<p dir="ltr">An EGR Pump and High-Efficiency turbo were installed on a 13.6 L John Deere diesel engine. The main objective of this study was to examine how a high-efficiency turbocharger and an electric EGR pump can work together to improve fuel efficiency in engines without increasing the emission of NOx. The focus is on finding a balance, between enhancing efficiency and controlling emissions which will ultimately contribute to making vehicles eco-friendly and fuel-efficient.</p>

<div>High speed laser diagnostics are performed in two vastly differing swirl combustors at conditions relevant for industrial gas turbines. This high quality data can not only be used to elucidate key features of the flow field but also for validation of computational models simulating turbulence, chemistry, and their interactions. The first combustor is a piloted lean premixed prevaporized arrangement common in aviation applications. Fueling parameters are varied and sensitivity towards the pilot flame is observed. Conditioning to the stagnation line demonstrates increased fluctuations of shear and rotation in the inner shear layer when the pilot fueling is reduced.</div><div><br></div><div>The second flame has a simpler configuration with a single swirler and combusting natural gas. Thermoacoustic instability coupled to a helical precessing vortex core is found at certain conditions. Sparse Dynamic Mode Decomposition and phase averaging is applied to the velocity fields to create a three dimensional reconstruction of the helical vortex core in a non-precessing reference frame. Heat release is found to be correlated to the interaction strength of the central recirculation bubble and the helical vortex core. </div><div><br></div><div> </div><div>Finally, intermittent phenomena within a thermoacoustic instability are examined. The most prominent deviation is that the flame is observed to randomly lift and reattach. In addition, a convolutional neural network is employed to extract the morphology from otherwise qualitative OH species imaging. The average characteristics of the lifted and attached flame are compared and dramatic differences are found. All of the flow structures have been altered such as the precessing vortex core being greatly intensified during flame lift-off. Evaluating the average events before flame lift-off revealed the importance of conditions at the combustor inlet. However, evidence for a future reattachment event was only found with a less spatially confined perspective. In addition, transition to lift-off was very sudden while reattachment was far slower.</div>

The scarcity of fossil energy resources in conjunction with increasing demand has recently created record commodity price rises. Global warming and dimming are some of the harmful effects of increasing use of this resource. Furthermore, fossil fuel exhaust emissions, produced in internal combustion engines (ICE), generate significant health concerns. For decades, fears and numerous alarms have been raised regarding these problems. Many researchers believe that hydrogen would be an ideal alternative solution. Reduced fossil fuel consumption and lower thermal emanations (CO, CO2, HC and NO) are expected if hydrogen is used, as a principal or supplementary fuel, in standard ICE’s. However, hydrogen dual-fuel use has historically been associated with injection and/or detonation problems. Direct injection (DI) strategy, in spark and compression engines, is commonly used to overcome some, but not all, of these difficulties. This experimental research investigated detonation free, diesel-hydrogen fuel consumptions, and exhaust emissions using an indirect injection (IDI) strategy in a generic compression diesel engine. A novel analogue Mechatronic Injection Unit (MICU) in conjunction with a multi point injection tactic (MPI) were devised to indirectly deliver low pressure hydrogen to a stationary Lister-Pitter diesel engine combustion chamber. The hydrogen injection system was created to be used as a generic dual-fuel kit. With off-the-shelf parts the MICU design was simple, robust, and purposeful in its function. The MICU component also formed an important element of a proposed innovative dual-fuel conversion kit. Nine hydrogen injection rates were tested. Diesel consumption savings were measured and the ‘effectiveness’ of hydrogen vitiated injection was computed. The research outcomes demonstrated that with a conventional diesel mechanical governor and an assumed engine compression ratio of 15.5, detonation free combustion can be achieved with low pressure hydrogen vitiation and enrichment . However, an injection rate limit existed above which detonation occurred. The study also demonstrated that through low pressure hydrogen vitiation and enrichment, diesel consumption savings were achieved. The research confirmed that the experimental fuel mass savings were lower than their expected/theoretical counterparts. The research particularly established that vitiation and enrichment effectiveness was only realised at low rather than high loads indicating that hydrogen achieved more than diesel mass substitutions. In this study a new confined area dual-fuel static emission testing procedure, coupled with an on-site use test cycle was proposed and termed the Dual-fuel fixed speed emission-testing guideline. Dry thermal emissions were measured, and both the cycle average and median dry- and wet-emissions were computed, substance/species comparisons were performed and conclusions were drawn. The shortcomings of the procedure however were also highlighted. Finally, the research established that one action or measure, such as dual-fuel hydrogen vitiation and enrichment, can not address all the environment and health concerns. Contrary to the common belief, green house gases, nitrogen oxides, hydrocarbons and opacity substances do not coincidently all increase and/or decrease. Indeed, this experiment demonstrated that although the diesel-hydrogen nitrogen monoxide (NO) wet-emissions at all injection rates were partially lower than the diesel baseline, carbon oxides, hydrocarbon emissions, opacity (N) and absorption coefficients (k) were higher. In other words, a measure taken to limit the harm done to human health can increase the damage to the environment and vice versa.

