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Transportation accounted for 28% of the total U.S. energy demand in 2011, with 93% of U.S. transportation energy coming from petroleum. The large impact of the transportation sector on global climate change necessitates more-efficient, cleaner-burning internal combustion engine operating strategies. One such strategy that has received substantial research attention in the last decade is Homogeneous Charge Compression Ignition (HCCI). Although the efficiency and emissions benefits of HCCI are well established, practical limits on the operating range of HCCI engines have inhibited their application in consumer vehicles. One such limit is at high load, where the pressure rise rate in the combustion chamber becomes excessively large. Fuel stratification is a potential strategy for reducing the maximum pressure rise rate in HCCI engines. The aim is to introduce reactivity gradients through fuel stratification to promote sequential auto-ignition rather than a bulk-ignition, as in the homogeneous case. A gasoline-fueled compression ignition engine with fuel stratification is termed a Gasoline Compression Ignition (GCI) engine. Although a reasonable amount of experimental research has been performed for fuel stratification in GCI engines, a clear understanding of how the fundamental in-cylinder processes of fuel spray evaporation, mixing, and heat release contribute to the observed phenomena is lacking. Of particular interest is gasoline's pressure sensitive low-temperature chemistry and how it impacts the sequential auto-ignition of the stratified charge. In order to computationally study GCI with fuel stratification using three-dimensional computational fluid dynamics (CFD) and chemical kinetics, two reduced mechanisms have been developed. The reduced mechanisms were developed from a large, detailed mechanism with about 1400 species for a 4-component gasoline surrogate. The two versions of the reduced mechanism developed in this work are: (1) a 96-species version and (2) a 98-species version including nitric oxide formation reactions. Development of reduced mechanisms is necessary because the detailed mechanism is computationally prohibitive in three-dimensional CFD and chemical kinetics simulations. Simulations of Partial Fuel Stratification (PFS), a GCI strategy, have been performed using CONVERGE with the 96-species reduced mechanism developed in this work for a 4-component gasoline surrogate. Comparison is made to experimental data from the Sandia HCCI/GCI engine at a compression ratio 14:1 at intake pressures of 1 bar and 2 bar. Analysis of the heat release and temperature in the different equivalence ratio regions reveals that sequential auto-ignition of the stratified charge occurs in order of increasing equivalence ratio for 1 bar intake pressure and in order of decreasing equivalence ratio for 2 bar intake pressure. Increased low- and intermediate-temperature heat release with increasing equivalence ratio at 2 bar intake pressure compensates for decreased temperatures in higher-equivalence ratio regions due to evaporative cooling from the liquid fuel spray and decreased compression heating from lower values of the ratio of specific heats. The presence of low- and intermediate-temperature heat release at 2 bar intake pressure alters the temperature distribution of the mixture stratification before hot-ignition, promoting the desired sequential auto-ignition. At 1 bar intake pressure, the sequential auto-ignition occurs in the reverse order compared to 2 bar intake pressure and too fast for useful reduction of the maximum pressure rise rate compared to HCCI. Additionally, the premixed portion of the charge auto-ignites before the highest-equivalence ratio regions. Conversely, at 2 bar intake pressure, the premixed portion of the charge auto-ignites last, after the higher-equivalence ratio regions. More importantly, the sequential auto-ignition occurs over a longer time period for 2 bar intake pressure than at 1 bar intake pressure such that a sizable reduction in the maximum pressure rise rate compared to HCCI can be achieved.
Conventional fossil fuels will constitute the majority of automotive fuels for the foreseeable future but will have to adapt to changes in engine technology. Unconventional transport fuels such as biofuels, gas-to-liquid fuels, compressed natural gas, and liquid petroleum gas will also play a role. Hydrogen might be a viable transport fuel if it overcomes barriers in production, transport, storage, and safety and/or if fuel cells become viable. This book opens by considering these issues and then introduces practical transport fuels. A chapter on engine deposits follows, which is an important practical topic about how fuels affect engines that is not usually considered in other books. The next three chapters discuss auto-ignition phenomena in engines. The auto-ignition resistance of fuels is the most important fuel property since it limits the efficiency of spark ignition engines and determines the performance of compression ignition engines. Moreover, the manufacture of fuels is primarily driven by the need to meet auto-ignition quality demands set by fuel specifications. The final chapter considers the implications for future fuels. The book covers the many important ways that fuels and engines interact and why and how fuels will need to change to meet the requirements of future engines, as well as the implications for fuels manufacture and specifications.
Various combinations of commercially available technologies could greatly reduce fuel consumption in passenger cars, sport-utility vehicles, minivans, and other light-duty vehicles without compromising vehicle performance or safety. Assessment of Technologies for Improving Light Duty Vehicle Fuel Economy estimates the potential fuel savings and costs to consumers of available technology combinations for three types of engines: spark-ignition gasoline, compression-ignition diesel, and hybrid. According to its estimates, adopting the full combination of improved technologies in medium and large cars and pickup trucks with spark-ignition engines could reduce fuel consumption by 29 percent at an additional cost of $2,200 to the consumer. Replacing spark-ignition engines with diesel engines and components would yield fuel savings of about 37 percent at an added cost of approximately $5,900 per vehicle, and replacing spark-ignition engines with hybrid engines and components would reduce fuel consumption by 43 percent at an increase of $6,000 per vehicle. The book focuses on fuel consumption-the amount of fuel consumed in a given driving distance-because energy savings are directly related to the amount of fuel used. In contrast, fuel economy measures how far a vehicle will travel with a gallon of fuel. Because fuel consumption data indicate money saved on fuel purchases and reductions in carbon dioxide emissions, the book finds that vehicle stickers should provide consumers with fuel consumption data in addition to fuel economy information.
