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Publications (10 of 19) Show all publications
Holmberg, T., Cronhjort, A. & Stenlaas, O. (2018). Pressure Amplitude Influence on Pulsating Exhaust Flow Energy Utilization. Paper presented at 10 April 2018 through 12 April 2018. SAE technical paper series, 2018-April
Open this publication in new window or tab >>Pressure Amplitude Influence on Pulsating Exhaust Flow Energy Utilization
2018 (English)In: SAE technical paper series, ISSN 0148-7191, Vol. 2018-AprilArticle in journal (Refereed) Published
Abstract [en]

A turbocharged Diesel engine for heavy-duty on-road vehicle applications employs a compact exhaust manifold to satisfy transient torque and packaging requirements. The small exhaust manifold volume increases the unsteadiness of the flow to the turbine. The turbine therefore operates over a wider flow range, which is not optimal as radial turbines have narrow peak efficiency zone. This lower efficiency is compensated to some extent by the higher energy content of the unsteady exhaust flow compared to steady flow conditions. This paper experimentally investigates the relationship between exhaust energy utilization and available energy at the turbine inlet at different degrees of unsteady flow. A special exhaust manifold has been constructed which enables the internal volume of the manifold to be increased. The larger volume reduces the exhaust pulse amplitude and brings the operating condition for the turbine closer to steady-flow. The operating points are defined by engine speed and boost pressure. From these values the isentropic turbine work is calculated and with the measured compressor work the mean turbine efficiency is estimated. The results show that more energy has to be provided to the turbine at larger exhaust manifold volumes to maintain a constant boost pressure, indicating that the efficiency of the turbine decreases. 

Place, publisher, year, edition, pages
SAE International, 2018
Keywords
Automobile engine manifolds, Diesel engines, Energy efficiency, Energy utilization, Steady flow, Turbines, Available energy, Operating condition, Operating points, Pressure amplitudes, Radial turbines, Transient torque, Turbine efficiency, Turbocharged diesel engine, Exhaust manifolds
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-227471 (URN)10.4271/2018-01-0972 (DOI)2-s2.0-85045521213 (Scopus ID)
Conference
10 April 2018 through 12 April 2018
Note

QC 20190213

Available from: 2018-05-16 Created: 2018-05-16 Last updated: 2019-02-13Bibliographically approved
Holmberg, T., Cronhjort, A. & Stenlaas, O. (2017). Pressure Ratio Influence on Exhaust Valve Flow Coefficients. Paper presented at 4 April 2017 through 6 April 2017. SAE technical paper series, 2017-March(March)
Open this publication in new window or tab >>Pressure Ratio Influence on Exhaust Valve Flow Coefficients
2017 (English)In: SAE technical paper series, ISSN 0148-7191, Vol. 2017-March, no MarchArticle in journal (Refereed) Published
Abstract [en]

In one dimensional engine simulation software, flow losses over complex geometries such as valves and ports are described using flow coefficients. It is generally assumed that the pressure ratio over the valve has a negligible influence on the flow coefficient. However during the exhaust valve opening the pressure difference between cylinder and port is large which questions the accuracy of this assumption. In this work the influence of pressure ratio on the exhaust valve flow coefficient has been investigated experimentally in a steady-flow test bench. Two cylinder heads, designated A and B, from a Heavy-Duty engine with different valve shapes and valve seat angles have been investigated. The tests were performed with both exhaust valves open and with only one of the two exhaust valves open. The pressure ratio over the exhaust port was varied from 1.1:1 to 5:1. For case A1 with a single exhaust valve open, the flow coefficient decreased significantly with pressure ratio. This trend was not replicated for the other single valve case B1, as pressure ratio only had a small influence on the flow coefficient. For the twin valve case A2, the pressure ratio influence was confined to the lower range of valve lifts as the limiting factor was the exhaust port outlet at higher valve lifts. The flow coefficient for the twin valve case B2 increased with pressure ratio in the mid-range of valve lifts.

