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Role of Piston Bowl Shape to Enhance Late-Cycle Soot Oxidation in Low-Swirl Diesel Combustion

SAE International Journal of Engines

AB Volvo, Sweden-Magnus Christensen
Chalmers University of Technology, Sweden-Jan Eismark, Mats Andersson, Anders Karlsson, Ingemar Denbratt
  • Journal Article
  • 03-12-03-0017
Published 2019-04-25 by SAE International in United States
Late-cycle soot oxidation in heavy-duty (HD) diesel engine low-swirl combustion was investigated using single-cylinder engine and spray chamber experiments together with engine combustion simulations. The in-cylinder flow during interactions between adjacent flames (flame-flame events) was shown to have a large impact on late-cycle combustion. To modify the flame-flame, a new piston bowl shape with a protrusion (wave) was designed to guide the near-wall flow. This design significantly reduced soot emissions and increased engine thermodynamic efficiency. The wave’s main effect was to enhance late-cycle mixing, as demonstrated by apparent rate of heat release after the termination of fuel injection. Combustion simulations showed that the increased mixing is driven by enhanced flow re-circulation, which produces a radial mixing zone (RMZ). The leading edge of the RMZ extends toward the center of the piston bowl, where unused ambient gas is available, promoting oxidation. The wave also enhances mixing in the trailing edge of the RMZ when it detaches from the wall, accelerating the burn-out of the RMZ. This flame interaction effect was isolated and studied further using a…
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Role of Late Soot Oxidation for Low Emission Combustion in a Diffusion-controlled, High-EGR, Heavy Duty Diesel Engine

Chalmers University of Technology-Ingemar Denbratt
Volvo Technology Corporation-Jan Eismark, Michael Balthasar, Anders Karlsson, Timothy Benham, Magnus Christensen
Published 2009-11-02 by SAE International in United States
Soot formation and oxidation are complex and competing processes during diesel combustion. The balance between the two processes and their history determines engine-out soot values. Besides the efforts to lower soot formation with measures to influence the flame lift-off distance for example or to use HCCI-combustion, enhancement of late soot oxidation is of equal importance for low-λ diffusion-controlled low emissions combustion with EGR. The purpose of this study is to investigate soot oxidation in a heavy duty diesel engine by statistical analysis of engine data and in-cylinder endoscopic high speed photography together with CFD simulations with a main focus on large scale in-cylinder gas motion. Results from CFD simulations using a detailed soot model were used to reveal details about the soot oxidation.A particular objective of the present study was to investigate the importance of enhancing soot oxidation after End of Injection (EOI) when temperature and NOx formation rapidly decreases. Geometrical measures to control flame propagation and different flame interactions were investigated. Such measures contribute to conserve available kinetic energy until late in the combustion…
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Analysis of the Effect of Geometry Generated Turbulence on HCCI Combustion by Multi-Zone Modeling

Lawrence Livermore National Laboratory-Salvador M. Aceves, Daniel L. Flowers, Joel Martinez-Frias, Francisco Espinosa-Loza
Lund Institute of Technology-Bengt Johansson
Published 2005-05-11 by SAE International in United States
This paper illustrates the applicability of a sequential fluid mechanics, multi-zone chemical kinetics model to analyze HCCI experimental data for two combustion chamber geometries with different levels of turbulence: a low turbulence disc geometry (flat top piston), and a high turbulence square geometry (piston with a square bowl). The model uses a fluid mechanics code to determine temperature histories in the engine as a function of crank angle. These temperature histories are then fed into a chemical kinetic solver, which determines combustion characteristics for a relatively small number of zones (40). The model makes the assumption that there is no direct linking between turbulence and combustion.The multi-zone model yields good results for both the disc and the square geometries. The model makes good predictions of pressure traces and heat release rates. The experimental results indicate that the high turbulence square geometry has longer burn duration than the low turbulence disc geometry. This difference can be explained by the sequential multi-zone model, which indicates that the cylinder with the square bowl has a thicker boundary layer…
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Pressure Oscillations During Rapid HCCI Combustion

