High Speed Knock in S.I. Engines

Arrigoni, V.; Cornetti, G. M.; Spallanzani, G.; Calvi, F.; Tontodonati, A.

doi:10.4271/741056

Cited by 25 publications

(5 citation statements)

References 9 publications

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“…It was found that the pressure traces under knocking conditions have two distinct features: the pressure fluctuation and the sharp pressure rise [30,31,32]. In this work, the start of the first distinct transition in the slope of the cylinder pressure trace, which is followed by consecutive pressure fluctuation, is taken as the knock onset position as shown in (11) It was found that a threshold value of 30 bar/CA 2 corresponds well with the knock occurrence in the tests and has been used to identify the knock in this study.…”

Section: Tests and Knock Identificationmentioning

confidence: 99%

A Zero-Dimensional Combustion Model with Reduced Kinetics for SI Engine Knock Simulation

Liu¹,

Chen²

2009

Combustion Science and Technology

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High load performance and fuel economy of gasoline engines are limited by knocks. Such limitations are becoming worse when the engine is heavily super-charged for high BMEP outputs. Spark ignition timing retardation has been an efficient method to avoid the knock but results in reduced engine performance and poor fuel economy. A better understanding of knock, which could be used to optimize the engine design, ignition timing optimization in particular, is important. In this research, a simulation model for SI engine knock has been developed. The model is based on a three-zone approach

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Section: Tests and Knock Identificationmentioning

confidence: 99%

A Zero-Dimensional Combustion Model with Reduced Kinetics for SI Engine Knock Simulation

Liu¹,

Chen²

2009

Combustion Science and Technology

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“…On the other hand, the pressure rise rate (PRR) following the knock point (KP) appeared to correlate with the reading of the knockmeter for the range of PRF blends tested. Conversely, Arrigoni et al had previously defined the sharp inflection point in the cylinder pressure trace to be the onset of knock in the CFR engine, while the amplitude of the subsequent high frequency pressure oscillation was found to be smaller than those measured in production spark ignition engines [22]. The high frequency oscillations are typically suggestive of the intensity of knock, and these have been characterized by the magnitude of the maximum oscillation.…”

Section: Introductionmentioning

confidence: 97%

Insights into Engine Knock: Comparison of Knock Metrics across Ranges of Intake Temperature and Pressure in the CFR Engine

Rockstroh¹,

Kolodziej²,

Jespersen³

et al. 2018

SAE Int. J. Fuels Lubr.

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Of late there has been a resurgence in studies investigating parameters that quantify combustion knock in both standardized platforms and modern spark-ignition engines. However, it is still unclear how metrics such as knock (octane) rating, knock onset and knock intensity are related, and how fuels behave according to these metrics across a range of conditions.As part of an ongoing study, the air supply system of a standard Cooperative Fuel Research (CFR) F1/F2 engine was modified to allow mild levels of intake air boosting while staying true to its intended purpose of being the standard device for ASTM-specified knock rating, or octane number tests. For instance, the carburation system and intake air heating manifold are not altered, but the engine was equipped with cylinder pressure transducers to enable both, logging of the standard knockmeter read-out, as well as state-of-theart indicated data.For this study, the engine was operated using primary reference fuel 90 (PRF90) at 600 rpm, first following the procedures of the ASTM D2699 research octane number test protocol in order to define the geometric compression ratio set point for standard knock number. Thereafter, compression ratio sweeps were conducted at intake temperatures ranging from 30 to 150 °C and intake air boost extending from 0 to 0.3 bar above ambient. The resulting operating map provided a broad envelope of compressed in-cylinder conditions relevant to modern spark ignition engines. Detailed analysis of the indicated data highlighted a poor correlation between established knock intensity metrics and the knockmeter reading, which is used to characterize a fuel's octane number. It was further found that the autoignition characteristics of PRF90 could be perturbed by means of intake air boosting and heating without being captured by the knockmeter reading.

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“…It measures 𝛥𝑝 𝛥𝑡 , the sudden pressure increase at the so-called "knock point" where the cylinder pressure trace bends upwards, moving away from the normal cylinder pressure trace, when knocking combustion occurs as illustrated in Figure 1. Arrigoni was one of the first scientists to investigate the knock phenomenon in depth in the 1970s [8], and they noticed high-frequency pressure oscillations around top dead centre (TDC) when knocking combustion occurred. These oscillations usually occur within a frequency range of 3.5 to 15 kHz and are represented by the pressure spikes in Figure 1.…”

Section: On =mentioning

confidence: 99%

“…In this case, the engine's knock sensor would "measure" another kind of "RON" than what would be measured by the D1 pickup. Arrigoni was one of the first scientists to investigate the knock phenomenon in depth in the 1970s [8], and they noticed high-frequency pressure oscillations around top dead centre (TDC) when knocking combustion occurred. These oscillations usually occur within a frequency range of 3.5 to 15 kHz and are represented by the pressure spikes in Figure 1.…”

Section: On =mentioning

confidence: 99%

A Pressure-Oscillation-Based RON Estimation Method for Spark Ignition Fuels beyond RON 100

Robeyn,

Sileghem,

Larsson

et al. 2024

Energies

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Knock in spark ignition (SI) engines occurs when the air–fuel mixture in the combustion chamber ignites spontaneously ahead of the flame front, reducing combustion efficiency and possibly leading to engine damage if left unattended. The use of knock sensors to prevent it is common practice in modern engines. Another measure to mitigate knock is the use of higher-octane fuels. The American Society for Testing and Materials’ (ASTM) determination of the Research Octane Number (RON) and Motor Octane Number (MON) of spark ignition fuels has been based on measuring cylinder pressure rise at the onset of knock since its inception in the 1930s. This is achieved through a low-pass filtered pressure signal. Knock detection in contemporary engines, however, relies on measuring engine vibrations caused by high-frequency pressure oscillations during knock. The difference between conditions in which fuels are evaluated for their octane rating and the conditions that generate a knock intensity signal from the knock sensor suggests a potential difference between octane rating and the knock limit typically identified by a contemporary knock sensor. To address this disparity, a modified RON measurement method has been developed, incorporating pressure oscillation measurements. This test method addresses the historical lack of correlation between RON and high-frequency pressure oscillation intensity during knock. Using toluene standardization fuels (TSFs) as a reference, the obtained results demonstrate excellent high-frequency knock intensity-based RON estimations for gasoline. The method is able to differentiate between two fuels that share the same ASTM RON, associating them with a RON-like metric that is more aligned with their performance in a modern SI engine. This alternative method could potentially serve as a template for an upgrade to the existing ASTM RON method without significantly disrupting the current approach. Additionally, its capability to evaluate fuels beyond RON 100 opens the door to assessing a wider range of fuels for antiknock properties and the intensity of fuel oscillations during knocking combustion.

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High Speed Knock in S.I. Engines

Cited by 25 publications

References 9 publications

A Zero-Dimensional Combustion Model with Reduced Kinetics for SI Engine Knock Simulation

A Zero-Dimensional Combustion Model with Reduced Kinetics for SI Engine Knock Simulation

Insights into Engine Knock: Comparison of Knock Metrics across Ranges of Intake Temperature and Pressure in the CFR Engine

A Pressure-Oscillation-Based RON Estimation Method for Spark Ignition Fuels beyond RON 100

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