| 1. |
- Agrell, Fredrik, et al.
(författare)
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Control of HCCI During Engine Transients by aid of Variable Valve Timings Through the use of Model Based Non-Linear Compensation
- 2005
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Ingår i: SAE transactions. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0096-736X. ; 114:3, s. 296-310
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Tidskriftsartikel (refereegranskat)abstract
- One of the main challenges with the Homogeneous Charge Compression Ignition, HCCI, combustion system is to control the Start Of Combustion, SOC, for varying load and external conditions. A method to achieve this on a cycle-by-cycle basis is to vary the valve timing based on a feedback signal from the SOC of previous cycles. The control can be achieved with two basic valve-timing strategies named the Overlap- and the IVC-method. The Overlap-method works by trapping of residuals while the IVC-method affects the effective compression ratio. In an earlier paper it has been shown that if the two methods are incorporated into one controller, SOC can be controlled in a relatively large operating window although the transient performance was not sufficient. The reason is that the simple PI-controller cannot be made fast enough to cope with the transients without magnifying the cycle-to-cycle variations of the combustion into instability. In this work a model based control system that features a non-linear compensation, based on the inverse of the non-linear function from valve timings to ignition delay, is suggested and evaluated. The results show good transient performance. Control performance from engine tests is reported. A combined engine and control simulation system is used for the development of the control strategies. The simulations are accomplished with a commercial cycle simulation code linked with a commercial control simulation code. The simulations are iteratively verified against engine test data. Engine tests are conducted on a single cylinder engine equipped with a hydraulic valve system.
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| 2. |
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| 3. |
- Andersson, Öivind, et al.
(författare)
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Crank Angle Resolved HC Detection Using LIF in the Exhausts of Small Two-Stroke Engines Running at High Engine Speed
- 1996
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Ingår i: SAE Transactions, Journal of Engines. - 0096-736X. ; 105:961927
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Tidskriftsartikel (refereegranskat)abstract
- In order to separate the HC-emissions from two-stroke engines into short-circuit losses and emissions due to incomplete combustion, Laser Induced Fluorescence (LIF) measurements were performed on the exhaust gases just outside the exhaust ports of two engines of different designs. The difference between the two engines was the design of the transfer channels. One engine had "finger" transfer channels and one had "cup handle" transfer channels. Apart from that they were similar. The engine with "finger" transfer channels was earlier known to give more short-circuiting losses than the other engine, and that behavior was confirmed by these measurements. Generally, the results show that the emission of hydrocarbons has two peaks, one just after exhaust port opening and one late in the scavenging phase. The spectral information shows differences between the two peaks and it can be concluded that the latter peak is due to short-circuiting and the earlier due to incomplete combustion. The flow outside the exhaust port was measured with Laser Doppler Velocimetry (LDV). These measurements confirm the occurrence of two emission peaks.
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| 4. |
- Blomé, Mikael, et al.
(författare)
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Simulation of human-vehicle interaction in vehicle design at Saab Automobile : present and future
- 2003
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Ingår i: Digital Human Modeling for Design and Engineering (DHM) SAE-conference. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. ; 112:7, s. 644-650
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Konferensbidrag (refereegranskat)abstract
- Developers, reviewers and users of human simulation tools claim that the use of these tools may reduce development time and development cost. However, before these benefits will be fully visible, there are some barriers to overcome. The aims of this case study are to identify which departments at Saab Automobile use some sort of human simulation tool today, and to identify the information flow and procedure when the tool is used. Four departments crash safety, packaging, production planning and vehicle ergonomics were identified as direct users of human simulation tools. The tools used were finite element with crash dummy representation, SAE human model, Safework and Ramsis. Communications between human simulation tool users are limited. Communications are done through the project management. The crash safety and packaging departments have formal descriptions of the human simulation process, whereas production planning and vehicle ergonomics have no formal process descriptions. To gain from the benefits of human simulation tools, Saab Automobile needs to adapt them to the organization and the organization to the tools. Integration of a working methodology is essential for effective and efficient use in the other human simulation departments where this is currently lacking.
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| 5. |
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| 6. |
- Christensen, Magnus, et al.
(författare)
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Influence of Mixture Quality on Homogeneous Charge Compression Ignition
- 1998
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Ingår i: SAE Transactions, Journal of Fuels and Lubricants. - 0096-736X. ; 107
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Tidskriftsartikel (refereegranskat)abstract
- The major advantages with Homogeneous Charge Compression Ignition, HCCI, is high efficiency in combination with low NOx emissions. The major drawback with HCCI is the problem to control the ignition timing over a wide load and speed range. Other drawbacks are the limitation in attainable IMEP and relatively high emissions of unburned hydrocarbons. But the use of Exhaust Gas Recycling (EGR) instead of only air, slows down the rate of combustion and makes it possible to use lower air/fuel ratio, which increases the attainable upper load limit. The influence of mixture quality was therefore experimentally investigated. The effects of different EGR rates, air/fuel rations and inlet mixture temperatures were studied. The compression ratio was set to 18:1. The fuels used were iso-octane, ethanol and commercially available natural gas. The engine was operated in naturally aspirated mode for all tests. Stable operation could be achieved with ethanol at about 5 bar of IMEP with a gross indicated efficiency close to 50%. Stable operation of the engine was achieved with over 60% EGR.
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| 7. |
- Christensen, Magnus, et al.
