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Effectiveness of Fuel Enrichment on Knock Suppression in a Gasoline Spark-Ignited Engine

King Abdullah University of Science & Tech.-Eshan Singh, Robert Dibble
Published 2018-09-10 by SAE International in United States
Knock, and more recently, super-knock, have been limiting factors on improving engine efficiency. As a result, engines often operate rich at high loads to avoid damage resulting from knock and protect the after-treatment system from excessive thermal stress. In this work, port-fuel injection and direct injection of excess fuel is explored as a mechanism to suppress knock and super-knock. Under naturally aspirated conditions, increasing the fuel enrichment initially increases knock intensity. However, further increasing fuel enrichment subsequently decreases knock intensity. The competing mechanism from calorific value and latent heat of vaporization can be used to explain the phenomenon. However, when directly injecting the excess fuel after the spark plug has been fired, knock intensity monotonically decreases with increasing fuel quantity. This decrease is shown to be due to fuel quenching the flame that is propagating from spark location. Under boosted conditions, the amount of fuel injected is of critical importance in avoiding super-knock. A lower fuel quantity leads to knock suppression. But beyond a critical value, higher quantities of fuel result in more interaction with…
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The Effect of Pressure, Temperature and Additives on Droplet Ignition of Lubricant Oil and Its Surrogate

King Abdullah University of Science & Tech.-Sumit Maharjan, William Roberts, Ayman Elbaz
Saudi Aramco, Research and Development-Yasser Qahtani
Published 2018-09-10 by SAE International in United States
Numerous studies have attributed pre-ignition events in turbocharged spark ignited engines to the auto-ignition of lubricant oil-fuel mixture droplets. These droplets result from the interaction of the directly injected fuel spray on the lubricant oil film on the cylinder walls, causing fuel splashing to pull oil off the walls, forming droplets. The dilution of the oil by the fuel also changes lubricant oil droplet properties. Therefore, it is important to understand lubricating oils, with and without fuel dilution, as a possible ignition source in pre-ignition and super knock events.In this work, a constant volume (4 L) combustion chamber (CVCC) that allows the introduction of a single droplet of lubricating oil has been built. It is capable of operation at elevated pressures and temperatures. To simulate the droplet-induced pre-ignition event, a droplet injection system was incorporated into the vessel. The oil droplet was suspended on the junction of a thermocouple where the instantaneous internal droplet temperature was measured throughout the oil droplet lifetime. The experiments were carried out in an air atmosphere heated to 300 °C.…
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Blending Octane Number of 1-Butanol and Iso-Octane with Low Octane Fuels in HCCI Combustion Mode

King Abdullah University of Science & Tech.-Muhammad Umer Waqas, Abdulrahman Mohammed, Jean-Baptiste Masurier, Bengt Johansson
Published 2018-09-10 by SAE International in United States
Due to their physical and chemical properties, alcohols such as ethanol and methanol when blended with gasoline provide high anti-knock quality and hence efficient engines. However, there are few promising properties of 1-butanol similar to conventional gasoline which make it a favorable choice for internal combustion engines. Previously the author showed that by blending ethanol and methanol with low octane fuels, non-linear increase in the HCCI fuel number occurs in HCCI combustion mode. Very few studies have been conducted on the use of 1-butanol in HCCI combustion mode, therefore for this work, 1-butanol with a RON 96 was selected as the high octane fuel. Three low octane fuels with octane number close to 70 were used as a base fuel. Two of the low octane fuels are Fuels for Advanced Combustion Engines (FACE gasolines), more specifically FACE I and FACE J and also primary reference fuel (PRF 70) were selected. In addition, iso-octane, which has a different chemical structure than 1-butanol but an octane number (100) close to 1-butanol, was also selected as high octane…
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A Computational Study of Lean Limit Extension of Alcohol HCCI Engines

