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On the Role of Nitric Oxide for the Knock-Mitigation Effectiveness of EGR in a DISI Engine Operated with Various Gasoline Fuels

SAE International Journal of Advances and Current Practices in Mobility

Sandia National Laboratories-Magnus Sjöberg, David Vuilleumier, Namho Kim
Toyota Motor Corporation-Nozomi Yokoo, Terutoshi Tomoda, Koichi Nakata
  • Journal Article
  • 2019-01-2150
Published 2019-12-19 by SAE International in United States
The knock-suppression effectiveness of exhaust-gas recirculation (EGR) can vary between implementations that take EGR gases after the three-way catalyst and those that use pre-catalyst EGR gases. A main difference between pre-and post-catalyst EGR gases is the level of trace species like NO, UHC, CO and H2. To quantify the role of NO, this experiment-based study employs NO-seeding in the intake tract for select combinations of fuel types and compression ratios, using simulated post-catalyst EGR gases as the diluent. The four investigated gasoline fuels share a common RON of 98, but vary in octane sensitivity and composition. To enable probing effects of near-zero NO levels, a skip-firing operating strategy is developed whereby the residual gases, which contain trace species like NO, are purged from the combustion chamber.Overall, the effects of NO-seeding on knock are consistent with the differences in knock limits for preand post-catalyst EGR gases. This suggests that for a majority of the conditions studied here, variations in NO concentration dominate the autoignition-influencing role of trace species that are present in pre-and post-catalyst EGR gases.…
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Using Chemical Kinetics to Understand Effects of Fuel Type and Compression Ratio on Knock-Mitigation Effectiveness of Various EGR Constituents

SAE International Journal of Advances and Current Practices in Mobility

Sandia National Laboratories-Namho Kim, David Vuilleumier, Magnus Sjöberg
Toyota Motor Corporation-Nozomi Yokoo, Terutoshi Tomoda, Koichi Nakata
  • Journal Article
  • 2019-01-1140
Published 2019-04-02 by SAE International in United States
Exhaust gas recirculation (EGR) can be used to mitigate knock in SI engines. However, experiments have shown that the effectiveness of various EGR constituents to suppress knock varies with fuel type and compression ratio (CR). To understand some of the underlying mechanisms by which fuel composition, octane sensitivity (S), and CR affect the knock-mitigation effectiveness of EGR constituents, the current paper presents results from a chemical-kinetics modeling study. The numerical study was conducted with CHEMKIN, imposing experimentally acquired pressure traces on a closed reactor model. Simulated conditions include combinations of three RON-98 (Research Octane Number) fuels with two octane sensitivities and distinctive compositions, three EGR diluents, and two CRs (12:1 and 10:1). The experimental results point to the important role of thermal stratification in the end-gas to smooth peak heat-release rate (HRR) and prevent acoustic noise. To model the effects of thermal stratification due to heat-transfer losses to the combustion-chamber walls, the initial temperature at the start of the CHEMKIN simulation was successively reduced below the adiabatic core temperature while observing changes in end-gas heat…
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Effects of EGR Constituents and Fuel Composition on DISI Engine Knock: An Experimental and Modeling Study

Sandia National Laboratories-David Vuilleumier, Namho Kim, Magnus Sjöberg
Toyota Motor Corp.-Nozomi Yokoo, Terutoshi Tomoda, Koichi Nakata
Published 2018-09-10 by SAE International in United States
The use of exhaust gas recirculation (EGR) in spark ignition engines has been shown to have a number of beneficial effects under specific operating conditions. These include reducing pumping work under part load conditions, reducing NOx emissions and heat losses by lowering peak combustion temperatures, and by reducing the tendency for engine knock (caused by end-gas autoignition) under certain operating regimes. In this study, the effects of EGR addition on knocking combustion are investigated through a combined experimental and modeling approach. The problem is investigated by considering the effects of individual EGR constituents, such as CO2, N2, and H2O, on knock, both individually and combined, and with and without traces species, such as unburned hydrocarbons and NOx. The effects of engine compression ratio and fuel composition on the effectiveness of knock suppression with EGR addition were also investigated.A parametric, experimental matrix of diluents, compression ratio, and fuels was tested to measure knock-limited combustion phasing of each combination. The resulting knock limits were evaluated in the context of thermodynamic effects on the closed cycle, chemical interactions…
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Theoretical Study on Spray Design for Small-Bore Diesel Engine (Second Report)

