An Assessment of fuel physical and chemical properties in the combustion of a Diesel spray

With the slow but ineluctable depletion of fossil fuels, several avenues are currently being explored in order to define the strategic boundaries for a clean and sustainable energetic future, while accounting for the specificities of each sectors involved. In regard to transport applications, alternative fuels may represent a promising solution, at least at short or middle term, such as the International Energy Agency foresees that their share could account for 9% of the road transport fuel needs by 2030 and 27 % by 2050, with the potential resources to reach 48% beyond. If they have already been included in significant blending proportions with conventional fossil fuel in most of the occidental countries, their introduction also coincides with a long-time established program of continuously more drastic standards for engine emissions of NOX and PM, now even further demanding by the seek for combustion efficiency aiming at reducing CO2 emissions. While several works discuss the alternative fuels effect on exhaust emissions when used directly in production Diesel engines, results and analysis are sometimes contradictory, depending sometimes on the conditions in which they were obtained, and the causes of these results remain unclear. Therefore, in order to better understand their effect on the combustion processes, and thus extract the maximum benefits from these fuels in the optimization of engine design and calibration, a detailed comprehension of their spray and combustion characteristics is essential. The approach of this study is mostly experimental and based on an incremental methodology of tests aiming at isolating injection and combustion processes with the objective to identify and quantify the role of both fuel physical and chemical properties at some key stages of the Diesel combustion process. After obtaining a detailed characterization of their properties, five fuels have been injected in an optical engine enabling a sharp control of the thermodynamic eNerva, J. (2013). An Assessment of fuel physical and chemical properties in the combustion of a Diesel spray [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/29767Palanci

Internal and near nozzle measurements of Engine Combustion Network "Spray G" gasoline direct injectors

[EN] Gasoline direct injection (GDI) sprays are complex multiphase flows. When compared to multi-hole diesel sprays, the plumes are closely spaced, and the sprays are more likely to interact. The effects of multi-jet interaction on entrainment and spray targeting can be influenced by small variations in the mass fluxes from the holes, which in turn depend on transients in the needle movement and small-scale details of the internal geometry. In this paper, we present a comprehensive overview of a multi-institutional effort to experimentally characterize the internal geometry and near-nozzle flow of the Engine Combustion Network (ECN) Spray G gasoline injector. In order to develop a complete pictitre of the near-nozzle flow, a standardized setup was shared between facilities. A wide range of techniques were employed, including both X-ray and visible-light diagnostics. The novel aspects of this work include both new experimental measurements, and a comparison of the results across different techniques and facilities. The breadth and depth of the data reveal phenomena which were not apparent from analysis of the individual data sets. We show that plume-to-plume variations in the mass fluxes from the holes can cause large-scale asymmetries in the entrainment field and spray structure. Both internal flow transients and small-scale geometric features can have an effect on the external flow. The sharp turning angle of the flow into the holes also causes an inward vectoring of the plumes relative to the hole drill angle, which increases with time due to entrainment of gas into a low-pressure region between the plumes. These factors increase the likelihood of spray collapse with longer injection durations.The X-ray experiments were performed at the 7-BM and 32-ID beam lines of the APS at Argonne National Laboratory. Use of the APS is supported by the U.S. Department of Energy (DOE) under Contract No. DE-AC02-06CH11357. Research was also performed at the Combustion Research Facility, Sandia National Laboratories, Livermore, California. Sandia National Laboratories is managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy National Nuclear Security Administration under contract DE-NA-0003525.Duke, DJ.; Kastengren, AL.; Matusik, KE.; Swantek, AB.; Powell, CF.; Payri, R.; Vaquerizo, D.... (2017). Internal and near nozzle measurements of Engine Combustion Network "Spray G" gasoline direct injectors. Experimental Thermal and Fluid Science. 88:608-621. https://doi.org/10.1016/j.expthermflusci.2017.07.015S6086218

Parametric study and optimization of diesel engine operation for low emissions using different injectors