(författare)
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Supercharged Homogeneous Charge Compression Ignition
- 1998
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Ingår i: SAE Transactions, Journal of Engines. - 0096-736X. ; 107:SAE Technical Paper 980787
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Tidskriftsartikel (refereegranskat)abstract
- The Homogeneous Charge Compression Ignition (HCCI) is the third alternative for combustion in the reciprocating engine. Here a homogeneous charge is used as in a spark-ignited engine, but the charge is compressed to autoignition as in a diesel. The main difference compared with the Spark Ignition (SI) engine is the lack of flame propagation and hence the independence from turbulence. Compared with the diesel engine, HCCI has a homogeneous charge and hence no problems associated with soot and NOdx formation. Earlier research on HCCI showed high efficiency and very low amounts of NOdx, but HC and CO were higher than in SI mode. It was not possible to achieve high IMEP values with HCCI, the limit being 5 bar. Supercharging is one way to dramatically increase IMEP. The influence of supercharging on HCCI was therefore experimentally investigated. Three different fuels were used during the experiments: iso-octane, ethanol and natural gas. Two different compression ratios were used, 17:1 and 19:1. The inlet pressure conditions were set to give 0, 1, or 2 bar of boost pressure. The highest attainable IMEP was 14 bar using natural gas as fuel at the lower compression ratio. The limit in achieving even higher IMEP was set by the high rate of combustion and a high peak pressure. Numerical calculations of the HCCI process have been performed for natural gas as fuel. The calculated ignition timings agreed well with the experimental findings. The numerical solution is, however, very sensitive to the composition of the natural gas.
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| 8. |
- Collin, Robert, et al.
(författare)
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Simultaneous OH- and Formaldehyde-LIF Measurements in an HCCI Engine
- 2003
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Ingår i: SAE Transactions, Journal of Fuels and Lubricants. - 0096-736X. ; 112:4, s. 2479-2486
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Tidskriftsartikel (refereegranskat)abstract
- Simultaneous OH- and formaldehyde LIF measurements have been performed in an HCCI engine using two laser sources working on 283 and 355 nm, respectively. Two ICCD camera systems, equipped with long-pass filters, were used to collect the LIF signals. The simultaneous images of OH and formaldehyde were compared with heat-release calculated from the pressure-trace matching the cycle for the LIF measurements. The measurements were performed on a 0.5-l, single-cylinder optical engine equipped with port-fuel injection system. A blend of iso-octane and n-heptane was used as fuel and the compression ratio was set to 12:1. The width of the laser sheet was 40 mm and hence covered approximately half of the cylinder bore. At some 20 CAD BTDC low temperature reactions are present and formaldehyde is formed. The formaldehyde signal is then rather constant until the main heat-release starts just before TDC, where the signal decreases rapidly to low values. From some 15 CAD to 5 CAD BTDC the formaldehyde is uniformly distributed in the imaged area. As formaldehyde decreases, OH increases and follows the main rate of heat release curve, though with a slight lag in phase. Thereafter OH is formed in the areas from which the formaldehyde has disappeared and the OH signal is present to some 20 CAD ATDC.
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| 9. |
- Gogan, Adina, et al.
(författare)
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Stochastic model for the investigation of the influence of turbulent mixing on engine knock
- 2004
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Ingår i: SAE Transactions Journal of Engines. - 0096-736X. ; 113:3, s. 1594-1603
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Tidskriftsartikel (refereegranskat)abstract
- A stochastic model based on a probability density function (PDF) was developed for the investigation of different conditions that determine knock in spark ignition (SI) engine, with focus on the turbulent mixing. The model used is based on a two-zone approach, where the burned and unburned gases are described as stochastic reactors. By using a stochastic ensemble to represent the PDF of the scalar variables associated with the burned and the unburned gases it is possible to investigate phenomena that are neglected by the regular existing models (as gas non-uniformity, turbulence mixing, or the variable gas-wall interaction). Two mixing models are implemented for describing the turbulent mixing: the deterministic interaction by exchange with the mean (IEM) model and the stochastic coalescence/ dispersal (C/D) model. Also, a stochastic jump process is employed for modeling the irregularities in the heat transfer. Parameter studies are carried out in order to assess the influence of the turbulence intensity and of the fluctuations in the gas - wall interactions.
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| 10. |
- Haraldsson, Göran, et al.
(författare)
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HCCI Closed-Loop Combustion Control Using Fast Thermal Management
- 2004
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Ingår i: SAE Transactions, Journal of Engines. - 0096-736X. ; 113:3, s. 599-610
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Tidskriftsartikel (refereegranskat)abstract
- This study applies Closed-Loop Combustion Control (CLCC) using Fast Thermal Management (FTM) on a multi-cylinder Variable Compression Ratio (VCR) engine together with load control, to achieve a favorable combustion phasing and load at all times. Step changes of set points for combustion phasing, Compression Ratio (CR), and load together with ramps of engine speed with either constant load, i.e., load control enabled, or constant fuel amount are investigated. Performances of the controllers are investigated by running the engine and comparing the result with CLCC using VCR, which was used in an earlier test. Commercial RON/MON 92/82 gasoline, which corresponds to US regular, is used in the transient tests. Limitations to the speed ramps are further examined and it is found that choice of fuel and its low temperature reaction properties has large impact on how the CLCC perform. The CLCC using FTM handles step changes in combustion phasing fairly well and has a time constant of 8 engine cycles, which is 57% faster than the CLCC using VCR even though it suffers from the large air volume between throttle and engine inlet.
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