Flame Speed Research Articles

Enhancing the Efficiency of Rotary Thermal Propulsion Systems

Transport electrification is essential for reducing CO2 emissions, and technologies such as hybrid and range-extended electric vehicles will play a crucial transitional role. Such vehicles employ an internal combustion engine for on-board chemical energy conversion. The Wankel rotary engine should be an excellent candidate for this purpose, offering a high power-to-weight ratio, simplicity, compactness, perfect balance, and low cost. Until recently, however, it has not been in production in the automotive market, due, in part, to relatively low combustion efficiency and high fuel consumption and unburnt hydrocarbon emissions, which can be traced to constraints on flame speed, an elongated combustion chamber, and relatively low compression ratios. This work used large eddy simulations to study the in-chamber flow in a peripherally ported 225cc Wankel rotary engine, providing insight into these limitations. Flow structures created during the intake phase play a key role in turbulence production but the presence of the pinch point inherent to Wankel engine combustion chambers inhibits flame propagation. Two efficiency-enhancement technologies are introduced as disruptive solutions: (i) pre-chamber jet ignition and (ii) a two-stage rotary engine. These concepts overcome the traditional efficiency limitations and show that the Wankel rotary engine design can be further enhanced for its role as a range extender in electrified vehicles.

Combustion Analysis of Active Pre-Chamber Design for Ultra-Lean Engine Operation

<div>In this article, the effects of mixture dilution using EGR or excessive air on adiabatic flame temperature, laminar flame speed, and minimum ignition energy are studied to illustrate the fundamental benefits of lean combustion. An ignition system developing a new active pre-chamber (APC) design was assessed, aimed at improving the indicated thermal efficiency (ITE) of a 1.5 L four-cylinder gasoline direct injection (GDI) engine. The engine combustion process was simulated with the SAGE detailed chemistry model within the CONVERGE CFD tool, assuming the primary reference fuel (PRF) to be a volumetric mixture of 93% iso-octane and 7% n-heptane. The effects of design parameters, such as APC volume, nozzle diameter, and nozzle orientations, on ITE were studied. It was found that the ignition jet velocity from the pre-chamber to the main chamber had a significant impact on the boundary heat losses and combustion phasing. The simulation showed that, under 16.46 compression ratio (CR) and 8.93 bar indicated mean effective pressure (IMEP) condition, it is possible to achieve the peak ITE of 49.85% with λ = 2.23.</div>

Flame morphology and laminar flame assessments affected by flames interaction using multi-ignition sources of NH3/H2-air flames

A detailed assessment of flame–flame interaction and laminar flame evolution using multi-ignition sources is experimentally studied. To understand the flame interaction, the centrally ignited flame is measured and calculated for comparison with multi-ignition sources hydrogen–ammonia/flame. The location of the external ignition source, the delay time, the hydrogen blending, and the mixture equivalence ratio at an initial pressure of 0.1 MPa affect the propagation and morphology of the flame. It can be observed that the advancement of the pressure wave of the external flame causes deformation to the central flame front; This deformation occurs even before the interaction of the flames. The deformation can be decomposed into horizontal deformation, which decelerates the flame front as a result of the drag or accelerates due to the thrust of the flow field on the flame front. At the same time, vertical deformation is influenced by drag and thrust-lift forces. Therefore, the equivalent flame decelerates with time. This effect gives a nonsymmetric shape for expanding flame, and the shape changes from spherical to ellipsoidal, then a triaxial quasi-ellipsoid flame (scalene). The equivalent flame speed and laminar burning velocity are maximized near stoichiometry for all delay times and locations of the ignition source. As the delay time of the stoichiometric hydrogen ammonia/air increases, the equivalent laminar flame speed and laminar burning velocity monotonously decrease, as well as the time and location of the interaction. The equivalent flame speed and laminar burning velocity for ignition sources 1 and 2 decreases with delay time, and this becomes evident on the rich side. While employing a third ignition source increases with delay time since the drag force get eliminated from the horizontal axis. Furthermore, the hydrogen blending effect enhances and highlights these tendencies.

