• Energy Research

Abstract This paper studies the influences of different fuel injection strategies on flame propagation and combustion characteristics in a glow plug assisted direct-injection natural gas engine. Our previously existing version of the KIVA-3V CFD code incorporates a model of internal flows in the gaseous fuel injector and also a detailed model of the glow plug and its shield. This study was conducted by using the KIVA-3V code with added improved emissions models, including a detailed kinetic chemical model and a modified phenomenological soot model. In the simulation, a low temperature natural gas mechanism is selected to estimate the gaseous species, and acetylene was chosen as the key species to model the soot formation. The simulation indicated that the fuel injection duration, injector nozzle size and injection angle can affect the natural gas combustion characteristics. Generally, shorter injection duration reduces both peak cylinder pressure and emissions in the natural gas engine; however, the natural gas flame propagation cannot be maintained once the injected fuel mass is lower than a limit. The simulation also reveals that the injector nozzle size highly affects the natural gas combustion by inducing diffusion combustion for a small diameter nozzle and partially premixed combustion for a large diameter nozzle. Compared to a large nozzle, a small nozzle results in a faster pressure rise with more engine emissions and lower combustion efficiency. The fuel injection angle can influence natural gas combustion characteristics by affecting the flame propagation out of the glow plug shield in the initial combustion stage.

This article presents the results of computational studies investigating the ignition of high-pressure natural gas jets in a compression-ignition engine with glow plug ignition assist. The simulation was conducted using a KIVA-3V-based three-dimensional engine model, along with an improved fuel injector model, a detailed cut-off glow plug shield model and a modified two-step methane reaction mechanism, to simulate the natural gas injection and ignition. The simulated results demonstrate the significance of using a shield for the glow plug. Compared to an unshielded (bare) glow plug, the shield not only reduces the heat loss from the hot glow plug surface to the cold intake air charge and the cold injected gas jet but also traps the fuel mixture to increase its residence time adjacent to the hot surface. Over a representative range of heavy-duty diesel engine operating conditions, a shielded glow plug greatly improves the natural gas engine performance and provides reliable ignition, while an unshielded glow plug can only be optimized for specific conditions. The understanding of glow plug shield behavior gained from the simulations suggests avenues for improved shield designs that would yield further reduced ignition delays.

Biodiesels have been promoted as a greener alternative to diesel with decreased emissions and health effects. To investigate the scientific basis of the suggested environmental and health benefits offered by biodiesel, this review examines the current state of knowledge and key uncertainties of pollutant profiles of biodiesel engine exhaust and the associated the respiratory and cardiovascular outcomes. The ease and low cost of biodiesel production has facilitated greater distribution and commercial use. The pollutant profile of biodiesel engine exhaust is distinct from diesel, characterised by increased NOx and aldehyde emissions but decreased CO and CO2. Lower engine-out particulate matter mass concentrations have also been observed over a range of feedstocks. However, these reduced emissions have been attributable to a shift towards smaller sized particulate emissions. The toxicity of biodiesel engine exhaust has been investigated in vitro using various lung cell, in vivo evaluating responses induced in animals and through several human exposure studies. Discrepancies exist across results reported by in vitro and in vivo studies, which may be attributable to differences in biodiesel feedstocks, engine characteristics, operating conditions or use of aftertreatment systems across test scenarios. The limited human testing further suggests short-term exposure to biodiesel engine exhaust is associated with cardiopulmonary outcomes that are comparable to diesel. Additional information about the health effects of biodiesel engine exhaust exposure is required for effective public health policy.

