Experimental Investigation of Advanced Ignition Systems for High Efficiency Combustion

Consumption of fossil and bio-derived fuels is growing due to energy demands associated with increase in population and standard of living across the globe. Power generation and transportation sectors are the primary two sources of fuel consumption, which have raised the demand for crude oil and led to serious environmental pollution issues. This demand for energy forced various government agencies to strengthen the allowable exhaust pollutant concentration limits. Recently, CO, CO2, particulate matter, and nitrogen oxides (NOx) emission restrictions have become more stringent to the extent that engines must operate at higher energy densities and efficiencies. Towards this goal, this doctoral study focused on evaluating advanced ignition systems and testing new biofuels for automotive combustion applications. First, a natural gas lean combustion mode was assessed by using advance ignition systems to provide higher brake power while maintaining the exhaust limits. A rigorous combustion data analysis was performed to identify the main reasons leading to improved performance in the case of prechamber equipped laser ignition. An overall efficiency improvement of 2.1% points was observed, compared to spark ignition, which in turn leads to save 633 PJ per year. In the second part of this dissertation, a spherical chamber was designed and validated to measure the laminar burning velocity (LBV) of a promising biofuel: 2,4-Dimethyl-3-pentanone, (DIPK), for homogenous charge compression ignition engines. LBV measurements were carried out with various diluent species (N2, Ar, and He) in order to provide several data points for development and validation of DIPK chemical kinetic mechanisms. It has been found that DIPK does not only have higher temperature and pressure sensitivities (compared to iso-octane), but additionally enabled a faster laminar burning velocity which leads to higher rate of heat release in reciprocating engines

Promising score for teaching and learning environment: an experience of a fledgling medical college in Saudi Arabia

Background: Professional competency of graduates of an institute reflects its teaching and learning environment (TLE). This study aimed to provide a preliminary assessment of the TLE at the College of Medicine at Majmaah University. Methods: A cross-sectional survey was conducted during the 2019-20 academic year among students at the College. A validated scoring tool “the Experience of Teaching and Learning Questionnaire” (available at https://bit.ly/3sVBuEw) was used. The mean score of each section and statement, the difference between the mean scores of different demographic groups, and correlations between sections were analysed. Results: A total of 234 (72.2%) enrolled students participated in this survey, with a male-to-female ratio and a ratio of participants from basic to clinical years being 2:1 and 1:1, respectively. Most participants reported a GPA of above 3/5. The overall mean score was 3.52/5 points. Section one “approaches to learning and studying” has the highest mean score (3.68), and no section scored a mean below three, though section three “demands made by the course” scored a borderline mean of 3.08. Students in clinical years had a significantly higher overall mean score compared to their counterparts (3.66 vs. 3.39, p < 0.001). Conclusions: Students at the College had a positive perception of the TLE, but face challenges in coping with the demands of acquiring knowledge and subject-based skills, and in appreciating the TLE especially during basic science years, highlighting the need for an atmosphere that allows them to meet demands and develop greater appreciation

Reduction Of Cyclic Variations By Using Advanced Ignition Systems In A Lean-Burn Stationary Natural Gas Engine Operating At 10 Bar Bmep And 1800 Rpm

In stationary natural gas engines, lean-burn combustion offers higher engine efficiencies with simultaneous compliance with emission regulations. A prominent problem that one encounters with lean operation is cyclic variations. Advanced ignition systems offer a potential solution as they suppress cyclic variations in addition to extending the lean ignition limit. In this article, the performance of three ignition systems-conventional spark ignition (SI), single-point laser ignition (LI), and prechamber equipped laser ignition (PCLI)-in a single-cylinder natural gas engine is presented. First, a thorough discussion regarding the efficacy of several metrics, besides coefficient of variation of indicated mean effective pressure (COV_IMEP), in representing combustion instability is presented. This is followed by a discussion about the performance of the three ignition systems at a single operational condition, that is, same excess air ratio (λ) and ignition timing (IT). Next, these metrics are compared at the most optimal operational points for each ignition system, that is, at points where λ and IT are optimized to achieve highest efficiency. From these observations, it is noted that PCLI achieves the highest increase in engine efficiency, Δη = 2.1% points, and outperforms the other two methods of ignition. A closer look reveals that the coefficient of variation in ignition delay (COV_ID) was negligible, whereas that in coefficient of variation in combustion duration (COV_CD) was significantly lower by 2.2% points. However, the metrics COV_ID and COV_CD are not well correlated with COV_IMEP

The Effect Of Diluent Gases On High Pressure Laminar Burning Velocity Measurements Of An Advanced Biofuel Ketone