Effect of flame characteristics on an isolated ethanol droplet evaporating through stagnation methane/air flames: An experimental and numerical study

A single ethanol droplet evaporation through laminar methane/air stagnation flame is investigated at lean, stoichiometric and rich conditions experimentally and numerically. For the droplets having initial diameters of 20-70μm, the particle Reynolds number is measured via PIV/PTV, resulting in the slip velocity between the droplet and gas flow being small and the surrounding gas being able to carry without any significant convective effects. Evaporation rates, computed from Abramzon–Sirignano for a moving droplet towards a stagnation flame field, satisfy the ones computed from empirically determined evaporation rates from ILIDS measurements as a function of flame temperature, flame speed and flame thickness. Nevertheless, Abramzon–Sirignano model slightly overestimates the vaporization constant for lean cases. The distance traveled by the droplet after leaving the flame zone determines the average critical diameter. Accordingly, droplets larger than 18μm can cross the flame, leading to local modifications in the flame region due to heat loss and vapor diffusion from the droplet. Novelty and Significance Energy conversion in combustion should be carried out by optimizing efficiency, minimizing pollution, and preventing further climate change. The multiphase nature of spray combustion particularly adds further complexity due to the strong coupling of atomization, evaporation, mixing, turbulence, and chemical reactions. Although spray combustion involves a cloud of polydispersed droplets, it is of fundamental importance to understand the dynamics of an isolated droplet and its interactions with the flame front, which can provide indispensable information for spray combustion models. In this study, an experimental and computational framework has been developed to investigate droplet-flame interactions. The dynamics and evaporation characteristics of an isolated droplets interacting with stagnation flames have been determined by coupling several laser diagnostics, while further enhanced with Eulerian–Lagrangian simulations under flame conditions. Thereupon, the outcomes help the design of injectors of spray combustion systems and enhancement of evaporation models.

Effects of the vent burst pressure on the duct-vented explosion of hydrogen-methane-air mixtures

The effects of the vent burst pressure (Pv) on the vented explosion of hydrogen-methane-air mixtures are investigated in a cylindrical vessel connected with a duct. The results demonstrate that Pv significantly affects the flame behaviors and overpressure inside and outside the venting configuration. The flame front velocity at the vent increases with Pv. Two pressure peaks, Pac, caused by the acoustically enhanced combustion, and Pse, caused by the secondary explosion, dominate within the vessel at Pv ＜ 132 kPa and Pv ≥ 132 kPa, respectively. The maximum overpressure (Pmax) inside the duct increases with Pv. The maximum pressure rise (dP/dt) of the duct is always higher than that of the vessel. As Pv increases, increased turbulence of unburned gases within the duct results in higher dP/dt. Exit flame speed increases with Pv. When Pv ≥ 153 kPa, “Mach disk” appears outside the relief duct. Three pressure peaks, Pa, Pb, and Pext, due to vent failure, the secondary explosion, and the external explosion, respectively, occur in the external pressure curve. Pb dominates outside the configuration except for Pv = 153 kPa.

Comparison and optimization of strategies for ammonia-diesel dual-fuel engine based on reactivity assisted jet ignition and reactivity turbulent jet disturbance under high load conditions

