CFD Modelling of Partial Fuel Stratification Combustion Using Detailed Fuel Surrogate Models and Tabulated Chemistry

2017 ◽  
Author(s):  
Seunghwan Keum ◽  
Ronald O. Grover ◽  
Casper Meijer ◽  
Ferry Tap
Keyword(s):  
Combustion Process ◽  
Lookup Table ◽  
Cfd Simulations ◽  
Ic Engine ◽  
Hcci Engine ◽  
Fuel Stratification ◽  
Flamelet Generated Manifold ◽  
Tabulated Chemistry ◽  
Chemistry Modeling ◽  
Different Levels

With ever more stringent emissions and performance regulations, more emphasis and efforts have been made in accurate modeling of the combustion process and engine-out emissions in engine development. However, accurate modeling of the combustion process requires detailed chemistry. Highly detailed mechanisms typically include hundreds of species and thousands of reactions, and solution of such reaction set has been one of the largest bottlenecks in numerical modeling of the IC engine with CFD. Typically, the accuracy in chemistry modeling is sacrificed by reducing the mechanism size for the sake of computational efficiency. In this study, a lookup-table based approach is applied for modeling the combustion process in an HCCI engine. Instead of solving chemistry on-the-fly during the CFD simulations, the chemistry is solved for possible combination of thermodynamic and mixing conditions. The turbulence-chemistry interaction is considered using a flamelet approach. Then, the solution is stored in a table, such that chemistry information can be retrieved during the CFD simulation. The lookup-table method, referred to as Flamelet Generated Manifold (FGM), provides significant runtime reduction in CFD simulations with high fidelity chemistry modeling. The FGM model was applied to a canonical HCCI experiment from Sandia National Laboratory. The experiment examined the effect of different levels of fuel stratification on ignition and combustion of a gasoline HCCI engine. The different levels of stratification were generated by controlling the amount of directly injected fuel. This case has been highly challenging for modeling using traditional modeling approaches. With FGM, it was possible to use the most detailed reaction mechanism to describe the chemistry as completely as one can. The effect of different surrogates on modeling results was investigated as well. It was found that the one proposed by Gauthier showed the most promising results in reproducing the highly complicated combustion with partial fuel stratification.

A Methodology for Steady and Unsteady Full-Engine Simulations

2019 ◽  
Author(s):  
Luigi Romagnosi ◽  
Yingchen Li ◽  
Mohamed Mezine ◽  
Mateus Teixeira ◽  
Stephane Vilmin ◽  
...  
Keyword(s):  
High Speed ◽  
Compressible Flows ◽  
Stokes Equations ◽  
High Reliability ◽  
Combustion Process ◽  
Combustion Model ◽  
Cfd Models ◽  
Flamelet Generated Manifold ◽  
Tabulated Chemistry ◽  
Fully Coupled

