Characterisation of flow structures inside an engine cylinder under steady state condition

The in-cylinder flow of internal combustion (IC) engines, formed during the intake stroke, is one of the most important factors that affect the quality of air-fuel mixture and combustion. The inducted airflow through the inlet valve is primarily influenced by the intake port design, intake valve design, valve lift and valve timing. Such parameters have a significant influence on the generation and development of in-cylinder flow motion. In most combustion systems the swirl and tumble motions are used to aid the air-fuel mixing with the subsequent decay of these bulk flow motions generating increased turbulence levels which then enhance the combustion processes in terms of rate of chemical reactions and combustion stability. Air motion formed inside the engine cylinder is three-dimensional, transient, highly turbulent and includes a wide spectrum of length and time scales. The significance of in-cylinder flow structures is mainly reflected in large eddy formation and its subsequent break down into turbulence kinetic energy. Analysis of the large scale and flow motions within an internal combustion engine are of significance for the improvement of engine performance. A first approximation of these flow structures can be obtained by steady state analysis of the in-cylinder flow with fixed valve lifts and pressure drops. Substantial advances in both experimental methods and numerical simulations provide useful research tools for better understanding of the effects of rotational air motion on engine performance. This study presents results from experimental and numerical simulations of in-cylinder flow structures under steady state conditions. Although steady state flow problem still includes complex three-dimensional geometries with high turbulence intensities and rotation separation, it is significantly less complex than the transient problem. Therefore, preliminary verifications are usually performed on steady state flow rig. For example, numerical investigation under steady state condition can be considered as a precondition for the feasibility of calculations of real engine cylinder flow. Particle Image Velocimetry (PIV) technique is used in the experimental investigations of the in-cylinder flow structures. The experiments have been conducted on an engine head of a pent-roof type (Lotus) for a number of fixed valve lifts and different inlet valve configurations at two pressure drops, 250mm and 635mm of H2O that correlate with engine speeds of 2500 and 4000 RPM respectively. From the 2-D in-cylinder flow measurements, a tumbling vortex analysis is carried out for six planes parallel to the cylinder axis. In addition, a swirl flow analysis is carried out for one horizontal plane perpendicular to the cylinder axis at half bore downstream from the cylinder head (44mm). Numerically, modelling of the in-cylinder flow is proving to be a key part of successful combustion simulation. The numerical simulations require an accurate representation of turbulence and initial conditions. This Thesis deals with numerical investigation of the in-cylinder flow structures under steady state conditions utilizing the finite-volume CFD package, STAR CCM+. Two turbulence models were examined to simulate the turbulent flow structure namely, Realizable k-ε and Reynolds Stress Turbulence Model, RSM. Three densities of generated mesh, which is polyhedral type, are examined. The three-dimensional numerical investigation has been conducted on the same engine head of a pent-roof type (Lotus) for a number of fixed valve lifts and both valves are opened configuration at two pressure drops 250mm and 635mm of H2O that is equivalent to engine speeds of 2500 and 4000 RPM respectively. The nature and modelling of the flow structure together with discussions on the influence of the pressure drop and valve lift parameters on the flow structures are presented and discussed. The experimental results show the advantage of using the planar technique (PIV) for investigating the complete flow structures developed inside the cylinder. It also highlighted areas where improvements need to be made to enhance the quality of the collected data in the vertical plane measurements. Based on the comparison between the two turbulence models, the RSM model results show larger velocity values of about 15% to 47% than those of the Realizable k-ε model for the whole regions. The computational results were validated through qualitative and quantitative comparisons with the PIV data obtained from the current investigation and published LDA data on both horizontal and vertical cross sections. The calculated correlation coefficient, which is above 0.6, indicated that a reasonable prediction accuracy for the RSM model. This verifies that the numerical simulation with the RSM model is a useful tool to analyse turbulent flows in complex engine geometries where anisotropic turbulence is created

Finite Element Simulation of a Steady-State Stress Distribution in a Four Stroke Compressed Natural Gas-Direct Injection Engine Cylinder Head

