Combustion Cycle Research Articles

Effects of Liquid LPG Injection on Combustion Stability in Spark Ignition Engine

LPG is an alternative fuel that commonly used in spark ignition engine. The research on introducing the LPG into the combustion chamber has been extended to the liquid injection rather than conventional method which is gas injection. The objective of this study specifically is to evaluate the effects of liquid LPG injection on the combustion stability as compared to the gasoline fuel. The study was conducted using 1600cc naturally aspirated engine at 2000rpm and 3000rpm at various throttle position, which were 25%, 50%, 75% and 100% of its opening. The statistical analysis has been used in determining the combustion effectiveness through peak pressure analysis from 250 continuous combustion cycle. The results were compared with the gasoline fuel for each experimental condition. The results showed that liquid LPG injection has produced better combustion stability than gasoline fuel at almost all tested conditions.

Cycle resolved control for HCCI engine load range expansion by combining ion current and pressure sensor

Homogeneous charge compression ignition (HCCI) offers a high potential in engine efficiency enhancement and ultra-low NOx raw emissions. However, the main difficulty in HCCI combustion is its controllability of the ignition, especially at boundary conditions. At these conditions, stochastic abnormal combustion may happen, such as incomplete combustion or knock. Traditional engine map-based control is not enough to overcome these problems. Real-time in-cylinder combustion diagnosis and cycle resolved combustion control are required. In this study, the ionization process during negative valve overlap (NVO) interval in HCCI engines is numerically studied. It is identified that the ion current can reflect the quality of fuel reforming, which has been validated in the experiments. Compared to other studies that only use a single sensor (pressure sensor or ion current sensor), here for the first time, two sensors are combined to enhance the diagnostic accuracy. Besides, for the first time, ion current during NVO is employed for control. The experiments were conducted both at light load and high load boundary conditions. For light load boundary condition, by combining two sensors, the diagnostic accuracy rate of stochastic incomplete combustion is about 91.3%, and the misjudgment rate is reduced by 30% compared to only use one of them. After the controller is activated, the standard deviations of CA50 (σCA50) and IMEP (σIMEP) are reduced by 14.6% and 11.3%, respectively. For high load boundary condition, σCA50 and σIMEP are reduced by 12.3% and 15.4% respectively. Besides, the knock intensity is reduced by 9%. Ultimately, IMEP of the minimal load is reduced from 0.23 MPa to 0.18 MPa with an extension of 22%, and IMEP of the maximum load is expanded from 0.33 MPa to 0.4 MPa with an expansion of 21%.

Numerical Investigation of Fuel Property Effects on Mixed-Mode Combustion in a Spark-Ignition Engine

Abstract In this study, lean mixed-mode combustion is numerically investigated using computational fluid dynamics (CFD) in a spark-ignition engine. A new E30 fuel surrogate is developed using a neural network model with matched octane numbers. A skeletal mechanism is also developed by automated mechanism reduction and by incorporating a NOx submechanism. A hybrid approach that couples the G-equation model and the well-stirred reactor model is employed for turbulent combustion modeling. The developed CFD model is shown to well predict pressure and apparent heat release rate (AHRR) traces compared with experiment. Two types of combustion cycles (deflagration-only and mixed-mode cycles) are observed. The mixed-mode cycles feature early flame propagation and subsequent end-gas auto-ignition, leading to two distinctive AHRR peaks. The validated CFD model is then employed to investigate the effects of NOx chemistry. The NOx chemistry is found to promote auto-ignition through the residual gas, while the deflagration phase remains largely unaffected. Sensitivity analysis is finally performed to understand effects of fuel properties, including heat of vaporization (HoV) and laminar flame speed (SL). An increased HoV tends to suppress auto-ignition through charge cooling, while the impact of HoV on flame propagation is insignificant. In contrast, an increased SL is found to significantly promote both flame propagation and end-gas auto-ignition. The promoting effect of SL on auto-ignition is not a direct chemical effect; it is rather caused by an advancement of the combustion phasing, which increases compression heating of the end-gas.

