Sotirios Mamalis
Stony Brook University
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Publication
Featured researches published by Sotirios Mamalis.
International Journal of Engine Research | 2014
Sotirios Mamalis; Aristotelis Babajimopoulos; Dennis N. Assanis; Claus Borgnakke
Low-temperature combustion has shown the potential to provide solutions for future clean and efficient powertrain systems. Traditional approaches using the first law of thermodynamics have been established for describing energy flows within engine systems and comparing losses between low-temperature and traditional combustion modes. An augmented approach, using the second law of thermodynamics, can be utilized to gain insight into the exergy flows within the system and thus identify areas of irreversibilities and inefficiencies. The present article aims at introducing the required framework for the second law analysis of low-temperature combustion concepts and demonstrating its application to boosted homogeneous charge compression ignition engines. The framework consists of a combination of the first law and second law expressions combined with the University of Michigan homogeneous charge compression ignition combustion model and was applied on a modeled light-duty four-cylinder boosted homogeneous charge compression ignition engine. It was found that combustion irreversibilities in homogeneous charge compression ignition were ∼25% more than traditional spark ignition or diesel engines and increased with dilution. On the other hand, exergy transfer to the walls was reduced with low-temperature combustion. It was also found that the combination of negative valve overlap and turbocharging is not beneficial for high-load operation. Exergy analysis of the exhaust system revealed that turbine useful work was lower than 50% of exergy at the exhaust ports and indicated that boosting performance may be improved by manipulating exergy transfer in the exhaust manifold. Results from the present study are focused on boosted homogeneous charge compression ignition, but the conclusions reached are applicable to other low-temperature combustion concepts as well.
International Journal of Engine Research | 2014
Sotirios Mamalis; Aristotelis Babajimopoulos; Orgun A. Guralp; Paul M. Najt; Dennis Assanis
This study discusses a novel approach toward homogeneous charge compression ignition operation in the 5 - 10 bar net indicated mean effective pressure range. This approach is based on the combination of boosting and variable valve actuation to maximize engine efficiency. Compression ratio plays a key role and determines low-temperature combustion feasibility in modern gasoline compression ignition concepts. In order to explore the interactions between compression ratio, boosting system and variable valve actuation, multi-cylinder engine models were utilized which employed the University of Michigan combustion model. Valve strategies featured switching from low-lift negative valve overlap to high-lift positive valve overlap, and the switching point was found to be dependent on compression ratio. A recent study by the authors suggested that heating the charge from external compression is more efficient than heating by residual gas retention strategies. Use of non-cooled intake air allows for valve events and combustion phasing that promote turbocharger performance and alleviate the backpressure problems often associated with low temperature combustion engines. Elevated intake pressure and reduced pumping work allow for improvements in efficiency with minimal NOx formation and acceptable ringing. It was found that further efficiency benefits can be realized by increasing compression ratio. Identification of trade-offs between engine hardware and combustion mode appears to be critical for homogeneous charge compression ignition operation in the 5 -10 bar net indicated mean effective pressure range. By focusing on this operating range, the present modeling study attempts to shed some light on practical applications of light-duty gasoline compression ignition concepts.
Journal of Engineering for Gas Turbines and Power-transactions of The Asme | 2018
Mozhgan Rahimi Boldaji; Aimilios Sofianopoulos; Sotirios Mamalis; Benjamin Lawler
Homogeneous Charge Compression Ignition (HCCI) combustion has the potential for high efficiency with very low levels of NOx and soot emissions. However, HCCI has thus far only been achievable in a laboratory setting due to the following challenges: 1) there is a lack of control over the start and rate of combustion, and 2) there is a very limited and narrow operating range. In the present work, the injection of water directly into the combustion chamber was investigated to solve the aforementioned limitations of HCCI. This new advanced combustion mode is called Thermally Stratified Compression Ignition (TSCI). A 3-D CFD model was developed using CONVERGE CFD coupled with detailed chemical kinetics to gain a better understanding of the underlying phenomena of the water injection event in a homogeneous, low temperature combustion strategy. The CFD model was first validated against previously collected experimental data. The model was then used to simulate TSCI combustion and the results indicate that injecting water into the combustion chamber decreases the overall unburned gas temperature and increases the level of thermal stratification prior to ignition. The increased thermal stratification results in a decreased rate of combustion, thereby providing control over its rate. The results show that the peak pressure and gross heat release rate decrease by 37.8% and 83.2%, respectively, when 6.7 mg of water were injected per cycle at a pressure of 160 bar. Finally, different spray patterns were simulated to observe their