Increased efficiency through gasoline engine downsizing

CONTENTS: Introduction; Technologies for Downsizing; Low-Speed Pre-Ignition; LSPI Mechanisms; Research; Conclusion

Laser Induced Ignition with Resonant Multiphoton Absorption in Oxygen

A novel resonant laser-induced breakdown scheme has been demonstrated to provide precision spatial guidance of spark formation within an air flow and has been further demonstrated successfully in resonant laser-induced ignition of a moderate-speed flow of an air-propane mixture. This scheme could potentially provide ignition within a combustion system with a laser trigger leading to breakdown of an air-fuel flow within a high-voltage gap using a compact low power laser source. The laser scheme involves resonant enhanced multiphoton ionization (REMPI) in molecular oxygen and subsequent laser field-enhanced electron avalanche to generate a pre-ionized micro-plasma path between high voltage electrodes and thus guide the ignition spark through fuel-rich areas of the air-fuel flow. With this resonant method, sufficient photo-ionization and laser field-enhanced electron avalanche ionization have been generated for inducing air breakdown at a relatively low laser power compared to most laser breakdown concepts. This low power requirement may allow for a laser source to be transmitted to an ignition chamber via fiber optic coupling. Results of this study include high speed photographic analyses of flame ignition in an air-propane flow, showing the spatial and temporal evolution of the laser-induced spark and flame kernel leading to combustion.https://corescholar.libraries.wright.edu/physics_seminars/1017/thumbnail.jp

Characterization of the Ignition and Early Flame Propagation of Pre-Chamber Ignition System in a High Pressure Combustion Cell

The Pre-Chamber spark plug, already in its most simple configuration, allows a cycle fuel consumption reduction of 2-3% (WLTC) by enabling a significant compression ratio increase due to its huge knock mitigation effect. This benefit can be strongly extended in the homogeneous lean burn operation mode with very low nitrogen oxide emissions by a novel approach of injecting a well prepared fuel-air-mixture inside the Pre-Chamber. An increase of the engine compression ratio allows further the development of a new combustion process referred as the Pre-Chamber supported self-ignition process, which enable an increased thermodynamic efficiency at part load operating points of a gasoline engine. The development of a suitable Pre-Chamber ignition system requires the technical understanding of the Pre-Chamber geometry parameters on the combustion process. The impact of the overflow channel design on the flame propagation and ignition of the fuel-air mixture inside the main chamber must be understood in greater detail. This in turn requires a high-fidelity combustion model which is capable of predicting the impact of the overflow channel geometry on e.g. flame extinction, radical recombination on the walls of the Pre-Chamber orifice and finally the behavior of main chamber inflammation regardless of the Pre-Chamber ignition regime. Focus of this work is to discuss the impact of the Pre-Chamber geometry onto the inflammation and early flame propagation inside the main combustion chamber by means of experiments in an optical high pressure vessel under simplified boundary conditions. As a basis, the simultaneous high speed measurement of Schlieren and OH* chemiluminescence serve as a fundamental means to analyze ignition performance and early flame propagation in order to develop and validate an accurate combustion model. Initially, the general impact of the chamber pressure will be discussed emphasizing specifically on the differences between certain Pre-Chamber layouts and the conventional ignition system onto flame speed and ignition probability. Furthermore, variations of e.g. the number of overflow holes, the orifice diameter and the volume of the Pre- Chamber aids to identify the most relevant parameters responsible for flame extinction and combustion performance inside the main chamber

Experimental assessment of ignition characteristics of lubricating oil sprays related to low-speed pre-ignition (LSPI)

This is the author's version of a work that was accepted for publication in International Journal of Engine Research. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published as https://doi.org/10.1177/14680874211013268[EN] Low-speed pre-ignition (LSPI) remains one of the challenges of Direct Injection (DI) Spark Ignition (SI) engines due to its potential to induce a heavy knock. Several mechanisms have been identified in the literature as plausible causes for LSPI. The physical and chemical properties of lubricant oils play a role on some of these causes. The present work aims at getting an independent procedure to determine the proneness of lubricant oils to ignite. To this end, the ignition delay (ID) of different oil formulations is experimentally determined in a constant-pressure flow facility through two different optical techniques: Schlieren and OH* chemiluminescence imaging. The investigation explores the effect of base-stock formulation, oil specification quality level, different additive types content, aging, and oxidation on oil reactivity for several thermodynamic conditions. Differences in ignition delay were found among base stocks, correlating with the American Petroleum Institute (API) group classification. However, no significant differences were found among additive packages previously reported to yield different LSPI occurrences. Hence, differences in reactivity among lubricating oil formulations are not the determining factor explaining their different LSPI occurrences in an engine. Similarly, specific lubricant additive content, aging, and oxidation do not importantly modify the measured ignition delay.The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: Part of the experimental hardware used in this work was purchased through funds obtained from IDIFEDER/2018/037 ``Diagnostico optico a alta velocidad para el estudio de procesos termo-fluidodinamicos en sistemas de inyeccion.''Tormos, B.; García-Oliver, JM.; Carreres, M.; Moreno-Montagud, C.; Domínguez, B.; Cárdenas, MD.; Oliva, F. (2022). Experimental assessment of ignition characteristics of lubricating oil sprays related to low-speed pre-ignition (LSPI). International Journal of Engine Research. 23(8):1327-1338. https://doi.org/10.1177/146808742110132681327133823