The 2,4-Dimethyl-3-pentanone (DIPK) is a promising biofuel candidate for automotive applications that is produced by the endophytic fungal conversion process which can be optimized for widespread utilization. There are some studies in the literature on combustion properties of DIPK, such as ignition delay times and laminar burning velocity (LBV) measurements. However, most studies are conducted at low pressures (near 1 atm) which are far away from the high pressure conditions present inside reciprocating engines. Therefore, we present LBV measurements at high pressures up to 10 atm for this fuel using a spherical flame speed facility. It is known that the flame in a constant volume chamber develops cellular structure (hydrodynamic instability) as the initial pressure increases because of the reduction in flame thickness and the increase of density jump along one isentrope. In addition, the diffusional-thermal instability prevents experiments for rich mixtures because of the reduction of Lewis number. An earlier study from our lab showed that the flame instability prevented a proper extraction of LBV for stoichiometric and rich mixtures at 5 atm if N2 was used as the diluent. Therefore, helium (He), and argon (Ar) were used to suppress flame instability at 5 atm in the present study. Several oxygen to diluent ratios were used at 5 atm, 403 K, and a wide range of equivalence ratios (0.8-1.6) to provide the general trend of LBV. It was observed that He provided a smooth spherical flame without cellular structure even at a rich equivalence ratio of 1.6, and delivered a wider range of data points compared to Ar diluted mixtures. A similar observation was noticed by increasing the diluent ratio from 3.76 to 5, because of the increase in flame thickness relative to the density jump. Since the constant volume approach is used for determining LBV, many data points can be extracted out of a single experiment (up to 10 atm and 503 K) which brings several validation targets for DIPK chemical kinetic mechanisms

Laminar Burning Velocity Measurements In Dipk-An Advanced Biofuel

The biofuel and engine co-development framework was initiated at Sandia National Labs. Here, the synthetic biologists develop and engineer a new platform for drop-in fuel production from lignocellulosic biomass, using several endophytic fungi. Hence this process has the potential advantage that expensive pretreatment and fuel refining stages can be optimized thereby allowing scalability and cost reduction; two major considerations for widespread biofuel utilization. Large concentrations of ketones along with other volatile organic compounds were produced by fungi grown over switchgrass media. The combustion and emission properties of these new large ketones are poorly known. Therefore, fundamental measurements of representative molecules are needed to provide feedback on their desirability in advanced combustion engines (e.g., HCCI: homogeneous charge compression ignition engines) and their impact on emissions, as well as other combustion devices such as micro-combustors. 2,4-Dimethyl-3-pentanone, also known as diisopropyl ketone (DIPK), is a promising candidate biofuel for automotive applications produced by the fungal conversion process. Laminar burning velocity (LBV) is an important fundamental property of a fuel/air mixture and it depends on the composition, temperature, and pressure. Therefore, the knowledge of the dependence of the laminar burning velocity on above mentioned parameters can be used to design advanced engines as it can affect efficiency and heat release rates. We provide LBV measurements for DIPK, using the University of Central Florida (UCF) spherical flame chamber connected to a modified spark plug. Both pressure and direct flame visualization (shadowgraph) were utilized to ensure that the flame is spherical and stable (no cellular structure was observed within the flame) in order to provide reliable results with the constant volume approach. LBV measurements were also performed in iso-octane (C8H18), a relatively well characterized fuel, in order to validate our facility and measurement technique. The LBV results of C8H18/air and DIPK/air mixtures are compared with several oxygenated fuels in the literature and numerical values predicted by two chemical kinetic mechanisms

Laminar Burning Velocity Measurements in DIPK-An Advanced Biofuel

The biofuel and engine co-development framework was initiated at Sandia National Labs. Here, the synthetic biologists develop and engineer a new platform for drop-in fuel production from lignocellulosic biomass, using several endophytic fungi. Hence this process has the potential advantage that expensive pretreatment and fuel refining stages can be optimized thereby allowing scalability and cost reduction; two major considerations for widespread biofuel utilization. Large concentrations of ketones along with other volatile organic compounds were produced by fungi grown over switchgrass media. The combustion and emission properties of these new large ketones are poorly known. Therefore, fundamental measurements of representative molecules are needed to provide feedback on their desirability in advanced combustion engines (e.g., HCCI: homogeneous charge compression ignition engines) and their impact on emissions, as well as other combustion devices such as micro-combustors. 2,4-Dimethyl-3-pentanone, also known as diisopropyl ketone (DIPK), is a promising candidate biofuel for automotive applications produced by the fungal conversion process. Laminar burning velocity (LBV) is an important fundamental property of a fuel/air mixture and it depends on the composition, temperature, and pressure. Therefore, the knowledge of the dependence of the laminar burning velocity on above mentioned parameters can be used to design advanced engines as it can affect efficiency and heat release rates. We provide LBV measurements for DIPK, using the University of Central Florida (UCF) spherical flame chamber connected to a modified spark plug. Both pressure and direct flame visualization (shadowgraph) were utilized to ensure that the flame is spherical and stable (no cellular structure was observed within the flame) in order to provide reliable results with the constant volume approach. LBV measurements were also performed in iso-octane (C8H18), a relatively well characterized fuel, in order to validate our facility and measurement technique. The LBV results of C8H18/air and DIPK/air mixtures are compared with several oxygenated fuels in the literature and numerical values predicted by two chemical kinetic mechanisms