effect on the level of thermal stratification prior to ignition. The results show that symmetric patterns with more nozzle holes were generally more effective at increasing thermal stratification. INTRODUCTION Internal combustion (IC) engines play an important role in transportation and stationary power generation. US Government projections for the transportation sector indicate that the IC engine will remain the dominant prime mover for the next several decades [1]. For this reason, it is paramount to achieve both high efficiency and low levels of harmful emissions from IC engines. Low temperature combustion (LTC) is one potential technology that achieves high efficiency with low levels of harmful emissions. Homogeneous Charge Compression Ignition (HCCI) is one example of an LTC mode, which combines the favorable characteristics of both diesel and spark ignition (SI) engines. However, HCCI suffers from a lack of control over the start and rate of combustion, which results in a limited operating range. In recent years, research has focused on strategies to control the start of ignition and heat release in HCCI. One such strategy that has been investigated is exhaust gas recirculation (EGR) [16]. Yao et al. [2-4] indicated that the EGR rate is an important parameter for controlling HCCI combustion. They showed that by adjusting the external, cooled EGR rate, the ignition timing and combustion duration can be regulated to some extent. Yap et al. [5] combined inlet charge boosting with internal, hot EGR in a single cylinder engine to extend its upper load HCCI limit. Cairns and Blaxill proposed employing both internal and external EGR in order to expand the upper load limit [6]. They were able to extend the upper load limit by 20-65% when higher external EGR fractions were considered. Another strategy for controlling heat release in HCCI is Variable Compression Ratio (VCR). Heyvonen et al. [7] combined VCR and inlet air preheating by exhaust heat recovery in an attempt to expand the
International Journal of Engine Research | 2018
Mozhgan Rahimi Boldaji; Aimilios Sofianopoulos; Sotirios Mamalis; Benjamin Lawler
Advanced combustion concepts, like homogeneous charge compression ignition, are limited by their narrow operating range, which stems from a lack of control over the heat release process. This study explores a new advanced combustion mode, called thermally stratified compression ignition, which uses a direct water injection event to control the heat release process in low-temperature combustion. A three-dimensional computational fluid dynamics model coupled with detailed chemical kinetics is used to better understand the effects of direct water injection on thermal stratification in the cylinder and the resulting heat release process. Previous results showed that increasing the injection pressure results in a significantly broader temperature distribution due to increased evaporative cooling. In this way, direct water injection can control low-temperature combustion heat release and extend significantly the operable load range. In this study, simulations were performed over a range of start of injection timings in order to determine its effect on thermal stratification and heat release. The results show that for both low and high injection pressures advancing the start of water injection results in increased thermal stratification and reduced peak pressure and heat release rate for injections occurring after −60 °CAD. Before −60 °CAD, advancing the water injection has a varied effect on thermal stratification and heat release depending on the injection pressure and mass of the injected water.
International Journal of Engine Research | 2018
Aimilios Sofianopoulos; Mozhgan Rahimi Boldaji; Benjamin Lawler; Sotirios Mamalis
The operating range of Homogeneous Charge Compression Ignition (HCCI) engines is limited to low and medium loads by high heat release rates. Negative valve overlap can be used to control ignition timing and heat release by diluting the mixture with residual gas and introducing thermal stratification. Cyclic variability in HCCI engines with NVO can result in reduced efficiency, unstable operation, and excessive pressure rise rates. Contrary to spark-ignition engines, where the sources of cyclic variability are well understood, there is a lack of understanding of the effects of turbulence on cyclic variability in HCCI engines and the dependence of cyclic variability on thermal stratification. A three-dimensional computational fluid dynamics (CFD) model of a 2.0L GM Ecotec engine cylinder, modified for HCCI combustion, was developed using Converge. Large Eddy Simulations (LES) were combined with detailed chemical kinetics for simulating the combustion process. Twenty consecutive cycles were simulated and the results were compared with individual cycle data of 300 consecutive experimental cycles. A verification approach based on the LES quality index indicated that this modeling framework can resolve more than 80% of the kinetic energy of the working fluid in the combustion chamber at the pre-ignition region. Lower cyclic variability was predicted by the LES model compared to the experiments. This difference is attributed to the resolution of the sub-grid velocity field, time averaging of the intake manifold pressure boundary conditions, and different variability in the equivalence ratio compared to the experimental data. Combustion phasing of each cycle was found to depend primarily on the bulk cylinder temperature, which agrees with established findings in the literature. Large cyclic variability of turbulent mixing and spatial distribution of temperature was predicted. However, both of these parameters were found to have a small effect on the cyclic variability of combustion phasing.
