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CFD Simulations of Pre-Chamber Jets' Mixing Characteristics in a Heavy Duty Natural Gas Engine

Lund University-Ashish Shah, Per Tunestål, Bengt Johansson
Published 2015-09-01 by SAE International in United States
The effect of pre-chamber volume and nozzle diameter on performance of pre-chamber ignition device in a heavy duty natural gas engine has previously been studied by the authors. From the analysis of recorded pre- and main chamber pressure traces, it was observed that a pre-chamber with a larger volume reduced flame development angle and combustion duration while at a given pre-chamber volume, smaller nozzle diameters provided better ignition in the main chamber. The structure of pre-chamber jet and its mixing characteristics with the main chamber charge are believed to play a vital role, and hence CFD simulations are performed to study the fluid dynamic aspects of interaction between the pre-chamber jet and main chamber charge during the period of flame development angle, i.e. before main chamber ignition. It has been observed that jets from a larger pre-chamber penetrates through the main chamber faster due to higher momentum and generates turbulence in the main chamber earlier. At a given pre-chamber volume, smaller nozzle diameter causes higher velocity jet also causing high turbulence built up and better…
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How Hythane with 25% Hydrogen can Affect the Combustion in a 6-Cylinder Natural-gas Engine

SAE International Journal of Fuels and Lubricants

Lund Univ.-Mehrzad Kaiadi
Lund University-Per Tunestål, Bengt Johansson
  • Journal Article
  • 2010-01-1466
Published 2010-05-05 by SAE International in United States
Using alternative fuels like Natural Gas (NG) has shown good potentials on heavy duty engines. Heavy duty NG engines can be operated either lean or stoichiometric diluted with EGR. Extending Dilution limit has been identified as a beneficial strategy for increasing efficiency and decreasing emissions. However dilution limit is limited in these types of engines because of the lower burnings rate of NG. One way to extend the dilution limit of a NG engine is to run the engine on Hythane (natural gas + some percentage hydrogen). Previously effects of Hythane with 10% hydrogen by volume in a stoichiometric heavy duty NG engine were studied and no significant changes in terms of efficiency and emissions were observed.This paper presents results from measurements made on a heavy duty 6-cylinder NG engine. The engine is operated with NG and Hythane with 25% hydrogen by volume and the effects of these fuels on the engine performance are studied. Different experiments were designed and performed to investigate the parameters like knocking margin, dilution limit, lean limit, different efficiencies, emissions…
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The Effect of Intake Temperature in a Turbocharged Multi Cylinder Engine operating in HCCI mode

SAE International Journal of Engines

Faculty of engineering, Lund University-Thomas Johansson, Bengt Johansson, Per Tunestål
GM Powertrain AB, Sweden-Hans Aulin
  • Journal Article
  • 2009-24-0060
Published 2009-09-13 by Consiglio Nazionale delle Ricerche in Italy
The operating range in HCCI mode is limited by the excessive pressure rise rate and therefore high combustion induced noise. The HCCI range can be extended with turbocharging which enables increased dilution of the charge and thus a reduction of combustion noise. When the engine is turbocharged the intake charge will have a high temperature at increased boost pressure and can then be regulated in a cooling circuit. Limitations and benefits are examed at 2250 rpm and 400 kPa indicated mean effective pressure. It is shown that combustion stability, combustion noise and engine efficiency have to be balanced since they have optimums at different intake temperatures and combustion timings. The span for combustion timings with high combustion stability is narrower at some intake temperatures and the usage of external EGR can improve the combustion stability. It is found that the standard deviation of combustion timing is a useful tool for evaluating cycle to cycle variations. One of the benefits with HCCI is the low pumping losses, but when load and boost pressure is increased there…
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Using Hythane as a Fuel in a 6-Cylinder Stoichiometric Natural-gas Engine

