| 1. |
- Tunestål, Per
(författare)
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Estimation of the In-Cylinder Air/Fuel Ratio of an Internal Combustion Engine by the Use of Pressure Sensors
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis investigates the use of cylinder pressure measurements for estimation of the in-cylinder air/fuel ratio in a spark ignited internal combustion engine. An estimation model which uses the net heat release profile for estimating the cylinder air/fuel ratio of a spark ignition engine is developed. The net heat release profile is computed from the cylinder pressure trace and quantifies the conversion of chemical energy of the reactants in the charge into thermal energy. The net heat release profile does not take heat- or mass transfer into account. Cycle-averaged air/fuel ratio estimates over a range of engine speeds and loads show an RMS error of 4.1% compared to measurements in the exhaust. A thermochemical model of the combustion process in an internal combustion engine is developed. It uses a simple chemical combustion reaction, polynomial fits of internal energy as function of temperature, and the first law of thermodynamics to derive a relationship between measured cylinder pressure and the progress of the combustion process. Simplifying assumptions are made to arrive at an equation which relates the net heat release to the cylinder pressure. Two methods for estimating the sensor offset of a cylinder pressure transducer are developed. Both methods fit the pressure data during the pre-combustion phase of the compression stroke to a polytropic curve. The first method assumes a known polytropic exponent, and the other estimates the polytropic exponent. The first method results in a linear least-squares problem, and the second method results in a nonlinear least-squares problem. The nonlinear least-squares problem is solved by separating out the nonlinear dependence and solving the single-variable minimization problem. For this, a finite difference Newton method is derived. Using this method, the cost of solving the nonlinear least-squares problem is only slightly higher than solving the linear least-squares problem. Both methods show good statistical behavior. Estimation error variances are inversely proportional to the number of pressure samples used for the estimation as predicted by the central limit theorem.
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| 2. |
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| 3. |
- Borgqvist, Patrick, et al.
(författare)
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Comparison of Negative Valve Overlap (NVO) and Rebreathing Valve Strategies on a Gasoline PPC Engine at Low Load and Idle Operating Conditions
- 2013
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Ingår i: SAE Technical Paper Series. - : SAE International. - 0148-7191.
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Konferensbidrag (refereegranskat)abstract
- Gasoline partially premixed combustion (PPC) has the potential of high efficiency and simultaneous low soot and NOx emissions. Running the engine in PPC mode with high octane number fuels has the advantage of a longer premix period of fuel and air which reduces soot emissions. The problem is the ignitability at low load and idle operating conditions. In a previous study it was shown that it is possible to use NVO to improve combustion stability and combustion efficiency at operating conditions where available boosted air is assumed to be limited. NVO has the disadvantage of low net indicated efficiency due to heat losses from recompressions of the hot residual gases. An alternative to NVO is the rebreathing valve strategy where the exhaust valves are reopened during the intake stroke. The net indicated efficiency is expected to be higher with the rebreathing strategy but the question is if similar improvements in combustion stability can be achieved with rebreathing as with NVO. The results show that the rebreathing valve strategy has similar improvements on combustion stability as NVO when the same fuel injection strategy is used. This work also includes results with the NVO valve strategy where a fuel injection is added during the NVO. When a fuel injection is added during the NVO, an additional improvement on combustion stability can be seen which is unmatched by the rebreathing valve strategy.
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| 4. |
- Dahlström, Jessica, et al.
(författare)
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Experimental Evaluation of a Novel High Frequency Ignition System Using a Flow-Reactor Set-up
- 2013
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Ingår i: SAE Technical Paper Series. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191.
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Konferensbidrag (refereegranskat)abstract
- Using diluted methane/air mixtures in internal combustion engines has a potential of reducing emissions and increasing efficiency. However, the ignition systems used today show difficulties igniting lean mixtures. For this purpose a new high frequency (HF) ignition system using pulse generators and a resonance circuit to achieve a controlled number of sparks during a controlled period of time has been developed. A first prototype of this high frequency system has been tested in a flow-reactor and compared to a conventional ignition system. Results show that the high frequency system improves the flame development under lean conditions compared to the conventional system. Higher frequencies have higher capability of igniting lean mixtures than lower frequencies. Lower spark frequencies were found to travel faster across the electrodes than high frequencies and also compared to the conventional system. High pressure and high flow rates affected the lean limit of all ignition strategies, but especially high spark frequencies had difficulties igniting the charge under high pressures, due to the resonant frequency changing with pressure. The high frequency system was also limited in the amount of available voltage. However, this will be improved with further development of the ignition system.