Advanced Combustion Modelling of High BMEP Engines under Water Injection Conditions with Chemical Correlations Generated with Detailed Kinetics and Machine Learning Algorithms

<div class="section abstract"><div class="htmlview paragraph">Water injection is becoming a technology of increasing interest for SI engines development to comply with current and prospective regulations. To perform a rapid optimization of the main parameters involved by the water injection process, it is necessary to have reliable CFD methodologies capable of capturing the most important phenomena. In the present work, a methodology for the CFD simulation of combustion cycles of SI GDI turbocharged engines under water injection operation is proposed. The ECFM-3Z model adopted for combustion and knock simulations takes advantages by the adoption of correlations for the laminar flame speed, flame thickness and ignition delay times prediction obtained by a detailed chemistry calculation. The latter uses machine learning algorithms to reduce the time to generate the full database while still maintaining an even distribution along the variables of interest. The results demonstrate the applicability of the proposed methodology, capable of capturing not only the thermodynamic effects of water injection but also the chemical kinetics aspects related to the mixture water dilution whose prediction is mandatory for addressing the engine design according to different goals: complying with new emission directives and limits, turbine inlet temperature constraints, minimization of the BSFC and possibly engine power increase.</div></div>

Numerical studies on unstable oscillatory direct contact condensation (DCC) of oxygen vapor jets in subcooled flowing liquid oxygen

At the booster turbopump exit of a high pressure staged combustion cycle based cryogenic rocket engine, hot gaseous oxygen after driving the booster turbine mixes with subcooled liquid oxygen from the booster pump leading to a complex phenomena of direct contact condensation of hot oxygen gas. The aim of the present investigation is to numerically study the condensation of oxygen vapor jets in subcooled liquid oxygen using a two-fluid two-phase model in the Eulerian framework to understand the mixing process at the booster turbopump exit. The unstable nature of the oxygen plume shapes at cryogenic temperatures have been examined and the stable to unstable transition in an unstable direct contact condensation cycle have been analyzed. A detailed parametric study has been conducted using the Box-Behnken design and suitable correlations are developed for the critical design parameters viz., overall averaged heat transfer coefficient and dimensionless maximum vapor penetration length. Finally, the maximum pressure oscillation amplitudes associated with unstable oscillatory oxygen direct contact condensation are characterized. The results of the present investigation will be helpful in designing experimental set-up for studying the unstable direct contact condensation at cryogenic temperatures and will serve as preliminary guidelines for the design of an oxygen direct contact condenser, which hitherto is unavailable in the open literature.

Investigation of cycle-to-cycle variations in a spark-ignition engine based on a machine learning analysis of the early flame kernel

High-speed Mie scatter imaging and in-cylinder pressure measurements are performed in an optically accessible four-stroke spark-ignition engine to investigate cycle-to-cycle variations (CCVs). Droplet Mie scattering is used to measure the cross-sectional flame contour. Machine learning (ML) methods are applied to predict combustion cycles of high maximum in-cylinder pressure based on flame cross-sections at -15 °CA (crank angle degrees before top dead center). All tested ML methods (decision tree-based, multi-layer perceptron, and logistic regression) are able to predict high energy engine cycles given only partial flame topology information at a temporal snapshot of the flame propagation. Feature importance analyses, employed using decision tree methods, reveal that a combination of flame position and shape features of the flames' cross-section is necessary in achieving a high prediction accuracy. These sensitivity analyses can be used to gain insight into the combustion processes and to strategically reduce the number of features. This enables the addition of new physical quantities in future investigations.

