The Experts below are selected from a list of 237 Experts worldwide ranked by ideXlab platform
A. Stefanopoulou - One of the best experts on this subject based on the ideXlab platform.
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Control of charge dilution in turbocharged diesel engines via Exhaust Valve timing
Proceedings of the 2003 American Control Conference 2003., 2003Co-Authors: H. Yilmaz, A. StefanopoulouAbstract:Stringent constraints in oxides of nitrogen (NOx) and particulate emission require high levels of Exhaust gas recirculation. In this paper we employ a Variable Valve Timing methodology that in steady-state achieves large levels of internal Exhaust Gas Recirculation (iEGR) or charge dilution in Diesel engines. We develop a crankangle based dynamic nonlinear model of a six-cylinder 12 liter turbocharged (TC) Diesel engine. This model captures the transient interactions between VVT actuation, the turbocharger dynamics, and the cylinder-to-cylinder breathing characteristics. Low order linear multi-input multi-output (MIMO) models are then identified using cycle-sampled or -averaged data from the higher order non-linear model. A model-based controller is designed that varies Exhaust Valve Closing (EVC) to maximize the internal Exhaust gas recirculation under air-to-fuel ratio (AFR) constraints during transient fueling demands. The closed-loop controller is based on tracking optimal and achievable set-points of burned gas fraction. Simulation results are shown on the full order model.
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Torque management of engines with variable cam timing
IEEE Control Systems Magazine, 1998Co-Authors: M. Jankovic, F. Frischmuth, A. Stefanopoulou, J.a. CookAbstract:This paper describe the variable cam timing (VCT) system which addresses both the drivability and emission performance by utilising an electric hydraulic mechanism to rotate the camshaft relative to the crankshaft in order to retard the cam timing with respect to the intake and Exhaust strokes of the engine. By retarding the Exhaust Valve Closing further into the intake stroke, more Exhaust gas is drawn into the cylinder providing internal Exhaust gas recirculation. In this manner, the amount of residual gas trapped in the cylinder at the end of the Exhaust stroke is controlled by cam timing, suppressing NOx formation and reducing the pumping losses. Furthermore, this residual contains some unburned hydrocarbons; consequently, retaining it in the cylinder through two combustion cycles also reduces hydrocarbon emissions. In addition to the reduction of NOx and HC emissions, variable cam timing permits the engine designer to optimize cam timing over a wide range of engine operating conditions.
Hua Zhao - One of the best experts on this subject based on the ideXlab platform.
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effect of air dilution and effective compression ratio on the combustion characteristics of a hcci homogeneous charge compression ignition engine fuelled with n butanol
Energy, 2015Co-Authors: Bangquan He, Hua ZhaoAbstract:Biobutanol, i.e. n-butanol, is a promising biofuel of internal combustion engines. In this work, HCCI (homogeneous charge compression ignition) operation was achieved on a single cylinder four-stroke n-butanol engine through altering EVC (Exhaust Valve Closing) timings and/or IVC (intake Valve Closing) timings when the amount of fuel injected in a cycle was fixed. To retard HCCI autoignition timing, the effect of air dilution (excess air) and ECR (effective compression ratio) on combustion event was investigated. The results show that air dilution and the decrease in ECR can retard the autoignition timing of n-butanol and effectively decrease the MPRR (maximum pressure rise rate) of the HCCI engine. However, the delayed autoignition timing caused by diluted air is restricted by combustion instability. Furthermore, in the case of air dilution, the indicated thermal efficiency is higher and the temperature at IVC timing is lower while the in-cylinder temperature to initiate autoignition is higher compared with that of decreased ECR. In addition, air dilution is more effective in reducing the MPRR, but leads to longer combustion duration as compared to decreased ECR.
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Comparison of combustion characteristics of n-butanol/ethanol-gasoline blends in a HCCI engine.
