Phenomenological Combustion Model Research Articles

Effect of flexible camshaft technology on dual-fuel engine performance using phenomenological combustion model

AbstractThe objective of the current study is to investigate the effect of tunable valve timings on the performance and emissions of a dual-fuel marine engine. A simulation model was developed in MATLAB to simulate the valvetrain mechanism. The model generates different valve lift curves depending on the input conditions, and after that, it tests them against any possible collision with the piston. The valid valve lift curves were exported to a two-zone combustion model in AVL CRUISE-M platform. The combustion model depends on the fractal principle and aims to predict the in-cylinder parameters. In addition, it contains sub-models to calculate the ignition delay and emissions formation. Model results were compared against experimental data, as the latter were obtained from a heavy-duty, medium-speed, single-cylinder research engine, which employs natural gas as a main fuel. The results showed good agreement and the model was used for further investigations with other cam pairs. It has been found that the fractal combustion model can effectively represent the combustion behavior in the dual-fuel engine. Furthermore, valve timing has a significant influence on the engine performance and exhaust emissions. Results also revealed that applying Miller cycle can reduce the nitrogen oxides emissions, while the higher valve overlap period had a negative effect on methane slip.

Hydrogen-diesel dual-fuel combustion sensitivity to fuel injection parameters in a multi-cylinder compression-ignition engine

Adding hydrogen to the intake of a diesel engine offers a near-term route to reducing greenhouse gas emissions from heavy-duty commercial vehicles. Variations in combustion behavior between cylinders can limit the performance and H2 utilization in these engines. This research evaluates the impacts of varying H2 concentrations between cylinders due to the phasing of pulsed fuel injection in the intake manifold, and the potential to optimize the diesel injection strategy for each cylinder to compensate for these effects. The study is conducted using a predictive phenomenological combustion model for H2-diesel combustion within the GT-SUITE™ software environment calibrated and validated using experimental data from a 4-cylinder, 5.2 L engine at three loads and at two different H2 concentrations per load. Predictions of engine and combustion performance were within 5% of the experimental results for key parameters. The validated model is then used to quantify the impacts of varying H2 distribution between cylinders on combustion performance and hardware limitations including peak cylinder pressure, rate of pressure rise, and exhaust temperature. From these results, the diesel injection parameters, including timing and quantity of both pilot and main injections, are optimized for each cylinder to minimize variations in engine performance. The results indicate that cylinder-to-cylinder variations in H2 concentration increased with more rapid H2 injection, due to limited dispersion of H2 between the cylinders. Variations in indicated power approached 13.5% between cylinders, with those with high H2 content encountering a substantial risk of knock and noise. Adjusting the diesel injected mass per cylinder balanced power variations, while adjusting pilot injection timing minimized variations in the rate of pressure rise (dP/dCA). Exhaust temperature and efficiency were most sensitive to the timing of the main diesel injection. Combined, these control approaches reduced diesel fuel consumption and CO2 emission by 5.2 and 6.2%, respectively, where an average 3.8% increase in the engine's indicated efficiency was observed. The optimization findings offer a promising approach for balancing the engine performance when there is unbalanced H2 distribution between the cylinders.

Advanced turbulence and combustion modeling for the study of a swirl-assisted natural gas spark-ignition heavy-duty engine

Increasing demands on higher performance and lower fuel consumption and emissions have led the path for internal combustion engine development; this race is nowadays directly related to CO2 emissions reduction. To drive engine development and reduce the time-to-market, the employment of numerical analysis is mandatory. This requires a continuous improvement of the simulation models toward real predictive analyses able to reduce the experimental R&D efforts. In this framework, 1D numerical codes are fundamental tools for system design, energy management optimization, and calibration. The present work is focused on the improvement of the phenomenological turbulence model, originally conceived to describe turbulence evolution in tumble-promoting engines. The turbulence model is developed with reference to a SI heavy-duty CNG engine derived from a diesel engine. In this architecture, due to the flat cylinder head, turbulence is also generated by swirl and squish flow motions, in addition to tumble motion. The presented turbulence model is validated against 3D CFD results, demonstrating to properly predict turbulence and swirl/tumble evolution under two different operating conditions, without the need for any case-dependent tuning. The developed turbulence model is coupled to a phenomenological combustion model based on the fractal geometry theory applied to the flame front surface, where the turbulence is assumed to support flame propagation through an enhancement of the flame front area with respect to the laminar counterpart. The combustion model is validated against an extensive experimental dataset, composed of 25 operating points at different engine rotational speeds and loads. The numerical/experimental comparisons of global performance parameters are satisfactory, leading to maximum errors around ±2% for the BSFC, ±2° for the main combustion events, and ±1 bar for the in-cylinder peak pressure. Burn rate profiles are very well captured by the combustion model at changing operating conditions, not requiring any case-dependent tuning. The presented results demonstrate that the turbulence/combustion models could constitute a reliable virtual test facility, contributing to supporting and driving experimental activities.

