Search Results (14)

This study investigates the performance and combustion behavior of a spark ignition engine retrofitted to operate on compressed natural gas (CNG), with a focus on a newly developed stratified charge pre-chamber design. The engine was modified to include an auxiliary intake valve that enables partial enrichment of the pre-chamber mixture without the need for a dedicated fuel injector. This hybrid approach combines the mechanical simplicity of passive systems with the enhanced combustion control of active pre-chambers. Both experimental tests and computational fluid dynamics (CFD) analyses were carried out under partial load conditions (8 Nm) and engine speeds ranging from 900 to 1700 rpm. The results demonstrate improvements in indicated mean effective pressure (IMEP), combustion stability, and flame propagation speed—particularly at lower engine speeds where stratified combustion effects are more pronounced. However, increasing engine speed resulted in reduced volumetric efficiency and elevated exhaust temperatures, indicating potential for further optimization via turbocharging or advanced scavenging techniques. Overall, the findings validate the effectiveness of the proposed design in enhancing thermal efficiency and ignition stability in CNG-fueled engines, especially under urban driving conditions. Full article

Hydrogen and its unique properties pose major challenges to the development of innovative combustion engines, while it represents a viable alternative when it is based on renewable energy sources. The present paper deals with the holistic approach of hydrogen combustion modeling from a 0D/1D reactor evaluation with Cantera up to complete engine simulations in the 3D-CFD tool QuickSim. The obtained results are referenced to the current literature and calibrated with experimental data. In particular, the engine simulations are validated against measurements of a single-cylinder research engine, which was specifically adapted for lean hydrogen operation and equipped with port fuel injection and a passive pre-chamber system. Special attention is hereby given to the influence of different engine loads and varying lambda operation. The focus of this work is the complementary numerical investigation of the hydrogen flame speed and its self-ignition resistance under the consideration of various reaction mechanisms. A detailed transfer from laminar propagation under laboratory conditions to turbulent flame development within the single-cylinder engine is hereby carried out. It is found that the relatively simple reaction kinetics of hydrogen can lead to acceptable results for all mechanisms, but there are particular effects with regard to the engine behavior. The laminar flame speed and induction time vary greatly with the inner cylinder conditions and significantly affect the entire engine’s operation. The 3D-CFD environment offers the opportunity to analyze the interactions between mixture formation and combustion progress, which are indispensable to evaluate advanced operating strategies and optimize the performance and efficiency, as well as the reliability, of the engine. Full article

There are considerably fewer requirements for the quality of hydrogen combusted in an engine than its quality for fuel cells. Therefore, the analysis was carried out on the combustion of hydrogen–helium mixtures in an engine with a two-stage combustion system (TJI—Turbulent Jet Ignition). A single-cylinder research engine with a passive and active prechamber was used. A hydrogen–helium mixture was supplied to the main chamber in proportions of 100:0, 90:10, 80:20, 30:70, and 60:40 volume fractions. The prechamber was fueled only with pure hydrogen. Combustion was carried out in the lean charge range (λ = 1.5–3) and at a constant value of the Center of Combustion (CoC = 8–10 deg aTDC). It was found that the helium concentration in the mixture affected the changes in combustion pressure, heat release rate and the amount of heat release. It was observed that increasing the proportion of helium in the mixture by 10% also reduces the IMEP by approximately 10% and reduces the rate of heat release by approximately 20%. In addition, helium influences knock combustion. Limits of MAPO = 1 bar mean assumed that knock combustion occurs in the main chamber at values of λ < 1.9. Increasing the excess air ratio results in a gradual reduction in the temperature of the exhaust gas, which has a very rapid effect on changes in the concentration of nitrogen oxides. Studies carried out on the helium addition in hydrogen fuel indicate that it is possible to use such blends with a partial deterioration of the thermodynamic properties of the two-stage combustion process. Full article