Energy Conversion and Management, 2015Co-Authors: Mao-bin Liu, Hua ZhaoAbstract:Abstract As a sustainable biofuel, n-butanol can be used in conventional spark ignition (SI) and compression ignition (CI) engines in order to reduce the dependence on fossil fuel. Homogeneous charge compression ignition (HCCI) is a novel combustion to improve the thermal efficiency of conventional SI engines at part loads. To understand the effect of alcohol structure on HCCI combustion under stoichiometric conditions highly diluted by Exhaust gases, the combustion characteristics of n-butanol, ethanol and their blends with gasoline were investigated on a single cylinder port fuel injection gasoline engine with fixed intake/Exhaust Valve lifts at the same operating conditions in this study. The results show that autoignition timing for alcohol–gasoline blends is dependent on alcohol types and its concentration in the blend, engine speed and intake Valve opening (IVO)/Exhaust Valve Closing (EVC) timing. In the operating conditions with the residual gases more than 38% by mass in the mixture, alcohol–gasoline blends autoignite more easily than gasoline. Autoignition timing for n-butanol–gasoline blend is earlier than that for ethanol–gasoline blend with the same alcohol volume fraction at 1500 rpm in most cases while the autoignition timings for the blends with alcohol are relatively close at 2000 rpm at the same IVO/EVC timing. Combustion stability is improved with advanced EVC timing at a fixed IVO timing, which is benefit for the improvement in the thermal efficiency in the case of alcohol–gasoline blends. In addition, n-butanol–gasoline blends autoignite earlier than their ethanol–gasoline counterparts with identical oxygen mass content in the blend at the same IVO/EVC timings regardless of engine speeds. For alcohol–gasoline blends, the effect of IVO/EVC timing on the thermal efficiency of the HCCI engine is dependent on autoignition timing, fuel types and engine speeds. However, advanced autoignition timing for the blends with alcohol worsens the thermal efficiency of the HCCI engine in most cases.
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Combustion and emission characteristics of a HCCI engine fuelled with n-butanol–gasoline blends
Fuel, 2013Co-Authors: Mao-bin Liu, Jie Yuan, Hua ZhaoAbstract:Biobutanol, i.e. n-butanol, is a promising alternative fuel or fuel blend to gasoline to reduce the consumption of fossil fuel and carbon dioxide emissions from spark ignition (SI) and homogeneous charge compression ignition (HCCI), also known as controlled autoignition (CAI), engines. In this work, investigation was conducted on a single cylinder port fuel injection four-stroke HCCI/CAI engine fuelled with gasoline (Bu0), the blend containing 30% n-butanol and 70% gasoline by volume (Bu30), and pure n-butanol (Bu100). The HCCI/CAI operation was achieved by the negative Valve overlap strategy through variable Exhaust and intake Valve timing and lift devices. The results show that independent of engine speeds at a given Exhaust Valve Closing (EVC) timing, the onset of the autoignition occurs earlier and combustion duration becomes shorter when an increasing amount of n-butanol is used in place of gasoline. The increase in the engine speed also advances the autoignition timing. However, indicated mean effective pressure (IMEP) decreases with increasing n-butanol in the blends and engine speeds. Furthermore, the effect of n-butanol on the emissions was studied, including oxides of nitrogen, formaldehyde, acetaldehyde, ethanol and aromatics in the engine Exhaust.
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Study on spark assisted compression ignition (SACI) combustion with positive Valve overlap at medium–high load
Applied Energy, 2013Co-Authors: Hui Xie, Tao Chen, Xinyan Wang, Hua ZhaoAbstract:The spark-assisted compression ignition (SACI) is widely used to expand the high load limit of homogeneous charge compression ignition (HCCI), as it can reduce the high heat release rate effectively while partially maintain the advantage of high thermal efficiency and low NOx emission simultaneously. This research is focused on the SACI combustion using positive Valve overlap (PVO) strategy to optimize the gasoline engine performance at medium–high load. The influences of PVO configurations on gas exchange and combustion process are investigated and analyzed, based on the classification through Exhaust gas re-breathing way. It is shown that the PVO formed by late Exhaust Valve Closing (LEVC) is beneficial to achieve higher iEGR and higher inhomogeneous in-cylinder distribution than that formed by early intake Valve opening (EIVO). Compared with EIVO strategy, the SACI combustion employing LEVC strategy is apt to achieve a relatively high in-cylinder thermal state but with deteriorated pumping loss. The results also reveal that the load of SACI combustion is mainly controlled by PVO and eEGR, and affected by the combustion timing, under stoichiometric operating condition. Within the acceptable combustion stability range, small PVO combined with high eEGR is recommended for better fuel economy at the same engine load. The rules of adjusting SACI combustion with PVO are also concluded, according to the analysis of ideal demand and actual management of iEGR and eEGR. Based on that, the fuel efficient strategy for SACI combustion at medium–high load is identified. Using the optimized PVO strategy, stable SACI combustion is achieved in a wider load range, with significant improvements on fuel economy, pumping loss and NOx emission.