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| 5. |
- Johansson, Thomas, et al.
(författare)
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The Effect of Intake Temperature in a Turbocharged Multi Cylinder Engine operating in HCCI mode
- 2009
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Ingår i: ICE 2009. - : SAE International. ; 2:2, s. 452-466
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Konferensbidrag (refereegranskat)abstract
- 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 is an increase in pumping losses when using negative valve overlap. The pumping losses can then be circumvented to some extent with a low intake temperature or EGR, leading to more beneficial valve timings at high load.
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| 6. |
- Narayanan, Prakash, et al.
(författare)
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A Comparative Analysis of WHR System in HD Engines Using Conventional Diesel Combustion and Partially-Premixed Combustion
- 2012
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Ingår i: SAE Technical Paper Series. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191.
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Konferensbidrag (refereegranskat)abstract
- In the truck industry there is a continuous demand to increase the efficiency and to decrease the emissions. To acknowledge both these issues a waste heat recovery system (WHR) is combined with a partially premixed combustion (PPC) engine to deliver an efficient engine system. Over the past decades numerous attempts to increase the thermal efficiency of the diesel engine has been made. One such attempt is the PPC concept that has demonstrated potential for substantially increased thermal efficiency combined with much reduced emission levels. So far most work on increasing engine efficiency has been focused on improving the thermal efficiency of the engine while WHR, which has an excellent potential for another 1-5 % fuel consumption reduction, has not been researched that much yet. In this paper a WHR system using a Rankine cycle has been developed in a modeling environment using IPSEpro. A comparative investigation of the WHR potential between the existing conventional diesel combustion and the novel PPC combustion is done. Even though the PPC is a low temperature combustion concept (LTC), implying that the exhaust temperatures are lower than for the traditional diesel combustion, the EGR quantity is higher which in total still offers improved WHR potential as that of conventional combustion. The EGR cooler offers higher quality heat when compared to exhaust gas and CAC, hence the WHR potential using only the EGR system is considered in this paper.
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| 7. |
- Narayanan, Prakash, et al.
(författare)
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Waste Heat Recovery from Multiple Heat Sources in a HD Truck Diesel Engine Using a Rankine Cycle - A Theoretical Evaluation
- 2012
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Ingår i: SAE Technical Paper Series. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191.
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Konferensbidrag (refereegranskat)abstract
- Few previous publications investigate the possibility of combining multiple waste heat sources in a combustion engine waste heat recovery system. A waste heat recovery system for a HD truck diesel engine is evaluated for utilizing multiple heat sources found in a conventional HD diesel engine. In this type of engine more than 50% of heat energy goes futile. The majority of the heat energy is lost through engine exhaust and cooling devices such as EGRC (Exhaust gas recirculation cooler), CAC (Charge air cooler) and engine cooling. In this paper, the potential of usable heat recuperation from these devices using thermodynamic analysis was studied, and also an effort is made to recuperate most of the available heat energy that would otherwise be lost. A well-known way of recuperating this heat energy is by employing a Rankine cycle circuit with these devices as heat sources (single loop or dual loop), and thus this study is focused on using a Rankine cycle for the heat recovery system. Furthermore, this paper investigates the possibilities and challenges involved in coupling these different sources in a single Rankine cycle and the selection of suitable working fluid for this Rankine cycle. The study shows that with recuperation from these multiple sources it is possible to recover 5-10% of the otherwise wasted heat energy, which results in ~5% power increase. REFPROP was used for studying fluid properties, and the commercial software IPSEpro is used to build and simulate the Rankine cycle.
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| 8. |
- Shah, Ashish, et al.
(författare)
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Scalability Aspects of Pre-Chamber Ignition in Heavy Duty Natural Gas Engines
- 2016
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191.