A Phenomenological Combustion Model for Diesel–Methanol Dual-Fuel Engines

Abstract Strict emission regulations and energy security concerns have led to various alternative concepts for the engine operation. Diesel–Methanol dual-fuel combustion solution has gained momentum over the past decade due to the fact that the technology required to convert a pure diesel engine to a dual-fuel one is mature, and methanol is a well-known substance in the industry. However, designing, tuning, and optimizing these engines require fast and reliable simulation models. For this purpose in the present study, a phenomenological combustion model, for a four-stroke port-injected methanol diesel engine, is established. The model is tuned with in-cylinder combustion data. The heat release rate is estimated via a triple-Wiebe function. Ignition delay is modeled with an Arrhenius-type expression, utilizing the methanol and diesel equivalence ratio, among other operational parameters. Other model parameters are obtained from data-driven functions, correlating the basic parameters of the combustion. The data used for model calibration and validation were generated with a computational fluid dynamic numerical model, and it was verified with data provided in the literature.

A transient and spatially confined phenomenological combustion model for direct-injection, compression-ignition engines in fuel-rich applications: N-Stage Lagrangian (NSL)

Previous efforts aimed at increasing the efficiencies of systems where a piston engine serves as a primary work producer have led to interest in operating direct-injection, compression-ignition (DI/CI) engines at overall stoichiometric or fuel-rich equivalence ratios. In order to extend the current understanding of DI/CI combustion to applications in this regime, a phenomenological model is proposed. The model builds on previous conceptual and phenomenological models that describe steady, reacting free jets and applies the underlying concepts to a spatially confined, transient system. The model is assessed in its ability to describe and interpret experimental data through comparisons to experimental data collected in this regime, with a particular focus on its ability to address the observed trends in exhaust gas species concentrations. Through this comparison to experimental data, potential insights provided by the model are discussed.

Development of a diesel engine’s digital twin for predicting propulsion system dynamics

A digital twin is the essential part of a recent and unavoidable trend in ship operation digitalisation. The digital twin is a virtual replica of real ship or a particular system that coexists with its physical counterpart and maps the dynamic behaviour in real-time. Thus, the digital twin combines physical space real-time data with a set of dynamic models representing the physical counterpart in the cyberspace. The problem of digital twin development is a trade-off between insight into the dynamic process and real-time execution constraint. This paper describes a modelling approach that combines continuous time-domain cycle-mean value engine model with the crank-angle resolved phenomenological combustion model, satisfying the real-time execution constraint. The set of conservation laws, notably energy and mass, supplemented with the phenomenological Wiebe combustion model, is treated in the integral form allowing transformation into a set of nonlinear algebraic equations. The solution of the resulting system exhibits fast speed and accuracy as compared with the traditional approach combining differential equations and Runge-Kutta solver.

Combustion details of raw and torrefied biomass fuel particles with individually-observed size, shape and mass

A unique approach and proposed methodology was implemented to determine char burning rates in conjunction to their prevailing structure from detailed results on the combustion histories of small biomass fuel particles, exposed to elevated temperatures (>1000 K) at very high heating rates (104–105 K/s). Analogous conditions typically prevail in pulverized fuel utility boilers for power generation. Individual particles of pre-measured size, shape, aspect ratio and mass from five different types of raw and torrefied biomass were selected for this study. The particles were injected into a transparent drop-tube furnace, electrically heated to 1400 K, where they were rapidly heated, ignited and burned in air. Temperature-time histories of the individual particles were recorded pyrometrically and were used to assess their individual combustion rates. These particles burned in distinct volatile and char phases. A published phenomenological combustion model for carbonaceous fuel particles was enhanced and applied to the experimental data to calculate the char burning rates. Important information on the nature of these chars, which formed inside volatile matter envelope flames, was obtained by juxtaposition of the knowledge of their original properties with the pyrometric observations and the numerical simulations. It was concluded that, under the conditions of these experiments, chars of most types of biomass consisted of thin-wall cenospherical particles. The modeling results show that this predominant particle structure needs to be considered for reliable burnout predictions.