Based on a constant volume combustion chamber, the initial ambient pressure effect on gasoline combustion performance and flame propagation of the active and passive pre-chamber ignition systems were studied. Compared with the passive pre-chamber, the active pre-chamber can significantly expand the lean combustion limit from 1.2 to 1.5, enhance the ignition and combustion performance, and speed up the combustion of the main combustion chamber. At slightly lean combustion conditions, the heat release performance has a positive correlation with the initial ambient pressure. As the premixed λ increases, the heat release performance and the initial ambient pressure begin to become negatively correlated. Ignition delay can be decreased by approximately 50% at an initial pressure of 0.75 MPa, premixed lambda of 1.2 with APC compared with PPC. The high ambient pressure (1.0 MPa) in the constant volume chamber greatly reduces the mixture entrainment ability of the jet flame at lean combustion conditions, thereby reducing the combustion speed and peak heat release rate. Full article

The use of a two-stage combustion system in a hydrogen-fueled engine is characteristic of modern internal combustion engines. The main problem with hydrogen combustion in such systems is knocking combustion. This paper contains the results of research under knock combustion conditions with a single-cylinder internal combustion engine equipped with a turbulent jet ignition system (TJI). A layout with a passive pre-chamber and a variable value of the excess air ratio range λ = 1.25–2.0 with a constant value of the center of combustion (CoC = 4 deg) after top dead center (TDC) was used. Two indicators of knock combustion were analyzed: maximum oscillation of pressure and the Mahle Knock Index. Analyses were also carried out taking into account the rate of heat release and the amount of heat released. As a result of the investigation, it was found that knock combustion occurs intensively at small values of the air excess ratio. Hydrogen knock combustion disappears for λ = 2.0 and greater. The pressure oscillation index was found to be more applicable, as its limiting value (>1 bar) allows easy diagnosis of knock combustion. The Mahle Knock Index is a quantity that allows interval analysis of the knock. The choice of classes and weighting coefficients requires an iterative operation, as they strictly depend on engine characteristics, load, and knock magnitude. Full article

Hydrogen-fueled engines require large values of the excess air ratio in order to achieve high thermal efficiency. A low value of this coefficient promotes knocking combustion. This paper analyzes the conditions for the occurrence of knocking combustion in an engine with a turbulent jet ignition (TJI) system with a passive pre-chamber. A single-cylinder engine equipped with a TJI system was running with an air-to-fuel equivalence ratio λ in the range of 1.25–2.00, and the center of combustion (CoC) was regulated in the range of 2–14 deg aTDC (top dead center). Such process conditions made it possible to fully analyze the ascension of knock combustion until its disappearance with the increase in lambda and CoC. Measures of knock in the form of maximum amplitude pressure oscillation (MAPO) and integral modulus of pressure oscillation (IMPO) were used. The absolute values of these indices were pointed out, which can provide the basis for the definition of knock combustion. Based on our own work, the MAPO index > 1 bar was defined, determining the occurrence of knocking (without indicating its quality). In addition, taking into account MAPO, it was concluded that IMPO > 0.13 bar·deg is the quantity responsible for knocking combustion. Full article

To evaluate the significance of the geometrical parameters of a passive pre-chamber on engine performance, this study investigated the design of a plug-and-play passive pre-chamber in a 15 L heavy-duty natural gas engine. Multi-dimensional numerical investigations were conducted for parametric studies involving lateral angle, orifice diameter, and vertical angle. A compressive flow solver was employed for Navier–Stoke equations, coupled with detailed sub-models and a chemical kinetic scheme. The combustion model was calibrated and could well predict the engine combustion and operating performance. Seven pre-chamber schemes were evaluated, and four optimal ones were selected for experimental tests. The characteristics of the scavenging process, turbulent jet ignition, and main-chamber combustion were investigated and analyzed. The results show that, considering the trade-off between the ignition energy and the scavenging efficiency, the ratio of the pre-chamber to clearance volume is recommended to be 0.2~0.7%, and the corresponding area–volume ratio is 0.003~0.006 mm⁻¹. Compared with the original natural gas engine, the pre-chamber retrofit can save up to 13.2% of fuel consumption, which presents a significant improvement in fuel economy. Full article

