| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 4. |
- 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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| 5. |
- 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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| 6. |
- 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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| 7. |
- 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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| 8. |
- Vressner, Andreas, et al.
(författare)
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Fuel Effects on Ion Current in an HCCI Engine
- 2005
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Ingår i: SAE Transactions, Journal of Engines. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0096-736X. ; 114:3, s. 1382-1395
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Tidskriftsartikel (refereegranskat)abstract
- An interest in measuring ion current in Homogeneous Charge Compression Ignition (HCCI) engines arises when one wants to use a cheaper probe for feedback of the combustion timing than expensive piezo electric pressure transducers. However the location of the ion current probe, in this case a spark plug, is of importance for both signal strength and the crank angle position where the signal is obtained. Different fuels will probably affect the ion current in both signal strength and timing and this is the main interest of this investigation. The measurements were performed on a Scania D12 engine in single cylinder operation and ion current was measured at 7 locations simultaneously. By arranging this setup there was a possibility to investigate if the ion current signals from the different spark plug locations would correlate with the fact that, for this particular engine, the combustion starts at the walls and propagates towards the center of the combustion chamber. The fuels investigated were isooctane, n-heptane, PRF80, gasoline, diesel, ethanol and methanol. A special interest was how the ion current timing was affected by low temperature reactions, which were present with the n-heptane and diesel fuels as well as mixtures of isooctane and n-heptane, i.e., PRF80. The most interesting results were that ion current is both affected by the ion current probe location in the combustion chamber and the fuel used. Fuels with higher octane numbers seem to provoke ion current more easily, thus with LTR fuels as n-heptane and diesel ion current was only achieved at richer mixtures. The cycle-to-cycle variations of ion current increased with leaner mixtures. Ion current was also affected by combustion phasing and engine speed.
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| 9. |
- Vressner, Andreas, et al.
(författare)
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Multiple Point Ion Current Diagnostics in an HCCI Engine
- 2004
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Ingår i: SAE Transactions, Journal of Engines. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0096-736X. ; 113:3, s. 544-550
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Tidskriftsartikel (refereegranskat)abstract
- Interest in ion current sensing for HCCI combustion arises when a feedback signal from some sort of combustion sensor is needed in order to determine the state of the combustion process. A previous study has revealed that ion current sensors in the form of spark plugs can be used instead of expensive piezoelectric transducers for HCCI combustion sensing. Sufficiently high ion current levels were achieved when using relatively rich mixtures diluted with EGR. The study also shows that it is not the actual dilution per se but the actual air/fuel equivalence ratio which is important for the signal level. Conclusions were made that it is possible to obtain information on combustion timing and oscillating wave phenomena from the measurements. However, the study showed that the ion current is local compared to the pressure which is global in the combustion chamber. This observation triggered the present study where the aim is to investigate the ion current at different locations in the combustion chamber. The ion current was measured simultaneously at seven locations in the combustion chamber. In order to achieve this, 6 spark plugs were fitted circumferentially in a spacer placed between the cylinder block and the head. The seventh spark plug was placed in the cylinder head. Individual DC sources of 85 volts were applied across the spark plug gaps. The present study indicates that the combustion timing seems to be dependent on the wall temperature at the different spark plug locations. The largest difference in timing between different locations in the combustion chamber was 2 CAD. The ion current amplitude varies with different spark plug locations up to 1.5 μA. The signal strength increases with decreasing air/fuel ratio and is also affected by dilution.
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| 10. |
- García, Antonio, et al.
(författare)
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Performance and emissions of a series hybrid vehicle powered by a gasoline partially premixed combustion engine
- 2019
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Ingår i: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311. ; 150, s. 564-575
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Tidskriftsartikel (refereegranskat)abstract
- This work evaluates the performance and emissions of the series hybrid vehicle concept powered by a gasoline partially premixed internal combustion engine. To do so, experimental data was collected from a Volvo VED-D4 Euro 6 four-cylinder compression ignition engine running under gasoline partially premixed combustion. Two series hybrid vehicle models were developed in GT-Power®, which were fed with the experimental data to evaluate the potential of the hybrid concept. First of all, the battery charging strategy of the hybrid vehicles was optimized in terms of number of power levels and operating conditions. For this, a design of experiments was performed in GT-Power®, which enabled to obtain a predictive model of the performance and emissions. The predictive model was used to obtain the optimized NOx-fuel consumption Pareto frontiers for each charging strategy proposed. Finally, the GT-Power® vehicle models were run with the optimal operating conditions (selected from each Pareto) in both the new European driving cycle and worldwide harmonized light vehicles test cycle. The results show that the hybrid powertrain running with partially premixed combustion is able to achieve similar or better performance than the commercial diesel vehicle with low engine-out emissions. Moreover, comparing the results from both vehicles, it was confirmed that the hybridization results in better improvements when applied to urban traffic than for highway conditions where the power request is higher and the potential for regenerative braking is reduced.
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