The objective of this research was to develop advanced diesel combustion strategies for emissions reduction in a multi-cylinder diesel engine. The engine was equipped with an electronically-controlled, common-rail fuel injection system, and an exhaust gas recirculation (EGR) system. This experimental setup allowed a wide range of operating conditions to be explored. Effects of various injector parameters with various EGR levels on emissions were studied. Injector parameters included the injector flow number, nozzle hole geometry (straight, convergent), and nozzle arrangement (6-hole, 10-hole, 16-hole). The included spray angle was kept constant at 133 deg. Other engine parameters included the EGR rate (0-41%), injection pressure (150-225 MPa), start of injection (SOI) (-20 to 5 ATDC), start of pilot injection (-40 to -15 ATDC), and pilot fuel percentage (0-25%). For single injection operations, a simultaneous reduction of NOx and particulate matter (PM) was achieved by using high EGR (30%) with late injection timing (0 to 5 ATDC) at high injection pressures (150 MPa). For double injection operations, NOx and PM emissions were reduced using 30% EGR, 15% pilot injection at an early pilot timing (-30 ATDC) and late main injection (5 ATDC). Injectors with low flow numbers were able to produce low emissions at high EGR levels (\u3e35%) and high injection pressures (\u3e150 MPa). The combustion was stable at these high EGR levels as the SOI was held at 0 ATDC. On the other hand, injectors with high flow numbers were not able to produce stable combustion at such high EGR levels with late SOI. Small nozzle holes in the 10-hole injector helped reduce NOx and PM emissions significantly. However, a 16-hole injector with a similar nozzle hole diameter produced very high PM emissions due to poor air utilization. To improve the speed of optimization for lower emissions, particle swarm optimization (PSO), a stochastic, population-based evolutionary optimization algorithm, was applied to both engine experiments and numerical simulation. The algorithm was tested using test functions that were used in the field of optimization to ensure reaching a global optimum. A merit function was defined to help reduce multiple emissions simultaneously. The PSO was found to be very effective in finding the optimal operating conditions for low emissions. The optimization usually took 40-70 experimental runs to find the optimum. High EGR levels, late main injection, and small pilot amount were suggested by the PSO. Multiple emissions were reduced simultaneously without a compromise in the brake specific fuel consumption. In some cases, the NOx and PM emissions were reduced to as low as 0.41 and 0.0092 g/kW-h, respectively. The operating conditions at this point were 34% EGR, 5 ATDC main SOI, -24 ATDC pilot SOI, and 5% pilot fuel. The PSO was also integrated with an engine simulation code and applied to engine optimization numerically. The results showed that optimization of engine combustion using PSO with numerical simulation was an effective means in the development of future emission reduction strategies

Fuel Injection

Fuel Injection is a key process characterizing the combustion development within Internal Combustion Engines (ICEs) and in many other industrial applications. State of the art in the research and development of modern fuel injection systems are presented in this book. It consists of 12 chapters focused on both numerical and experimental techniques, allowing its proper design and optimization

The influence of inter-jet spacing and jet-swirl interaction on flame image velocimetry (FIV) derived flow fields in a small-bore diesel engine

This study applies Flame Image Velocimetry (FIV) to show the in-flame flow field development with an emphasis on the jet-jet interaction and jet-swirl interaction phenomena in a single-cylinder small-bore optically accessible diesel engine. Two-hole nozzle injectors with three different inter-jet spacing angles of 45°, 90° and 180° are prepared to cause different levels of jet-jet interaction. The engine has a swirl ratio of 1.7, which is used to evaluate jet-swirl interaction of the selected 180° inter-jet spacing nozzle. High-speed soot luminosity imaging was performed at a high frame rate of 45 kHz for the FIV processing. For each inter-jet spacing angle, a total of 100 individual combustion cycles were recorded to address the cyclic variations. The ensemble averaged flow fields are shown to illustrate detailed flow structures while the Reynolds decomposition using spatial filtering is applied to analyse turbulence intensity. The results showed reduced bulk flow magnitude and turbulence intensity at smaller inter-jet spacing, suggesting the two opposed wall-jet heads colliding immediately after the jet impingement on the wall can cause flow suppression effects. This raised a concern on the mixing as lower inter-jet spacing creates more fuel-rich mixtures in the jet-jet interaction region. Despite lower flow magnitude, the cyclic variation was also estimated higher for narrower inter-jet spacing, which is another drawback of the significant jet-jet interaction. Regarding the jet-swirl interaction, the wall-jet head penetrating on the up-swirl side showed lower bulk flow magnitude as the counter-flow arrangement suppressed the flow, similar with the narrower interact-jet spacing results. However, the turbulence intensity was measured higher on the up-swirl side, suggesting the relatively weaker swirl flow vectors opposed to the penetrating wall-jet head could in fact enhance the mixing

