Spark ignition (SI) and compression ignition (CI) engine fuels are characterized by standards developed in 1927 and 1932, respectively. Over the course of these years, modern engines have drastically changed their operating conditions; however, these fuel indexes are still used today with no significant change to their definition. The requirements for fuels in future advanced engines, employing low temperature combustion (LTC) concepts, may be somewhere between gasoline and diesel in terms of their autoignition characteristics. With this focus, this study examines methodologies to bridge the gap between those fuels classified between gasoline and diesel. First, the ignition delay times (IDTs) at various temperatures obtained from an ignition quality tester (IQT), was correlated with the octane index (OI), an anti-knock scale combining the effect of the operating condition and the anti-knock quality of the fuel given by the RON/MON. This study was extended to introduce a new concept of IDT sensitivity (IDS) in an IQT. It was observed that IDS could be correlated with fuel octane sensitivity (OS = RON − MON), offering an additional methodology to estimate RON/MON with an IQT. Chemical kinetics are most sensitive to fuel molecular structure; remarkable progress has been made in covering high carbon-number fuels, relevant to gasoline fuels, for better understanding of the chemical processes that lead to engine knock. To this end, a methodology to relate IDTs calculated from homogeneous batch-reactor simulations with gasoline fuel indexes was developed. This methodology enabled correlation of a kinetic property (i.e., IDT) with RON/MON values. The influence of various components present in gasolines, and their anti-knock quality, was investigated. A spinning band distillation system was utilized to separate the components of various gasolines. Ignition quality and the functional group distribution of various boiling ranges were investigated with an IQT and 1H nuclear magnetic resonance (NMR) spectroscopy. Finally, the importance of physical and chemical fuel properties in fuel stratification in LTC engine concepts was undertaken in a CI engine with a multi hole solid-cone injector. The findings suggest that the physical properties of fuel played a dominant role when fuel stratification occurred in the engine combustion chamber.

<div>The United States Environmental Protection Agency (EPA) is charged with pro-tecting human health and the environment. Part of this mission involves regulating heavy-duty trucks that produce particulate matter (PM), unburned hydrocarbons (UHC), carbon dioxide (CO2), and nitrogen oxides (NOx). A byproduct of lean burn combustion in diesel engines is NOx. NOx output limits from commercial vehicles have been reduced significantly from 10 g/hp-hr in 1979 to 0.2 g/hp-hr in 2010. Ad-ditional reductions are expected in the near future.</div><div><br></div><div>One pathway to meet future NOx emissions regulations in a fuel efficient manner is with higher performing exhaust aftertreatment systems through improved engine air handling. As exhaust aftertreatment’s capability to convert harmful NOx into harmless N2 and H2O is a function of temperature, a key performance factor is how quickly does the exhaust aftertreatment system heat up (warm-up), and how well does the system stay at elevated temperatures (stay-warm).</div><div><br></div><div>When the warm-up strategy of iEGR was implemented over the heavy duty federal test procedure (HD-FTP) drive-cycle, it was able to get the SCR above the critical 250◦C peak NOx conversion threshold 100 seconds earlier than the TM baseline. While iEGR consumed 2.1% more fuel than the TM baseline, it reduced predicted tailpipe NOx by 7.9%.</div><div><br></div><div>CDA implemented as a stay-warm strategy over the idle portions of the HD-FTP successfully kept the SCR above the 250◦C threshold for as long as the TM baseline and consumed 3.0% less fuel. Implementing CDA both at idle and from 0 to 3 bar BMEP consumed an additional 0.4% less fuel, for a total fuel consumption reduction of 3.4%.</div><div><br></div><div>A method to predict and avoid compressor surge (which can destroy turbochargers and in fact did so during the HD-FTP experiments) instigated by CDA was devel-oped, as discussed later, and implemented with staged cylinder deactivation to avoid compressor surge.</div><div><br></div><div>The literature does not consider the fidelity of road grade data required to ad-equately predict vehicle fuel consumption and operational behavior. This work ad-dresses this issue for Class 8 trucks by comparing predicted fuel consumption and operation (shifting, engine torque/speed, and braking) of a single Class 8 truck simu-lated with grade data for the same corridor from different sources. The truth baseline road grade (best fidelity available with LiDAR) was obtained previously. This work compares road grade data to the truth baseline from four other typical methods i) utilizing GPS to record horizontal position and vertical elevation, ii) logging the pitch of a cost effective, commercially available IMU, iii) integrating the horizontal and ver-tical velocities of the same IMU, and iv) a commercially available dataset (Comm). Comm grade data (R2=0.992) best matches the LiDAR reference over a 5,432 m stretch of US 231 where high quality LiDAR data was available, followed in quality by the integrated IMU velocity road grade (R2=0.979). Limitations of the Comm dataset are shown, namely missing road grade (decreased point density) for up to 1 km spans on other sections of US 231, as well as for Interstate 69. Vehicle simulations show that both the Comm data (where available and accurate) and integrated IMU road grade data result in fuel consumption predictions within 2.5% of those simulated with the truth reference grade data.</div><div><br></div><div>The simulation framework described in Chapter 6 combines high fidelity vehicle and powertrain models (from Chapter 5) with a novel production-intent platooning controller. This controller commands propulsive engine torque, engine-braking, or friction-braking to a rear vehicle in a two-truck platoon to maintain a desired following distance. Additional unique features of the framework include high fidelity road grade and traffic speed data. A comparison to published experimental platooning results is performed through simulation with the platooning trucks traveling at a constant 28.6 m/s (64 MPH) on flat ground and separated by 11 m (36 ft). Simulations of platooning trucks separated by a 16.7 m (54.8 ft) gap are also performed in steady-state operation, at different speeds and on different grades (flat, uphill, and downhill), to demonstrate how platooning affects fuel consumption and torque demand (propulsive and braking) as speed and grade are varied. For instance, while platooning trucks with the same 16.7 m gap at 28.6 m/s save the same absolute quantity of fuel on a 1% grade as on flat ground (1.00 per-mile, normalized), the trucks consume more fuel overall as grade increases, such that relative savings for the platoon average decrease from 6.90% to 4.94% for flat vs. 1% grade, respectively. Furthermore, both absolute and relative fuel savings improve during platooning as speed increases, due to increase in aerodynamic drag force with speed. There are no fuel savings during the downhill operation, regardless of speed, as the trucks are engine braking to maintain reasonable speeds and thus not consuming fuel. Results for a two-truck platoon are also shown for moderately graded I-74 in Indiana, using traffic speed from INDOT for a typical Friday at 5PM. A 16.7 m (54.8 ft) gap two-truck platoon decreases fuel consumption by 6.18% over the baseline without degradation in trip time (average speed of 28.3 m/s (63.3 MPH)). The same platooning trucks operating on aggressively graded I-69 in Indiana shows a lower platoon-average 3.71% fuel savings over baseline at a slower average speed of 24.5 m/s (54.8 MPH). The impact of speed variation over, and grade difference between, these realistic routes (I-74 & I-69) on two-truck platooning is described in detail.<br></div><div><br></div>