This work shows the results of an experimental campaign carried out in two spark ignition engines, a small optical research engine and its commercial counterpart, using a turbulent ignition system (pre-chamber) specifically designed for small engines. Advanced optical techniques and conventional methods were used to study the combustion process under various operating conditions. The pre-chamber operated actively in the research engine and passively in the commercial engine. Results showed that the pre-chamber configuration resulted in an increase in indicated mean effective pressure (IMEP) and a decrease in the coefficient of variation (CoV) of IMEP. These improvements compensated for challenges such as slow methane combustion rate, poor lean burn capability, and air displacement. In addition, the pre-chamber configuration exhibited lower fuel consumption and specific exhaust emissions compared to the standard ignition system. The novelty of this work lies in the successful implementation of the turbulent ignition system as a retrofit solution for SI engines, showing improved combustion efficiency and lower emissions. The study goes beyond previous efforts by demonstrating the benefits of the pre-chamber configuration in small engines without requiring extensive modifications. The results provide valuable insights into the automotive industry’s pursuit of engine optimization and highlight the significance of innovative approaches for spark ignition engines in contributing to sustainable mobility. Full article

The icing of bridge pylon crossbeams is a problem that could pose a serious threat to traffic during a cold winter. However, little research has been carried out on the problem and few corresponding countermeasures have been provided. This paper aims to propose a novel heating system, and to study the feasibility of beam de-icing and the related de-icing strategies so as to provide a reference scheme for the practical application of beam de-icing. A number of icing and de-icing tests were carried out on a scale model of Wuhan Yangtze River Second Bridge in the cold chamber. The de-icing effects of the beam in different environments and different de-icing methods were compared, and the recommended pre-heating time, applicable environment range, and heating method were given. The results of the model experiments show that pre-heating the heating system can prevent the surface of the beam from freezing and that the anti-icing method is more suitable for beam de-icing than the passive de-icing method. When the pre-heating time exceeds 7 min, the entire anti-icing process can be ice-free. When the wind velocity exceeds 5 m/s, it is safer to shut down the heating system, and using the passive de-icing method at the end of the icing can also eliminate the hidden danger of beam icing. Full article

Stable ultra-lean combustion is an effective way for natural gas engines to reduce NOx emissions, but it also has higher requirements for ignition stability. The passive pre-chamber can effectively increase the ignition energy and extend the lean-burn limit of natural gas engines. However, the scavenging capacity of the pre-chamber limits its performance under low engine load. In this paper, several passive pre-chambers are designed, and the CFD simulation is carried out to investigate the influence of direction, number and diameter of the nozzle on the scavenging process. The discharge of residual gas in the pre-chamber is mainly affected by the nozzle diameter, which varies from 5.9% to 1% when the nozzle diameter increases from 0.8 mm to 1.6 mm. At the same time, claw-shaped electrodes are applied in the pre-chamber to increase the combustion rate, which is validated in a cylinder combustion simulation. Finally, the passive pre-chamber is tested on a 6-cylinder natural gas engine under 25% load. The results show that, under the proper ignition timing, the excess air ratio (λ) can reach 1.9 under 25% load of propulsion characteristic with a low level of cyclic variation. At this time, the NOx emission can be as low as 0.34 g/kWh without aftertreatment equipment. Full article

Pre-chamber turbulent jet ignition represents one of the most promising techniques to improve spark ignition engines efficiency and reduce pollutant emissions. This technique consists of igniting the air-fuel mixture in the main combustion chamber by means of several hot turbulent flame jets exiting a pre-chamber. In the present study, the combustion process of a 4-stroke, gasoline SI, PFI engine equipped with a passive pre-chamber has been investigated through three-dimensional CFD (Computational Fluid Dynamics) analysis. A detailed chemistry solver with a reduced reaction mechanism was employed to investigate ignition and flame propagation phenomena. Firstly, the combustion model was validated against experimental data for the baseline engine configuration (i.e., without pre-chamber). Eventually, the validated numerical model allowed for predictive simulations of the pre-chamber-equipped engine. By varying the shape of the pre-chamber body and the size of pre-chamber orifices, different pre-chamber configurations were studied. The influence of the geometrical features on the duration of the combustion process and the pressure trends inside both the pre-chamber and main chamber was assessed and discussed. Since the use of a pre-chamber can extend the air-fuel mixture ignition limits, an additional sensitivity on the air-fuel ratio was carried out, in order to investigate engine performance at lean conditions. Full article