Place, publisher, year, edition, pages
SAE International, 2017
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-216545 (URN)10.4271/2017-01-0530 (DOI)2-s2.0-85019012516 (Scopus ID)
Conference
4 April 2017 through 6 April 2017
Note

QC 20171108

Available from: 2017-11-08 Created: 2017-11-08 Last updated: 2019-02-25Bibliographically approved
Puttige, A. R., Hamberg, R., Linschoten, P., Reddy, G., Cronhjort, A. & Stenlåås, O. (2017). Surge Detection Using Knock Sensors in a Heavy Duty Diesel Engine. Paper presented at SAE 13th International Conference on Engines and Vehicles, ICE 2017; Capri, Napoli; Italy; 10 September 2017 through 14 September 2017. SAE technical paper series, 2017
Open this publication in new window or tab >>Surge Detection Using Knock Sensors in a Heavy Duty Diesel Engine
Show others...
2017 (English)In: SAE technical paper series, ISSN 0148-7191, Vol. 2017Article in journal (Refereed) Published
Abstract [en]

Improving turbocharger performance to increase engine efficiency has the potential to help meet current and upcoming exhaust legislation. One limiting factor is compressor surge, an air flow instability phenomenon capable of causing severe vibration and noise. To avoid surge, the turbocharger is operated with a safety margin (surge margin) which, as well as avoiding surge in steady state operation, unfortunately also lowers engine performance. This paper investigates the possibility of detecting compressor surge with a conventional engine knock sensor. It further recommends a surge detection algorithm based on their signals during transient engine operation. Three knock sensors were mounted on the turbocharger and placed along the axes of three dimensions of movement. The engine was operated in load steps starting from steady state. The steady state points of operation covered the vital parts of the engine speed and load range. The collected data was analysed with the objective of extracting information of a surging or non-surging compressor. In the charging system studied, the knock sensors detected a profound frequency peak between 5.0 Hz to 7.0 Hz. Another surge related frequency component of about 25 kHz was also observed, dependent on the turbocharger speed. Two surge detection algorithms were evaluated, one based on short time Fourier transform (STFT) and one based on the correlation integral (CI). These algorithms where then validated against temperature measurements at the compressor inlet and visual observation of oscillations of the air inlet piping. The surge detection algorithms were compared for accuracy and repeatability. The accuracy of the methods was found to be 73 % and 71 % respectively when compared to the temperature rise in the compressor inlet.

Place, publisher, year, edition, pages
SAE International, 2017
Keywords
Compressors, Diesel engines, Signal detection, Superchargers, Temperature measurement, Turbomachinery, Accuracy and repeatabilities, Conventional engine, Correlation Integral, Extracting information, Frequency components, Heavy-duty diesel engine, Short time Fourier transforms, Steady-state operation, Engines
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-216576 (URN)10.4271/2017-24-0050 (DOI)2-s2.0-85028994896 (Scopus ID)
Conference
SAE 13th International Conference on Engines and Vehicles, ICE 2017; Capri, Napoli; Italy; 10 September 2017 through 14 September 2017
Note

QC 20171101

Available from: 2017-11-01 Created: 2017-11-01 Last updated: 2019-02-13Bibliographically approved
Kerres, B., Nair, V., Cronhjort, A. & Mihaescu, M. (2016). Analysis of the Turbocharger Compressor Surge Margin Using a Hurst-Exponent-based Criterion. SAE International Journal of Engines, 9(3)
Open this publication in new window or tab >>Analysis of the Turbocharger Compressor Surge Margin Using a Hurst-Exponent-based Criterion
2016 (English)In: SAE International Journal of Engines, ISSN 1946-3936, E-ISSN 1946-3944, Vol. 9, no 3Article in journal (Refereed) Published
Abstract [en]