Ammonia (NH3), as a zero carbon, easy to synthesize, and easily obtainable fuel, is one of the choices for future internal combustion engine fuels. However, the slow laminar flames speed and high ignition temperature of NH3 seriously hinder the development of NH3 engines. Efficiently igniting NH3 and ensuring its stable combustion is currently a challenging research topic. Utilizing diesel to optimize the NH3 combustion process is one effective solution. However, the increase of unburned ammonia (UNH3) and unstable combustion, under high load conditions have always been technical challenges that constrain the development of ammonia-diesel dual-fuel (ADDF) engines. Previous studies have found that pre-chambers (PC) have a significant effect on improving ammonia combustion characteristics. Therefore, based on the PC system, this study proposes two combustion modes: Reactivity Assisted Jet Ignition (RAJI) and Reactivity Turbulent Jet Disturbance (RTJD), which greatly optimize the combustion characteristics of ADDF engines under high load conditions. The research results indicate that the RAJI mode effectively improves the thermal environment inside the cylinder. Setting the start of diesel injection of pre-chamber (SODI-PC) at −14 °CA after top dead center (ATDC) can increase the cylinder temperature by 25.05% before the start of diesel injection of main chamber (SODI-MC). The improvement of thermal environment reduces the average generation of N2O to 13.56% of the traditional mode. However, if SODI-PC is postponed to −8 °CA ATDC, the effect of creating a thermal environment is no longer significant. Research on the RTJD mode has found that adopting the RTJD mode can significantly optimize emissions. Compared with traditional modes, N2O, UNH3, and Soot decreased by 28.81%, 27.79%, and 35.08%, respectively. Additionally, SODI-PC is delayed until after 4 °CA ATDC, CO and UHC will be further reduced to 50.00% and 12.24% of the traditional mode, respectively. In addition, the RTJD mode overcomes the deficiency of the slow laminar flame speed of NH3, shortening the combustion duration by 23.46%, and effectively improving the gross indicated thermal efficiency (ITEg) by an average increase of 1.08%, with the highest increase reaching 47.57%. This paper provides ideas for optimizing the structure and strategy of ADDF engines, as well as theoretical support and empirical reference for achieving clean and efficient combustion of engines.

Comparison of Tabulated and Complex Chemistry Approaches for Ammonia–Diesel Dual-Fuel Combustion Simulation

<div>Using ammonia as a carbon-free fuel is a promising way to reduce greenhouse gas emissions in the maritime sector. Due to the challenging fuel properties, like high autoignition temperature, high latent heat of vaporization, and low laminar flame speeds, a dual-fuel combustion process is the most promising way to use ammonia as a fuel in medium-speed engines.</div> <div>Currently, many experimental investigations regarding premixed and diffusive combustion are carried out. A numerical approach has been employed to simulate the complex dual-fuel combustion process to better understand the influences on the diffusive combustion of ammonia ignited by a diesel pilot. The simulation results are validated based on optical investigations conducted in a rapid compression–expansion machine (RCEM). The present work compares a tabulated chemistry simulation approach to complex chemistry-based simulations. The investigations evaluate the accuracy of both modeling approaches and point out the limitations and weaknesses of the tabulated chemistry approach. When using two fuels, the tabulated chemistry approach cannot reproduce misfiring events due to inherent model limitations. By adjusting the model parameters of the tabulated chemistry model, it is possible to reproduce experimental results accurately for a specific case. However, using the adjusted parameters for simulations with changed injection timing or interaction angle between the sprays shows that no predictive calculations are possible. The parameter set is only valid for a single operation point.</div> <div>Further simulations show that the complex chemistry approach can capture the complex interaction between both directly injected fuels for different operation points. It correctly predicts the ignition as well as heat release. Therefore, the approach allows predictive combustion simulations. Furthermore, it reproduces the occurrence of misfiring in cases of unsuitable interaction of both sprays and injection timing.</div>

Assessing Hydrogen–Ammonia Ratios to Achieve Rapid Kernel Inception in Spark-Ignition Engines

Abstract In the quest for decarbonizing internal combustion engines, ammonia (NH3) is recognized as a viable alternative fuel due to its zero-carbon emission profile, positioning it as a potential substitute for conventional petroleum fuels. However, the suboptimal combustion characteristics of ammonia pose challenges for its direct application in engines. The introduction of hydrogen (H2) as a combustion enhancer shows promise in improving ammonia viability for engine use. While previous studies have confirmed the benefits of hydrogen addition to ammonia for enhanced engine performance, comprehensive analysis of the precise ammonia-to-hydrogen ratio for optimal efficacy remains scarce. This research aims to bridge this gap by evaluating hydrogen–ammonia mixtures for achieving methane-equivalent laminar flame speeds under typical engine conditions, with a focus on the kernel inception process primarily driven by laminar flames. The findings indicate that a minimum of 20% hydrogen mixed with ammonia is necessary to facilitate rapid spark inception, although it does not reach the laminar flame speed of methane. Additionally, employing a high compression ratio and operating near stoichiometry could lower the required hydrogen–ammonia ratio. Considering the challenges in generating ample hydrogen with NH3 dissociators and the need for operational conditions like full-load and low-speed to lessen hydrogen demand, ammonia–hydrogen fuel blends are deemed most suitable for stationary engine applications in the near term.