Flame Propagation In Premixed Mixtures Of Liquid Biofuels

There is a great potential for biofuels in automotive applications because they show advantages in mitigating greenhouse-gases, improving air quality, and reducing our dependence of fossil fuels. Ketones are new class of biofuels produced from endophytic conversion of cellulose. 2,4-Dimethyl-3-pentanone (DIPK) is a promising ketone for automotive applications. In this study, the laminar burning velocity (LBV) of DIPK was investigated in a spherical combustion chamber at initial T=120°C and various initial pressures using two ignition (laser and spark) techniques. Both constant pressure and constant volume approaches were used to derive the LBV values. The flame stability was assessed based on Markstein length, linear, and nonlinear extrapolation methods. The extended LBV values along one isentrope in constant volume method, helps in obtaining LBV values in a high pressure and temperature environment similar to automotive engines. Current data can be compared to the predictions of recent DIPK chemical kinetic mechanisms

The Effect Of Diluent Gases On High-Pressure Laminar Burning Velocity Measurements Of An Advanced Biofuel Ketone

The 2,4-dimethyl-3-pentanone (DIPK) is a promising biofuel candidate for automotive applications that is produced by the endophytic fungal conversion process which can be optimized for widespread utilization. There are some studies in the literature on combustion properties of DIPK, such as ignition delay times and laminar burning velocity (LBV) measurements. However, most studies are conducted one atmospheric (atm) pressure which are far away from the high-pressure conditions present inside reciprocating engines. Therefore, we present LBV measurements at high pressures up to 10 atm for this fuel using a spherical flame speed facility. It is known that the flame in a constant volume chamber develops cellular structure (hydrodynamic instability) as the initial pressure increases because of the reduction in flame thickness. In addition, the diffusional-thermal instability prevents experiments for rich mixtures because of the reduction of Lewis number (Le). An earlier study from our lab showed that the flame instability prevented a proper extraction of LBV for stoichiometric and rich mixtures at 5 atm with nitrogen (N2) diluent. Therefore, helium (He) and argon (Ar) were used to suppress flame instability in the present study. Several oxygen-to-diluent ratios were used at 5 atm, 403 K, and a wide range of equivalence ratios (0.8-1.6) to provide the general trend of LBV. It was observed that He provided a smooth spherical flame without cellular structure even at a rich equivalence ratio of 1.6 and delivered a wider range of data points compared to other gases. A similar observation was noticed by increasing the diluent ratio from 3.76 to 5, because of the increase in flame thickness relative to the density jump or density difference between unburned and burned gases. Since the constant volume approach is used for determining LBV, many data points can be extracted out of a single experiment (up to 10 atm and 503 K) which brings several validation targets for DIPK chemical kinetic mechanisms

Laser Ignition And Burning Velocity Measurements In Natural Gas/Air Mixtures

The laminar burning velocities of methane/air have been obtained using UCF\u27s high-pressure combustion bomb facility. High-speed schlieren photography is utilized to present the flame development propagation in select cases. Additionally, the flammability limits of methane-air mixtures are studied following ignition using Nd;YAG laser at 1064nm. Pressure traces and flame images are presented near the flammability limits. The laminar burning velocity of methane-air mixture is determined for initial temperature of 25 and 120 C, equivalence ratio range 0.7-1.4 and an initial pressure of 1 and 3 bar. The results of methane-air mixture study are compared with the laminar burning velocity measurements in the literature and the values predicted by two existing kinetic mechanisms. Current experiments are in very good agreement with existing literature data and the numerical model predictions

Premixed Flame Propagation In Mixtures Of Cyclopentanone/Air

There are several promising biofuel candidates for automotive applications that reduce greenhouse gases, improve air quality, and reduce the dependence on foreign oil. Currently, gasoline fuel properties such as octane number, pressure and temperature sensitivities limit the operating range of reciprocating engines. Because of those limitations, and the need to operate at a higher load to increase engine efficiencies, advanced fuels must be used. Cyclopentanone (C5H8O) is among one of the biofuel candidates considered for t U.S. Department of Energy\u27s Co-Optimization of Fuels and Engines (Co-Optima). In this study, laminar burning velocity (LBV) of cyclopentanone was measured in a spherical combustion chamber at initial conditions of 408 K, and atmospheric pressure for various equivalent ratios (φ) from 0.7 to 1.4. LBV is defined as the velocity at which unburned gases moves in the normal direction to the combustion wave surface. This is a crucial property in spark ignition engines because it affects the combustion duration. High-speed schlieren photography method was used to capture the flame propagation events. The flame stability was assessed based on Markstein length, and both linear and nonlinear extrapolation methods were utilized and compared