A Novel Laminar Flame Speed Correlation for the Refinement of the Flame Front Description in a Phenomenological Combustion Model for Spark-Ignition Engines

A Novel Laminar Flame Speed Correlation for the Refinement of the Flame Front Description in a Phenomenological Combustion Model for Spark-Ignition Engines

A phenomenological HCCI combustion model in 0D and 3D-CFD

A phenomenological combustion model for HCCI applications – the 3-Stage heat release model – which predicts low, intermediate and high temperature heat release (LTR, ITR and HTR) is developed and validated for six automotive surrogate fuels. The contribution of all three combustion phases to the overall heat release and their durations are modeled based on rapid compression and expansion (RCEM) single-zone adiabatic simulations with detailed chemical kinetic mechanisms for all six fuels. This allows “pure” chemical effects on combustion to be included in the proposed 3-Stage heat release model, avoiding any combustion chamber related uncertainties such as blow-by, heat losses or trapped mass in crevices. Agreement between the 3-Stage heat release model and virtual RCEM (VRCEM) reference data is good. In a second step, a zero-dimensional HCCI model (0D model) is presented. To predict the onset of combustion, the low temperature ignition term of a previously developed and validated 3-Arrhenius auto-ignition model is employed in conjunction with the ignition integral of Livengood and Wu. Thereafter the 3-Stage heat release model predicts chemical heat release. Results show that the 0D model gives excellent predictions of ignition delays and combustion progress compared to the single-zone RCEM simulations using detailed chemical reaction mechanisms. Furthermore, including ITR in the 0D model is shown to be of essential importance to correctly predict high temperature ignition delay. As a final step a 3D HCCI model (3D model) is presented. The onset of combustion is again predicted by the low temperature ignition term of the 3-Arrhenius auto-ignition model, implemented via the source term of the transport equation into the 3D-CFD code. To predict heat release, the source term of the enthalpy equation is used to incorporate the 3-Stage heat release model into the 3D-CFD code. A simplified RCEM geometry is used for the simulations. Validation of the 3D model is made by a comparison to a chemical kinetic mechanism that is directly integrated into the 3D-CFD code. Combustion progress, temperature stratification in the combustion chamber and ignition delay times agree well with the reference data. The combination of the 3-Arrhenius auto-ignition model and 3-stage heat release model, their integration into 0D or 3D-CFD as a fully predictive HCCI model and their very low computational cost suggest the proposed model constitutes a promising approach for the development of future HCCI combustion engines.

Simultaneous Application of Exhaust Gas Recirculation and Non-Constant Injection Rates to Reduce NOx and Soot Emissions in Diesel Engines

A combination of EGR and variation of injection rate has been used to keep both NOx and soot emissions at an acceptable level. To do so, a two-dimensional multi-zone phenomenological diesel engine combustion model has been developed. The model consists of several sub-models for spray development, fuel atomization, evaporation, combustion, and emission formation. The fuel spray is divided into several small packets called zones, and consequently, the equations for conservation of mass and energy are solved for each individual zone at each time step, from which the cylinder temperature and pressure are calculated. Additionally, the formation of emissions is tracked as soon as the combustion starts. Moreover, parallel processing programming techniques have been utilized, which reduce the computational time of the model considerably, making it a fast and reliable tool for combustion simulation. Using the model, different rates of EGR are applied, which as expected shows a noticeable decrease in NOx emissions. Thanks to the modular design of the model, injection profile can be changed easily. Instead of using a constant rate injection, three different injection patterns are used. First, an upward step profile is used, in which fuel is initially injected with a lower and then with a higher rate. After that, a downward step profile was applied, which injects the fuel first with a lower and then a higher rate. Finally, a combination of the above profiles is used, i.e., the fuel is injected initially at a low rate, and then, the injection rate is increased, and finally decreased again. It is shown that use of EGR with a combined injection pattern at the same time can keep the NOx and soot emissions of the diesel engine at an acceptable level.