Experimental and numerical study on natural gas explosion evolution in open space under different initial conditions

The vapor cloud explosion in open space are greatly affected by the initial conditions of gas cloud and the surrounding environment, while in the gas compressor station, these factors are ubiquitous. While the researches of external influencing factors like the obstacle and initial turbulence effect on natural gas explosion in open space are rare. In this paper, a series of natural gas explosion experiments were conducted and a long-distance natural gas pipeline compressor station was taking as an example to simulate the natural gas leakage and explosion in the typical location. Results showed that the greater the initial turbulence, the greater the peak overpressure of gas explosion. When the initial wind speed is 5 m/s, the peak overpressure can promote 73.4 % higher than that without initial turbulence. However, the overpressure doesn't linearly increase with the increasing of initial wind speed. What's more, the flame speed showed the same law with the overpressure, and the effect of concentration on overpressure is lower than that of initial turbulence and obstacle density. The explosion damaging range in the condenser area is larger than that in the separator area, and the maximum overpressure can reach about 21 kPa and the temperature can reach above 2280K, which provides an important basis for the safety prevention and personnel protection in natural gas compressor station.

Study on suppression mechanism of NH4H2PO4 inhibiting gas flame of red pine pyrolysis

Ammonium phosphate fire extinguishing agents, due to their excellent cost-effectiveness and suitability for forest fires, have become one of the most commonly used fire suppressants for forest fire control. Among them, NH4H2PO4 fire extinguishing agent is the most widely applied. In this study, NH4H2PO4 (>90%) as the main component of dry powder fire extinguishers was selected as the suppressant to investigate the reaction mechanism of NH4H2PO4 interacting with red pine wood pyrolysis gas flames. Initially, we constructed a Bunsen burner experimental system suitable for NH4H2PO4/red pine wood pyrolysis gas/air. Although experimental methods yield the most intuitive empirical conclusions, measuring only the laminar flame speed of red pine wood pyrolysis gas/NH4H2PO4/air mixture does not adequately analyze the inhibitory mechanism of NH4H2PO4 on red pine wood pyrolysis gas flames. Additionally, due to limitations in experimental equipment and methods, it is not feasible to extend equivalence ratios and NNH4H2PO4 doses to large or small working conditions. Therefore, in this study, we utilized Chemkin software to construct theoretical models of flames under different conditions and performed calculations. We comprehensively analyzed the kinetic regulatory mechanisms of NH4H2PO4 interacting with red pine wood pyrolysis gas flames from aspects such as chemical inhibition, sensitivity of elementary reactions, elementary reaction yields, and chemical reaction pathways.

Development and validation of a phenomenological model for hydrogen fueled PFI internal combustion engines considering Thermo-Diffusive effects on flame speed propagation

This paper proposes a 1D numerical/experimental study on a single-cylinder research ICE equipped with a hydrogen Port Fuel Injection (PFI) system. The experimental campaign covered tests at the fixed speed of 1500 rpm and different levels of load, from 5 bar to 11 bar IMEP, and of air excess, with a relative air-to-fuel ratio ranging from 1.4 to 4.0. A 0D/1D model of the investigated ICE is developed, including detailed combustion, turbulence, and NOx emission sub-models. In particular, combustion model is based on the fractal approach, k-K-T model is adopted for describing turbulent phenomena and NOx emissions are predicted by the Zeldovich mechanism. A sub-model was developed to assess the influence of Thermo-Diffusive (TD) instabilities on the freely propagating flame speed accounting for equivalence ratio, variable transport coefficients and reaction orders. This evaluation considered the impact of TD instabilities commonly observed in lean premixed hydrogen combustion on the flame front. The engine model calibration process enabled the comparison between numerical predictions and experimental observations, encompassing pressure cycles, burn rate traces, and main engine performance (air flow rate, IMEP, indicated efficiency, and timing of main combustion events). The model replicated the IMEP with an average error of 2.5%, gross indicated efficiency with an average error of 1.6%, main combustion angles with an average error of 3.8 CAD on CA50, and NOx emissions satisfactorily, showing high sensitivity to operational parameters. Nonetheless, less accurate predictions occur in cases with significantly elevated λ values (λ>3.6), which were attributed to the presence of thickened flames, where some assumptions inherent to the adopted combustion model may fail. Finally, a comparison between the proposed approach and the one proposed in Ballerini et al. (2022) is presented, and readers are provided with recommendations for further development of future models that account for Thermo-Diffusive instabilities in lean hydrogen combustion.