Turbocharger compressors are limited in their operating range at low mass flows by compressor surge, thus restricting internal combustion engine operation at low engine speeds and high mean effective pressures. Since the exact location of the surge line in the compressor map depends on the whole gas exchange system, a safety margin towards surge must be provided. Accurate early surge detection could reduce this margin. During surge, the compressor outlet pressure fluctuates periodically. The Hurst exponent of the compressor outlet pressure is applied in this paper as an indicator to evaluate how close to the surge limit the compressor operates. It is a measure of the time-series memory that approaches zero for anti-persistence of the time series. That is, a Hurst exponent close to zero means a high statistical preference that a high value is followed by a low value, as during surge. Maps of a passenger-car sized turbocharger compressor with inlet geometries that result in different surge lines are measured on a cold gas stand. It is demonstrated that the Hurst exponent in fact decreases as the compressor moves towards surge, and that a constant value of the Hurst exponent can be used as a threshold for stable operation. Transient pressure signals of the compressor entering surge are analyzed in order to evaluate the time lag until surge can be detected using the Hurst exponent. Two surge cycles are usually needed to detect unstable operation. However, since the amplitude of these oscillations is relatively small for the first cycles, detection is possible before the oscillations grow into deep surge.

Place, publisher, year, edition, pages
SAE International, 2016
Keywords
Centrifugal compressor, surge analysis, surge detection, surge margins, Turbocharging, Hurst exponent
National Category
Mechanical Engineering
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-185757 (URN)10.4271/2016-01-1027 (DOI)000390595900038 ()2-s2.0-84975230385 (Scopus ID)
Projects
Compressor Off-design Operation- CCGEx
Funder
Swedish Energy Agency
Note

QC 20160429

Available from: 2016-04-26 Created: 2016-04-26 Last updated: 2019-02-20Bibliographically approved
Gundmalm, S., Cronhjort, A. & Ångström, H.-E. (2013). Divided Exhaust Period: Effects of Changing the Relation between Intake, Blow-Down and Scavenging Valve Area. In: SAE World Congress 2013: . Paper presented at SAE World Congress, April 16-18, 2013, Detroit, Michigan, USA.
Open this publication in new window or tab >>Divided Exhaust Period: Effects of Changing the Relation between Intake, Blow-Down and Scavenging Valve Area
2013 (English)In: SAE World Congress 2013, 2013Conference paper, Published paper (Refereed)
Abstract [en]

In a previous paper we showed the effects of applying the Divided Exhaust Period (DEP) concept on two heavy-duty diesel engines, with and without Exhaust Gas Recirculation (EGR). Main findings were improved fuel consumption due to increased pumping work, improved boost control and reduced residual gas content. However, some limitations to the concept were discovered.  In the case of high rates of short route EGR, it was apparent that deducting the EGR flow from the turbine manifold impaired optimal valve timing strategies. Furthermore, for both of the studied engines it was clear that the size and ratio of blow-down to scavenging valve area is of paramount importance for engine fuel efficiency.

In this paper, the DEP concept has been studied together with a long route EGR system. As expected it gave more freedom to valve timing strategies when driving pressure for EGR is no longer controlled with the valve timing, as in the short route case. However, when evaluating different combinations of intake, blow-down and scavenging valve area, the optimal relation proves to be strongly dependent on the current EGR system and EGR rates. Hence, for different engine setups the trade-off between total intake and total exhaust area needs to be re-evaluated for optimal engine fuel efficiency. This paper also presents general trends in how different valve timing strategies and EGR rates affect both pumping work and boost pressure.

National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-109528 (URN)
Conference
SAE World Congress, April 16-18, 2013, Detroit, Michigan, USA
Note

QC 20130108

Available from: 2013-01-07 Created: 2013-01-07 Last updated: 2019-02-25Bibliographically approved
Gundmalm, S., Cronhjort, A. & Ångström, H.-E. (2013). Divided Exhaust Period: Effects of Changing the Relation between Intake, Blow-Down and Scavenging Valve Area. SAE International Journal of Engines, 6(2), 739-750
Open this publication in new window or tab >>Divided Exhaust Period: Effects of Changing the Relation between Intake, Blow-Down and Scavenging Valve Area
2013 (English)In: SAE International Journal of Engines, ISSN 1946-3936, Vol. 6, no 2, p. 739-750Article in journal (Refereed) Published
Abstract [en]