SAE International Journal of Engines

Toyota Central R&D Labs Inc.-Kazuhisa Inagaki, Kiyomi Kawamura
Toyota Motor Corporation-Noriyuki Takada, Takeshi Hashizume, Terutoshi Tomoda
  • Journal Article
  • 2017-01-0704
Published 2017-03-28 by SAE International in United States
Generally, soot emissions increase in diesel engines with smaller bore sizes due to larger spray impingement on the cavity wall at a constant specific output power. The objective of this study is to clarify the constraints for engine/nozzle specifications and injection conditions to achieve the same combustion characteristics (such as heat release rate and emissions) in diesel engines with different bore sizes. The first report applied the geometrical similarity concept to two engines with different bore sizes and similar piston cavity shapes. The smaller engine emitted more smoke because air entrainment decreases due to the narrower spray angle. A new spray design method called spray characteristics similarity was proposed to suppress soot emissions. However, a smaller nozzle diameter and a larger number of nozzle holes are required to maintain the same spray characteristics (such as specific air-entrainment and penetration) when the bore size decreases. This second report proposes another approach that maintains the same nozzle diameter and number of nozzle holes. When the similarity ratio is defined as the ratio of the bore diameter between…
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Development of Closed-Loop Robust Control System for Diesel Engines - Combustion Monitoring by Crank Angular Velocity Analysis and its Applications -

Toyota Motor Corporation-Yukitoshi Aoyama, Ryo Hasegawa, Tomomi Yamada, Takekazu Itoh, Terutoshi Tomoda, Yuichi Shimasaki
Published 2012-04-16 by SAE International in United States
Closed-loop robust control system that can monitor combustion state and control it into optimal state using crank angular velocity analysis was established. The system can be constructed without any change of the current hardware. It can avoid engine stall, deterioration of drivability and white smoke emission by misfire after filling low cetane fuels. This study was attempted to grasp the frequency characteristics of crank angular velocity both normal combustion and misfire with FFT (Fast Fourier Transform) and Wavelet Transform. FFT used for frequency analysis is generic method to acquire the frequency characteristics of steady oscillation, however is unsuitable for acquiring the frequency characteristics of transient oscillation. Therefore authors adopted Wavelet Transform and succeeded in grasping the phenomenon in misfiring in time sequential. With this knowledge, this study was attempted to determine the combustion instability by extracting frequency element of the 0.5 order of engine speed that is the characteristic frequency element in misfiring from pulse signal of the crank angle sensor with digital filters. With this method, misfire and combustion instability with white smoke caused…
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Diesel Combustion Prediction in Transient Operation Using a New Cycle-Simulation (the Fourth Report)~Transient Performance Prediction Using the Engine Control Model

Yusuke Takasu, Satoshi Kaneko, Hiroyuki Tominaga, Terutoshi Tomoda, Yoshikazu Namura, Matsuei Ueda, Kazuhisa Inagaki
  • Technical Paper
  • 2011-08-0504
Published 2011-10-12 by Society of Automotive Engineers of Japan in Japan
A transient engine simulation model, which consists of a zero-dimensional diesel combustion model, a one-dimensional gas flow model and an engine control model, was developed. By combining the engine control model with the previously developed engine model, it was made possible to predict the change of the combustion characteristics with the calibration of the engine control program. Application of this model to the New European Driving Cycle showed a good agreement with the measured data.
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Study of Diesel Engine System for Electric Hybrid Vehicle

