumed globally every day. Alternatives to fossil fuels are needed to ensuresufficient supply in the future. The Swedish Armed Forces have been tasked by theGovernment to investigate and examine the possibility of operating their vehicles onrenewable fuels.Military organizations strive for the use of a single fuel concept. A single fuel conceptmeans that only one kind of fuel is used in all vehicles and machines. The majorreason for this is the simplified logistics that can be achieved if only one fuel is used.This paper has sought an alternative fuel that can also be used as a single fuel in theSwedish Armed Forces. In order to solve the problem of changing to a renewable andto a single fuel in one single step.The main conclusion drawn in this paper is that Fischer-Tropsch fuels have thepotential to be a single fuel from a technical perspective. The high flashpoint ofFischer-Tropsch fuels could mean that they might also be used in navy vessels.However, there is currently insufficient availability and production is in thedevelopment stages.

Idag är marinindustrin helt beroende av fossila bränslen. I detta arbete har en kvalitativ litteraturstudie genomförts i syfte att presentera ett perspektiv på vad som skulle kunna vara realistiskt möjligt idag när det gäller användning av alternativa bränslen för att begränsa växthusgasutsläppen från sjöfartsindustrin. Det finns många olika bränslen som kan användas i antingen en förbränningsmotor eller i bränsleceller. Vätgas har den ultimata lösningen när det gäller hållbarhet på grund av den tekniska enkelheten i utvinningen och förutsägbara utsläpp. På grund av bristen på tekniska lösningar som säkerställer driftstabilitet och tillgång är vätgas inte möjligt att införa i stor industriell skala för närvarande. Metanol verkar ha en mer lovande framtid på kort sikt och sekundärt biobränslen, inklusive förnybar metanol, på lång sikt. Metanol har redan en befintlig infrastruktur och används redan som framdrivningsmedel i vissa fartyg. Just nu kommer nästan all metanol från fossila bränslen. Även om tillgången på metanol är fossil, bidrar den ändå till mindre utsläpp i en livscykel än av konventionellt marint bränsle gör. För det andra kan den produceras via en förnybar process som involverar biomassa bland annat. Andra biobränslen som biodiesel har liknande egenskaper som konventionell marin diesel och är förnybar, koldioxidneutral och kan produceras från en rad olika råvaror. Den geografiska spridningen av råvaror kan dock vara en utmaning för den lokala tillgången, men det betyder inte automatiskt att det inte kan distribueras över hela världen. Ett annat problem som är förknippat med biobränslen är tillgången på biomassa. Tillgången till biomassa är begränsad på grund av efterfrågan på mat, därför kommer produktion av icke-ätbara grödor som odlas för det enda syftet att producera biobränsle att behövas för att överkomma en eventuell tillgångsproblematik i framtiden. Mängden bränsle som marinindustrin efterfrågar kan sannolikt inte produceras från ett enda råmaterial i framtiden, så det är troligt att en blandning av olika biobränslen som produceras från olika råvaror kan vara en realistisk möjlighet i framtiden. / Today the marine industry is fully dependent on fossil fuels. In this paper a qualitative literature study has been performed to present a perspective of what could be realistically possible today in terms of usage of alternative fuels to limit the GHG-emissions caused by the marine shipping industry. There are a lot of different fuels than can be applied in either an internal combustion engine or in fuel cells. Hydrogen possesses the ultimate solution in terms of sustainability because of the technical simplicity of extraction and predictable emissions. However, due to the lack of technical solutions that will ensure operational stability and supply, hydrogen is not feasible on a large industrial scale at this time. Methanol seems to have a more promising future in short term and secondly biofuels, including renewable methanol, in the long term. Methanol already has an existing infrastructure and is already being used in ships. However, as of right now almost all methanol is derived from fossil fuels. Even though the supply of methanol is fossil, it still contributes to less emissions than of conventional marine fuel. Secondly it can be produced with a renewable process involving biomass. Other biofuels like biodiesel possess similar properties that of conventional marine diesel and is renewable, carbon neutral and can be produced from a range of different feedstocks. However, the geographic diffusion of feedstocks can be a challenge to local supply, but that does not automatically mean that it can’t be distributed worldwide. Another problem that is associated is with biofuels is the availability of biomass. Biomass availability is limited due to demand of food, hence production of non-edible crops that are grown for the sole purpose of biofuel production will be needed to overcome supply issues in the future. The volume of fuel that the marine industry demands likely can’t be produced from a single feedstock in the future so it’s likely that a blend of different biofuels produced from different feedstocks could be a possibility in the future.