Modeling Ammonia-Hydrogen-Air Combustion and Emission Characteristics of a Generic Swirl Burner

Abstract The combustion process of both pure NH3 and a NH3/H2 fuel blends is here analyzed using two kinetics processors, i.e., Chemkin-Pro-and CANTERA: detailed kinetic mechanisms have been tested and compared in terms of laminar flame speed and ignition delay time (IDT) with the aim to identifying the most suitable ones for the evaluation of NOx emissions. The generic swirl burner being used in Cardiff University's Gas Turbine Research Center has been considered as validation test case. In addition, this paper presents an experimental campaign followed by a computational fluid dynamics (CFD) approach for the assessment of NOx emission using axisymmetric Reynolds-Averaged Navier–Stokes (RANS) simulations, leading to a significant reduction of the computational time. Different pressures and mass flow rates are evaluated to understand correlations of NOx formation for pollutants reduction purpose. A direct comparison between experimental and numerical results is carried out in terms of flow field, flame shape, and NOx emissions. Results show that the increase in pressure from 1.1 bar to 2 bar results in reduction of NOx emissions from 2515 ppmv to 885 ppmv, also indicating guidelines for using a simplified RANS analysis, which leads to improved computational efficiency, allowing wide sensitivity and optimization analysis to support the design development of an industrial combustion system.

Numerical modeling of combustion in gas engines with prechamber ignition

A numerical model is developed to predict the combustion processes in large-bore gas engines featuring prechamber ignition systems and being coupled with Computational Fluid Dynamics (CFD). The proposed combustion model is based on the simultaneous modeling of premixed and partially-premixed flames by an extended progress variable approach. By introducing an additional fuel scalar to track the externally injected fuel of the scavenged prechamber and depending on a gradient criteria of the fuel scalar, regions of locally premixed or partially-premixed state can be differentiated. The reaction rate for premixed combustion is described through a turbulent flame speed closure approach, whereas the partially-premixed combustion is described by a pre-tabulated flamelet chemistry approach. For the validation of the combustion model and its performance in the different flame propagation phases, that is, prechamber flame ignition and main-chamber flame propagation, experimental data of two large-bore gas engines with different operating conditions, prechamber configurations and engine geometries are taken into account. A good agreement of the simulations with the experimental results is shown for the variety of operating conditions and engine configurations. The developed combustion model is able to predict the combustion process in the prechamber as well as the ignition of the main chamber charge by means of the protruding flame jets through the prechamber nozzles. The prechamber ignition system accelerates the early flame phase and hence shortens the burning duration due to the deep-penetrating and turbulence-inducing flame jets in comparison to a conventional spark plug engine.

Development of a reduced mechanism for methane combustion in OpenFOAM: A computational approach for efficient and accurate simulations

The primary aim of this study is to develop a more efficient reaction mechanism for accurately simulating methane combustion, with a specific focus on ignition delay, laminar flame speed, and 2-D simulated flames, while also reducing computational time. Ten reduced reaction mechanisms for methane combustion were evaluated, with only one, "SK30," meeting the required accuracy standards. However, SK30 proved to be computationally intensive when simulating a 2-D premixed flame at a microscale. To address this challenge, a two-step reduction process was implemented. Firstly, an automated algorithm utilized direct relation graphs and sensitivity analysis with ignition delays as a reference to streamline the mechanism while maintaining accuracy. Subsequently, the second step involved identifying key reactions that had a more significant impact on flame speed than ignition delay through sensitivity analysis. Any missing reactions were then added judiciously, prioritizing the retrieval of the missing but important reactions to overall accuracy while minimizing computational cost. This process resulted in a novel mechanism comprising 25 species and 132 reactions for methane-air combustion. The validity of this mechanism was confirmed through comparison with a benchmark model, demonstrating satisfactory agreement in 1-D flame speed and 2-D premixed flame modeling. Most notably, the new mechanism substantially reduced processing time, achieving a 50 % speedup compared to SK30.