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Konferensbidrag (refereegranskat)abstract
- This article presents a study related to application of pre-chamber ignition system in heavy duty natural gas engine which, as previously shown by the authors, can extend the limit of fuel-lean combustion and hence improve fuel efficiency and reduce emissions. A previous study about the effect of pre-chamber volume and nozzle diameter on a single cylinder 2 liter truck-size engine resulted in recommendations for optimal pre-chamber geometry settings. The current study is to determine the dependency of those settings on the engine size. For this study, experiments are performed on a single cylinder 9 liter large bore marine engine with similar pre-chamber geometry and a test matrix of similar and scaled pre-chamber volume and nozzle diameter settings. The effect of these variations on main chamber ignition and the following combustion is studied to understand the scalability aspects of pre-chamber ignition. Indicated efficiency and engine-out emission data is also presented. It has been found that the performance of a pre-chamber is strongly affected by the size of the engine is it being used in. Even with the same energy content in the pre-chamber at the time of spark, the resulting initial main chamber heat release has been found to scale with engine size, and hence the optimal settings for pre-chamber volume and nozzle diameter are also found to scale with engine size.
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| 9. |
- Stenlåås, Ola, et al.
(författare)
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Reformed Methanol Gas as Homogeneous Charge Compression Ignition Engine Fuel
- 2004
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Ingår i: SAE Special Publications. ; 2004:1896, s. 127-140
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Konferensbidrag (refereegranskat)abstract
- Hydrogen has been proposed as a possible fuel for automotive applications. Methanol is one of the most efficient ways to store and handle hydrogen. By catalytic reformation it is possible to convert methanol into hydrogen and carbon monoxide. This paper reports an experimental investigation of Reformed Methanol Gas as Homogeneous Charge Compression Ignition (HCCI) engine fuel. The aim of the experimental study is to investigate the possibility to run an HCCI engine on a mixture of hydrogen and carbon monoxide, to study the combustion phasing, the efficiency and the formation of emissions. Reformed Methanol Gas (RMG) was found to be a possible fuel for an HCCI engine. The heat release rate was lower than with pure hydrogen but still high compared to other fuels. The interval of possible start of combustion crank angles was found to be narrow but wider than for hydrogen. The high rate of heat release limited the operating range to lean (glmg3) cases as with hydrogen. On the other hand, operation on extremely lean mixtures (glme6) was possible. The operating range was investigated using intake air temperature for control and also this control interval was found to be narrow but more extensive than for pure hydrogen, especially when richer cases were run. The maximal load in HCCI mode was a net Indicated Mean Effective Pressure (IMEPn) of 3.5 bar for RMG. This is the same maximum IMEPn as for hydrogen. It is about half the load possible in Spark Ignition (SI) mode and about half the maximal load in HCCI mode with other fuels. For the loads where HCCI operation was possible, indicated thermal efficiency for HCCI was superior to that of SI operation. The indicated overall efficiency of the engine-reformer system is as high for SI as for HCCI operation when RMG is used as fuel. NOx emissions were, as expected, found to decrease when the equivalence ratio was lowered. High levels of carbon monoxide were found in the exhaust. Emissions of hydrocarbons were detected, probably originating from evaporated and partially oxidized lubrication oil.
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| 10. |
- Trajkovic, Sasa, et al.
(författare)
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Investigation of different valve geometries and valve timing strategies and their effect on regenerative efficiency for a pneumatic hybrid with variable valve actuation
- 2008
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Ingår i: SAE Technical Paper Series. - : SAE International. - 0148-7191.
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Konferensbidrag (refereegranskat)abstract
- In the study presented in this paper a single-cylinder Scania D12 diesel engine has been converted to work as a pneumatic hybrid. 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 an air-motor driven by the previously stored pressurized air. The compressed air is stored in a pressure tank connected to one of the inlet ports. One of the engine inlet valves has been modified to work as a tank valve in order to control the pressurized air flow to and from the pressure tank. In order to switch between different modes of engine operation there is a need for a VVT system and the engine used in this study is equipped with pneumatic valve actuators that uses compressed air in order to drive the valves and the motion of the valves are controlled by a combination of electronics and hydraulics. This paper describes the introduction of new tank valve geometry to the system with the intent to increase the pneumatic hybrid regenerative efficiency. The new tank valve has a larger valve head diameter than the previously used setup described in order to decrease the pressure drop over the tank valve. In order to ensure tank valve operation during high in-cylinder pressures the valve is combined with an in-house developed pneumatic valve spring which makes the tank valve pressure compensated. A comparison between the old and the new tank valve geometry and their effect on the pneumatic hybrid efficiency has been done. Also, optimization of the valve timings for both CM (Compressor Mode) and AM (Air-motor Mode) has been done in order to achieve further improvements on regenerative efficiency.
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