NOx Emission Reduction Technology for Marine Engine Based on Tier-III: A Review

The development of maritime trade has greatly promoted the development of diesel engines. However, with the increasingly serious environmental problems, more and more attention has been paid to the exhaust emissions of high-power marine diesel engines. The restrictions on SOx have been implemented globally, and the limitation of the NOx will be the next priority. This paper illustrates (a) Principle and research progress of NOx emissions-reduction technology of marine diesel engine; (b) Summary of advantages and disadvantages among various reduction technologies and their reduction effects; (c) The application effect of mainstream technology on board. Firstly, since exhaust gas recirculation (EGR) can achieve Tier-III directly from Tier-I without considering the increased fuel consumption. It is deemed as the most promising technology to reduce emissions by controlling combustion condition. However, EGR has shortcomings of excessive increase in fuel consumption and generation of waste water, which need to be solved immediately. Secondly, selective catalytic reduction (SCR) is the most effective and straightforward means to achieve Tier-III. Despite of the continuous optimization of SCR unit volume, the problem of scrap catalyst seriously limits its wide application. How to match the supercharger more efficiently is a key factor in choosing between high and low pressure SCR. Thirdly, nature gas (NG) engines are capable of achieving a reduction in NOx, but in order to meet the requirements of Tier-III, it still needs to be assisted by other technologies. The emissions of hydrocarbon (HC) and CO in NG engines are huge defects that must be solved. Lastly, technologies such as the Miller cycle, Two-stage supercharging and mixed-water combustion can also reduce emissions but were rarely used alone. These technologies can be combined with EGR, SCR and NG engines to optimize the engines’ economy and emission characteristics.

A control strategy for cylinder deactivation

Cylinder deactivation is an effective measure to reduce the fuel consumption of internal combustion engines. This paper presents a control strategy for the cylinder deactivation (CDA) process and the cylinder reactivation (CRA) process, based on the inversion of a control-oriented discrete-event model. The focus of this paper lies on quantity-controlled stoichiometrically-operated engines with different layouts. Nevertheless, the main results are transferable to other engines, including quality-controlled engines. Two major aspects of CDA and CRA are considered in detail in this paper.The first aspect is the cycle-averaged torque during the CDA and CRA. Due to the reciprocating behaviour of the engine, an unavoidable discontinuity in the cycle-averaged torque is identified, irrespective of the type of engine. The amplitude of this torque ripple depends on the duration of the CDA or CRA and can be quantified a priori. A trade-off between the torque ripple amplitude and the CDA or CRA duration is identified.The second aspect is the amount of fuel consumed during the CDA and CRA. It is shown that to achieve a CDA or CRA with a limited torque ripple amplitude, some combustion cycles at unfavourable low-load conditions must occur. For example, ignition retardation might be used resulting in a significant portion of the fuel energy being lost. As a result an increase in the amount of fuel consumed during the CDA or CRA compared to that of continued operation in activated cylinder mode may arise. The conducted investigations show that this increase in fuel consumption is compensated after a few seconds of operation in the more fuel-efficient deactivated cylinder mode.

Assessment of the External Costs of Life Cycle of Coal: The Case Study of Southwestern China

Coal will continue to be the main energy source in China for the immediate future, although the environmental pollution and ecological impacts of each stage in the full life cycle of coal mining, transportation, and combustion generate large quantities of external costs. The Late Permian coals in southwestern (SW) China usually contain high amounts of fluorine (F), arsenic (As), and ash, which together with high-F clays cause abnormally high levels of endemic fluorosis, As poisoning, and lung cancer in areas where coal is mined and burned. In this paper, we estimate the external costs of the life cycle of coal. The results show that the externalities of coal in SW China are estimated at USD 73.5 billion or 284.3 USD/t, which would have accounted for 6.5 % of the provincial GDP in this area in 2018. The external cost of human health accounts for 87.2% of the total external costs, of which endemic skeletal fluorosis diseases and related lung cancers have the most important impact. Our study provides a more precise estimate of externalities compared with its counterparts in other provinces in China. Therefore, several policy recommendations would be proposed to internalize the external cost.

Emission flame characteristics for cyclic combustion of liquid fuels

The paper considers issues related to the emissivity of the flame generated in the cylinder of a high-speed piston internal combustion engine and, in particular, diesel and the effect of soot particles formed during the combustion of motor fuel on this process. The factors determining this process are presented, the data of various researchers involved in these processes are analyzed. Data are presented that establish the relationship between the amount of soot particles formed and the emission characteristics of the flame, on which the thermal loading of the parts of the cylinder-piston group depends.