Evaluation of the Predictive Capabilities of a Phenomenological Combustion Model for Natural Gas SI Engine

Abstract The current study evaluates the predictive capabilities of a new phenomenological combustion model, available as a part of the GT-Suite software package. It is comprised of two main sub-models: 0D model of in-cylinder flow and turbulence, and turbulent SI combustion model. The 0D in-cylinder flow model (EngCylFlow) uses a combined K-k-ε kinetic energy cascade approach to predict the evolution of the in-cylinder charge motion and turbulence, where K and k are the mean and turbulent kinetic energies, and ε is the turbulent dissipation rate. The subsequent turbulent combustion model (EngCylCombSITurb) gives the in-cylinder burn rate; based on the calculation of flame speeds and flame kernel development. This phenomenological approach reduces significantly the overall computational effort compared to the 3D-CFD, thus allowing the computation of full engine operating map and the vehicle driving cycles. Model was calibrated using a full map measurement from a turbocharged natural gas SI engine, with swirl intake ports. Sensitivity studies on different calibration methods, and laminar flame speed sub-models were conducted. Validation process for both the calibration and sensitivity studies was concerning the in-cylinder pressure traces and burn rates for several engine operation points achieving good overall results.

Model-based virtual engine calibration with the help of phenomenological methods for spark-ignited engines

High-efficiency energy conversion in modern spark-ignited combustion engines can be achieved via extensive variabilities considering the valve train, fuel injection and load control. As a significant number of parallel functionalities are required to provide control, engine calibration efforts are very high and need to be reduced by introducing virtual methods. In this paper, quasi-dimensional combustion prediction is used in combination with a gas exchange analysis to virtually calibrate the engine control unit (ECU) function for engine torque and the exhaust gas temperature. To achieve this, a phenomenological combustion model is set up. The cylinder thermodynamics, combustion-relevant turbulence and ignition delay are modeled and validated. The modeling is completed with a calculation of overall heat release rates following an entrainment approach. Targeted accuracies are met in a wide range of engine operations, especially a margin of ±6% for the high-pressure indicated work. Finally, the model’s successful application is demonstrated in terms of ECU functions for the crankshaft torque and exhaust gas temperature. The virtual methodology developed can now be used in the field of ECU calibration as well as for issues where engine design is influenced by ECU calibration.

A phenomenological combustion analysis of a dual-fuel natural-gas diesel engine

Energy security concerns and an abundant supply of natural gas in the USA provide the impetus for engine designers to consider alternative gaseous fuels in the existing engines. The dual-fuel natural-gas diesel engine concept is attractive because of the minimal design changes, the ability to preserve a high compression ratio of the baseline diesel, and the lack of range anxiety. However, the increased complexity of a dual-fuel engine poses challenges, including the knock limit at a high load, the combustion instability at a low load, and the transient response of an engine with directly injected diesel fuel and port fuel injection of compressed natural gas upstream of the intake manifold. Predictive simulations of the complete engine system are an invaluable tool for investigations of these conditions and development of dual-fuel control strategies. This paper presents the development of a phenomenological combustion model of a heavy-duty dual-fuel engine, aided by insights from experimental data. Heat release analysis is carried out first, using the cylinder pressure data acquired with both diesel-only and dual-fuel (diesel and natural gas) combustion over a wide operating range. A diesel injection timing correlation based on the injector solenoid valve pulse widths is developed, enabling the diesel fuel start of injection to be detected without extra sensors on the fuel injection cam. The experimental heat release trends are obtained with a hybrid triple-Wiebe function for both diesel-only operation and dual-fuel operation. The ignition delay period of dual-fuel operation is examined and estimated with a predictive correlation using the concept of a pseudo-diesel equivalence ratio. A four-stage combustion mechanism is discussed, and it is shown that a triple-Wiebe function has the ability to represent all stages of dual-fuel combustion. This creates a critical building block for modeling a heavy-duty dual-fuel turbocharged engine system.