Abstract Use of a shielded glow plug (GP) for ignition assist enables operation of direct-injection engines on 100% natural gas. The shield improves ignition performance by reducing GP cooling from impinging intake air and injected natural gas jets and by trapping mixture adjacent to the hot surface thereby increasing residence time. After ignition, flame must propagate out of the shield to consume fuel in the combustion chamber. The number, size, and position of openings in the GP shield determines the path of flame propagation from the shield. This study computationally investigated the performance of a shield with multiple openings arranged in a diamond pattern compared to a basic single-opening shield. A KIVA-3V based engine model coupled with the CANTERA kinetics package was used and incorporated a multi-step phenomenological soot model to predict the formation of soot particles. The results illustrate that the new multi-opening shield has significant influence on both the flow of injected fuel into the shield and the flame propagation out of the shield. The multi-opening shield design reduces the fuel flow into the shield during injection and improves fuel distribution within the shield compared to the single-opening shield. With the multi-opening shield, the initial flame propagating out moves towards the combustion chamber wall to consume the adjacent fuel jets before spreading in the swirl direction. Both shields result in comparable pressure rise, but the multi-opening shield reduces overall soot emissions by 46.6%, with similar methane emissions, compared to the single-opening shield.

In this paper, we demonstrate through examples how the concept of a Semantic Web based knowledge graph can be used to integrate combustion modeling into cross-disciplinary applications and in particular how inconsistency issues in chemical mechanisms can be addressed. We discuss the advantages of linked data that form the essence of a knowledge graph and how we implement this in a number of interconnected ontologies, specifically in the context of combustion chemistry. Central to this is OntoKin, an ontology we have developed for capturing both the content and the semantics of chemical kinetic reaction mechanisms. OntoKin is used to represent the example mechanisms from the literature in a knowledge graph, which itself is part of the existing, more general knowledge graph and ecosystem of autonomous software agents that are acting on it. We describe a web interface, which allows users to interact with the system, upload and compare the existing mechanisms, and query species and reactions across the knowledge graph. The utility of the knowledge-graph approach is demonstrated for two use-cases: querying across multiple mechanisms from the literature and modeling the atmospheric dispersion of pollutants emitted by ships. As part of the query use-case, our ontological tools are applied to identify variations in the rate of a hydrogen abstraction reaction from methane as represented by 10 different mechanisms.

Abstract The influences of different fuel injection strategies on emission characteristics in a glow plug assisted direct-injection natural gas engine were computationally investigated by a KIVA-3V engine model. A detailed chemical kinetic model and a phenomenological soot model were implemented in the simulation to predict the formation of engine emissions. The simulation reveals that the sac volume of the fuel injector is one of the major contributors to the methane emissions, and the use of a bigger injector nozzle and shorter injection duration can reduce the fuel storage inside the sac volume. In addition, the glow plug shield will trap some fuel mixture and induce relatively rich combustion that contributes a significant amount to both of methane emission and soot particles. Additional openings in the upper part of the glow plug shield may be needed to improve the flow exchange between the shield and the combustion chamber, in order to reduce the emission formation. Further simulation suggests that different fuel injection strategies, such as changing the injection angle and using different injector nozzle sizes associated with different injection durations, could affect the fuel injection, flame propagation and then emission formation inside the glow plug shield and combustion chamber. An optimized fuel injection strategy thereby has potential of reducing the local emission formation inside the glow plug shield and its contribution to the final combustion emissions.

The addition of metallic precursors to flames evinces interest because of their potential ability to catalyze methane and ethanol combustion by means of supplemental gas-phase and surface reactions. A counterflow flame burner is used to spatially characterize and analyze the emissions from iron-pentacarbonyl-borne ethanol and methane combustion. Samples of the flue gases are obtained from these laminar and planar flames and are quantified using gas chromatography (GC) and Fourier transform infrared (FTIR) spectroscopy, while solid particles are examined through X-ray diffraction (XRD). Measurements from ethanol and methane flames are compared and analyzed, to investigate the role of metal particles derived from iron pentacarbonyl. Experimental data demonstrate, in both flames, a significant influence of the additive on combustion emissions, such as NO and soot precursors. The addition of iron pentacarbonyl is found to be more effective in restricting soot precursors in methane flames compared to ethanol f...