Experimental and numerical study on flow/flame interactions and pollutant emissions of premixed methane-air flames with enhanced lean blowout hydrogen injection

This study investigates experimentally and numerically the stability, combustion, and emissions characteristics of premixed swirl-stabilized methane/air flames with enhanced lean blowout (ELBO) injection of hydrogen in the non-premixed mode for higher turndown ratio gas turbines. The study analyzed the effects of hydrogen fraction (HF: volumetric percentage of H2 in the total fuel) ranging from 0 to 25% and equivalence ratio (φ) ranging from 0.5 to 0.893 on flow/flame interactions and flame stability, structure, and emissions. The introduction of non-premixed H2 yields two conflicting outcomes, with enhancements in reaction kinetics and flame speed yet counteracted by increased hydrogen jet momentum dispersing the flame. The combustor lean blowout (LBO) limit remains relatively unaffected (φoverall≈ 0.5) by H2 injection. Flame temperature is primarily influenced by φ and minorly by HF. Increasing HF resulted in localized temperature rises around H2 jets without an overall increase in flame temperature, offering a promising strategy for reduction of NOx emissions. Nevertheless, using H2 as a pilot fuel leads to an increase in intermediate species like OH, H, and O, contributing to flame stabilization. However, this practice also results in higher CO and unburned hydrocarbons emissions due to the inherent characteristics and heightened reactivity of H2.

The trade-off characteristic between battery thermal runaway and combustion

Lithium iron phosphate (LFP) lithium-ion batteries are widely believed to be more thermally safe than nickel-rich layered LiNixCoyMnzO2 (NCM) batteries because LFP cathodes are more stable. However, LFP batteries have been reported to cause serious combustion accidents. The relationship between internal thermal runaway and external combustion in LFP and NCM batteries remain unclear. Herein, we found that there is a trade-off between thermal runaway within the battery and external combustion. Cathode oxidizability is linearly correlated with the intensity of thermochemical reactions within battery components. The nickel-rich LiNi0.9Co0.05Mn0.05O2|Graphite (NCM955|Gr) battery exhibits the most intense exothermic reactions and energy release due to the strong oxidation of its cathode, leading to the highest thermal runaway temperature of 862.4 °C within the battery. The LiFePO4|Graphite (LFP|Gr) battery with the weak cathode oxidizability shows the lowest temperature of 297.4 °C within the battery, but with the highest laminar flame speed of 55 cm s−1 outside the battery. The reason for this is that the LFP cathode rarely oxidizes the electrolyte, instead, the electrolyte reacts with the anode primarily, thereby generating substantial reductive gases and accumulating the explosion risks. This work provides the theoretical basis and data support for future battery selection and design.

Toward zero carbon emissions: High thermal efficiency low speed two-stroke marine engine using pure ammonia fuel

As the future development trend and the crucial link to achieving the carbon peaking and carbon neutrality goals in China, the achievement of “zero carbon” emissions in low-speed two-stroke marine engines is currently in the preliminary stages of exploration. Ammonia fuel is one of the main zero-carbon energy sources of interest for marine engines. The primary challenges associated with ammonia application include its high self-ignition temperature, low laminar flame speed, and lengthy ignition delay time. Although stable combustion can be achieved with the assistance of a small amount of highly active carbon-based fuel, carbon emissions are still inevitable. To obtain “zero carbon” emissions, the high-temperature cylinder gas recirculation strategy (HTCGR) was innovatively proposed to realize the possible application of pure ammonia. However, the heat transfer loss by using pure ammonia fuel is enhanced by 289% compared to the diesel mode. Therefore, the main objective of this article is to investigate ways to decrease heat transfer loss and further improve the thermal efficiency of the two-stroke engine from the perspective of energy distribution, and the effect of the circulating high-temperature gas, swirl ratio, and fuel distribution on heat transfer loss was systematically numerically studied in this manuscript. As a result, the heat transfer losses can be decreased up to 38.80% by lowering the CGR rate and adjusting the fuel distribution, and the ITE can be improved from 48.85% in the diesel model to 51.19% in the ammonia mode. However, to avoid incomplete combustion in the engine, a minimum CGR rate of 13.3% is basically required for the compression ignition of pure ammonia fuel.