Phenomenological modeling of combustion and NOx emissions using detailed tabulated chemistry methods in diesel engines

Enhancing the predictive quality of engine models, while maintaining an affordable computational cost, is of great importance. In this study, a phenomenological combustion and a tabulated NOx model, focusing on efficient modeling and improvement of computational effort, is presented. The proposed approach employs physical and chemical sub-models for local processes such as injection, spray formation, ignition, combustion, and NOx formation, being based on detailed tabulated chemistry methods. The applied combustion model accounts for the turbulence-controlled as well as the chemistry-controlled combustion. The phenomenological combustion model is first assessed for passenger car application, especially with multiple pilot injections and high exhaust gas recirculation ratios for low-load operating points. The validation results are presented for representative operating conditions from a single-cylinder light-duty diesel engine and over the entire engine map of a heavy-duty diesel engine. In the second part of this study, a novel approach for accurate and very fast modeling of NO formation in combustion engines is proposed. The major focus of this study is on the development of a very fast-running NO mechanism for usage in the next generation of the engine control units. This approach is based on tabulation of a detailed chemical kinetic mechanism and is validated against the detailed chemical reaction mechanism at all engine-relevant conditions with the variation in pressure, temperature, and air–fuel ratio under stationary and ramp-type transient conditions in a perfectly stirred reactor. Using this approach, a very good match to the results from calculations with the detailed chemical mechanism is observed. Finally, the tabulated NOx kinetic model is implemented in the combustion model for in-cylinder NOx prediction and compared with the experimental engine measurement data.

Comparative Numerical Study of Four Biodiesel Surrogates for Application on Diesel 0D Phenomenological Modeling

To meet more stringent norms and standards concerning engine performances and emissions, engine manufacturers need to develop new technologies enhancing the nonpolluting properties of the fuels. In that sense, the testing and development of alternative fuels such as biodiesel are of great importance. Fuel testing is nowadays a matter of experimental and numerical work. Researches on diesel engine’s fuel involve the use of surrogates, for which the combustion mechanisms are well known and relatively similar to the investigated fuel. Biodiesel, due to its complex molecular configuration, is still the subject of numerous investigations in that area. This study presents the comparison of four biodiesel surrogates, methyl-butanoate, ethyl-butyrate, methyl-decanoate, and methyl-9-decenoate, in a 0D phenomenological combustion model. They were investigated for in-cylinder pressure, thermal efficiency, andNOxemissions. Experiments were performed on a six-cylinder turbocharged DI diesel engine fuelled by methyl ester (MEB) and ethyl ester (EEB) biodiesel from wasted frying oil. Results showed that, among the four surrogates, methyl butanoate presented better results for all the studied parameters. In-cylinder pressure and thermal efficiency were predicted with good accuracy by the four surrogates.NOxemissions were well predicted for methyl butanoate but for the other three gave approximation errors over 50%.

Combustion modelling for a diesel engine with multi-stage injection using a stochastic combustion model

This study presents the development of a phenomenological combustion model to simulate the combustion processes in diesel engines with multi-stage fuel injection. A newly developed zero-dimensional spray propagation model and a model of spray-to-spray interaction were combined with a stochastic combustion model, which had been developed for the calculation of diesel combustion in the case of single-stage injection. In this model, the combustion chamber is divided into an ambient air zone and several spray zones, where the spray formed by each injection is treated as a spray zone. The turbulent mixing, the fuel evaporation, the heat loss and the chemical reactions are calculated in each spray zone separately. A zero-dimensional spray propagation model including the spray evolution after the end of injection and a model of interaction between the sprays from sequential injections are developed to describe the spray behaviour for the case of multi-stage injection. Then the developed combustion model is validated against the experimental data from a single-cylinder direct-injection diesel engine with two-stage pilot–main injection, in which the pilot injection conditions are varied with a fixed main-injection timing. Based on the analysis of the heat release rate, the entrainment rate and the microscopic information inside the spray, such as the probability density function of the equivalence ratio, the effects of the wall impingement and the interaction between adjacent sprays on the fuel–air mixing rate and the entrainment rate are formularized and employed to reproduce the measured histories of the heat release rate. The reduction in the fuel–air mixing rate is considered when the spray flows into the squish region after wall impingement, which is effective in obtaining the measured decrease in the heat release of the pilot spray with advancing pilot injection timing. The effects of the wall impingement of the main spray and the interaction between adjacent sprays are modelled to reproduce the heat release rate during the initial part and later part of the mixing-controlled combustion. After these improvements, the heat release rates of the test engine when varying the pilot injection conditions were successfully predicted.

