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Is the “K Value” of an Engine Truly Fuel Independent?

Nissan Motor Co., Ltd.-Masaharu Kassai, Taisuke Shiraishi
Shell Global Solutions (Deutschland) GmbH-Sandro Gail
  • Technical Paper
  • 2020-01-0615
To be published on 2020-04-14 by SAE International in United States
The octane appetite of an engine is frequently characterised by the so-called K value. It is usually assumed that K is dependent only on the thermodynamic conditions in the engine when knock occurs. In this work we test this hypothesis: further analysis was conducted on experimental results from SAE 2019-01-0035 in which a matrix of fuels was tested in a single cylinder engine. The fuels consisted of a relatively small number of components, thereby simplifying the analysis of the chemical kinetic proprieties.Through dividing the original fuel matrix into subsets, it was possible to explore the variation of K value with fuel properties. It was found that K value tends to increase slightly with RON. The explanation for this finding is that higher RON leads to advanced ignition timing (i.e. closer to MBT conditions) and advanced ignition timing results in faster combustion because of the higher pressures and temperatures reached in the thermodynamic trajectory. The Livengood-Wu integral can be employed to show that for higher octane fuels, knock onset occurs at a higher temperature and pressure.…
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In-cylinder flow design based on the representative scales of turbulence and premixed combustion

Nissan Motor Co., Ltd.-Yuko Mito, Taisuke Shiraishi, Atsushi Teraji
  • Technical Paper
  • 2019-01-2210
Published 2019-12-19 by SAE International in United States
Dilution combustion with exhaust gas recirculation (EGR) has been applied for the improvement of thermal efficiency. In order to stabilize the high diluted combustion, it is important to form an appropriate turbulence in the combustion cylinder. Turbulent intensity needs to be strengthened to increase the combustion speed, while too strong turbulence causes ignition instability. In this study, the factor of combustion instability under high diluted conditions was analyzed by using single cylinder engine test, optical engine test and 3D CFD simulation. Finally, methodology of in-cylinder flow design is attempted to build without any function by taking into account the representative scales of turbulence and premixed combustion.
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Influence of Component Proportion on Multi-Component Surrogate Fuel Spray Characteristics under Subcooled and Superheated Conditions

Nissan Motor CO., LTD. 560-2, Okatsukoku, Atsugi-shi, Kanaga-Ryo Uchida, Taisuke Shiraishi
School of Mechanical Engineering, Shanghai Jiao Tong Univers-Shangze Yang, Xuesong Li, Min Xu
  • Technical Paper
  • 2019-01-2250
Published 2019-12-19 by SAE International in United States
Good comprehension of multi-component fuel spray behavior is essential for the improved performance of GDI engines. In this study, the spray characteristics of three distinct multi-component surrogate fuels with various proportions of n-pentane, iso-octane, and n-decane were investigated using multiple diagnostics including macroscopic imaging, planar laser Mie-scattering, and phase doppler interferometry (PDI). These surrogate fuels were used to mimic different distillation characteristics of regular unleaded gasoline with different vaporization behaviors. Test measurements show that under subcooled test conditions, the spray geometry is mainly influenced by dynamic viscosity. On the contrary, under superheated test conditions, spray geometry is controlled by the specific component of fuel which has the highest vapor pressure. A triangular methodology is created to evaluate the influence of component proportion on spray characteristics. A hierarchical model is then developed to illustrate the macroscopic behavior of multi-component fuel spray which explains well the effect of each component's proportion on the overall spray characteristics.
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A Study of Particulate Emission Formation Mechanism from Injector Tip in Direct-Injection Gasoline Engines