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Understanding the infiuence of Valve timings on controlled autoignition combustion in a four-stroke port fuel injection engine
Proceedings of the Institution of Mechanical Engineers Part D: Journal of Automobile Engineering, 2005Co-Authors: Li Cao, Hua Zhao, Xi Jiang, Navin KalianAbstract:Controlled autoignition (CAI) combustion, also known as homogeneous charge compression ignition (HCCI), was achieved through the negative Valve overlap approach by using small-lift camshafts. Three-dimensional multicycle engine simulations were carried out in order better to understand the effects of variable intake Valve timings on the gas exchange process, mixing quality, CAI combustion, and pollutant formation in a four-stroke port fuel injection (PFI) gasoline engine. Full engine cycle simulation, including complete gas exchange and combustion processes, was carried out over several cycles in order to obtain the stable cycle for analysis. The combustion models used in the present study are a modified shell ignition model and a laminar and turbulent characteristic time model, which can take high residual gas fraction into account. After the validation of the model against experimental data, investigations of the effects of variable intake Valve timing strategies on the CAI combustion process were carried out. These analyses show that the intake Valve opening (WO) and intake Valve Closing (IVC) timings have a strong influence on the gas exchange and mixing processes in the cylinder, which in turn affect the engine performance and emissions. Symmetric IVO timing relative to Exhaust Valve Closing (EVC) timing tends to produce a more stratified mixture, earlier ignition timing, and localized combustion, and hence higher NO, and lower unburned HC and CO emissions, whereas retarded WO leads to faster mixing, a more homogeneous mixture, and uniform temperature distribution.
H. Yilmaz - One of the best experts on this subject based on the ideXlab platform.
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Control of Charge Dilution in Turbocharged Diesel Engines via Exhaust Valve Timing
Journal of Dynamic Systems Measurement and Control, 2004Co-Authors: H. Yilmaz, Anna G. StefanopoulouAbstract:In this paper we extend an existing crank angle resolved dynamic nonlinear model of a six-cylinder 12 l turbocharged (TC) Diesel engine with Exhaust Valve Closing (EVC) variability. Early EVC achieves a high level of internal Exhaust gas recirculation (iEGR) or charge dilution in Diesel engines, and thus reduces generated oxides of nitrogen (NOx). This model is validated in steady-state conventional (fixed EVC) engine operating points. It is expected to capture the transient interactions between EVC actuation, the turbocharger dynamics, and the cylinder-to-cylinder breathing characteristics, although this has not been explicitly validated due to lack of hardware implementation. A nominal low order linear multi-input multi-output model is then identified using cycle-sampled or cycle-averaged data from the higher order nonlinear simulation model. Various low-order controllers that vary EVC to maximize the steady-state iEGR under air-to-fuel ratio (AFR) constraints during transient fueling demands are suggested based on different sensor sets. The difficulty in the control tuning arises from the fact that the EVC affects both the AFR and engine torque requiring coordination of fueling and EVC. Simulation results are shown on the full order model.
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Control of charge dilution in turbocharged diesel engines via Exhaust Valve timing
Proceedings of the 2003 American Control Conference 2003., 2003Co-Authors: H. Yilmaz, A. StefanopoulouAbstract:Stringent constraints in oxides of nitrogen (NOx) and particulate emission require high levels of Exhaust gas recirculation. In this paper we employ a Variable Valve Timing methodology that in steady-state achieves large levels of internal Exhaust Gas Recirculation (iEGR) or charge dilution in Diesel engines. We develop a crankangle based dynamic nonlinear model of a six-cylinder 12 liter turbocharged (TC) Diesel engine. This model captures the transient interactions between VVT actuation, the turbocharger dynamics, and the cylinder-to-cylinder breathing characteristics. Low order linear multi-input multi-output (MIMO) models are then identified using cycle-sampled or -averaged data from the higher order non-linear model. A model-based controller is designed that varies Exhaust Valve Closing (EVC) to maximize the internal Exhaust gas recirculation under air-to-fuel ratio (AFR) constraints during transient fueling demands. The closed-loop controller is based on tracking optimal and achievable set-points of burned gas fraction. Simulation results are shown on the full order model.
Ock Teack Lim - One of the best experts on this subject based on the ideXlab platform.
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Erratum to “Effective release energy, residual gas, and engine emission characteristics of a V-twin engine with various Exhaust Valve Closing timings”
Journal of Mechanical Science and Technology, 2020Co-Authors: Nguyen Xuan Khoa, Ock Teack LimAbstract:There is one correction to make to the original article. Acknowledgments should be corrected as follows: This research was financially supported by the Centre for Environmentally Friendly Vehicle as the Global Top Project of KMOE (2016002070009, Development of Engine System and Adapting Vehicle for Model 110cc and 300cc Correspond to EURO-5 Emission). This research was financially supported by the Energy Technology Development Project of the Korea Energy Technology Evaluation and Planning (20182010106370, Demonstration Research Project of Clean Fuel DME Engine for Fine Dust Reduction), Republic of Korea.