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>

<p>In Chapter 2, an experiment has been developed to investigate the passive pre-chamber jet ignition process in gasoline engine configurations and low-load operating conditions. The apparatus adopted a modified 4-cylinder 2.0L gasoline engine to enable single-cylinder operation. To reduce the complexity, the piston position was fixed at a predefined position relative to the top dead center (TDC) to simulate thermodynamic conditions at ignition and injection timings. High-speed Infrared (IR) imaging was applied to visualize the jet penetration and ignition process inside the main cylinder and to investigate the cyclic spatial variability. Two passive pre-chambers with different total nozzle areas and numbers of nozzles were used. In addition, the pre-chamber volume and pressure at ignition timing were varied to examine their effect on jet ignition performance. Misfire behavior was observed in the main chamber of all test cases, and the results suggested that the main cause is a high Residual Mass Fraction (RMF) in the pre-chamber affecting the subsequent cycle. A larger total nozzle area, smaller volume, higher pressure, and fuel-lean operation tended to mitigate the misfire behavior. For a test case with a spark pressure of 6 bar, a reduced cyclic variability in terms of coefficient of variation peak cylinder pressure (COVPmax) from 10.03% to 7.38% and combustion phasing variation from 81 crank angle degree (CAD) to 12 CAD were observed with increasing pre-chamber volume-to-area (V/A) ratio from 59.37 m to 103.11 m, but slightly higher misfire frequency was observed, from 46.67% to 50.00%, suggesting an accurate combination of pre-chamber design parameters is needed to improve overall performance at low-load operation.</p> <p>In Chapter 3, it examines the influence of passive pre-chamber nozzle diameter and dilution level on jet formation and engine performance. Utilizing a modified constant-volume gasoline direct injection engine with an optically-accessible piston, we tested three passive pre-chambers with nozzle diameters of 1.2, 1.4, and 1.6 mm, while nitrogen dilution varied from 0 to 20%. With the help of high-speed imaging, we captured pre-chamber jet formations and subsequent flame propagation within the main chamber. Our novel findings reveal that asymmetric temporal and spatial jet formation patterns arising from pre-chambers significantly impact engine performance. The larger nozzle diameter pre-chambers exhibited the least variation in jet formation due to their improved scavenging and main mixture filling processes, but had the slowest jet velocity and lowest jet penetration depth. At no dilution condition, the 1.2 mm-PC demonstrated superior performance attributed to higher pressure build-up in the pre-chamber, resulting in accelerated jet velocity and increased jet penetration depth. However, at high dilution condition, the 1.6 mm-PC performed better, highlighting the importance of scavenging and symmetry jet formation. This study emphasizes the importance of carefully selecting the pre-chamber nozzle diameter, based on the engine's operating conditions, to achieve an optimal and balanced configuration that can improve both jet formation and jet characteristics, as well as scavenging.</p> <p>In Chapter 4, it investigates the influence of passive pre-chamber nozzle diameter on jet ignition and subsequent main chamber combustion under varying load conditions and dilution levels using a constant-volume optical gasoline direct injection engine. The results reveal that as the load decreases, both fuel availability and flow conditions deteriorate, leading to delayed and inferior jet characteristics that affect main chamber ignition and combustion processes. In high and medium load conditions without dilution, the smallest nozzle diameter pre-chamber (1.2mm-PC) shows improved jet ignition and main combustion due to earlier jet ejection, enhanced penetration, and intensified jet. This is facilitated by the smaller nozzle diameter enabling faster and higher pre-chamber pressurization. Conversely, under low load conditions, the largest nozzle diameter pre-chamber (1.6mm-PC) performs better, likely due to improved scavenging and reduced residual levels, resulting in less compromised pre-chamber combustion and subsequent jet characteristics. The nozzle diameter also has a significant impact on cycle-to-cycle variations, with smaller diameters enhancing jet ignition performance but increasing variability. The effect of external residuals (dilution) on jet ignition performance varies depending on the nozzle diameter, with the 1.6mm-PC exhibiting less degradation and demonstrating earlier jet ejection and CA50 timing compared to smaller nozzle diameter pre-chambers at higher dilution conditions. The improved scavenging and relatively lower residual levels in the larger nozzle diameter pre-chamber contribute to its increased resistance to dilution and potential extension of dilution tolerance.