SAE International Journal of Advances and Current Practices in Mobility

Nissan Motor Co., Ltd.-Yoshihiro Imaoka, Yutaka Hashizume, Takao Inoue, Taisuke Shiraishi
  • Journal Article
  • 2019-01-2244
Published 2019-12-19 by SAE International in United States
The mechanism causing in-cylinder injector tip soot formation, which is the main source of particle number (PN) emissions under operating conditions after engine warm-up, was analyzed in this study. The results made clear a key parameter for reducing injector tip soot PN emissions. An evaluation of PN emissions for different amounts of injector tip wetting revealed that an injector with larger tip wetting forms higher PN emissions. The results also clarified that the amount of deposits does not have much impact on PN emissions. The key parameter for reducing injector tip soot is injector tip wetting that has a linear relationship with injector tip soot PN emissions.
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A Study of Low Temperature Plasma-Assisted Gasoline HCCI Combustion

SAE International Journal of Engines

Nissan Motor Co., Ltd., Japan-Taisuke Shiraishi
  • Journal Article
  • 03-12-01-0008
Published 2019-01-29 by SAE International in United States
In this study low temperature plasma technology was applied to expand auto-ignition operation region and control auto-ignition phasing of the homogeneous charge compression ignition (HCCI) combustion. The low temperature plasma igniter of a barrier discharge model (barrier discharge igniter (BDI)) with high-frequency voltage (15 kHz) was provided at the top center of the combustion chamber, and the auto-ignition characteristics of the HCCI combustion by the low temperature plasma assistance was investigated by using a single-cylinder gasoline engine. HCCI combustion with compression ratio of 15:1 was achieved by increasing the intake air temperature. The lean air-fuel (A/F) ratio limit and visualized auto-ignition combustion process on baseline HCCI without discharge assistance, spark-assisted HCCI, and BDI-assisted HCCI were compared. BDI assist in the intake stroke improved the HCCI ignitability, thereby expanding the region of stable HCCI operation on the lean mixture side and on the low intake air temperature side. The effect of the BDI assist on improvement of HCCI ignitability was substantially greater than a spark assist. The HCCI combustion process was clearly different between spark assist…
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Mechanism Analysis on the Effect of Fuel Properties on Knocking Performance at Boosted Conditions

Nissan Motor Co., Ltd.-Masaharu Kassai, Cagdas Aksu, Taisuke Shiraishi
Shell Global Solutions-Roger Cracknell
Published 2019-01-15 by SAE International in United States
In recent years, boosted and downsized engines have gained much attention as a promising technology to improve fuel economy; however, knocking is a common issue of such engines that requires attention.To understand the knocking phenomenon under downsized and boosted engine conditions deeply, fuels with different Research Octane Number (RON) and Motor Octane Number (MON) were prepared, and the knocking performances of these fuels were evaluated using a single cylinder engine, operated under a variety of conditions.Experimental results showed that the knocking performance at boosted conditions depend on both RON and MON. While higher RON showed better anti-knocking performance, lower MON showed better anti-knocking performance. Furthermore, the tendency for a reduced MON to be beneficial became stronger at lower engine speeds and higher boost pressures, in agreement with previously published modelling work.A new method of interpreting octane appetite is presented which relates the gradient of contour lines of MB50 in RON/MON space to K value.The results can be further interpreted by understanding the relative contribution of low temperature oxidation (LTO) pathways under the prevailing temperature/pressure conditions…
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An Investigation on the Ignition Characteristics of Lubricant Component Containing Fuel Droplets Using Rapid Compression and Expansion Machine

SAE International Journal of Fuels and Lubricants

Nissan Motor Co., Ltd.-Masaharu Kassai, Taisuke Shiraishi, Toru Noda
Waseda University-Mamoru Hirabe, Yoshiki Wakabayashi, Jin Kusaka, Yasuhiro Daisho
  • Journal Article
  • 2016-01-2168
Published 2016-10-17 by SAE International in United States
With the development of downsized spark ignition (SI) engines, low-speed pre-ignition (LSPI) has been observed more frequently as an abnormal combustion phenomenon, and there is a critical need to solve this issue. It has been acknowledged that LSPI is not directly triggered by autoignition of the fuel, but by some other material with a short ignition delay time. It was previously reported that LSPI can be caused by droplets of lubricant oil intermixed with the fuel.In this work, the ignition behavior of lubricant component containing fuel droplets was experimentally investigated by using a constant volume chamber (CVC) and a rapid compression and expansion machine (RCEM), which enable visualization of the combustion process in the cylinder. Various combinations of fuel compositions for the ambient fuel-air mixture and fractions of base oil/metallic additives/fuel for droplets were tested.CVC results confirmed the high ignitability of lubricant component containing fuel droplets in pre-heated air, which was responsible for the early timing of LSPI. RCEM results also revealed the high ignitability of lubricant component containing fuel droplets in the premixed fuel/air…
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Research on the Effect of Lubricant Oil and Fuel Properties on LSPI Occurrence in Boosted S. I. Engines