Division of Combustion Engines, Lund Institute of Technology-Andreas Vressner, Andreas Lundin, Magnus Christensen, Per Tunestål, Bengt Johansson
Published 2003-10-27 by SAE International in United States
This work has focused on studying the in-cylinder pressure fluctuations caused by rapid HCCI combustion and determine what they consist of. Inhomogeneous autoignition sets up pressure waves traversing the combustion chamber. These pressure waves induce high gas velocities which causes increased heat transfer to the walls or in worst case engine damage. In order to study the pressure fluctuations a number of pressure transducers were mounted in the combustion chamber. The multi transducer arrangement was such that six transducers were placed circumferentially, one placed near the centre and one at a slight offset in the combustion chamber. The fitting of six transducers circumferentially was enabled by a spacer design and the two top mounted transducers were fitted in a modified cylinder head. During testing a disc shaped combustion chamber was used. The results of the tests conducted were that the in-cylinder pressure experienced during rapid HCCI-combustion is inhomogeneous. Pressure oscillations were experienced which showed good accordance to vibration mode shapes and frequencies suggested by acoustic vibration theory. The pressure waves manifested largest intensities for the…
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Ion Current Sensing for HCCI Combustion Feedback

Dept. of Automatic Control, Lund Institute of Technology-Johan Bengtsson, Rolf Johansson
Div. of Combustion Engines, Lund Institute of Technology-Andreas Vressner, Per Tunestål, Bengt Johansson
Published 2003-10-27 by SAE International in United States
Measurement of ion current signal from HCCI combustion was performed. The aim of the work was to investigate if a measurable ion current signal exists and if it is possible to obtain useful information about the combustion process. Furthermore, influence of mixture quality in terms of air/fuel ratio and EGR on the ion current signal was studied. A conventional spark plug was used as ionization sensor. A DC voltage (85 Volt) was applied across the electrode gap. By measuring the current through the gap the state of the gas can be probed. A comparison between measured pressure and ion current signal was performed, and dynamic models were estimated by using system identification methods.The study shows that an ion current signal can be obtained from HCCI combustion and that the signal level is very sensitive to the fuel/air equivalence ratio. The most important result from this study is that the ion current signal proved to be an excellent indicator of the actual combustion timing which is crucial piece of information for HCCI control.
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Modeling the Effects of Geometry Generated Turbulence on HCCI Engine Combustion

Division of Combustion Engines, Lund Institute of Technology-Magnus Christensen, Bengt Johansson
Engine Research Center, University of Wisconsin-Madison-Song-Charng Kong, Rolf D. Reitz
Published 2003-03-03 by SAE International in United States
The present study uses a numerical model to investigate the effects of flow turbulence on premixed iso-octane HCCI engine combustion. Different levels of in-cylinder turbulence are generated by using different piston geometries, namely a disc-shape versus a square-shape bowl. The numerical model is based on the KIVA code which is modified to use CHEMKIN as the chemistry solver. A detailed reaction mechanism is used to simulate the fuel chemistry. It is found that turbulence has significant effects on HCCI combustion. In the current engine setup, the main effect of turbulence is to affect the wall heat transfer, and hence to change the mixture temperature which, in turn, influences the ignition timing and combustion duration. The model also predicts that the combustion duration in the square bowl case is longer than that in the disc piston case which agrees with the measurements. The results imply that it is preferable to incorporate detailed chemistry in CFD codes for HCCI combustion simulations so that the effect of turbulence on wall heat transfer can be better simulated. On the…
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Piston-Liner Crevice Geometry Effect on HCCI Combustion by Multi-Zone Analysis