Heart myocardia are critical to the facilitation of heart pumping and blood circulating around the body. The biaxial mechanical testing of the left ventricle (LV) has been extensively utilised to build the computational model of the whole heart with little importance given to the unique mechanical properties of the right ventricle (RV) and cardiac septum (SPW). Most of those studies focussed on the LV of the heart and then applied the obtained characteristics with a few modifications to the right side of the heart. However, the assumption that the LV characteristics applies to the RV has been contested over time with the realisation that the right side of the heart possesses its own unique mechanical properties that are widely distinct from that of the left side of the heart. This paper evaluates the passive mechanical property differences in the three main walls of the rat heart based on biaxial tensile test data. Fifteen mature Wistar rats weighing 225 ± 25 g were euthanised by inhalation of 5% halothane. The hearts were excised after which all the top chambers comprising the two atria, pulmonary and vena cava trunks, aorta, and valves were all dissected out. Then, 5 × 5 mm sections from the middle of each wall were carefully dissected with a surgical knife to avoid overly pre-straining the specimens. The specimens were subjected to tensile testing. The elastic moduli, peak stresses in the toe region and stresses at 40% strain, anisotropy indices, as well as the stored strain energy in the toe and linear region of up to 40% strain were used for statistical significance tests. The main findings of this study are: (1) LV and SPW tissues have relatively shorter toe regions of 10–15% strain as compared to RV tissue, whose toe region extends up to twice as much as that; (2) LV tissues have a higher strain energy storage in the linear region despite being lower in stiffness than the RV; and (3) the SPW has the highest strain energy storage along both directions, which might be directly related to its high level of anisotropy. These findings, though for a specific animal species at similar age and around the same body mass, emphasise the importance of the application of wall-specific material parameters to obtain accurate ventricular hyperelastic models. The findings further enhance our understanding of the desired mechanical behaviour of the different ventricle walls. Full article

The research on two-stroke engines has been focused lately on the development of direct injection systems for reducing the emissions of hydrocarbons by minimizing the fuel short-circuiting. Low temperature combustion (LTC) may be the next step to further improve emissions and fuel consumption; however, LTC requires unconventional ignition systems. Jet ignition, i.e., the use of prechambers to accelerate the combustion process, turned out to be an effective way to perform LTC. The present work aims at proving the feasibility of adopting passive prechambers in a high-pressure, direct injection, two-stroke engine through non-reactive computational fluid dynamics analyses. The goal of the analysis is the evaluation of the prechamber performance in terms of both scavenging efficiency of burnt gases and fuel/air mixture formation inside the prechamber volume itself, in order to guarantee the mixture ignitability. Two prechamber geometries, featuring different aspect ratios and orifice numbers, were investigated. The analyses were replicated for two different locations of the injection and for three operating conditions of the engine in terms of revolution speed and load. Upon examination of the results, the effectiveness of both prechambers was found to be strongly dependent on the injection setup. Full article

My paper addresses the non-human turn in Joyce’s work from the perspective of genetic phenomenology. I begin by commenting on Joyce’s characterization of Molly Bloom as a non-human apparition. I unpack the notion of a non-human apparition in light of Joyce’s interest in the idea of the earth as a generative matrix, and I relate this idea to a genetic enquiry into problems of passive synthesis and the givenness of objects to sense perception. I then trace the elaboration of this theme in a cluster of rhetorical figures from the later novels—puns, clichés, and metonymic associations—that play on the senses of matrix, materiality, and the sex of the mother. The second part turns to representations of the earth in Finnegans Wake. Focusing on scenes of interment and becoming one with the landscape, descriptions of tombs as echo chambers, and of geological sites as giant human bodies, I read Joyce’s earth as the crowning expression of his experiments with a radical (pre- and post-human) phenomenology. Full article