The search for quieter internal combustion engines drives the quest for a better understanding of the acoustic properties of engine duct components. Simulations are an important tool for enhanced understanding; they give insight into the flow-acoustic interaction in components where it is difficult to perform measurements. In this work the acoustics is obtained directly from a compressible Large Eddy Simulation (LES). With this method complex flow phenomena can be captured, as well as sound generation and acoustic scattering. The aim of the research is enhanced understanding of the acoustics of engine gas exchange components, such as the turbocharger compressor.In order to investigate methods appropriate for such studies, a simple constriction, in the form of an orifice plate, is considered. The flow through this geometry is expected to have several of the important characteristics that generate and scatter sound in more complex components, such as an unsteady shear layer, vortex generation, strong recirculation zones, pressure fluctuations at the plate, and at higher flow speeds shock waves. The sensitivity of the scattering to numerical parameters, and flow noise suppression methods, is investigated. The most efficient method for reducing noise in the result is averaging, both in time and space. Additionally, non-linear effects were found to appear when the amplitude of the acoustic velocity fluctuations became larger than around 1~\% of the mean velocity, in the orifice. The main goal of the thesis has been to enhance the understanding of the flow and acoustics of a thick orifice plate, with a jet Mach number of 0.4 to 1.2. Additionally, we evaluate different methods for analysis of the data, whereby better insight into the problem is gained. The scattering of incoming waves is compared to measurements with in general good agreement. Dynamic Mode Decomposition (DMD) is used in order to find significant frequencies in the flow and their corresponding flow structures, showing strong axisymmetric flow structures at frequencies where a tonal sound is generated and incoming waves are amplified.The main mechanisms for generating plane wave sound are identified as a fluctuating mass flow at the orifice openings and a fluctuating force at the plate sides, for subsonic jets. This study is to the author's knowledge the first numerical investigation concerning both sound generation and scattering, as well as coupling sound to a detailed study of the flow.With decomposition techniques a deeper insight into the flow is reached. It is shown that a feedback mechanism inside the orifice leads to the generation of strong coherent axisymmetric fluctuations, which in turn generate a tonal sound. / <p>QC 20121113</p>

The author focuses on the possibility of using wood chips as fuel for tractors and machinery in agriculture and related fields, in order to increase self-sufficiency and achieving carbon neutrality. The work compares wood and conventional motor fuels in the real operation. Part of this thesis is to design a functional device with an output of 5-10 kW.

This thesis deals with turbulent mixing processes occuring in internal combustion engines, when applying exhaust gas recirculation (EGR). EGR is a very efficient way to reduce emissions of nitrogen oxides (NOx) in internal combustion engines. Exhaust gases are recirculated and mixed with the intake air of the engine, thus reducing the oxygen concentration of the combustion gas and the maximum combustion tempera- ture. This temperature decrease results in a reduction of NOx emissions, since NOx is produced at high temperatures.The issue of NOx reduction is of high importance for current engine development (particularly for heavy-duty engines), since NOx is the main cause for smog formation and subject to increasingly stronger emission legislation. One of the practical problems when applying EGR is the non-uniformity of the mixture among and inside the cylinders deteriorating the engine and emission performance.The aim of this work is to develop and assess methods suited for the computation of turbulent mixing processes in engine conditions. More specifically, RANS and LES computations are considered. The flow structures responsible for the mixing are analyzed for two different T-junctions and a six-cylinder Scania engine-manifold. Shortcomings and advantages of the applied mixing models are explained.The main results are, that commonly applied scalar flux models for the RANS framework do not predict correct scalar flux directions. In stationary flow, the applied k-ε-model in combination with a gradient-diffusion-model gives too small mixing rates as compared to LES and experiments. Furthermore, the LES computations of the T-junctions show, that Dean vortices occuring due to the curvature of the flow are broken up and dissipated only a few diameters downstream of the junction. The RANS computations do not predict this break-up, giving fundamentally different flow structures and mixing distributions. In pulsating flow, a resonance between the natural stabilities and the pulsation frequency is found by LES results, which could not be predicted by RANS.Computations of the flow in a Scania intake manifold with generic boundary con- ditions indicate, that inlet pulsations are important for the mixing process and that the smoothing effect of URANS is not adequate for accurate mixing computations. LES, on the other hand, is more promising, since it is able to capture the physics of pulsating flows much better. / QC 20111117

<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>