Abstract With the increase of computational power, more sophisticated computational methods can be used, larger systems simulated, and complex phenomena predicted more reliably. Nevertheless, up to now, when turbomachinery systems are numerically optimized, each of the components, i.e., the compressor, combustor, and turbine, is simulated separately from the other two. While this approach allows the use of highly dedicated simulation tools, it does not account for the interactions between the different components. With the purpose to meet the future requirements in terms of low emissions, high reliability and efficiency, a novel, highly efficient, fully-coupled, approach based on the Reynolds-Averaged Navier-Stokes equations (RANS) has been developed, enabling a steady or time-accurate simulation of a full aero-engine within a single code. One of the advantages of a steady, fully coupled approach over a steady component-by-component approach, is that the boundary conditions at the interfaces do not need to be guessed. A fully coupled, time-accurate simulation has furthermore the advantage that the effect of the non-uniform temperature distribution at the outlet of the combustor is accounted for in the determination of the thermal field of the turbine. A Smart Interface methodology permits a direct coupling between the different engine components, compressor-combustor-turbine, and allows the Computational Fluid Dynamics (CFD) models to vary between each component within the same code. This allows the user to switch off, for instance, the combustion model in the turbine and compressor blocks. For the simulation of the combustion process, the Flamelet Generated Manifold (FGM) method is applied. While the approach is superior to classical tabulated chemistry approaches and reliably captures finite-rate effects, it is computationally inexpensive since it only requires the solution of a few extra scalars and the look-up of a combustion table. The model has been extended so that high-speed compressible flows can be simulated and the potential effects between the combustor and the adjacent blade rows can be accounted for. The Nonlinear Harmonic (NLH) method is used to model the unsteady interactions between the blade rows as well as the influence of the inhomogeneities at the combustor outlet on the downstream turbine blade rows. Compared to conventional time-accurate RANS simulations (URANS), this method is two to three orders of magnitude faster and makes time-accurate turbomachinery simulations affordable. With the aim of ensuring thermodynamic consistency between the different components of the engine, the same form of the energy equation is solved in all engine elements. Furthermore, the same thermodynamic coefficients, which are used to describe the reacting processes in the combustor, are used for a caloric description of the fluid in the compressor and turbine blocks. The thermodynamic data between the blocks is transferred using the OpenLabs™ module. The developed approach is described in detail and the potential of the novel full-engine methodology is exploited on the KJ66 micro-turbine gas engine case. The results of both the steady and the time-accurate, fully coupled approaches are analyzed and the interaction between the different components of the KJ66 engine discussed.

scholarly journals Modeling diesel combustion with tabulated kinetics and different flame structure assumptions based on flamelet approach

2019 ◽  
Vol 21 (1) ◽  
pp. 89-100 ◽  
Author(s):  
Tommaso Lucchini ◽  
Daniel Pontoni ◽  
Gianluca D’Errico ◽  
Bart Somers
Keyword(s):  
Soot Formation ◽  
Flame Structure ◽  
Combustion Process ◽  
Computational Cost ◽  
Pollutant Emissions ◽  
Diesel Combustion ◽  
Flamelet Generated Manifold ◽  
Tabulated Chemistry ◽  
Computational Fluid Dynamics Analysis ◽  
The Impact

Computational fluid dynamics analysis represents a useful approach to design and develop new engine concepts and investigate advanced combustion modes. Large chemical mechanisms are required for a correct description of the combustion process, especially for the prediction of pollutant emissions. Tabulated chemistry models allow to reduce significantly the computational cost, maintaining a good accuracy. In the present work, an investigation of tabulated approaches, based on flamelet assumptions, is carried out to simulate turbulent Diesel combustion in the Spray A framework. The Approximated Diffusion Flamelet is tested under different ambient conditions and compared with Flamelet Generated Manifold, and both models are validated with Engine Combustion Network experimental data. Flame structure, combustion process and soot formation were analyzed in this work. Computed results confirm the impact of the turbulent–chemistry interaction on the ignition event. Therefore, a new look-up table concept Five-Dimensional-Flamelet Generated Manifold, that accounts for an additional dimension (strain rate), has been developed and tested, giving promising results.

scholarly journals Optical Investigation of a Partial Fuel Stratification Strategy to Stabilize Overall Lean Operation of a DISI Engine Fueled with Gasoline and E30

Energies ◽  
2021 ◽  
Vol 14 (2) ◽  
pp. 396
Author(s):  
Cinzia Tornatore ◽  
Magnus Sjöberg
Keyword(s):  
Volume Fraction ◽  
Direct Injection ◽  
Combustion Process ◽  
Pilot Injection ◽  
Optical Investigation ◽  
Flame Kernel ◽  
Lean Combustion ◽  
Fuel Stratification ◽  
Spark Plug ◽  
Initial Flame