</p> <p>In Chapter 5, it presents an analysis of the effects of pre-chamber nozzle orientation on dilution tolerance in a constant-volume optical engine. Using a combination of experimental and numerical methodologies, we provide novel insights into how variations in nozzle number, orientation, and size influence combustion performance under different dilution conditions. The findings reveal that an increase in the number of nozzles, for a fixed A/V ratio, tends to enhance ignition performance and stability across a range of dilution scenarios, primarily due to an increase in ignition points and a larger ignition surface area. Meanwhile, swirling pre-chambers, despite their potential to boost initial combustion performance at no dilution condition, may limit dilution tolerance due to the complexity of their internal flow dynamics and increased heat loss through nozzle surfaces. Furthermore, pre-chambers combining swirling and straight nozzle orientations fail to synergize the benefits of each type, and instead, exacerbate challenges such as heat loss, flame quenching, and unfavorable flow dynamics. These findings emphasize the complexity and nuanced trade-offs involved in optimizing pre-chamber design for improved dilution tolerance and suggest potential directions for future research in this area.</p> <p>In Chapter 6, it investigates the behavior of pre-chamber knock in comparison to traditional spark ignition engine knock, using a modified constant-volume gasoline engine with an optically-accessible piston. The aim is to provide a deeper understanding of pre-chamber knock combustion and its potential for mitigating knock. Five passive pre-chambers with different nozzle diameters, volumes, and nozzle numbers were tested, and nitrogen dilution was varied from 0 to 10%. The stochastic nature of knock behavior necessitates the use of statistical methods, leading to the proposal of a high-frequency band-pass filter (37-43 kHz) as an alternative pre-chamber knock metric. Pre-chamber knock combustion was found to exhibit fewer strong knock cycles compared to SI engines, indicating its potential for mitigating knock intensity. High-speed images revealed pre-chamber knock primarily occurs near the liner, where end-gas knock is typically exhibited. The study identified that increasing pre-chamber nozzle diameter resulted in a larger dispersion of knock cycles and more severe knock intensity, likely due to shorter jet penetration depth requiring more time for end-gas consumption. Strategies for mitigating knock in pre-chamber combustion systems include reducing the pre-chamber volume for a fixed A/V ratio and increasing dilution level. The results of this study offer valuable insights for developing effective knock mitigation approaches in pre-chamber combustion systems, contributing to the advancement of more efficient and reliable engines.</p> <p>In Chapter 7, a numerical investigation of different premixed gaseous injection strategies was performed to understand their impact on the scavenging and mixture formation of an air-fuel premixed pre-chamber with high exhaust gas recirculation (EGR) operations. EGR dilution is effective for reducing coolant heat loss, pumping work at throttled conditions, and mitigates knock at high-load conditions, thus increasing engine efficiency. To further extend the EGR limit of an air-fuel premixed pre-chamber engine, the effects of different injection strategies (including timing, duration, pressure, pre-chamber volume, and hardware) on the EGR level, trap efficiency, and parasitic loss were determined. Regardless of injection duration and upstream pressure, injecting too early not only increased the amount of the injected premixed gas leaking into the main chamber but also was inefficient in reducing the EGR level in the pre-chamber. To reduce the EGR level in the pre-chamber to a level where successful ignition and combustion of the pre-chamber mixture is possible, the injection timing should be delayed to be close to the ignition timing. A premixed air-fuel injection is thus proposed to reduce the time required for air-fuel mixing in the pre-chamber. With a delayed end of injection (EOI), both leakage amount and EGR level were reduced compared to the cases with earlier injection timings. The results show that an injection with 15 bar upstream pressure, 20 CA duration, EOI of −20 CAD aTDC (ignition timing), and with guided injection hardware for the base pre-chamber volume resulted in about 0.17% air compression parasitic loss, over a 94% trap efficiency, at the same time maintaining the mean EGR level in the pre-chamber below 20%, ensuring good pre-chamber combustion. With a 50% increase in pre-chamber volume from the base case, the parasitic loss increased by 65% (from 0.17% to 0.28% loss), indicating a problem with a larger pre-chamber with a separate air valve and injector.</p>

<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>