In a previous paper we showed the effects of applying the Divided Exhaust Period (DEP) concept on two heavy-duty diesel engines, with and without Exhaust Gas Recirculation (EGR). Main findings were improved fuel consumption due to increased pumping work, improved boost control and reduced residual gas content. However, some limitations to the concept were discovered. In the case of high rates of short route EGR, it was apparent that deducting the EGR flow from the turbine manifold impaired optimal valve timing strategies. Furthermore, for both of the studied engines it was clear that the size and ratio of blow-down to scavenging valve area is of paramount importance for engine fuel efficiency. In this paper, the DEP concept has been studied together with a long route EGR system. As expected it gave more freedom to valve timing strategies when driving pressure for EGR is no longer controlled with the valve timing, as in the short route case. However, when evaluating different combinations of intake, blow-down and scavenging valve area, the optimal relation proves to be strongly dependent on the current EGR system and EGR rates. Hence, for different engine setups the trade-off between total intake and total exhaust area needs to be re-evaluated for optimal engine fuel efficiency. This paper also presents general trends in how different valve timing strategies and EGR rates affect both pumping work and boost pressure.

Keywords
Boost control, Boost pressure, Engine fuels, Exhaust gas recirculation (EGR), General trends, Heavy-duty diesel engine, Residual gas, Valve timing
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-134247 (URN)2-s2.0-84878805923 (Scopus ID)
Note

QC 20131121

Available from: 2013-11-21 Created: 2013-11-20 Last updated: 2019-02-26Bibliographically approved
Gundmalm, S., Cronhjort, A. & Ångström, H.-E. (2012). Divided Exhaust Period on Heavy-Duty Diesel Engines. In: : . Paper presented at THIESEL 2012 Conference on Thermo- and Fluid Dynamic Processes in Direct Injection Engines.
Open this publication in new window or tab >>Divided Exhaust Period on Heavy-Duty Diesel Engines
2012 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Divided Exhaust Period (DEP) has previously been studied on SI engines while results fromHD diesels are scarcer. In this paper the DEP concept has been numerically simulated on two HD dieselengines; one without EGR and one with high rates of short route EGR. The aim is to reduce fuelconsumption, residual gas content and to improve boost control, while current EGR rates are maintained.

The central idea of the DEP concept is to let the initial high energy blow-down pulse feed theturbocharger, but bypass the turbine during the latter part of the exhaust stroke when back pressuredominates the pumping work. The exhaust flow from the cylinder is divided between two exhaust manifoldsof which one is connected to the turbine, and one bypasses the turbine. The flow split betweenthe manifolds is controlled with a variable valve train system.

Results show a reduction of pumping losses for both engine configurations. In the non-EGRcase, the DEP concept offers the possibility to control the mass flow and pressure ratio over the turbine.This allows the turbocharger to operate in a high efficiency mode for a wide range of engine loadpoints. For the EGR case, there is less freedom in control of turbine mass flow, since the blow-downphase is used for both turbine work and EGR flow. Therefore the fuel consumption benefit is reduced.

The conclusion of this paper is that the simulations of the DEP concept show improvements toengine performance and efficiency. In the case of high EGR rates it is shown that the EGR flow shouldnot be deducted from the blow-down phase.

National Category
Engineering and Technology Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-107725 (URN)
Conference
THIESEL 2012 Conference on Thermo- and Fluid Dynamic Processes in Direct Injection Engines
Note

QC 20130108

Available from: 2012-12-17 Created: 2012-12-17 Last updated: 2019-02-25Bibliographically approved
Wåhlin, F. & Cronhjort, A. (2008). Impinging Diesel Sprays. Atomization and sprays, 18(2), 97-127
Open this publication in new window or tab >>Impinging Diesel Sprays
2008 (English)In: Atomization and sprays, ISSN 1044-5110, E-ISSN 1936-2684, Vol. 18, no 2, p. 97-127Article in journal (Refereed) Published
Abstract [en]

Diesel fuel sprays from a common-rail injector have been optically investigated with respect to their macroscale characteristics. The tested nozzle designs were of standard plain orifice type, as well as the impinging-spray type, in which two orifices intersect at a specific angle at the exit. Testing was conducted using a pressurized vessel at room temperature. The impinging sprays were found to be low penetrating and widely dispersed compared to the nonimpinging sprays. The shape of the impinging sprays was as one homogeneous spray with no trace of individual sprays. It was found that impinging diesel sprays can be predicted in a manner similar to standard nonimpinging sprays, using a dimensionless penetration correlation. The cone angle of the impinging sprays increases with the impingement angle, and in contrast to nonimpinging sprays, appears insensitive to ambient density. The results indicate that the impinging spray has a larger spray volume at lower ambient densities. However, at higher ambient densities, the volume of the nonimpinging sprays is larger.

