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Role of Piston Bowl Shape to Enhance Late-Cycle Soot Oxidation in Low-Swirl Diesel Combustion

SAE International Journal of Engines

AB Volvo, Sweden-Magnus Christensen
Chalmers University of Technology, Sweden-Jan Eismark, Mats Andersson, Anders Karlsson, Ingemar Denbratt
  • Journal Article
  • 03-12-03-0017
Published 2019-04-25 by SAE International in United States
Late-cycle soot oxidation in heavy-duty (HD) diesel engine low-swirl combustion was investigated using single-cylinder engine and spray chamber experiments together with engine combustion simulations. The in-cylinder flow during interactions between adjacent flames (flame-flame events) was shown to have a large impact on late-cycle combustion. To modify the flame-flame, a new piston bowl shape with a protrusion (wave) was designed to guide the near-wall flow. This design significantly reduced soot emissions and increased engine thermodynamic efficiency. The wave’s main effect was to enhance late-cycle mixing, as demonstrated by apparent rate of heat release after the termination of fuel injection. Combustion simulations showed that the increased mixing is driven by enhanced flow re-circulation, which produces a radial mixing zone (RMZ). The leading edge of the RMZ extends toward the center of the piston bowl, where unused ambient gas is available, promoting oxidation. The wave also enhances mixing in the trailing edge of the RMZ when it detaches from the wall, accelerating the burn-out of the RMZ. This flame interaction effect was isolated and studied further using a…
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Water Injection Benefits in a 3-Cylinder Downsized SI-Engine

SAE International Journal of Advances and Current Practices in Mobility

Chalmers University of Technology-Jayesh Khatri, Ingemar Denbratt, Petter Dahlander, Lucien Koopmans
  • Journal Article
  • 2019-01-0034
Published 2019-01-15 by SAE International in United States
With progressing electrification of automotive powertrains and demands to meet increasingly stringent emission regulations, a combination of an electric motor and downsized turbocharged spark-ignited engine has been recognized as a viable solution. The SI engine must be optimized, and preferentially downsized, to reduce tailpipe CO2 and other emissions. However, drives to increase BMEP (Brake Mean Effective Pressure) and compression ratio/thermal efficiency increase propensities of knocking (auto-ignition of residual unburnt charge before the propagating flame reaches it) in downsized engines.Currently, knock is mitigated by retarding the ignition timing, but this has several limitations. Another option identified in the last decade (following trials of similar technology in aircraft combustion engines) is water injection, which suppresses knocking largely by reducing local in-cylinder mixture temperatures due to its latent heat of vaporization. Addition of adequate water can lead to stoichiometric air/fuel ratio engine operation, and hence both reduction in fuel consumption and full utilization of a three-way catalytic converter (TWC).Further information about effects of various water injection parameters is required. Thus, in this study, a 4-stroke, 1.5 liter, 3-cylinder…
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Optical Diagnostics of Spray Characteristics and Soot Volume Fractions of n-Butanol, n-Octanol, Diesel, and Hydrotreated Vegetable Oil Blends in a Constant Volume Combustion Chamber

Chalmers University of Technology-Tankai Zhang, Mats Andersson, Karin Munch, Ingemar Denbratt
Published 2019-01-15 by SAE International in United States
The effects of using n-butanol, n-octanol, fossil Diesel, hydrotreated vegetable oil (HVO), and blends of these fuels on spray penetration, flame and soot characteristics were investigated in a high-pressure high-temperature constant volume combustion chamber designed to mimic a heavy duty Diesel engine. Backlight illumination was used to capture liquid and vapor phase spray images with a high-speed camera. The flame lift-off length (LOL) and ignition delay were determined by analyzing OH* chemiluminescence images. Laser extinction diagnostics were used to measure the spatially and temporally resolved soot volume fraction. The spray experiments were performed by injecting fuels under non-combusting (623 K) and combusting (823 K) conditions at a fixed ambient air density of 26 kg/m3. A Scania 0.19 mm single straight hole injector and Scania XPI common rail fuel supply system were used to produce injection pressures of 120 MPa and 180 MPa. To evaluate the effect of cetane number (CN) variation on combustion processes and soot emissions, di-tertiary-butyl peroxide (DTBP) was added to one blend to modify its CN without greatly altering its composition. The…
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Comparison of Long-Chain Alcohol Blends, HVO and Diesel on Spray Characteristics, Ignition and Soot Formation