Effect of Hydroxy Gas Addition in Gasoline-ethanol Fuel Mixture on Performance of Spark Ignition Engine

Fossil fuel continues as primary energy source for the transportation industry, particularly for the fuel used in spark ignition (SI) engines. The use of biofuels such as bioethanol is a solution to the reliance on fossil fuels to reduce green-house gas emissions in the atmosphere and improve environmental air quality. However, the use of bioethanol as a fuel for the SI engine has limitations, such as a reduction in power produced as compared to pure gasoline due to the low energy input contained by bioethanol compared to gasoline. The objective of this study is to improve the energy conversion efficiency of the SI engine by adding Hydroxy (HHO) from water electrolysis to the gasoline-bioethanol mixture, allowing for increasing application of bioethanol at higher concentrations as an additive in future. The test was performed on a 155 cc SI engine equipped with an Engine Control Unit (ECU) to control the fuel injection. The pressure, temperature, oxygen, and throttle position sensors located on the engine and connected to a NI-MyRIO microcontroller. The injection duration of HHO gas based on the duration of gasoline fuel injection, both of fuel are injected through each injector at the intake manifold. The result shows the characteristics of HHO gas improved the disadvantages of biofuels, which have a lower heating value and higher flame speed of bioethanol and gasoline fuel. The presence of HHO gas into the bioethanol-gasoline blend affected to increase the produced power, torque and thermal efficiency of the SI engine. An increase in thermal efficiency at 9.16% obtained at concentration of 20% bioethanol and HHO.

0/1 and 3 - dimensional cold flow analysis of a diesel engine: A case study

Gas motion in the engine cylinder plays a critical role in diesel engines' air-fuel mixing and combustion processes. Moreover, it influences the engine's performance, emissions, and heat transfer. The intake air motion regulates the main phases of the flow in the cylinder, which is characterized by swirl, squish, and turbulence. Inducing swirl and tumble in the intake process provides high turbulence levels at ignition, resulting in more effective flame speeds and better combustion for lean air-fuel ratios or with EGR. Computational fluid dynamics (CFD) software is used to enhance in-cylinder flow characteristics. In this study, a cold flow simulation of a naturally aspirated, direct injection diesel engine was conducted with different piston bowls using AVL Fire M R2022.2. Swirl, tumble, and TKE parameters were investigated to make a detailed analysis of the in-cylinder flow for the relevant engine. Contrary to the expectation, the swirl ratio for the Piston B configuration is less than that for the original piston configuration. It causes a decrement of swirl ratio compared to the initial piston geometry and the maximum decrement is about 19%. In both cases, the second peak of TKE corresponding to the reverse-squish is around at the -30 CA and the difference between the curves is about ±8%.

Laminar flame speed measurement and combustion mechanism optimization for ethylene–air mixtures

AbstractEthylene plays a crucial role as an intermediate component in the cracking and combustion processes of large molecular alkane and olefins. In this article, the laminar flame speed of ethylene–air mixtures was measured using the heat flux method. The mechanism of ethylene was simplified by utilizing the error propagation directed relationship graph (DRGEP) and sensitivity analysis (SA), and the Arrhenius pre‐exponential factors for 20 selected reactions in the skeletal mechanism were optimized using the particle swarm optimization (PSO) algorithm. Finally, an ethylene optimization mechanism including 39 species and 85 reactions was obtained. The prediction results for flame speed, ignition delay time, and species concentration were compared with experimental data and other mechanisms, covering a wide range of temperatures (298–1725 K), pressures (1–22.8 atm), and equivalence ratios (0.5–2.0). The findings demonstrate that the optimization mechanism not only improves the prediction results of laminar flame speed in the rich combustion zone and low oxygen environment but also enhances the prediction accuracy of the ignition delay time at high pressure and in the lean combustion zone, as well as the prediction accuracy of C2H4 and H2O radicals. In conclusion, the optimized mechanism exhibits higher accuracy and broader applicability.