This paper offers new insights into a partial fuel stratification (PFS) combustion strategy that has proven to be effective at stabilizing overall lean combustion in direct injection spark ignition engines. To this aim, high spatial and temporal resolution optical diagnostics were applied in an optically accessible engine working in PFS mode for two fuels and two different durations of pilot injection at the time of spark: 210 µs and 330 µs for E30 (gasoline blended with ethanol by 30% volume fraction) and gasoline, respectively. In both conditions, early injections during the intake stroke were used to generate a well-mixed lean background. The results were compared to rich, stoichiometric and lean well-mixed combustion with different spark timings. In the PFS combustion process, it was possible to detect a non-spherical and highly wrinkled blue flame, coupled with yellow diffusive flames due to the combustion of rich zones near the spark plug. The initial flame spread for both PFS cases was faster compared to any of the well-mixed cases (lean, stoichiometric and rich), suggesting that the flame propagation for PFS is enhanced by both enrichment and enhanced local turbulence caused by the pilot injection. Different spray evolutions for the two pilot injection durations were found to strongly influence the flame kernel inception and propagation. PFS with pilot durations of 210 µs and 330 µs showed some differences in terms of shapes of the flame front and in terms of extension of diffusive flames. Yet, both cases were highly repeatable.

scholarly journals Dependence of the Flue Gas Flow on the Setting of the Separation Baffle in the Flue Gas Tract

2021 ◽  
Vol 11 (7) ◽  
pp. 2961
Author(s):  
Nikola Čajová Kantová ◽  
Alexander Čaja ◽  
Marek Patsch ◽  
Michal Holubčík ◽  
Peter Ďurčanský
Keyword(s):  
Particulate Matter ◽  
Flue Gas ◽  
Gas Flow ◽  
Negative Impact ◽  
Combustion Process ◽  
Cfd Simulations ◽  
Piv Measurements ◽  
Computational Fluid Dynamics Cfd ◽  
Particle Imaging ◽  
Combustion Of Solid Fuels

With the combustion of solid fuels, emissions such as particulate matter are also formed, which have a negative impact on human health. Reducing their amount in the air can be achieved by optimizing the combustion process as well as the flue gas flow. This article aims to optimize the flue gas tract using separation baffles. This design can make it possible to capture particulate matter by using three baffles and prevent it from escaping into the air in the flue gas. The geometric parameters of the first baffle were changed twice more. The dependence of the flue gas flow on the baffles was first observed by computational fluid dynamics (CFD) simulations and subsequently verified by the particle imaging velocimetry (PIV) method. Based on the CFD results, the most effective is setting 1 with the same boundary conditions as those during experimental PIV measurements. Setting 2 can capture 1.8% less particles and setting 3 can capture 0.6% less particles than setting 1. Based on the stoichiometric calculations, it would be possible to capture up to 62.3% of the particles in setting 1. The velocities comparison obtained from CFD and PIV confirmed the supposed character of the turbulent flow with vortexes appearing in the flue gas tract, despite some inaccuracies.

Diesel engine performance mapping using a parametrized mixing time model

2017 ◽  
Vol 19 (2) ◽  
pp. 202-213 ◽  
Author(s):  
Michal Pasternak ◽  
Fabian Mauss ◽  
Christian Klauer ◽  
Andrea Matrisciano
Keyword(s):  
Diesel Engine ◽  
Fuel Injection ◽  
Mixing Time ◽  
Combustion Process ◽  
Engine Performance ◽  
Injection Timing ◽  
Engine Control ◽  
Reactor Model ◽  
Time Model ◽  
Tabulated Chemistry

A numerical platform is presented for diesel engine performance mapping. The platform employs a zero-dimensional stochastic reactor model for the simulation of engine in-cylinder processes. n-Heptane is used as diesel surrogate for the modeling of fuel oxidation and emission formation. The overall simulation process is carried out in an automated manner using a genetic algorithm. The probability density function formulation of the stochastic reactor model enables an insight into the locality of turbulence–chemistry interactions that characterize the combustion process in diesel engines. The interactions are accounted for by the modeling of representative mixing time. The mixing time is parametrized with known engine operating parameters such as load, speed and fuel injection strategy. The detailed chemistry consideration and mixing time parametrization enable the extrapolation of engine performance parameters beyond the operating points used for model training. The results show that the model responds correctly to the changes of engine control parameters such as fuel injection timing and exhaust gas recirculation rate. It is demonstrated that the method developed can be applied to the prediction of engine load–speed maps for exhaust NOx, indicated mean effective pressure and fuel consumption. The maps can be derived from the limited experimental data available for model calibration. Significant speedup of the simulations process can be achieved using tabulated chemistry. Overall, the method presented can be considered as a bridge between the experimental works and the development of mean value engine models for engine control applications.