The main aim of this work is to predict the design performance based on the stress/strain and thermal stress behaviour of cylinder head under various operating conditions. The effects of engine operating conditions such as combustion gas temperature and maximum internal pressure, components initial temperature and engine speed on the stress and thermal stress behaviour of the cylinder head have been analyzed. The analysis was carried out using a finite element analysis (FEA) software package, MSC.NASTRAN which is use to simulate and predict the von-Mises stress and strain pattern and thermal distribution of the cylinder head structure during the combustion process in the engine and the geometry modelling was carried out using a popular computeraided engineering tool, CATIA V5. The result can be used to determine the quality of the design as well as identify areas which require further improvement. In this investigation, structural analyses of the cylinder head highlight several areas of interest. The maximum stress is found not exceeding the material strength of cylinder head, and thus the basic design criteria, namely no yielding and no structural failure under firing load case, can be satisfied. In addition, the effect of thermal stress/strain provides a good indication on structural integrity and reliability of the cylinder head, which can be improved in the early stages of design. This steadystate finite element method (FEM) stress analysis can play a very effective role in the rapid prototyping of the cylinder head

Determination of the resonance response in an engine cylinder with a bowl-in-piston geometry by the finite element method for inferring the trapped mass

[EN] Cylinder resonance phenomenon in reciprocating engines consists of high-frequency pressure oscillations excited by the combustion. The frequency of these oscillations is proportional to the speed of sound on pent-roof combustion chambers and henceforth the resonance frequency can be used to estimate the trapped mass, but in bowl-in-piston chambers a geometrical factor must be added in order to deal with the bowl disturbance. This paper applies the finite element method (FEM) to provide a resonance calibration for new design combustion chambers, which are commonly dominated by the bowl geometry near the top dead centre. The resonance calibration does not need any sensor information when it is solved by a FEM procedure, and consequently, is free from measurement errors. The calibration is proven to be independent of the chamber conditions and the results obtained are compared with experimental data by using spectral techniques and measuring precisely the trapped mass.[EN]This research has been partially supported by the European Union in framework of the POWERFUL project, seventh framework program FP7/2007-2013, theme 7, sustainable surface transport (grant agreement number SCP8-GA-2009-234032).Broatch Jacobi, JA.; Guardiola, C.; Bares-Moreno, P.; Denia Guzmán, FD. (2016). Determination of the resonance response in an engine cylinder with a bowl-in-piston geometry by the finite element method for inferring the trapped mass. International Journal of Engine Research. 17(5):534-542. https://doi.org/10.1177/1468087415589701S534542175Powell, J. D. (1993). Engine Control Using Cylinder Pressure: Past, Present, and Future. Journal of Dynamic Systems, Measurement, and Control, 115(2B), 343-350. doi:10.1115/1.2899074Desantes, J. M., Galindo, J., Guardiola, C., & Dolz, V. (2010). Air mass flow estimation in turbocharged diesel engines from in-cylinder pressure measurement. Experimental Thermal and Fluid Science, 34(1), 37-47. doi:10.1016/j.expthermflusci.2009.08.009Finol, C. A., & Robinson, K. (2006). Thermal modelling of modern engines: A review of empirical correlations to estimate the in-cylinder heat transfer coefficient. Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 220(12), 1765-1781. doi:10.1243/09544070jauto202Torregrosa, A. J., Broatch, A., Martín, J., & Monelletta, L. (2007). Combustion noise level assessment in direct injection Diesel engines by means of in-cylinder pressure components. Measurement Science and Technology, 18(7), 2131-2142. doi:10.1088/0957-0233/18/7/045Luján, J. M., Bermúdez, V., Guardiola, C., & Abbad, A. (2010). A methodology for combustion detection in diesel engines through in-cylinder pressure derivative signal. Mechanical Systems and Signal Processing, 24(7), 2261-2275. doi:10.1016/j.ymssp.2009.12.012Payri, F., Broatch, A., Tormos, B., & Marant, V. (2005). New methodology for in-cylinder pressure analysis in direct injection diesel engines—application to combustion noise. Measurement Science and Technology, 16(2), 540-547. doi:10.1088/0957-0233/16/2/029Zhen, X., Wang, Y., Xu, S., Zhu, Y., Tao, C., Xu, T., & Song, M. (2012). The engine knock analysis – An overview. Applied Energy, 92, 628-636. doi:10.1016/j.apenergy.2011.11.079Draper C. S. The physical effects of detonation in a closed cylindrical chamber. Technical report, National Advisory Committee for Aeronautics, 1938.Payri, F., Olmeda, P., Guardiola, C., & Martín, J. (2011). Adaptive determination of cut-off frequencies for filtering the in-cylinder pressure in diesel engines combustion analysis. Applied Thermal Engineering, 31(14-15), 2869-2876. doi:10.1016/j.applthermaleng.2011.05.012Hickling, R., Feldmaier, D. A., Chen, F. H. K., & Morel, J. S. (1983). Cavity resonances in engine combustion chambers and some applications. The Journal of the Acoustical Society of America, 73(4), 1170-1178. doi:10.1121/1.389261Bodisco, T., Reeves, R., Situ, R., & Brown, R. (2012). Bayesian models for the determination of resonant frequencies in a DI diesel engine. Mechanical Systems and Signal Processing, 26, 305-314. doi:10.1016/j.ymssp.2011.06.014Guardiola, C., Pla, B., Blanco-Rodriguez, D., & Bares, P. (2014). Cycle by Cycle Trapped Mass Estimation for Diagnosis and Control. SAE International Journal of Engines, 7(3), 1523-1531. doi:10.4271/2014-01-1702Torregrosa, A. J., Broatch, A., Margot, X., Marant, V., & Beauge, Y. (2004). Combustion chamber resonances in direct injection automotive diesel engines: A numerical approach. International Journal of Engine Research, 5(1), 83-91. doi:10.1243/146808704772914264Broatch, A., Margot, X., Gil, A., & Christian Donayre, (José). (2007). Computational study of the sensitivity to ignition characteristics of the resonance in DI diesel engine combustion chambers. Engineering Computations, 24(1), 77-96. doi:10.1108/02644400710718583Payri, F., Molina, S., Martín, J., & Armas, O. (2006). Influence of measurement errors and estimated parameters on combustion diagnosis. Applied Thermal Engineering, 26(2-3), 226-236. doi:10.1016/j.applthermaleng.2005.05.006Mechel, F. P. (Ed.). (2008). Formulas of Acoustics. doi:10.1007/978-3-540-76833-3Samimy, B., & Rizzoni, G. (1996). Mechanical signature analysis using time-frequency signal processing: application to internal combustion engine knock detection. Proceedings of the IEEE, 84(9), 1330-1343. doi:10.1109/5.535251Lapuerta, M., Armas, O., & Hernández, J. J. (1999). Diagnosis of DI Diesel combustion from in-cylinder pressure signal by estimation of mean thermodynamic properties of the gas. Applied Thermal Engineering, 19(5), 513-529. doi:10.1016/s1359-4311(98)00075-1FUENMAYOR, F. J., DENIA, F. D., ALBELDA, J., & GINER, E. (2002). H -ADAPTIVE REFINEMENT STRATEGY FOR ACOUSTIC PROBLEMS WITH A SET OF NATURAL FREQUENCIES. Journal of Sound and Vibration, 255(3), 457-479. doi:10.1006/jsvi.2001.4165Benajes, J., Molina, S., García, A., Belarte, E., & Vanvolsem, M. (2014). An investigation on RCCI combustion in a heavy duty diesel engine using in-cylinder blending of diesel and gasoline fuels. Applied Thermal Engineering, 63(1), 66-76. doi:10.1016/j.applthermaleng.2013.10.052Chen, A., & Dai, X. (2010). Internal combustion engine vibration analysis with short-term Fourier-transform. 2010 3rd International Congress on Image and Signal Processing. doi:10.1109/cisp.2010.5646222Stanković, Lj., & Böhme, J. F. (1999). Time–frequency analysis of multiple resonances in combustion engine signals. Signal Processing, 79(1), 15-28. doi:10.1016/s0165-1684(99)00077-8Costa, A. H., & Boudreaux-Bartels, G. F. (1999). An overview of aliasing errors in discrete-time formulations of time-frequency representations. IEEE Transactions on Signal Processing, 47(5), 1463-1474. doi:10.1109/78.75724

