Using Chemical Kinetics to Understand Effects of Fuel Type and Compression Ratio on Knock-Mitigation Effectiveness of Various EGR Constituents

Kim, Nam-Ho; Vuilleumier, David; Sjöberg, Magnus; Yokoo, Nozomi; Tomoda, Terutoshi; Nakata, Kohei

doi:10.4271/2019-01-1140

Cited by 20 publications

(17 citation statements)

References 31 publications

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“…Moreover, the air entering the engine can be saturated, and some fuel can enter as liquid. This may lead to more pronounced temperature and equivalence ratio inhomogeneities in the charge, as well as the end-gas, altering the knocking tendency of the test fuel. − In contrast, the heater between the intake air thermocouple and the mixture thermocouple allows full vaporization of the PRFs, as well as alcohol fuels in MON tests. − This leads to superior performance from fuels with a higher latent heat of vaporization than PRF mixtures at RON conditions than at MON conditions. Discounting any impact of latent heat of vaporization, the fuels’ chemical reactivity may exhibit a different sensitivity to temperature.…”

Section: Fuel Response To Variation In Ron and Mon Test Conditionsmentioning

confidence: 99%

The Role of Intermediate-Temperature Heat Release in Octane Sensitivity of Fuels with Matching Research Octane Number

Singh

2021

Energy Fuels

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Improving the efficiency of internal combustion engines is important for reducing global greenhouse gas emissions; the efficiency of spark ignition (SI) engines is limited by the knock phenomenon. As opposed to naturally aspirated engines, turbocharged engines operate at beyond research octane number (RON) conditions, and fuel octane sensitivity (OS = RON − motor octane number (MON)) becomes important under such conditions. Previous work by this group [

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Section: Fuel Response To Variation In Ron and Mon Test Conditionsmentioning

confidence: 99%

The Role of Intermediate-Temperature Heat Release in Octane Sensitivity of Fuels with Matching Research Octane Number

Singh

2021

Energy Fuels

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“…The low temperature chemistry however does not scale with the engine speed, and is highly reliant on residence time, which decreases linearly with increasing engine speed. With lesser time for low temperature reactions at higher engine speeds, the PRF90 relative reactivity is not as high, compared to the one at low engine speeds [36]. This is pertinent to conventional octane ratings, RON and MON, wherein the engine is operated at 600 and 900 rpm, respectively.…”

Section: Resultsmentioning

confidence: 99%

On the Relevance of Octane Sensitivity in Heavily Downsized Spark-Ignited Engines

Singh

Mohammed

Gorbatenko

et al. 2021

SAE Technical Paper Series

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Over the years, spark-ignition engine operation has changed significantly, driven by many factors including changes in operating conditions. The variation in operating conditions impacts the state of the end-gas, and therefore, its auto-ignition. This can be quantified in terms of K-factor, which weighs the relative contribution of Research Octane Number (RON) and Motor Octane Number (MON) to knocking tendency at any operating condition. The current study investigates the fuel requirements when operating an engine at increasing intake air pressures. A model engine was operated at varying intake air pressure in GT-Power software, from naturally aspirated intake air to heavily boosted intake air pressure of 4 bar absolute. The pressure-temperature information from the GT-Power model was used to calculate ignition delay times of the unburnt endgas composed of a sensitive and a non-sensitive fuel in ChemKin software. The results show that high octane sensitivity is desired at negative K values (operating at high intake air pressures). In contrast, zero octane sensitivity fuel performed best at low load operation (positive K). Interestingly, the maximum benefit for using a sensitive fuel was achieved at an intake air pressure of 1.75 bar with diminishing returns at higher intake air pressure for 1000 rpm and at lower intake pressures, as engine speed increased. The pressure effect on autoignition tendency was also investigated over existing HCCI data. The auto-ignition tendency was found to be sensitive to octane index in a region of low K value (K~0). This region lies in the negative temperature coefficient (NTC) region, where Primary Reference Fuels (PRFs) shown an increased sensitivity to pressure variation.

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“…This suppression of LTHR at low temperatures may lead to a reduction in the charge heating of the end gas during normal combustion. While this process is beneficial in terms of a fuels knock resistance (by lowering the end gas temperature and pressure), − under normal combustion peak pressures it may be reduced. However, this seems unlikely to be significant at spark advance timings so far from knocking timings.…”

Section: Resultsmentioning

confidence: 99%

Influence of Iso-Butanol Blending with a Reference Gasoline and Its Surrogate on Spark-Ignition Engine Performance

Michelbach

Tomlin

2021

Energy Fuels

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This study investigated the ability of a five-component gasoline surrogate (iso-octane, toluene, n-heptane, 1-hexene, and ethanol) to replicate the combustion and knocking behavior of a reference gasoline (PR5801 – RON 95.4, MON 86.6), under pressure boosted spark-ignition engine conditions at various levels of blending with iso-butanol. The ability of the neat surrogate was first evaluated for stoichiometric air/fuel mixtures, at an intake temperature and pressure of 320 K and 1.6 bar, respectively, and an end of compression pressure of 30 bar, over a range of spark discharge timings. Throughout this regime, the surrogate was found to produce a good representation of the gasoline, particularly in terms of mean engine cycle properties, knock onsets, and knock intensities. This high degree of similarity between the surrogate and gasoline has also seen previous rapid compression machine work, at comparable end-gas temperatures (Int. J. Chem. Kinet.202153787808). However, significant differences were observed between the cyclic variability of surrogate and gasoline results, which was attributed to compositional differences between the two fuels. This study also investigated the impact of iso-butanol blending (at ratios of 5–70% iso-butanol by volume) on the performance of the gasoline at knocking and nonknocking conditions, as well as the ability of the surrogate to replicate the observed blending behavior, at the same experimental conditions. In general, increasing the iso-butanol volume was shown to decrease the knocking propensity of the fuel, except for a nonlinear crossover behavior witnessed for 5% and 10% iso-butanol blends, wherein the 5% blend became less reactive than the 10% blend due to the heavy suppression of NTC behavior in the 10% blend. Even at such low concentrations, iso-butanol appears to act as a strong radical sink, as identified by brute-force sensitivity analysis of predicted knock onsets. This is consistent with the findings of the aforementioned rapid compression machine study. Blends of 20–50% iso-butanol were found to be optimal for use in SI engines, providing considerable antiknock benefits and comparable indicated power to gasoline, with blends of 20–30% being the most viable due to the lower quantities of biofuel required. Under blending with iso-butanol, the surrogate continued to perform well, but blends were observably less reactive than the corresponding gasoline blends at spark advance timings <8 °CA before top dead center. The consistency found between trends within the literature sourced rapid compression machine measurements, and engine data presented in this study highlight the proficiency of fundamental measurements in predicting combustion behavior within an engine at similar thermodynamic conditions.

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Using Chemical Kinetics to Understand Effects of Fuel Type and Compression Ratio on Knock-Mitigation Effectiveness of Various EGR Constituents

Cited by 20 publications

References 31 publications

The Role of Intermediate-Temperature Heat Release in Octane Sensitivity of Fuels with Matching Research Octane Number

The Role of Intermediate-Temperature Heat Release in Octane Sensitivity of Fuels with Matching Research Octane Number

On the Relevance of Octane Sensitivity in Heavily Downsized Spark-Ignited Engines

Influence of Iso-Butanol Blending with a Reference Gasoline and Its Surrogate on Spark-Ignition Engine Performance

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