Effect of Fuel-Air Mixture Dilution on Knock Intensity in an SI Engine

Ohtomo, Manabu; Suzuoki, Tetsunori; Yamamoto, Seiji; Miyagawa, Hiroshi

doi:10.4271/2018-01-0211

Cited by 8 publications

(3 citation statements)

References 7 publications

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“…He used this theory to explain the conditions necessary to obtain super-knock from preignition in modern downsized engines [379]. In 2018, Ohtomo et al [380] of Toyota Central R&D Labs studied how to achieve autoignition without knock both in an RCM and in an engine through dilution. H 2 was mixed with gasoline in the engine intake to allow dilution levels up to 50%.…”

Section: The 2010s: Aggressive Co 2 Targets Electrification and Downs...mentioning

confidence: 99%

Knock: A Century of Research

Corrigan¹,

Fontanesi²

2021

SAE Int. J. Engines

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Knock is one of the main limitations on increasing spark-ignition (SI) engine efficiency. This has been known for at least 100 years, and it is still the case today. Knock occurs when conditions ahead of the flame front in an SI engine result in one or more autoignition events in the end gas. The autoignition reaction rate is typically much higher than that of the flame-front propagation. This may lead to the creation of pressure waves in the combustion chamber and, hence, an undesirable noise that gives knock its name. The resulting increased mechanical and thermal loading on engine components may eventually lead to engine failure. Reducing the compression ratio lowers end-gas temperatures and pressures, reducing end-gas reactivity and, hence, mitigating knock. However, this has a detrimental effect on engine efficiency.Automotive companies must significantly reduce their fleet carbon dioxide (CO 2 ) values in the coming years to meet targets resulting from the 2015 Paris Agreement. One path towards meeting these is through partial or full electrification of the powertrain. However, the vast majority of automobiles in the near future will still feature a gasoline-fueled SI engine; hence, improvements in combustion engine efficiency remain fundamental.As knock has been a key limitation for so long, there is a huge amount of literature on the subject. A number of reviews on knock have already been published, including in recent years. These generally concentrate on current understanding and status. The present work, in contrast, aims to track the progress of research on knock from the 1920s right through to the present day. It is hoped that this can be a useful reference for new and existing researchers of the subject and give further weight to occasionally neglected historical activity, which can still provide important insights today.

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Section: The 2010s: Aggressive Co 2 Targets Electrification and Downs...mentioning

confidence: 99%

Knock: A Century of Research

Corrigan¹,

Fontanesi²

2021

SAE Int. J. Engines

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“…In the case of SI engines, these references address stoichiometric combustion, lean burn [13][14] or other approaches requiring high dilution rates. This is the case for example for the D-EGR concept developed by Southwest Research Institute [15], or also for Ohtomo et al [16] using hydrogen to support the flame propagation process and study the auto-ignition intensity in highly diluted mixtures with air or with EGR.…”

Section: Introductionmentioning

confidence: 99%

“…Those properties contribute to extend the dilution limits and to improve the combustion stability. The use of hydrogen as a combustion "booster" has already been reported in the literature for both compression ignition and Spark-Ignition (SI) engines [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. Usually, a few percent of hydrogen in volume is added to the intake air to improve the combustion characteristics in terms of combustion timing and speed, combustion stability, and pollutant emissions.…”

Section: Introductionmentioning

confidence: 99%

Hydrogen as a Combustion Enhancer for Highly Efficient Ultra-Lean Spark-Ignition Engines

Zaccardi¹,

Pilla²

2019

SAE Int. J. Adv. & Curr. Prac. in Mobility

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Performance of lean burn gasoline spark-ignition engines can be enhanced through hydrogen supplementation. Thanks to its physicochemical properties, hydrogen supports the flame propagation and extends the dilution limits with improved combustion stability. These interesting features usually result in decreased emissions and improved efficiencies which is of the utmost importance for future SI engines targeting ultra-lean conditions at λ ≥ 2 and brake thermal efficiencies above 50%. Compared to previous studies of hydrogen supplementation, this article aims at demonstrating how hydrogen can support the combustion process with a modern combustion system optimized for extreme dilution rates and high efficiency. Experimental investigations performed with a single cylinder engine are reported and show that the minimal amount of hydrogen required to reach λ = 2 is in the range of 2 to 4% of the total intake volume flow rate. At low load, NOx emissions can be lowered down to 33 ppm at λ = 2 and results also show that a 10-fold decrease in NOx emissions is possible when the dilution rate increases from the lean limit without hydrogen up to λ = 2. In those ultra-lean conditions, particle emissions are also significantly lowered. Unburned energy is around 5% in low load conditions at λ = 2 but the engine-out unburned hydrocarbon concentration is maintained at an acceptable level. At high load, combustion timings can be improved thanks to the increase in the maximal dilution rate and to the better auto-ignition resistance of hydrogen. Consequently, the indicated efficiency is increased by more than 6% abs. compared to the reference stoichiometric conditions. Finally, a maximal indicated efficiency of 47.0% is obtained at λ = 2 with 3% of hydrogen at 3000 rpm-13 bar IMEP. For this operating point, similar performance are obtained with a dual air/EGR dilution.

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