Chalmers University of Technology-Josefine Kim Preuss, Karin Munch, Mats Andersson, Ingemar Denbratt
Published 2019-01-15 by SAE International in United States
Spray characteristics of fossil Diesel fuel, hydrotreated vegetable oil (HVO) and two oxygenated fuel blends were studied to elucidate the combustion process. The fuels were studied in an optically accessible high-pressure/high-temperature chamber under non-combusting (623 K, 4.69 MPa) and combusting (823 K, 6.04 MPa) conditions. The fuel blends contained the long-chain alcohol 2-ethylhexanol (EH), HVO and either 20 vol.% Diesel or 7 vol.% rapeseed methyl ester (RME) and were designed to have a Diesel-like cetane number (CN). Injection pressures were set to 120 MPa and 180 MPa and the gas density was held constant at 26 kg/m3. Under non-combusting conditions, shadow imaging revealed the penetration length of the liquid and vapor phase of the spray. Under combusting conditions, the lift-off length and soot volume fraction were measured by simultaneously recording time-resolved two-dimensional laser extinction, flame luminosity and OH* chemiluminescence images. The ignition delay and start of soot formation were also recorded. Under non-combusting conditions at both injection pressures, the liquid penetration length was higher for the blends and HVO compared to Diesel, whereas the vapor…
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A Method to Evaluate the Compression Ratio in IC Engines with Porous Thermal Barrier Coatings

Chalmers University of Technology-Michael Oevermann, Ingemar Denbratt
Volvo Car Corp.-Joop Somhorst, Mirko Bovo
Published 2018-09-10 by SAE International in United States
The compression ratio is an important engine design parameter. It determines to a large extend engine properties like the achievable efficiency, the heat losses from the combustion chamber and the exhaust losses. The same properties are affected by insulation of the combustion chamber. It is therefore especially important to know the compression ratio when doing experiments with thermal barrier coatings (TBC).In case of porous TBCs, the standard methods to measure the compression ratio can give wrong results. When measuring the compression ratio by volume, using a liquid, it is uncertain if the liquid fills the total porous volume of the coating. And for a thermodynamic compression ratio estimation, a model for the heat losses is needed, which is not available when doing experiments with insulation.The subject of this paper is the evaluation of an alternative method to assess the compression ratio. It is based on motored cylinder pressure data like other thermodynamic methods but does not need a model for the heat losses. The validation and application of the method is done with data from…
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Dual Fuel Methanol and Diesel Direct Injection HD Single Cylinder Engine Tests

Chalmers University of Technology-Michael Saccullo, Timothy Benham, Ingemar Denbratt
Published 2018-04-03 by SAE International in United States
Laws concerning emissions from heavy duty (HD) internal combustion engines are becoming increasingly stringent. New engine technologies are needed to satisfy these new requirements and to reduce fossil fuel dependency. One way to achieve both objectives can be to partially replace fossil fuels with alternatives that are sustainable with respect to emissions of greenhouse gases, particulates and nitrogen oxides (NOx). A suitable candidate is methanol. The aim of the study presented here was to investigate the possible advantages of combusting methanol in a heavy duty Diesel engine. Those are, among others, lower particulate emissions and thereby bypassing the NOx-soot trade-off. Because of methanol’s poor auto-ignition properties, Diesel was used as an igniting sources and both fuels were separately direct injected. Therefore, two separate standard common rail Diesel injection systems were used together with a newly designed cylinder head and adapted injection nozzles. This study serves as a proof-of-concept, demonstrating that methanol can successfully be used in a high pressure Diesel injection system. Additionally, the combustion properties of the dual fuel system were compared to those…
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Knock Phenomena under Very Lean Conditions in Gasoline Powered SI-Engines

SAE International Journal of Engines

Chalmers University of Technology-Gerben Doornbos, Stina Hemdal, Ingemar Denbratt
Volvo Cars-Daniel Dahl
  • Journal Article
  • 03-11-01-0003
Published 2018-03-13 by SAE International in United States
Homogeneous lean operation is a well-known strategy for enhancing the thermal efficiency of SI-engines. At higher load points the efficiency is often compromised by the need to suppress knock. Experiments were performed to determine the knock characteristics of SI engines using homogeneous lean operation at λ values of up to 1.8 with various hardware configurations that are commonly used to increase the lean limit. Changing λ altered the eigenfrequencies of the combustion chamber and the highest energy excitation mode. Increasing λ from 1.0 to 1.2 increased the knock tendency and led to an earlier knock onset. However, further increases in λ significantly reduced the knock tendency and retarded the knock onset. The knock signal energy increased for higher λ values and constant knock tendencies. The differences in knock characteristics between the various λ values became more pronounced upon raising the intake temperature from 40 °C to 90 °C. The trends in knock tendency and knock onset largely parallels that observed for engine out NOx emissions and thus the NOx concentration in the internal EGR. The increased knock…
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Combustion Characteristics for Partially Premixed and Conventional Combustion of Butanol and Octanol Isomers in a Light Duty Diesel Engine