Hierarchical 1D/3D Approach for the Development of a Turbulent Combustion Model Applied to a VVA Turbocharged Engine. Part II: Combustion Model

As discussed in the part I of this paper, 3D models represent a useful tool for a detailed description of the mean and turbulent flow fields inside the engine cylinder. 3D results are utilized to develop and validate a 0D phenomenological turbulence model, sensitive to the variation of operative parameters such as valve phasing, valve lift, engine speed, etc.In part II of this paper, a 0D phenomenological combustion model is presented, as well. It is based on a fractal description of the flame front and is able to sense each of the fuel properties, the operating conditions (air-to-fuel ratio, spark advance, boost level) and the combustion chamber geometry. In addition, it is capable to properly handle different turbulence levels predicted by means of the turbulence model presented in the part I.The turbulence and combustion models are included, through user routines, in the commercial software GT-Power™. With reference to a small twin-cylinder VVA turbocharged engine, the turbulence/combustion model, once properly tuned, is finally used to calculate in-cylinder pressure traces, rate of heat release and overall engine performance at full load operations and brake specific fuel consumption at part load, as well. An excellent agreement between numerical forecasts and experimental evidence is obtained.

HC1-1 Quasi-Dimensional Modeling of Partly Homogeneous and Homogeneous Diesel Combustion(HC: HCCI Combustion,General Session Papers)

During the conventional Diesel combustion soot and nitrogen oxide are formed due to the inhomogeneous mixture process. In homogeneous or partly homogeneous operation combustion occurs in premixed and lean conditions. Therefore soot and NOx emissions are significantly reduced. In the past the last-named operating modes have been investigated mostly by experimental test-bench measurements. So far, the nonexistence of easy to use and accurate combustion models for these types of combustion regimes have prevented researchers and developers from using one-dimensional simulation tools. Therefore a phenomenological combustion model for homogeneous and partly homogeneous Diesel combustion has been developed. The low temperature combustion and the ignition delays for high temperature combustion are calculated with a global reaction model. The high temperature combustion is modeled with a phenomenological approach which uses several fuel balance pools to represent different degrees of homogenization during partly homogeneous operating modes. A combined k-ε and density-difference approach is used to model the mixture formation during DI-modes. The developed model showed very good agreement with experimental results for homogeneous and partly homogeneous Diesel combustion with one set of parameters combined with very low computational time.

COMBUSTION MODEL FOR SPARK IGNITION ENGINES OPERATING ON GASOLINE-ETHANOL BLENDS

This article presents a phenomenological combustion model using turbulent flame propagation theory developed by Keck and coworkers, 1974. The model was adapted to work with gasoline-ethanol blends, following correlations presented by Bayraktar,2005. New sub-models were introduced for intake valve velocity and combustion efficiency. These allow simulating the effect of compression ratio, spark timing and fuel change. Results show good agreement with the ones in the original work as well as with experimental results in a Cooperative Fuels Research (CFR) engine.

Second law analysis of hydrogen–air combustion in a spark ignition engine

Besides its renewable nature and low emission advantage, hydrogen has higher exergetic efficiency of combustion compared to hydrocarbon fuels. This makes it an attractive alternative fuel for internal combustion engines. The present work concerns the estimation of irreversibilities associated with various sub-processes occurring during combustion in a hydrogen fueled spark ignition engine. A quasi-three zone phenomenological combustion model is used for predicting the pressure and temperature histories of a single cylinder, four stroke spark ignition engine operating at equivalence ratios of 0.3–0.75 in the speed range 1500–3500 rpm. For each sub-process, the history of availability destruction during combustion and the effects of operating conditions are discussed. Measures are proposed for improving the exergetic efficiency by mitigating availability destruction. It is observed that chemical reaction is the major contributor to irreversibility generation, followed by pressure equilibration and heat loss to walls. While more than 94% of the fuel supplied undergoes combustion, nearly 20–30% of the reactant availability is destroyed. Charge preheating, product mixing and piston motion are observed to have negligible effects on irreversibility generation.