SAE International Journal of Fuels and Lubricants

Division of Combustion Engines, Lund University-Mehrzad Kaiadi, Per Tunestål, Bengt Johansson
  • Journal Article
  • 2009-01-1950
Published 2009-06-15 by SAE International in United States
Combination of right EGR rates with turbocharging has been identified as a promising way to increase the maximum load and efficiency of heavy duty spark-ignited natural gas engines. With stoichiometric conditions a three way catalyst can be used which means that regulated emissions can be kept at very low levels. However dilution limit is limited in these types of engines because of the lower burnings rate of natural gas with higher EGR rates. One way to extend the dilution limit of a natural gas engine is to run the engine with Hythane (natural gas+ some percentage hydrogen). Previously benefits of hydrogen addition to a Lean Burn natural-gas fueled engine was investigated [1] however a complete study for stoichiometric operation was not performed.This paper presents measurements made on a heavy duty 6-cylinder natural gas engine. Three different experiments were designed and tested to investigate first of all if the engine encounters too severe knocking problems, second how and why, Hythane affect the running and finally how lean limit and dilution limit will be improved. The experiments…
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HCCI Operating Range in a Turbo-charged Multi Cylinder Engine with VVT and Spray-Guided DI

GM Powertrain AB-Hans Aulin
Lund University-Thomas Johansson, Bengt Johansson, Per Tunestål
Published 2009-04-20 by SAE International in United States
Homogenous charge compression ignition (HCCI) has been identified as a promising way to increase the efficiency of the spark-ignited engine, while maintaining low emissions. The challenge with HCCI combustion is excessive pressure rise rate, quantified here with Ringing Intensity. Turbocharging enables increased dilution of the charge and thus a reduction of the Ringing Intensity. The engine used is an SI four cylinder base with 2.2L displacement and is equipped with a turbocharger. Combustion phasing control is achieved with individual intake/ exhaust cam phasing. Fuel injection with spray guided design is used. Cycle resolved combustion state is monitored and used for controlling the engine either in closed or open loop where balancing of cylinder to cylinder variations has to be done to run the engine at high HCCI load. When load is increased the NOx levels rise, the engine is then run in stoichiometric HCCI mode to be able to use a simple three-way catalyst. The fuel used is 95 RON pump gasoline and injection strategies are evaluated in order to maintain low soot levels and…
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Evaluation of the Operating Range of Partially Premixed Combustion in a Multi Cylinder Heavy Duty Engine with Extensive EGR

Delphi Diesel Systems-Nathan Keeler, Simon Tullis, Nebojsa Milovanovic
Lund University-Magnus Lewander, Bengt Johansson, Per Tunestål
Published 2009-04-20 by SAE International in United States
Partially Premixed Combustion (PPC) is a combustion concept by which it is possible to get low smoke and NOx emissions simultaneously. PPC requires high EGR levels and injection timings sufficiently early or late to extend the ignition delay so that air and fuel mix extensively prior to combustion. This paper investigates the operating region of single injection diesel PPC in a multi cylinder heavy duty engine resembling a standard build production engine. Limits in emissions and fuel consumption are defined and the highest load that fulfills these requirements is determined. Experiments are carried out at different engine speeds and a comparison of open and closed loop combustion control are made as well as evaluation of an extended EGR-cooling system designed to reduce the EGR temperature.In this study the PPC operating range proved to be limited. The highest loads that fulfilled the emission criteria correspond to 30% of maximum load for conventional combustion at low speed and 21% of maximum load for conventional combustion at high speed. The effect of changes in combustion control was small…
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A Physical Two-Zone NOx Model Intended for Embedded Implementation