Toyota Motor Corp.-Tomomi Yamada, Hiroyuki Haga, Isao Matsumoto, Terutoshi Tomoda
  • Technical Paper
  • 2011-08-0214
Published 2011-10-12 by Society of Automotive Engineers of Japan in Japan
In this study, we combined a diesel engine with the Toyota Hybrid System (THS) for better fuel economy. However, the THS could not be utilized to its full advantage, since a conventional diesel engine has high NOx emissions in high load where fuel economy is good. Therefore, reducing engine friction, lowering the compression ratio, and a low pressure loop exhaust gas recirculation system (LPL-EGR) were examined to achieve both low fuel consumption and low NOx emissions over a wide operating range. Applying this system to a test vehicle, it was verified that the fuel economy greatly surpassed that of a conventional vehicle and that NOx emissions could be reduced below the Euro 6 regulations without DeNOx catalysts.
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Study of Diesel Engine System for Hybrid Vehicles

SAE International Journal of Alternative Powertrains

Toyota Motor Corp.-Tomomi Yamada, Hiroyuki Haga, Isao Matsumoto, Terutoshi Tomoda
  • Journal Article
  • 2011-01-2021
Published 2011-08-30 by SAE International in United States
In this study, we combined a diesel engine with the Toyota Hybrid System (THS). Utilizing the functions of the THS, reducing engine friction, lowering the compression ratio, and adopting a low pressure loop exhaust gas recirculation system (LPL-EGR) were examined to achieve both low fuel consumption and low nitrogen oxides (NOx) emissions over a wide operating range. After applying this system to a test vehicle it was verified that the fuel economy greatly surpassed that of a conventional diesel engine vehicle and that NOx emissions could be reduced below the value specified in the Euro 6 regulations without DeNOx catalysts.
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Development of Low Pressure Loop EGR System for Diesel Engines

Toyota Motor Corporation-Akira Yamashita, Hisashi Ohki, Terutoshi Tomoda, Koichiro Nakatani
Published 2011-04-12 by SAE International in United States
Low pressure loop (LPL) EGR systems are effective means of simultaneously reducing the NOx emissions and fuel consumption of diesel engines. Further lower emission levels can be achieved by adopting a system that combines LPL EGR with a NOx storage and reduction (NSR) catalyst. However, this combined system has to overcome the issue of combustion fluctuations resulting from changes in the air-fuel ratio due to EGR gas recirculation from either NOx reduction control or diesel particulate filter (DPF) regeneration. The aim of this research was to reduce combustion fluctuations by developing LPL EGR control logic.In order to control the combustion fluctuations caused by LPL EGR, it is necessary to estimate the recirculation time. First, recirculation delay was investigated. It was found that recirculation delay becomes longer when the LPL EGR flow rate or engine speed is low. In contrast, even if the engine speed changes, the delay was found to be proportional to the number of engine cycles. A model was developed to express this phenomenon. A good correlation was found between actual measurements and…
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Development of Low Pressure Loop EGR System for Diesel Engines~Development of Recirculation Control Logic for LPL-EGR and NOx storage Reduction Combined System

Toyota Motor Corp.-Akira Yamashita, Hisashi Ohki, Terutoshi Tomoda
  • Technical Paper
  • 2010-08-0411
Published 2010-05-19 by Society of Automotive Engineers of Japan in Japan
The Low Pressure Loop (LPL) EGR system is well known as an effective technology to reduce NOx emission and fuel consumption for diesel engines. A system that combines both LPL-EGR and a NOx storage reduction (NSR) catalyst will be able to achieve further lower emission levels. However, this combined system has to overcome the difficulties of combustion fluctuations due to the recirculation of rich gases coming from the NOx reduction control. This paper proposes a countermeasure based on the usage of Air-Fuel Ratio (A/F) sensors and a simple recirculation delay model.