Investigations of advanced injection and combustion strategies on DI diesel engine performance and emissions

The main driving force behind this research was the need for cleaner and more efficient engines to meet the ever-increasing demands on the modern automobile’s emissions. In recent years different studies have been carried out to analyze the combined effects of high-pressure injection, boost pressure, multiple injections, included spray angle and combustion chamber geometry. Though considerable research has shown these technologies can meet the low emission regulations, the careful optimization of the engine operating conditions is still required in order to get the full benefit of the different strategies. With these issues as motivation, the first important objective of this study was to gain a detailed understanding of the mechanisms through which fuel injection interacts with other engine parameters and influences diesel combustion and emissions, and hence to attempt to generalize the adoption of multiple injection strategies with regards to improving diesel engine performance. For this purpose, a modified parameter called “Homogeneity Factor of in-cylinder charge” (HF) was introduced and proposed as a new measure in combustion theory to analyze the combustion characteristics and air-fuel mixing process of diesel engines in more detail. The second part of this research builds upon a detail investigation on the included spray cone angle concept and explores further their use in conjunction with multiple-injection strategies in diesel engines. In addition, an investigation was performed in third phase of this research to analyze the effects of piston geometry on combustion, performance and exhaust emission characteristics. The results showed that employing a post-injection combined with a pilot injection results in reduced soot formation from diffusion combustion and enhances the soot oxidation process during the expansion stroke, resulting in decreased soot emissions, while the NOx concentration is maintained in low levels. It was also found that spray targeting is very effective for controlling the in-cylinder mixture distributions especially when it accompanied with advanced injection strategies. Moreover, the results confirmed that a narrower width of piston bowl has a higher unburned fuel air mixture region and hence results in higher soot emissions but with slightly larger piston surface area the optimum operating point could be obtaine

Spray Processes in Optical Diesel Engines - Air-Entrainement and Emissions

Internal combustion engines have been an important technological field for more than a century. It has had an important impact on society through improved transportation and industrial applications. However, concerns about environmental effects of exhaust gases and utilization of oil resources have pushed development of combustion engines towards cleaner combustion and higher efficiencies. The diesel engine is today an interesting solution in terms of fuel economy. However, emissions of pollutants such as soot particles are still a major concern for diesel engines. The combustion process in diesel engines is far from fully understood and there are many to questions to be answered about emissions formation and oxidation within the combustion chamber. The objective of this work is it to gain knowledge on in-cylinder processes related to engine-out emissions. More specifically, the focus is set on understanding the connections between spray processes and the formation of pollutants such as soot particles and unburned hydrocarbons by using optical diagnostics. Engines modified for optical studies allowing optical access inside the combustion chamber have been used in the different investigations presented in this thesis. The types of engines concerned here are four-stroke heavy- and light-duty diesel engines. Even though engines are complex systems with interacting sub-systems, such as turbochargers and after-treatment devices, the focus of this work is solely on the in-cylinder processes. The focus of this thesis is fuel-jet mechanisms related to air-entrainment and emission formations. The different investigations conducted in this work can be divided in two main categories. First, air-entrainment in fuel jets and its coupling to emissions formation were studied in different optical engines. Previous results in the field, often obtained in constant volume combustion vessels, were used for prediction calculations and comparison between free jets and jets in engine environment. Second, multiple injection strategies were investigated to reduce engine-out emissions of soot and unburned hydrocarbons and also to stabilize combustion in cold conditions. The results presented in this thesis can be divided in two main categories; air entrainment in fuel jets and multiple injection strategies. The first part regards air entrainment both upstream the lift-off length and in the interaction between adjacent jets. The second part presents multiple injections strategies as a tool for combustion stabilization in cold conditions and emissions reductio