Internal combustion engine heat release calculation using single-zone and CFD 3D numerical models

Abstract The present study deals with a comparative evaluation of a single-zone (SZ) thermodynamic model and a 3D computational fluid dynamics (CFD) model for heat release calculation in internal combustion engines. The first law, SZ, model is based on the first law of thermodynamics. This model is characterized by a very simplified modeling of the combustion phenomenon allowing for a great simplicity in the mathematical formulation and very low computational time. The CFD 3D models, instead, are able to solve the chemistry of the combustion process, the interaction between turbulence and flame propagation, the heat exchange with walls and the dissociation and re-association of chemical species. They provide a high spatial resolution of the combustion chamber as well. Nevertheless, the computation requirements of CFD models are enormously larger than the SZ techniques. However, the SZ model needs accurate experimental in-cylinder pressure data for initializing the heat release calculation. Therefore, the main objective of an SZ model is to evaluate the heat release, which is very difficult to measure in experiments, starting from the knowledge of the in-cylinder pressure data. Nevertheless, the great simplicity of the SZ numerical formulation has a margin of uncertainty which cannot be known a priori. The objective of this paper was, therefore, to evaluate the level of accuracy and reliability of the SZ model comparing the results with those obtained with a CFD 3D model. The CFD model was developed and validated using cooperative fuel research (CFR) engine experimental in-cylinder pressure data. The CFR engine was fueled with 2,2,4-trimethylpentane, at a rotational speed of 600 r/min, an equivalence ratio equal to 1 and a volumetric compression ratio of 5.8. The analysis demonstrates that, considering the simplicity and speed of the SZ model, the heat release calculation is sufficiently accurate and thus can be used for a first investigation of the combustion process

Large-Eddy Simulation and experimental study of cycle-to-cycle variations of stable and unstable operating points in a spark ignition engine

This article presents a comparison between experiments and Large-Eddy Simulation (LES) of a spark ignition engine on two operating points: a stable one characterized by low cycle-to-cycle variations (CCV) and an unstable one with high CCV. In order to match the experimental cycle sample, 75 full cycles (with combustion) are computed by LES. LES results are compared with experiments by means of pressure signals in the intake and exhaust ducts, in-cylinder pressure, chemiluminescence and OH Planar Laser Induced Fluorescence (PLIF). Results show that LES is able to: (1) reproduce the flame behavior in both cases (low and high CCV) in terms of position, shape and timing; (2) distinguish a stable point from an unstable one; (3) predict quantitatively the CCV levels of the two fired operating points. For the unstable case, part of the observed CCV is due to incomplete combustion. The results are then used to analyze the incomplete combustion phenomenon which occurs for some cycles of the unstable point and propose modification of the spark location to control CCV

On the Capabilities and Limitations of Predictive, Multi-Zone Combustion Models for Hydrogen-Diesel Dual Fuel Operation

Compared with traditional hydrocarbon fuels, hydrogen provides a high-energy content and carbon-free source of energy rendering it an attractive option for internal combustion engines. Co-combusting hydrogen with other fuels offers significant advantages with respect to thermal efficiency and carbon emissions. This study seeks to investigate the potential and limitations of multi-zone combustion models implemented in the GT-Power software package to predict dual fuel operation of a hydrogen-diesel common rail compression ignition engine. Numerical results for in-cylinder pressure and heat release rate were compared with experimental data. A single cylinder dual-fuel model was used with hydrogen being injected upstream of the intake manifold. During the simulations low (20 kW), medium (40 kW) and high (60 kW) load conditions were tested with and without exhaust gas recirculation (EGR) and at a constant engine speed of 1500 rpm. Both single and double diesel injection strategies were examined with hydrogen energy share ratio being varied from 0 to 57% and 0–42 respectively. This corresponds to a range in hydrogen air-equivalence ratios of approximately 0–0.29. The results show that for the single-injection strategy, the model captures in-cylinder pressure and heat release rate with good accuracy across the entire load and hydrogen share ratio range. However, it appears that for high hydrogen content in the charge mixture and equivalence ratios beyond the lean flammability limit, the model struggles to accurately predict hydrogen entrainment leading to underestimated peak cylinder pressures and heat release rates. For double-injection cases the model shows good agreement for hydrogen share ratios up to 26%. However, for higher energy share ratios the issue of erroneous hydrogen entrainment into the spray becomes more accentuated leading to significant under-prediction of heat release rate and in-cylinder pressure.</p