Lund University-Carl Wilhelmsson, Per Tunestål, Bengt Johansson Anders Widd, Rolf Johansson
Published 2009-04-20 by SAE International in United States
This paper offers a two-zone NOx model suitable for vehicle on-board, on-line implementation. Similar NOx modeling attempts have previously been undertaken. The hereby suggested method does however offer clear and important benefits over the previously methods, utilizing a significantly different method to handle temperature calculations within the (two) different zones avoiding iterative computation. The new method significantly improves calculation speed and, most important of all, reduces implementation complexity while still maintaining reasonable accuracy and the physical interpretation of earlier suggested methods. The equations commonly used to compute NOx emissions is also rewritten in order to suit a two-zone NOx model. An algorithm which can be used to compute NOx emissions is presented and the intended contribution of the paper is a NOx model, implementation feasible for an embedded system, e.g. embedded processor or embedded electronic hardware (FPGA). For that purpose parts of the algorithm can be pre-computed and stored in tables allowing significant acceleration of the computation.
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Simulation of a Pneumatic Hybrid Powertrain with VVT in GT-Power and Comparison with Experimental Data

Division of Combustion Engines, Lund University-Sasa Trajkovic, Per Tunestål, Bengt Johansson
Published 2009-04-20 by SAE International in United States
In the study presented in this paper, experimental data from a pneumatic hybrid has been compared to the results from a simulation of the engine in GT-Power. The engine in question is a single-cylinder Scania D12 diesel engine, which has been converted to work as a pneumatic hybrid. The base engine model, provided by Scania, is made in GT-Power and it is based on the same engine configuration as the one used during real engine testing.During pneumatic hybrid operation the engine can be used as a 2-stroke compressor for generation of compressed air during vehicle deceleration and during vehicle acceleration the engine can be operated as a 2-stroke air-motor driven by the previously stored pressurized air. There is also a possibility to use the stored pressurized air in order to supercharge the engine when there is a need for high torque, like for instance at take off after a standstill or during an overtake maneuver. Previous experimental studies have shown that the pneumatic hybrid is a promising concept and a possible competitor to the electric…
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Closed-Loop Combustion Control Using Ion-current Signals in a 6-Cylinder Port-Injected Natural-gas Engine

Lund University-Mehrzad Kaiadi, Per Tunestål, Bengt Johansson
Published 2008-10-06 by SAE International in United States
High EGR rates combined with turbocharging has been identified as a promising way to increase the maximum load and efficiency of heavy duty spark ignition engines. With stoichiometric conditions a three way catalyst can be used which means that regulated emissions can be kept at very low levels. Obtaining reliable spark ignition is difficult however with high pressure and dilution. There will be a limit to the amount of EGR that can be tolerated for each operating point. Open loop operation based on steady state maps is difficult since there is substantial dynamics both from the turbocharger and from the wall heat interaction. The proposed approach applies standard closed loop lambda control for controlling the overall air/fuel ratio. Furthermore, ion-current based dilution limit control is applied on the EGR in order to maximize EGR rate as long as combustion stability is preserved. The proposed control strategy has been successfully tested on a heavy duty 6-cylinder port injected natural gas engine and our findings show that 1.5-2.5 % units (depending on the operating points) improvement in…
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A Novel Model for Computing the Trapping Efficiency and Residual Gas Fraction Validated with an Innovative Technique for Measuring the Trapping Efficiency

Lund Institute of Technology-Vittorio Manente, Per Tunestål, Bengt Johansson
Published 2008-09-09 by SAE International in United States
The paper describes a novel method for calculating the residual gas fraction and the trapping efficiency in a 2 stroke engine. Assuming one dimensional compressible flow through the inlet and exhaust ports, the method estimates the instantaneous mass flowing in and out from the combustion chamber; later the residual gas fraction and trapping efficiency are estimated combining together the perfect displacement and perfect mixing scavenging models. It is assumed that when the intake port opens, the fresh mixture is pushing out the burned charge without any mixing and after a multiple of the time needed for the largest eddy to perform one rotation, the two gasses are instantly mixed up together and expelled. The result is a very simple algorithm that does not require much computational time and is able to estimate with high level of precision the trapping efficiency and the residual gas fraction in 2 stroke engines. The tuning and the validation of this algorithm are performed by measuring the trapping efficiency. These measurements are conducted with an innovative technique which consists in…
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