Integration of LNG Regasification Process in Natural Gas-Fired Power System with Oxy-Fuel Combustion

Oxy-fuel combustion power systems can utilize the cold energy released during the liquefied natural gas (LNG) regasification to reduce the power consumption of CO2 capture, but the specific LNG cold energy consumption of CO2 capture is still too large. To recover more CO2 with the limited LNG cold energy at a low energy cost, a novel natural gas-fired oxy-fuel power system with the cascade utilization of LNG cold energy is proposed in this work, where the LNG cold energy could be sequentially utilized in the air separation unit and the CO2 recovery process. The new system is evaluated with the Aspen Plus software. The results show that the net electrical efficiency and the specific primary energy consumption for CO2 avoided (SPECCA) of the new system are comparable to those of the chemical looping combustion cycle, and superior to those of the conventional O2/CO2 cycles. Moreover, the specific LNG needed for CO2 avoided (SLNCC) of the new system is more than 67.2% lower than the existing oxy-fuel power systems utilizing the LNG cold energy. Furthermore, it is found that the O2 purity of 97.0 mol.% and the CO2 capture ratio of 97.0% are optimal conditions, because the SPECCA, the specific exergy consumption for CO2 avoided (SECCA) and the SLNCC are at the minimum of 1.87 $${\rm{G}}{{\rm{J}}_{LHV}} \cdot {{\rm{t}}_{{\rm{C}}{{\rm{O}}_2}}}^{- 1},2.60\,\,{\rm{GJ}} \cdot {{\rm{t}}_{{\rm{C}}{{\rm{O}}_2}}}^{- 1}$$ and $$1.88\,\,{{\rm{t}}_{{\rm{LNG}}}} \cdot {{\rm{t}}_{{\rm{C}}{{\rm{O}}_2}}}^{- 1}$$ , respectively. Meanwhile, the net electrical efficiency and the exergy efficiency of the new system reach 51.51% and 49.23%, respectively.

Integrated chemical looping combustion in pulp mill for high energy efficiency and low carbon emission

Pulp making is a high-energy-consumption process that obtains its energy by directly combusting coal and black liquor in boiler, which is low efficiency and high emission. Mini-sulfide sulfite anthraquinone (MSSAQ) pulp making technology can reach 55%–66% pulping yield but suffers from bad economic performance. The combination of black liquor gasification (BLG) and chemical cycle combustion (CLC) can achieve high pulp production and clean production and has better economic performance. This research proposes an integrated CLC-BLG-MSSAQ pulp making process. Compared with conventional Kraft and MSSAQ processes, the CLC-BLG-MSSAQ process improves the energy efficiency by 6.2% and 12.2%, decreases carbon emissions by 0.62 t/ADt and 0.17 t/ADt. The economic analysis shows that under the scenario of USD 20/t CO2-eq or above, the CLC-BLG-MSSAQ process, which has higher combustion efficiency and lower carbon emission, will cost the least compared with Kraft and MSSAQ processes.

Molybdenum recovery from spent Mo-based dispersed catalyst accumulated in heavy oil steam cracking coke

Recovery of molybdenum has been studied from coke formed as a by-product of catalytic steam cracking of heavy oil containing a Mo-based nanodispersed unsupported catalyst, and from mixtures of industrial coke with Mo-based compounds – as model systems, via combustion in the fluidized bed of deep oxidation catalyst and the fixed bed of coke (without a catalyst). Quantitative carbon removal was found to be impossible even for several cycles of combustion in fluidized catalyst bed, most probably due to a drop of size of the coke particles to those of too small in order to have a sufficient contact time for the complete burning off. Non-catalytic combustion in the fixed bed mode showed best efficacy resulting in complete carbon removal without any Mo losses in the range of 450–750 °C.