Hydrogen SI and HCCI Combustion in a Direct-Injection Optical Engine

Hydrogen has been largely proposed as a possible alternative fuel for internal combustion engines. Its wide flammability range allows higher engine efficiency with leaner operation than conventional fuels, for both reduced toxic emissions and no CO2 gases. Independently, Homogenous Charge Compression Ignition (HCCI) also allows higher thermal efficiency and lower fuel consumption with reduced NOX emissions when compared to Spark-Ignition (SI) engine operation. For HCCI combustion, a mixture of air and fuel is supplied to the cylinder and autoignition occurs from compression; engine is operated throttle-less and load is controlled by the quality of the mixture, avoiding the large fluid-dynamic losses in the intake manifold of SI engines. HCCI can be induced and controlled by varying the mixture temperature, either by Exhaust Gas Recirculation (EGR) or intake air pre-heating. A combination of HCCI combustion with hydrogen fuelling has great potential for virtually zero CO2 and NOX emissions. Nevertheless, combustion on such a fast burning fuel with wide flammability limits and high octane number implies many disadvantages, such as control of backfiring and speed of autoignition and there is almost no literature on the subject, particularly in optical engines. Experiments were conducted in a single-cylinder research engine equipped with both Port Fuel Injection (PFI) and Direct Injection (DI) systems running at 1000 RPM. Optical access to in-cylinder phenomena was enabled through an extended piston and optical crown. Combustion images were acquired by a high-speed camera at 1°or 2°crank angle resolution for a series of engine cycles. Spark-ignition tests were initially carried out to benchmark the operation of the engine with hydrogen against gasoline. DI of hydrogen after intake valve closure was found to be preferable in order to overcome problems related to backfiring and air displacement from hydrogens low density. HCCI combustion of hydrogen was initially enabled by means of a pilot port injection of n-heptane preceding the main direct injection of hydrogen, along with intake air preheating. Sole hydrogen fuelling HCCI was finally achieved and made sustainable, even at the low compression ratio of the optical engine by means of closed-valve DI, in synergy with air-pre-heating and negative valve overlap to promote internal EGR. Various operating conditions were analysed, such as fuelling in the range of air excess ratio 1.2-3.0 and intake air temperatures of 200-400°C. Finally, both single and double injections per cycle were compared to identify their effects on combustion development. Copyright © 2009 SAE International

Numerical simulation of the flow and fuel-air mixing in an axisymmetric piston-cylinder arrangement

The implicit factored method of Beam and Warming was employed to describe the flow and the fuel-air mixing in an axisymmetric piston-cylinder configuration during the intake and compression strokes. The governing equations were established on the basis of laminar flow. The increased mixing due to turbulence was simulated by appropriately chosen effective transport properties. Calculations were performed for single-component gases and for two-component gases and for two-component gas mixtures. The flow field was calculated as functions of time and position for different geometries, piston speeds, intake-charge-to-residual-gas-pressure ratios, and species mass fractions of the intake charge. Results are presented in graphical form which show the formation, growth, and break-up of those vortices which form during the intake stroke and the mixing of fuel and air throughout the intake and compression strokes. It is shown that at bore-to-stroke ratio of less than unity, the vortices may break-up during the intake stroke. It is also shown that vortices which do not break-up during the intake stroke coalesce during the compression stroke. The results generated were compared to existing numerical solutions and to available experimental data