This book focuses on gasoline compression ignition (GCI) which offers the prospect of engines with high efficiency and low exhaust emissions at a lower cost. A GCI engine is a compression ignition (CI) engine which is run on gasoline-like fuels (even on low-octane gasoline), making it significantly easier to control particulates and NOx but with high efficiency. The state of the art development to make GCI combustion feasible on practical vehicles is highlighted, e.g., on overcoming problems on cold start, high-pressure rise rates at high loads, transients, and HC and CO emissions. This book will be a useful guide to those in academia and industry.
Many research studies have shown that low temperature combustion in compression ignition engines has the ability to yield ultra-low NOx and soot emissions while maintaining high thermal efficiency. To achieve low temperature combustion, sufficient mixing time between the fuel and air in a globally dilute environment is required, thereby avoiding fuel-rich regions and reducing peak combustion temperatures, which significantly reduces soot and NOx formation, respectively. It has been demonstrated that achieving low temperature combustion with diesel fuel over a wide range of conditions is difficult because of its properties, namely, low volatility and high chemical reactivity. On the contrary, gasoline has a high volatility and low chemical reactivity, meaning it is easier to achieve the amount of premixing time required prior to autoignition to achieve low temperature combustion. In order to achieve low temperature combustion while meeting other constraints, such as low pressure rise rates and maintaining control over the timing of combustion, in-cylinder fuel stratification has been widely investigated for gasoline low temperature combustion engines. The level of fuel stratification is, in reality, a continuum ranging from fully premixed (i.e. homogeneous charge of fuel and air) to heavily stratified, heterogeneous operation, such as diesel combustion. However, to illustrate the impact of fuel stratification on gasoline compression ignition, the authors have identified three representative operating strategies: partial, moderate, and heavy fuel stratification. Thus, this article provides an overview and perspective of the current research efforts to develop engine operating strategies for achieving gasoline low temperature combustion in a compression ignition engine via fuel stratification. In this paper, computational fluid dynamics modeling of the in-cylinder processes during the closed valve portion of the cycle was used to illustrate the opportunities and challenges associated with the various fuel stratification levels.
Fundamentals of Low Emission Flameless Combustion and Its Applications is a comprehensive reference on the flameless combustion mode and its industrial applications, considering various types of fossil and alternative fuel. Several experimental and numerical accomplishments on the fundamentals of state-of-the-art flameless combustion is presented, working to clarify the environmentally friendly aspects of this combustion mode. Author Dr. Hosseini presents the latest progresses in the field and highlights the most important achievements since invention, including the fundamentals of thermodynamics, heat transfer and chemical kinetics. Also analyzed is fuel consumption reduction and the efficiency of the system, emissions formation and the effect of the flameless mode on emission reduction.This book provides a solid foundation for those in industry employing flameless combustion for energy conservation and the mitigation of pollutant emissions. It will provide engineers and researchers in energy system engineering, chemical engineering, industrial engineers and environmental engineering with a reliable resource on flameless combustion and may also serve as a textbook for senior graduate students. - Presents the fundamentals of flameless combustion and covers advances since its invention - Includes experimental and numerical investigations of flameless combustion - Analyzes emission formation and highlights the effects of the flameless mode on emission reduction
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Varying the fuel stratification during gasoline compression ignition (GCI) combustion has been shown to impact important combustion parameters and emissions. The effect of varied injection pressure and injection timing on the fuel stratification and formation of nitric oxide (NOx) emissions was studied at two engine operating conditions. At a 1500 revolutions per minute (rpm) engine condition, a 100 bar increase in injection pressure required a 1.4o crankangle retard of the injection timing to maintain constant NOx emissions. The required injection timing shift to maintain constant NOx emissions at a 1900 rpm condition for a 100 bar increase in injection pressure was 2.5o crankangle. A skip-firing injection strategy illustrated the importance of the second injection in creating fuel stratification and promoting ignition for GCI combustion. The effects of injected fuel mass variability on combustion stability were investigated using a randomized injection strategy. Analysis showed that the injected fuel mass uncertainty required to induce combustion instability was between 3.2-4.8%. Three-dimensional computational fluid dynamics (CFD) and a one-dimensional (1-D) turbulent jet model were used to analyze the fuel-air mixing. A quasi-steady jet timescale was used to non-dimesionalize the time after start of injection. The ability of the timescale to collapse the jet vapor penetration and fuel-mass-weighted PDF of mixture fraction/equivalence ratio were evaluated for a variety of conditions at times significantly after end of injection. The quasi-steady jet timescale reasonably collapsed jet vapor penetration for various injection pressures but did not collapse the fuel-mass-weighted PDFs of equivalence ratio at times of interest during transient changes to the ambient gas density unless changes in spray spreading angle are accounted for. The 1-D jet model was benchmarked to CFD and evaluated at different conditions to analyze the assumptions of the 1-D model. A sensitivity analysis of the 1-D model was conducted. The 3-D CFD results are utilized to analyze the connection between the fuel-air distribution and the engine-out NOx emissions at the constant-NOx engine operating conditions. Computational fluid dynamics results showed similar equivalence ratio distributions resulted in relatively constant NOx emissions.