Jet Ignition Research for Clean Efficient Combustion Engines

poster abstractIgnition by a jet of hot gas has application in lean-burn pre-chamber internal combustion engines and in innovative pressure-gain combustors for gas turbine engines. Jet ignition offers the advantage of reliable fast ignition and complete combustion of leaner mixtures. Fast burn rates due to the energetic ignition source produce multiple, distributed ignition zones, which consume the fuel-air mixture rapidly. Chemically active radicals and fast turbulent mixing in the jets create an explosion much more energetic than a spark. This high energy ignition results from the partially combusted gas from the pre-chamber products initiating combustion in the main chamber mixture. IC engines using low-cost, low-carbon natural gas need improved methods for ignition of lean mixtures to avoid nitrogen oxide emissions. This usually requires a richer mixture in the pre-chamber which is spark-ignited using a little additional gas fuel or compression-ignited with diesel fuel, possibly with a glow plug. A jet of hot reactive gas then ignites the main chamber lean mixture. Novel approaches for gas turbine engines using constant-volume, pressure-gain combustion include the multi-chamber wave rotor combustor. A wave rotor combustion chamber is best ignited with a jet of hot gas that may come from a small separately fueled pre-chamber or from a previously combusted chamber. Experiments on traversing and stationary jets have been conducted using the constant-volume wave rotor combustor established at combustion and propulsion research laboratory, IUPUI. The ignitability limit and ignition delay time for various hydrocarbon fuels (methane, ethylene and propane) have been investigated. Ignition characteristics have been analyzed using the high speed camera images and pressure data. Numerical simulations have been carried out using a hybrid eddy-break-up combustion model including finite-rate chemistry and two-equation k-ω turbulence model. Numerical and experimental results showed similar trends, with the modeling results illuminate the jet ignition process

Impact of hydrogen injection strategies on ammonia internal combustion engines ignited with active pre-chambers

The ongoing global energy transition towards renewable zero-carbon energy carriers demands a disruptive evolution of the combustion process inside internal combustion engines (ICEs). In many ways, ammonia (NH3) is an ideal candidate as future energy carrier due to the absence of carbon content, a well-established renewable production process, and high liquid energy density. However, ammonia has significantly higher minimum ignition energy and lower combustion speed than fossil fuels, representing a significant research challenge for traditional premixed combustion systems. In this work, an active pre-chamber ignition concept is explored on a premixed ammonia-air engine configuration, with hydrogen as the directly-injected fuel into the pre-chamber. This solution combines the advantages of volumetric ignition (turbulent jet ignition) with high-reactivity of hydrogen, overcoming the high ignition energy and low flame speed of ammonia. Specifically, this investigation is focused on the impact of H2 injection strategies on main-chamber NH3 combustion development. First, an experimental activity is conducted on a flexible research engine configuration, modified for active pre-chamber operation. Then, a 3D computational fluid-dynamics (CFD) analysis examines complex phenomena affecting the dual-fuel, inhomogeneous premixed combustion process in terms of flame development and highlight challenges related to H2 injection strategies. Results show that H2 injection timing strongly influences the pre-chamber combustion process. Delayed injection timing promotes retention of H2 inside the pre-chamber, producing overly rich local equivalence ratios around the spark plug, leading to misfire. Injecting H2 into the pre-chamber earlier allows H2 to emerge from the pre-chamber nozzles and distribute throughout the main-chamber prior to ignition, which accelerates combustion in the cylinder. Additionally, the duration of the H2 injection mainly impacts the quantity of H2 entering into the main-chamber, modifying the auto-ignition limit of the engine. Therefore, in any practical implementation of the active H2 pre-chamber concept, the H2 injection strategy is a critical parameter to be optimized. Novelty and Significance Statement The novelty of this research is the understanding of the impact of active pre-chamber hydrogen injection on the turbulent jet ignition of a premixed ammonia-air mixture, and the subsequent turbulent combustion propagation inside the main chamber of an internal combustion engine. An elongated injection duration favors auto-ignition phenomena, promoting greater thermal and combustion efficiencies, while a delayed start of injection leads to unstable main-chamber ignition and possible misfire. This insight is achieved through a combined experimental-numerical research study, where 3D CFD is employed as diagnostic tool for a deeper understanding of the experimental findings. This research is significant because it demonstrates how hydrogen direct-injection enables actively-fueled pre-chamber ammonia ICEs. This technology is extremely promising in the energy transition context because it minimizes the need for high levels of hydrogen blending, enabling on-board hydrogen generation from catalytic dissociation of ammonia, a more efficient and economic solution than hydrogen storage