Numerical simulation of water hammer in liquid methane feedline based on two compressible fluid models

In order to improve the capability of distributed parameter modeling for water hammer of liquid methane propellant in a staged combustion cycle engine simulation library, pipeline flow models are established based on two different compressible fluid assumptions. One is the slightly compressible fluid assumption and the other is the completely compressible fluid. For the completely compressible fluid model, the SRK equation of state is utilized to calculate the pressure rather than the internal energy fitting formula. And for slightly compressible fluid model, the pressure equation is deduced from continuity equation by introducing sound velocity equation. One-dimensional finite volume method is used so that the two models could work well with other component models of a staged combustion cycle engine simulation library which are all programmed in Modelica language. The pressure surges of the liquid methane in a system are predicted due to valve closure. The results show a principal difference of pressure surge frequencies between two models, which is caused by the different ways of calculation of pressure. In addition, a method of numerical oscillation suppression for completely compressible fluid model is proposed and a best value of oscillation suppression coefficient is given in the present paper.

Study on the effect of gasification agents on the integrated system of biomass gasification combined cycle and oxy-fuel combustion

Abstract An integrated system of biomass gasification combined cycle with oxy-fuel combustion was proposed. Considering the neutral character of biomass, the “negative emissions” were achieved. Different gasifying agents, including steam, CO2, steam + O2, CO2 + O2, steam + CO2, and steam + CO2 + O2 were examined. The steam and CO2 in gasifying agents were directly separated from flue gas in power generation unit. The effects of equivalence ratios and gasifying agent to biomass ratios on syngas production were studied. The results revealed that steam contributed to the yield of H2, while it inhibited the generation of CO. CO2 in the gasifying agent promoted the yield of CO. O2 had little impact on H2 production, but it significantly reduced the generation of CO and CH4. The introduction of O2 in gasifying agent reduced the syngas LHV while it generally raised the gasification efficiency. Furthermore, when O2 was used to realize the autothermal gasification process, the net power generation efficiencies under steam + O2 gasification, CO2 + O2 gasification and steam + CO2 + O2 gasification were 26.3%, 28.3% and 27.6%, respectively. These efficiencies were competitive considering the biomass disposal and carbon capture.

Optimization of the Efficiency in a Syngas Powered Si Engine Through Numerical Studies Related to the Geometry of the Combustion Chamber

The combustion process occurring in an alternative Spark Ignition (SI) engine powered with bio-syngas from biomass gasification was previously studied by authors through the development of two different numerical models: a 0-1D model developed in the GT-Suite® environment, aimed at gaining a first look upon the main features of the heat release by the syngas and engine performances; a 3D Computational Fluid Dynamics (CFD) model developed within the AVL FireTM software reproducing the engine combustion cycle within a Reynolds Averaged Navier Stokes (RANS) schematization and employing a detailed chemical reaction mechanism to highlight the interaction between the fluid dynamics and the kinetics of the specific biofuel oxidation chain. The numerical results were validated with respect to experimental measurements in a baseline condition, where the presence of a relatively high amount of CO in the exhaust gases was noticed as related to an engine low combustion efficiency, mainly due to the peripheral spark plug position that determines the persistence of residual gases on the opposite side of the combustion chamber wall.The proposed work presents a numerical analysis made through the developed models on the effects of proper changes in the spark plug position. A multi-objective optimization problem is conducted also by varying the Start of Spark (SOS) and the mixture air-to-fuel ratio with the aim of reducing the engine environmental impact without affecting its performances. A centrally mounted spark, along with a correct calibration of the SOS and mixture ratio, allows a reduction of more than 90% of CO emission with respect to the baseline condition without penalizing the engine brake power and efficiency.

Pogo Stability Approaches for the Strap-On Launch Vehicle with Staged Combustion Cycle Engines

According to the new characteristics of the solid–liquid strap-on launch vehicle and the liquid oxygen/kerosene staged combustion cycle engines, a finite element model of the launch vehicle propulsion–structure coupled system subjected to pogo was presented in this paper. In the model, the structure was represented by a longitudinal–lateral–torsional integrated finite element model with a three-dimensional tank and one-dimensional beam–spring–mass. The propulsion system was represented by a transfer matrix model, which was fitted by the vector fitting method and transformed into a second-order differential equation. By assembling the structure dynamic equations and propulsion system, the governing equation of the coupled system can be established. After that, pogo stability was analyzed by solving the complex eigenvalues of the governing equations. The method developed in this paper can also be expanded to other liquid launch vehicles.