Nissan Motor Co., Ltd.-Masaharu Kassai, Ken Torii, Taisuke Shiraishi, Toru Noda
Shell Global Solutions (Deutschland) GMB-Tor Kit Goh, Karsten Wilbrand
Published 2016-10-17 by SAE International in United States
The effects of lubricant oil and fuel properties on low speed pre-ignition (LSPI) occurrence in boosted S.I. engines were experimentally evaluated with multi-cylinder engine and de-correlated oil and fuel matrices. Further, the auto-ignitability of fuel spray droplets and evaporated homogeneous fuel/oil mixtures were evaluated in a combustion bomb and pressure differential scanning calorimetry (PDSC) tests to analyze the fundamental ignition process.The work investigated the effect of engine conditions, fuel volatility and various lubricant additives on LSPI occurrence. The results support the validity of aspects of the LSPI mechanism hypothesis based on the phenomenon of droplets of lubricant oil/fuel mixture (caused by adhesion of fuel spray on the liner wall) flying into the chamber and autoigniting before spark ignition.Combustion bomb experiments confirmed that lubricant oil sprays have higher auto-ignitability than gasoline fuel components, and no particular effects of lubricant additives on ignitability were observed. However, under the conditions of the PDSC test, it was shown that the oxidative stability of fuel/oil mixtures is lower as the fuel/oil ratio is increased, and higher levels of calcium lubricant…
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Mechanism Analysis on LSPI Occurrence in Boosted S. I. Engines

Nissan Motor Co., Ltd.-Masaharu Kassai, Hiroki Hashimoto, Taisuke Shiraishi, Atsushi Teraji, Toru Noda
Published 2015-09-01 by SAE International in United States
Mechanism of suddenly occurring behavior of low speed pre-ignition (LSPI) in boosted spark ignition (SI) engines was analyzed with various experimental methodologies.Endoscope-visualized 1st cycle of LSPI showed droplet-like luminous flame kernels as the origin of flame propagation before spark ignition. With the oil lubricated visualization engine, droplets flying were observed only after enough accumulation of fuel at piston crevice. Also, it was confirmed that subsequent cycles of LSPI occur only after enough operation time.These results indicated that local accumulation of liner adhered fuel and saturation of oil dilution can be a contributing factor to the sudden occurrence of LSPI.
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The Effects of Ignition Environment and Discharge Waveform Characteristics on Spark Channel Formation and Relationship between the Discharge Parameters and the EGR Combustion Limit

SAE International Journal of Engines

Chiba University-Yasuo Moriyoshi
Nissan Motor. Co., Ltd.-Taisuke Shiraishi, Atsushi Teraji
  • Journal Article
  • 2015-01-1895
Published 2015-09-01 by SAE International in United States
In order to realize the high compression ratio and high dilution combustion toward improvement in thermal efficiency, the improvement in stability of ignition and initial phase of combustion under the high gas flow field is the major challenge. In terms of the shift on the higher power side of the operating point by downsizing and improvement of real world fuel consumption, the improvement of ignitability is increasingly expected in the wide operating range also including high load and high engine speed region. In this study, the effects of the gas pressure, gas flow velocity near the spark gap at ignition timing, and discharge current characteristics on spark channel formation were analyzed, focusing on restrike event and spark channel stretching in the spark channel formation process. And the relationship between the average discharge current until 1 ms and the EGR combustion limit was considered.
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