Ethers and esters as alternative fuels for internal combustion engine: A review

2021 ◽  
pp. 146808742110464
Author(s):  
Yang Hua
Keyword(s):  
Alternative Fuels ◽  
Combustion Engine ◽  
Combustion Process ◽  
Pressure Rise ◽  
Engine Performance ◽  
Internal Combustion ◽  
Operating Conditions ◽  
Future Research ◽  
Particulate Emissions ◽  
Ic Engine

Ether and ester fuels can work in the existing internal combustion (IC) engine with some important advantages. This work comprehensively reviews and summarizes the literatures on ether fuels represented by DME, DEE, DBE, DGM, and DMM, and ester fuels represented by DMC and biodiesel from three aspects of properties, production and engine application, so as to prove their feasibility and prospects as alternative fuels for compression ignition (CI) and spark ignition (SI) engines. These studies cover the effects of ether and ester fuels applied in the form of single fuel, mixed fuel, dual-fuel, and multi-fuel on engine performance, combustion and emission characteristics. The evaluation indexes mainly include torque, power, BTE, BSFC, ignition delay, heat release rate, pressure rise rate, combustion duration, exhaust gas temperature, CO, HC, NOx, PM, and smoke. The results show that ethers and esters have varying degrees of impact on engine performance, combustion and emissions. They can basically improve the thermal efficiency of the engine and reduce particulate emissions, but their effects on power, fuel consumption, combustion process, and CO, HC, and NOx emissions are uncertain, which is due to the coupling of operating conditions, fuel molecular structure, in-cylinder environment and application methods. By changing the injection strategy, adjusting the EGR rate, adopting a new combustion mode, adding improvers or synergizing multiple fuels, adverse effects can be avoided and the benefits of oxygenated fuel can be maximized. Finally, some challenges faced by alternative fuels and future research directions are analyzed.

Thermodynamic Performance Optimization of Reciprocating Internal Combustion (IC) Engines

2008 ◽  
Author(s):  
George A. Adebiyi ◽  
Kalyan K. Srinivasan ◽  
Charles M. Gibson
Keyword(s):  
Performance Optimization ◽  
Combustion Process ◽  
Design Parameters ◽  
Second Law ◽  
Ic Engine ◽  
Thermodynamic Performance ◽  
Second Law Analysis ◽  
Compression And Expansion ◽  
Dual Cycle ◽  
Ic Engines

Reciprocating IC engines are traditionally modeled as operating on air standard cycles that approximate indicator diagrams obtained in experiments on real engines. These indicator diagrams can best be approximated by the dual cycle for both gasoline and diesel engines. Analysis of air standard cycles unfortunately fails to capture second law effects such as exergy destruction due to the irreversibility of combustion. Indeed, a complete thermodynamic study of any process requires application of both the first and second laws of thermodynamics. This article gives a combined first and second law analysis of reciprocating IC engines in general with optimization of performance as primary goal. A practical dual-like cycle is assumed for the operation of a typical reciprocating IC engine and process efficiencies are assigned to allow for irreversibilities in the compression and expansion processes. The combustion process is modeled instead of being replaced simply by a heat input process to air as is common in air standard cycle analysis. The study shows that performance of the engine can indeed be optimized on the basis of geometrical design parameters such as the compression ratio as well as the air-fuel ratio used for the combustion.