Chalmers University of Technology-Tankai Zhang, Karin Munch, Ingemar Denbratt
Published 2017-10-08 by SAE International in United States
Reducing emissions and improving efficiency are major goals of modern internal combustion engine research. The use of biomass-derived fuels in Diesel engines is an effective way of reducing well-to-wheels (WTW) greenhouse gas (GHG) emissions. Moreover, partially premixed combustion (PPC) makes it possible to achieve very efficient combustion with low emissions of soot and NOx. The objective of this study was to investigate the effect of using alcohol/Diesel blends or neat alcohols on emissions and thermal efficiency during PPC. Four alcohols were evaluated: n-butanol, isobutanol, n-octanol, and 2-ethylhexanol. The alcohols were blended with fossil Diesel fuel to produce mixtures with low cetane numbers (26-36) suitable for PPC. The blends were then tested in a single cylinder light duty (LD) engine. To optimize combustion, the exhaust gas recirculation (EGR) level, lambda, and injection strategy were tuned. The measured emissions and thermal efficiencies for PPC with the blends were compared to those for conventional combustion with production engine settings.The study showed a viable way to achieve PPC by low CN alcohol/Diesel blends in a single cylinder LD engine.…
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High Pressure Ethanol Injection under Diesel-Like Conditions

Chalmers University of Technology-Michael Saccullo, Mats Andersson, Ingemar Denbratt
Volvo-Jan Eismark
Published 2017-03-28 by SAE International in United States
Laws concerning to emissions from heavy duty (HD) internal combustion engines are becoming increasingly stringent. New engine technologies are therefore needed to satisfy these new legal requirements and reduce fossil fuel dependency. One way to achieve both objectives is to partially replace fossil fuels with alternatives that are more sustainable with respect to emissions of greenhouse gas, particulates and NOx. As a first step towards the development of a direct injected dual fuel engine using diesel fuel and renewable alcohols such as methanol or ethanol, we have studied ethanol (E100) sprays generated with a standard high pressure diesel fuel injection system in a high pressure/temperature spray chamber with optical access. The experiments were performed at a gas density of ∼27kg/m3 at ∼550 °C and ∼60 bar, representing typical operating conditions for a HD engine at low loads. High speed video images of the developing sprays were recorded, enabling measurement of spray parameters such as the liquid cone angle, liquid penetration length and vapor penetration at injection pressures between 500 and 2200 bar. The results obtained…
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Transient Responses of Various Ammonia Formation Catalyst Configurations for Passive SCR in Lean-Burning Gasoline Engines under Various Real Engine Conditions.

Chalmers Univ. of Technology-Gerben Doornbos, Stina Hemdal, Ingemar Denbratt
Volvo Car Corporation-Daniel Dahl
Published 2016-04-05 by SAE International in United States
Passive selective catalyst reduction (SCR) systems can be used as aftertreatment systems for lean burn spark ignition (SI)-engines. Their operation is based on the interaction between the engine, an ammonia formation catalyst (AFC), and an SCR catalyst. Under rich conditions the AFC forms ammonia, which is stored in the SCR catalyst. Under lean conditions, the SCR catalyst reduces the engine out NOx using the stored NH3.This study compared the ammonia production and response times of a standard three way catalyst (TWC) and a Pd/Al2O3 catalyst under realistic engine operating conditions. In addition, the relationships between selected engine operating parameters and ammonia formation over a TWC were investigated, considering the influence of both the chosen load point and the engine settings.Tests at the loadpoint of 1500 rpm/2.63 bar break mean effective pressure (BMEP) showed that most ammonia was formed over a TWC at a lambda of 0.93 with a 50% mass fraction burned (MFB) at 3 crank angle degrees (CAD) after top dead centre (aTDC), when valve overlap was minimised. The response time of the TWC…
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