International Journal of Engine Research | 2018
Yingcong Zhou; Aimilios Sofianopoulos; Benjamin Lawler; Sotirios Mamalis
A reciprocating engine without a crank-slider mechanism is called a free-piston engine. If the piston is directly connected to a linear alternator, it is called a free-piston linear alternator. Free-piston engines and free-piston linear alternators have the potential to offer solutions for future hybrid electric vehicles and stationary power generation, by enabling direct conversion of mechanical energy to electricity. They benefit from reduced friction losses compared to conventional engines and can have variable compression ratio, which enables combustion control and optimization. Their widespread application has been limited by the necessity for high-speed control strategies. However, their operating characteristics can provide high efficiency, especially when used with low temperature combustion strategies. Low temperature combustion combines the high thermal efficiency of diesel engines, with the low soot emissions of spark-ignition engines, and low NO x emissions because of low burned gas temperatures. This article provides a comprehensive review of free-piston engine technology, with a focus on advanced combustion processes and their potential for use in future powertrain systems.
Frontiers in Mechanical Engineering | 2018
Mozhgan Rahimi Boldaji; Aimilios Sofianopoulos; Sotirios Mamalis; Benjamin Lawler
There is continuously growing interest in renewable biofuels for combustion engines to help reduce transportation energy consumption. In the present work, ethanol and a Primary Reference Fuel (PRF) were studied in an advanced LTC concept using CFD. A split injection strategy was used where the majority of the fuel was injected early during the intake stroke to create a well-mixed charge, while a portion of the charge was direct injected closer to ignition to induce forced thermal and equivalence ratio stratification in a strategy similar to partial fuel stratification (PFS). This way, the combustion process in LTC can be better controlled by staggering the autoignition process through mixture stratification. The unique characteristics of ethanol, such as its high latent heat of vaporization and reduced ϕ-sensitivity, result in unique features for a PFS-style advanced LTC mode, explored in this paper. A 3D CFD model with detailed chemistry was implemented in CONVERGE. The results showed that for both ethanol and PRF fuels, a split direct injection strategy lowers the peak heat release rate and elongates the combustion process compared to a single early direct injection due to the increased stratification. However, this effect was more pronounced for ethanol compared to PRF90 due to its higher latent heat of vaporization and reduced ϕ-sensitivity. For a 60%-40% split injection, the burn duration increased by 118% for ethanol and 91.6% for PRF90. The temperature, equivalence ratio, and OH mass fraction distributions illustrated that ethanol is primarily temperature-sensitive, while PRF90 shows a degree of ϕ-sensitivity in conjunction with temperature-sensitivity. The split direct injection of fuel creates an equivalence ratio and temperature distribution that are coupled due to the latent heat of vaporization of the fuel. For the PRF, these two effects are competing; whereas for the ethanol, the autoignition event is dictated by the thermal gradients since the fuel has a higher latent heat of vaporization and is not as ϕ-sensitive. Therefore, a PFS-style injection strategy is able to elongate the heat release rates more significantly with ethanol compared to a PRF.
Journal of Renewable and Sustainable Energy | 2015
Devinder Mahajan; David J. Tonjes; Sotirios Mamalis; Rebecca Boudreaux; Julia Hasty; Xin Danhui; Zhao Youcai; Cao Jianglin; Zhao Wentao; Chai Xiaoli
In keeping with the Energy and Environment theme of the EcoPartnership program, the Stony Brook-Tongji collaboration is addressing greenhouse gas emissions from landfills, one of the most critical issues of our time. Tongji is developing a model that can significantly improve the accuracy of emissions estimates, while Stony Brook is perfecting an innovative technology to economically removal impurities and produce a clean fuel for transportation, heating, or electricity generation. The environmental impact of the process being developed under this collaboration versus releasing fugitive gases is noted. By the culmination of this partnership, both sides have developed economical pathways to effectively utilize fugitive gases and commercialized technologies for transportation use and power generation for offering in both countries.
Applied Thermal Engineering | 2017
Benjamin Lawler; Sotirios Mamalis; Satyum Joshi; Joshua Lacey; Orgun A. Guralp; Paul M. Najt
Applied Thermal Engineering | 2017
Aimilios Sofianopoulos; Yingcong Zhou; Benjamin Lawler; Sotirios Mamalis