Fuel Injection Control for a Valve Array in a Shockless Explosion Combustor

2018 ◽  
Author(s):  
Jan-Simon Schäpel ◽  
Rudibert King ◽  
Fatma Yücel ◽  
Fabian Völzke ◽  
Christian Oliver Paschereit ◽  
...  
Keyword(s):  
Fuel Injection ◽  
Combustion Process ◽  
Firing Frequency ◽  
Mixed Integer ◽  
Test Rig ◽  
Proportional Valve ◽  
Control Approach ◽  
Fuel Stratification ◽  
Auto Ignition ◽  
Filling Time

Approximate constant volume combustion (aCVC) is a promising way to optimize the combustion process in a gas turbine, which would exceed the gain in efficiency resulting from optimizing other components significantly. This work deals with a recently proposed approach: shockless explosion combustion (SEC). Compared to already known concepts, such as pulsed detonation combustion (PDC), it overcomes several disadvantages, e.g., sharp pressure transitions and entropy generation due to shock waves. For an SEC, accurate fuel stratification is required to achieve a quasi-homogeneous auto-ignition. In an atmospheric test rig quasi-homogeneous ignitions were achieved previously in non-resonant operation. To achieve a resonant operation, which goes along with a higher firing frequency, lower ignition and injection times are required. For this purpose, an array of solenoid valves was designed to allow for highly dynamic operation within short filling time spans. Using a novel mixed-integer control approach, these solenoid valves were actuated such that a desired fuel profile was generated. In this paper, the mentioned test rig was used for non-reacting fuel measurements to compare the quality of the axial fuel stratification achieved by using the valve array with the one achieved by using a slower proportional valve. In the experimental investigation the actuation with the valve array proved to adjust the required fuel stratification with the same quality as the actuation with the proportional valve, which was already successfully applied to the reactive set-up. Hence, the mixed-integer controlled valve array is considered a useful concept for upcoming resonant reactive SEC investigations.

Chemical-looping combustion — a thermodynamic study

2008 ◽  
Vol 222 (6) ◽  
pp. 1005-1019 ◽  
Author(s):  
N R McGlashan
Keyword(s):  
Heat Exchange ◽  
Redox Reactions ◽  
Oxygen Carrier ◽  
Combustion Process ◽  
Reduction Process ◽  
Equilibrium Temperature ◽  
Working Fluid ◽  
Chemical Looping Combustion ◽  
Chemical Looping ◽  
Ic Engine

The poor performance of internal combustion (IC) engines can be attributed to the departure from equilibrium in the combustion process. This departure is expressed numerically, as the difference between the working fluid's temperature and an ideal ‘combustion temperature’, calculated using a simple expression. It is shown that for combustion of hydrocarbons to be performed reversibly in a single reaction, impractically high working fluid temperatures are required — typically at least 3500 K. Chemical-looping combustion (CLC) is an alternative to traditional, single-stage combustion that performs the oxidation of fuels using two reactions, in separate vessels: the oxidizer and reducer. An additional species circulates between the oxidizer and reducer carrying oxygen atoms. Careful selection of this oxygen carrier can reduce the equilibrium temperature of the two redox reactions to below current metallurgical limits. Consequently, using CLC it is theoretically possible to approach a reversible IC engine without resorting to impractical temperatures. CLC also lends itself to carbon capture, as at no point is N2 from the air allowed to mix with the CO2 produced in the reduction process and therefore a post-combustion scrubbing plant is not required. Two thermodynamic criteria for selecting the oxygen carrier are established: the equilibrium temperature of both redox reactions should lie below present metallurgical limits. Equally, both reactions must be sufficiently hot to ensure that their reaction velocity is high. The key parameter determining the two reaction temperatures is the change in standard state entropy for each reaction. An analysis is conducted for an irreversible CLC system using two Rankine cycles to produce shaft work, giving an overall efficiency of 86.5 per cent. The analysis allows for irreversibilites in turbine, boiler, and condensers, but assumes reactions take place at equilibrium. However, using Rankine cycles in a CLC system is considered impractical because of the need for high-temperature, indirect heat exchange. An alternative arrangement, avoiding indirect heat exchange, is discussed briefly.

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