Lawrence Livermore National Laboratory-Salvador M. Aceves, Daniel L. Flowers, Francisco Espinosa-Loza, Joel Martinez-Frias
Lund Institute of Technology, Lund, Sweden-Magnus Christensen, Bengt Johansson
Published 2002-10-21 by SAE International in United States
A multi-zone model has been developed that accurately predicts HCCI combustion and emissions. The multi-zone methodology is based on the observation that turbulence does not play a direct role on HCCI combustion. Instead, chemical kinetics dominates the process, with hotter zones reacting first, and then colder zones reacting in rapid succession. Here, the multi-zone model has been applied to analyze the effect of piston crevice geometry on HCCI combustion and emissions. Three different pistons of varying crevice size were analyzed. Crevice sizes were 0.26, 1.3 and 2.1 mm, while a constant compression ratio was maintained (17:1).The results show that the multi-zone model can predict pressure traces and heat release rates with good accuracy. Combustion efficiency is also predicted with good accuracy for all cases, with a maximum difference of 5% between experimental and numerical results. Carbon monoxide emissions are underpredicted, but the results are better than those obtained in previous publications. The improvement is attributed to the use of a 40-zone model, while previous publications used a 10-zone model. Hydrocarbon emissions are well predicted. For…
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Hydrogen Addition For Improved Lean Burn Capability of Slow and Fast Burning Natural Gas Combustion Chambers

Lund Institute of Technology-Per Tunestål, Magnus Christensen, Patrik Einewall, Tobias Andersson, Bengt Johansson
Swedish Gas Center-Owe Jönsson
Published 2002-10-21 by SAE International in United States
One way to extend the lean burn limit of a natural gas engine is by addition of hydrogen to the primary fuel. This paper presents measurements made on a one cylinder 1.6 liter natural gas engine. Two combustion chambers, one slow and one fast burning, were tested with various amounts of hydrogen (0, 5, 10 and 15 %-vol) added to natural gas. Three operating points were investigated for each combustion chamber and each hydrogen content level; idle, part load (5 bar IMEP) and 13 bar IMEP (simulated turbocharging). Air/fuel ratio was varied between stoichiometric and the lean limit. For each operating point, a range of ignition timings were tested to find maximum brake torque (MBT) and/or knock. Heat-release rate calculations were made in order to assess the influence of hydrogen addition on burn rate. Addition of hydrogen showed an increase in burn rate for both combustion chambers, resulting in more stable combustion close to the lean limit. This effect was most pronounced for lean operation with the slow combustion chamber.
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The Effect of In-Cylinder Flow and Turbulence on HCCI Operation

Div. of Combustion Engines, Lund Institute of Technology-Magnus Christensen, Bengt Johansson
Published 2002-10-21 by SAE International in United States
The effect of in-cylinder flow and turbulence on HCCI operation has been experimentally studied by changing the combustion chamber geometry and the swirl ratio. Four different levels of turbulence were achieved, by altering the swirl ratio both for a high turbulent square bowl-in-piston combustion chamber and for a low turbulent disc combustion chamber. The swirl ratio was altered by using different inlet port designs.The results showed that the combustion chamber geometry plays a large role in HCCI combustion. With the same operating conditions, the combustion duration for the square bowl-in-piston combustion chamber was much longer compared to the disc combustion chamber. On the other hand, a moderate change in swirl ratio proved to have only modest effect on the combustion process. With early combustion timing, the gross indicated efficiency was higher when the square bowl-in-piston combustion chamber. Although, with late combustion timing, the disc combustion chamber gave the highest efficiency. When the disc combustion was used, the indicated efficiency was rather unaffected by a change in swirl ratio. However, with the square bowl-in-piston combustion chamber…
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The Effect of Combustion Chamber Geometry on HCCI Operation

Div. of Combustion Engines, Lund Institute of Technology-Magnus Christensen, Bengt Johansson
Scania CV-Anders Hultqvist
Published 2002-03-04 by SAE International in United States
The effect of the combustion chamber geometry and the turbulence on Homogeneous Charge Compression Ignition (HCCI) operation has been experimentally investigated. A high turbulent square bowl in piston combustion chamber has been compared with a low turbulent disc combustion chamber.The results showed that the combustion chamber geometry plays large role for HCCI combustion. At the same operating conditions, the peak combustion rate for the square bowl combustion chamber was much lower compared to the disc combustion chamber. The combustion duration was in some cases almost a factor two longer for the square bowl combustion chamber. The lower combustion rate with the square bowl was due larger heat losses, lower combustion efficiency and higher turbulence.
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