Hydrogen SI and HCCI Combustion in a Direct-Injection Optical Engine

Hydrogen has been largely proposed as a possible alternative fuel for internal combustion engines. Its wide flammability range allows higher engine efficiency with leaner operation than conventional fuels, for both reduced toxic emissions and no CO2 gases. Independently, Homogenous Charge Compression Ignition (HCCI) also allows higher thermal efficiency and lower fuel consumption with reduced NOX emissions when compared to Spark-Ignition (SI) engine operation. For HCCI combustion, a mixture of air and fuel is supplied to the cylinder and autoignition occurs from compression; engine is operated throttle-less and load is controlled by the quality of the mixture, avoiding the large fluid-dynamic losses in the intake manifold of SI engines. HCCI can be induced and controlled by varying the mixture temperature, either by Exhaust Gas Recirculation (EGR) or intake air pre-heating. A combination of HCCI combustion with hydrogen fuelling has great potential for virtually zero CO2 and NOX emissions. Nevertheless, combustion on such a fast burning fuel with wide flammability limits and high octane number implies many disadvantages, such as control of backfiring and speed of autoignition and there is almost no literature on the subject, particularly in optical engines. Experiments were conducted in a single-cylinder research engine equipped with both Port Fuel Injection (PFI) and Direct Injection (DI) systems running at 1000 RPM. Optical access to in-cylinder phenomena was enabled through an extended piston and optical crown. Combustion images were acquired by a high-speed camera at 1°or 2°crank angle resolution for a series of engine cycles. Spark-ignition tests were initially carried out to benchmark the operation of the engine with hydrogen against gasoline. DI of hydrogen after intake valve closure was found to be preferable in order to overcome problems related to backfiring and air displacement from hydrogens low density. HCCI combustion of hydrogen was initially enabled by means of a pilot port injection of n-heptane preceding the main direct injection of hydrogen, along with intake air preheating. Sole hydrogen fuelling HCCI was finally achieved and made sustainable, even at the low compression ratio of the optical engine by means of closed-valve DI, in synergy with air-pre-heating and negative valve overlap to promote internal EGR. Various operating conditions were analysed, such as fuelling in the range of air excess ratio 1.2-3.0 and intake air temperatures of 200-400°C. Finally, both single and double injections per cycle were compared to identify their effects on combustion development. Copyright © 2009 SAE International

Development and Application of a Reduced Chemical Kinetics Model for Low-Speed Pre-Ignition Investigation

Gasoline direct injection engines, with downsized boosted technology, present a promising option for enhancing power density and reducing fuel consumption for next-generation engine designs to meet stringent fuel economy and emission standards. However, these developments in the low-speed and high-load operating regime are challenged by the occurrence of a new knocking combustion phenomenon: low-speed pre-ignition. Lubricant oil droplets and their constituents, when diluted with gasoline injection, have been suggested as a key characteristic affecting this phenomenon. We have developed a reduced chemical kinetics model that represents gasoline, lubricant base oil, and oil additive constituents, and validated it against both literature detailed chemical kinetics models and experimental data from jet-stirred reactors and shock tubes. Preliminary application of this reduced chemical kinetics models via direct injection engine simulations at lowspeed, high-load operating conditions has triggered pre-ignition event when a lubricant oil droplet is present in the combustion chamber, indicating a promising outlook for this field of research. This study represents the first step in the development of an effective chemical kinetics model able to be incorporated in a multidimensional computational fluid dynamics framework for engine applications and low-speed pre-ignition investigation

A multi-physics simulation approach to Investigating the underlying mechanisms of Low-Speed Pre-Ignition

As part of the effort to improve thermal efficiency, engines are being significantly downsized. A common issue in gasoline engines which limits thermal efficiency and is further exacerbated by downsizing, is low speed pre ignition (LSPI). This thesis uses a Multiphysics approach, initially using a validated 1D engine performance model of a GTDI engine, to define realistic boundary conditions. A strong emphasis on validating each simulation methodology as much as possible is maintained at each stage. A hydrodynamic model of the ring-liner and Lagrangian CFD model are used to investigate the impact of engine oil fluid properties on the mass of oil transported from the crevice volume to the combustion chamber. A heat transfer and evaporation model of a single droplet inside an engine environment was developed for alkanes of chain lengths representing the extremes of the chain lengths present in engine oil. It was found the droplet generally evaporates at a crank angle which is close to the point where LSPI is observed. The hydrocarbon study ends with a CFD constant volume simulation to understand why engine oil like hydrocarbons ignite in rig tests but not in an engine. This research then proceeds to develop a single particle detergent model in an engine environment, to initially understand why ignition occurs when a calcium Ca based detergent is present but not in the case of a magnesium Mg detergent. It was found from simulation that the common theory of calcium oxide CaO resulting from thermal degradation from the previous cycle then reacting with Carbon dioxide CO2 late in the compression stroke is unlikely. There is a stronger case for the CaO particle causing ignition as it is present in fresh engine oil sprayed onto the liner. As predicted by the hydrocarbon evaporation model the oil will cover and protect the CaO particle until late in the compression stroke when the oil will evaporate, exposing the CaO particle to CO2