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Effective release energy, residual gas, and engine emission characteristics of a V-twin engine with various Exhaust Valve Closing timings
Journal of Mechanical Science and Technology, 2020Co-Authors: Nguyen Xuan Khoa, Ock Teack LimAbstract:There is one correction to make to the original article. Acknowledgments should be corrected as follows: This research was financially supported by the Centre for Environmentally Friendly Vehicle as the Global Top Project of KMOE (2016002070009, Development of Engine System and Adapting Vehicle for Model 110cc and 300cc Correspond to EURO-5 Emission). This research was financially supported by the Energy Technology Development Project of the Korea Energy Technology Evaluation and Planning (20182010106370, Demonstration Research Project of Clean Fuel DME Engine for Fine Dust Reduction), Republic of Korea.
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Effective release energy, residual gas, and engine emission characteristics of a V-twin engine with various Exhaust Valve Closing timings
Journal of Mechanical Science and Technology, 2020Co-Authors: Nguyen Xuan Khoa, Ock Teack LimAbstract:This article presents a study for determining the effective release energy, residual gas, and peak firing pressure rise of a V-twin engine with various Exhaust Valve timings. The effect of Exhaust Valve Closing timing (EVCT) on effective release energy, peak firing pressure rise, residual gas, engine performance, and engine emission are completely discussed for the first time. Results show that EVCT had a significant effect on residual gas, peak firing pressure rise, and effective release energy. When the EVCT increased from 10 deg to 90 deg ATDC, the residual gas ratio increased from 0.2 % to 1.7 %. The peak firing pressure rise and effective release energy increased until reaching maximum values of 4.59 bar/deg and 0.64 kJ, respectively, and decreased as the EVCT continued to increase. The engine performed at its optimal efficiency when the EVCT was at 50 deg ATDC. The maximum brake mean effective pressure was 7.74 bar, the minimum brake specific fuel consumption was 399.35 g/kWh, and the maximum engine brake torque was 16.92 Nm. The minimum NO_x emission was 7.54 g/kWh at a 30 deg ATDC of EVCT.
Kangyao Deng - One of the best experts on this subject based on the ideXlab platform.
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Thermodynamic analysis of the turbocharged marine two-stroke engine cycle with different scavenging air control technologies
Energy, 2020Co-Authors: Sipeng Zhu, Hao Yuan, Kangyao DengAbstract:Abstract Scavenging air control has been recognized as a practical approach to optimizing the marine two-stroke engine performance under off-design conditions. This paper aims at providing a comprehensive comparison of different tuning technologies from thermodynamic perspectives. A new theoretical model for the marine two-stroke diesel engine is first built with all assumptions of an air-standard cycle relaxed. Thermodynamic characteristics of the two-stroke engine cycle integrating the turbocharged scavenging process are then studied, followed by parametric studies of different scavenging air control methods. The results show that there exists an optimal Exhaust Valve Closing timing to minimize the so-called “Miller loss” with the high-pressure tuning. Despite similar fuel saving potential of 2.5 g/kWh is observed at low to medium loads, the high-pressure tuning is superior to the Exhaust gas bypass tuning because of a lower engine thermal load. The power turbine bypass appears to be the best solution when the engine frequently operates at loads higher than 60%, while the sequential turbocharging system shows better performance at engine loads lower than 50%. Thus, factors including the engine thermal and mechanical limitations, ship’s operational profile, cost and package should be considered for selecting the optimal scavenging tuning method in a practical case.
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An integrated model for negative Valve overlap early injection HCCI combustion
Journal of the Energy Institute, 2014Co-Authors: Yong Gui, Kangyao Deng, Lei Shi, Youcheng SunAbstract:Abstract Using Exhaust top dead center injection (ETCI) mode to realize homogeneous charge compression ignition (HCCI) combustion would cause fuel wall wetting and combustion efficiency reduction, and there is no effective one-dimension simulation model to calculate and analyze the fuel wall wetting and evaporation process. In the research, a new type of integrated model is developed for the new application, HCCI combustion simulation based on ETCI mode. The model includes the following sub-models: fuel injection model, impingement model, film evaporation model, and combustion model. The improved Hiroyasu model and the Bai's model are coupled with homogenous combustion model and film evaporation model to calculate impingement fuel evaporation. The developed model is validated by experiment in a single cylinder diesel engine with ETCI combustion mode. The simulation and experimental results show that, film evaporation is mainly related to cylinder gas temperature and wall temperature, and there is an evident two stage heating process. The cumulate heat release rate is linear with Exhaust Valve Closing (EVC) timing and wall temperature. The burned fuel fraction increases by 6 percent as the EVC timing advances by every 10 °CA, and increases by 4 percent as the wall temperature increases by every 50 K. The cumulate heat release rate decreases with the increase of boosting pressure, and the higher the boosting pressure, the smaller the decrease degree of cumulate heat release rate is.