King Abdullah University of Science & Tech.-Mohammed Jaasim Mubarak Ali, Balaji Mohan, Hong Im
Shanghai Jiao Tong University-Qiyan Zhou, Xing-Cai Lu
Published 2018-09-10 by SAE International in United States
The purpose of present numerical study was to extend the operating range of alcohol (methanol and ethanol) fueled Homogeneous Charge Compression Ignition (HCCI) engine under low load conditions. Ignition of pure methanol and ethanol under HCCI mode of operation requires high intake temperatures and misfires at low loads are common in HCCI engines. Three methods have been adapted to optimize the use of methanol and ethanol for HCCI operation without increasing the intake temperature. First, blending methanol and ethanol with ignition improver, namely di-methyl ether (DME) and di-ethyl ether (DEE), was used to increase the cetane number and ignitability of premixed charge. Second, based on the blended fuels, the spark assistance was used to reduce required intake temperature for auto-ignition. Third, DME and DEE were directly injected to methanol and ethanol operated HCCI engine, in the form of Reactivity Controlled Compression Ignition (RCCI) combustion. Negligible improvement in reducing intake temperature was observed in spark-assisted HCCI combustion due to the slow flame propagation speed under the lean premixed condition with blended fuels. In all three methods,…
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Probabilistic Approach to Predict Abnormal Combustion in Spark Ignition Engines

King Abdullah University of Science & Tech.-Mohammed Jaasim Mubarak Ali, Minh Bau Luong, Aliou Sow, Francisco Hernandez Perez, Hong Im
Published 2018-09-10 by SAE International in United States
This study presents a computational framework to predict the outcome of combustion process based on a given RANS initial condition by performing statistical analysis of Sankaran number, Sa, and ignition regime theory proposed by Im et al. [1]. A criterion to predict strong auto-ignition/detonation a priori is used in this study, which is based on Sankaran-Zeldovich criterion. In the context of detonation, Sa is normalized by a sound speed, and is spatially calculated for the bulk mixture with temperature and equivalence ratio stratifications. The initial conditions from previous pre-ignition simulations were used to compute the spatial Sa distribution followed by the statistics of Sa including the mean Sa, the probability density function (PDF) of Sa, and the detonation probability, PD. Sa is found to be decreased and detonation probability increased significantly with increase of temperature. The statistic mean Sa calculated for the entire computational domain and the predicted Sa from the theory were found to be nearly identical. The predictions based on the adapted Sankaran-Zel’dovich criterion and detonation probability agree well with the results of…
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Compression Ignition of Low Octane Gasoline under Partially Premixed Combustion Mode

King Abdullah University of Science & Tech.-Yanzhao An, Mohammed Jaasim Mubarak Ali, R Vallinayagam, Abdullah AlRamadan, Hong Im, Bengt Johansson
Saudi Aramco-Jaeheon Sim, Junseok Chang
Published 2018-09-10 by SAE International in United States
Partially premixed combustion (PPC) is an operating mode that lies between the conventional compression ignition (CI) mode and homogeneous charge compression ignition (HCCI) mode. The combustion in this mixed mode is complex as it is neither diffusion-controlled (CI mode) nor governed solely by chemical kinetics (HCCI mode). In this study, CFD simulations were performed to evaluate flame index, which distinguishes between zones having a premixed flame and non-premixed flame. Experiments performed in the optical engine supplied data to validate the model. In order to realize PPC, the start of injection (SOI) was fixed at −40 CAD (aTDC) so that a required ignition delay is created to premix air/fuel mixture. The reference operating point was selected to be with 3 bar IMEP and 1200 rpm. Naphtha with a RON of 77 and its corresponding PRF surrogate were tested. The simulations captured the general trends observed in the experiments well. The flame index was noted to be an indicator to evaluate and quantify the in-cylinder combustion development under PPC engine operating condition. The evolution of premixed flames…
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Effects of Injection Rate Profiles on Auto-Ignition in Ignition Quality Tester