Keywords
Correlation methods; Fuel injection; Pressure vessels; Spraying; Impinging sprays; Room temperature; Diesel fuels; Correlation methods; Diesel fuels; Fuel injection; Pressure vessels; Spraying
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-6776 (URN)10.1615/AtomizSpr.v18.i2.10 (DOI)000248847200001 ()
Note

QC 20100825. Uppdaterad från Accepted till Published 20100825.

Available from: 2007-02-14 Created: 2007-02-14 Last updated: 2019-02-13Bibliographically approved
Desantes, J., Arrègle, J., López, J. & Cronhjort, A. (2006). Scaling Laws for Free Turbulent Gas Jets and Diesel-Like Sprays. Atomization and sprays, 16(4), 443-474
Open this publication in new window or tab >>Scaling Laws for Free Turbulent Gas Jets and Diesel-Like Sprays
2006 (English)In: Atomization and sprays, ISSN 1044-5110, E-ISSN 1936-2684, Vol. 16, no 4, p. 443-474Article in journal (Refereed) Published
Abstract [en]

Scaling laws for free turbulent gas jets and diesel-like sprays are deduced and experimentally validated. The analysis is based on basic conservation equations and experimental evidence. As a new contribution, the effect of the Schmidt number on the scaling laws is analyzed and included, which leads to a more general set of normalized parameters. By analyzing the scaling laws, it is possible to obtain a clear comprehension of gas-jet or diesel-spray behavior, as well as an understanding of the relationship between input and output parameters. Two new parameters are introduced that characterize mass and momentum transfer in the radial direction of the gas jet or diesel spray, thus providing valuable information about the mixing process.

National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-180066 (URN)10.1615/AtomizSpr.v16.i4.60 (DOI)000238233600006 ()2-s2.0-33745037011 (Scopus ID)
Note

QC 20160205

Available from: 2016-01-07 Created: 2016-01-07 Last updated: 2019-02-25Bibliographically approved
Cronhjort, A. (2005). Optical Studies in a Direct Injected Diesel Engine. In: : . Paper presented at Fifth Symposium "Towards Clean Diesel Engines", Lund, 2-3 June 2005.
Open this publication in new window or tab >>Optical Studies in a Direct Injected Diesel Engine
2005 (English)Conference paper, Published paper (Other academic)
Abstract [en]

A heavy-duty diesel engine with optical access through an extended piston has been used to study diesel spray combustion. Conventional photography using a solid-state camera was adopted to image the flames. The images were parameterized using image processing software. Due to extended crevices and reduced stiffness as compared to the original engine, the effective compression ratio was slightly lower in the optical cylinder. To compensate for the lowered compression ratio, the inlet pressure as well as the inlet temperature were increased. As top dead center conditions regarding gas density and temperature were desired to be maintained, this approach resulted in an increased overall air to fuel ratio. However, despite these drawbacks, the engine allows for spray combustion studies under realistic diesel engine conditions regarding pressure and temperature. The inlet pressure was kept at 400 kPa absolute and the temperature was 325 K. To predict the air mass in the cylinder as accurately as possible, the exhaust back pressure was always kept equal to the inlet pressure. To minimize the thermal load on the piston, fuel was injected only when an image was to be exposed. This was also beneficial when estimating the air mass in the cylinder, as the temperature of the rest gas was quite low. A nozzle with eight orifices fitted to a common-rail injector was used to generate the sprays. The rail pressures used were 160 MPa and 220 MPa, the injected amount of fuel was varied between 80 mg and 240 mg.

National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-180067 (URN)
Conference
Fifth Symposium "Towards Clean Diesel Engines", Lund, 2-3 June 2005
Note

QC 20160107

Available from: 2016-01-07 Created: 2016-01-07 Last updated: 2019-02-25Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-9483-7992

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