Expansion, injection and micro-explosion phenomena during the full combustion cycle of mixed fuel droplets of ethyl alcohol and biodiesel

In this study, mixed fuel droplets of ethyl alcohol and biodiesel with different volumes or ratios were prepared and the related expansion, injection and micro-explosion phenomena were investigated. During the tests, a mixed-fuel droplet was hung on a high-temperature-resistant Cr-Ni wire, which was transported to the preheating piston for heating and then was ignited automatically. Micro-needles and an infusion set also were employed to prepare mixed droplets with identical ratios but different volumes. Using a single-lens-reflex (SLR) camera, colour videos that captured the combustion process of the mixed droplets were taken and were processed into colour images using Adobe Premiere Pro CC. The colour image series were analysed to determine the ignition delay time, the burnout time and the flame characteristics during combustion of mixed droplets with different ratios. Instantaneous grey images were obtained by means of high-speed photography during combustion of the mixed droplets with different volumes and different ratios, and of droplets of E40 (in which the volume ratio of ethyl alcohol was 40%). Using Image pro plus and Origin software, the variation of normalised mean droplet diameter with time over the whole combustion cycle was calculated and the underlying reasons for various combustion phenomena were analysed.

Viabilidade econômica para a geração de energia elétrica a partir do biogás produzido em estação de tratamento de esgoto

Objetivo do estudo: apresentar a análise dos dados coletados referentes às características de esgoto afluente da Estação de Tratamento de Esgoto Serraria, em Porto Alegre/RS.Metodologia / abordagem: pesquisa descritiva com abordagem quantitativa e centralizada no estudo de caso da exploração de biogás gerada para produção de energia elétrica.Originalidade/relevância: este estudo concentra-se na viabilidade técnica e econômica para a geração de eletricidade a partir de efluente de biogás para uso na própria estação, atendendo a maioria das cargas locais, e também, da tecnologia de conversão de energia empregada a partir do ciclo de combustão interna Otto, com seus acessórios.Principais resultados: os custos de instalação, operação e manutenção por cinco anos estão estimados em torno de R$ 4.500.000,00. Além disso, o retorno sobre o capital investido ocorre, no máximo, em 4 anos e 7 meses.Contribuições teóricas / metodológicas: há uma tendência de aumento da eletricidade a partir da tarifa da rede e do fluxo de insumos nos UASBs, tornando a autogeração ainda mais viável. Atualmente, o biogás é queimado e o lodo gerado é depositado em aterros sanitários, o que possibilita a produção de energia elétrica e fornecimento à rede de distribuição.Conclusão: as usinas de estação de tratamento de esgoto constituídas de depósito de lodo anaeróbio de fluxo ascendente seguida de lodos ativos têm como objetivo o tratamento de efluentes, isto é, promover a separação dos gases, sólidos e líquidos como forma de tratamento sustentável e, além disso, proporcionar benefícios e recursos sustentáveis para a sociedade.

Multi sites vs single site for catalytic combustion of methane over Co3O4(110): A first-principles kinetic Monte Carlo study

AbstractSingle-atom catalysts have been applied in many processes recently. The difference of their kinetic behavior compared to the traditional heterogeneous catalysts has not been extensively discussed yet. Herein a complete catalytic cycle of CH4 combustion assuming to be confined at isolated single sites of the Co3O4(110) surface is computationally compared with that on multi sites. The macroscopic kinetic behaviors of CH4 combustion on Co3O4(110) is systematically and quantitatively compared between those on the single site and multi sites utilizing kinetic Monte Carlo simulations upon the energetic information from the PBE + <I>U</I> calculation and statistic mechanics. The key factors governing the kinetics of CH4 combustion are disclosed for both the catalytic cycles respectively following the single-site and multi-site mechanisms. It is found that cooperation of multi active sites can promote the activity of complete CH4 combustions substantially in comparison to separated single-site catalyst whereas the confinement of active sites could regulate the selectivity of CH4 oxidation. The quantitative understanding of catalytic mechanism paves the way to improve the activity and selectivity for CH4 oxidation.