King Abdullah University of Science & Tech.-Mohammed Jaasim Mubarak Ali, Hong Im
Shanghai Jiao Tong University-Yueqi Luo, Zhen Huang
Published 2018-09-10 by SAE International in United States
Ignition quality tester (IQT) is a standard experimental device to determine ignition delay time of liquid fuels in a controlled environment in the absence of gas exchange. The process involves fuel injection, spray breakup, evaporation and mixing, which is followed by auto-ignition. In this study, three-dimensional computational fluid dynamics (CFD) is used for prediction of auto-ignition characteristics of diethyl ether (DEE) and ethanol. In particular, the sensitivity of the ignition behavior to different injection rate profiles is investigated. Fluctuant rate profile derived from needle lift data from experiments performs better than square rate profile in ignition delay predictions. DEE, when used with fluctuant injection rate profile resulted in faster ignition, while for ethanol the situation was reversed. The contrasting results are attributed to the difference in local mixing. The fluctuant injection profile yields larger spray velocity variations promoting fuel evaporation and local turbulent mixing. The suitable ignition conditions were reached earlier for DEE with fluctuant injection profile, whereas ethanol exhibits pseudo-homogeneous mixing due to its lower cetane number. Ignition was faster for square rate profile…
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Effect of Mixture Formation and Injection Strategies on Stochastic Pre-Ignition

King Abdullah University of Science & Tech.-Eshan Singh, Mohammed Jaasim Mubarak Ali, Adrian Ichim, Robert Dibble
Saudi Aramco-Kai Morganti
Published 2018-09-10 by SAE International in United States
Stochastic pre-ignition remains one of the major barriers limiting further engine downsizing and down-speeding; two widely used strategies for improving the efficiency of spark-ignited engines. One of the most cited mechanisms thought to be responsible for pre-ignition is the ignition of a rogue droplet composed of lubricant oil and fuel. This originates during mixture formation from interactions between the fuel spray and oil on the cylinder liner. In the present study, this hypothesis is further examined using a single cylinder supercharged engine which employs a range of air-fuel mixture formation strategies. These strategies include port-fuel injection (PFI) along with side and central direct injection (DI) of an E5 gasoline (RON 97.5) using single and multiple injection events. Computational fluid dynamic (CFD) calculations are then used to explain the observed trends. Overall, this study reinforces that interactions between the fuel spray and oil on the cylinder liner can be an important contributor towards stochastic pre-ignition. The occurrence of pre-ignition, as shown by CFD calculations, is successful after completion of two stages. The first stage involves the…
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Combustion Behavior of n-Heptane, Isooctane, Toluene and Blends under HCCI Conditions in the Pressure-Temperature Diagram

King Abdullah University of Science & Tech.-Jean-Baptiste Masurier, Omar Altoaimi, Abdulrahman Mohammed, Muhammad Waqas, Bengt Johansson
Published 2018-09-10 by SAE International in United States
Homogeneous charge compression ignition (HCCI) experiments were run with the aid of a Cooperative fuel research (CFR) engine, operating at 600 rpm and under very lean conditions (ϕ = 0.3). This study seeks to examine the combustion behavior of different fuels by finding the pressure-temperature (p-t) conditions that instigate the start of combustion, and the transition from low temperature combustion to principal combustion. The pressure-temperature diagram emphasizes p-t conditions according to their traces through the compression stroke. In each fuel tested, p-t traces were examined by a sweep of the intake temperature; and for each experimental point, combustion phasing was maintained at top dead center by adjusting the compression ratio of the engine. In addition to the p-t diagram, results were analyzed using a compression ratio-intake temperature diagram, which showed the compression ratio required with respect to intake temperature.Pure n-heptane, isooctane and toluene were investigated first. The results showed that these three fuels ignited in accordance with their octane number. The compression ratio-intake temperature diagram shows that the compression ratio decreased linearly with increased intake…
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