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Hua Zhao - One of the best experts on this subject based on the ideXlab platform.
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High load performance and combustion analysis of a four-Valve direct injection gasoline engine running in the two-stroke cycle
Applied Energy, 2015Co-Authors: Macklini Dalla Nora, Hua ZhaoAbstract:With the introduction of CO2 emissions legislation or fuel economy standards in Europe and many countries, significant effort is being made to improve spark ignition gasoline engines because of their dominant market share in passenger cars and potential for better fuel economy. Amongst several approaches, the engine downsizing technology has been adopted by the automotive companies as one of the most effective methods to reduce fuel consumption of gasoline engines. However, aggressive engine downsizing is constrained by excessive thermal and mechanical loads as well as knocking combustion and low speed pre-ignition (also known as super-knock). In order to overcome such difficulties, a gasoline direct injection single cylinder engine was modified to run under the two-stroke cycle by operating the intake and exhaust Valves around bottom dead centre (BDC) at every crankshaft revolution. The combustion products were scavenged by means of a reversed tumble flow of compressed air during the positive Valve overlap period at BDC. The engine output was determined by the charging and trapping efficiencies, which were directly influenced by the intake and exhaust Valve timings and boost pressures. In this research a Valve timing optimisation study was performed using a fully flexible Valve train unit, where the intake and exhaust Valve timings were advanced and retarded independently at several speeds and loads. A supercharger was used to vary the load by increasing the intake pressure. The effects of Valve timing and boost pressure in this two-stroke Poppet Valve engine were investigated by a detailed analysis of the gas exchange process and combustion heat release. Gaseous and smoke emissions were measured and analysed. The results confirmed that the two-stroke cycle operation enabled the indicated mean effective pressure to reach 1.2MPa (equivalent to 2.4MPa in a four-stroke cycle) with an in-cylinder pressure below 7MPa at an engine speed as low as 800rpm. The engine operation was limited by scavenging inefficiencies and short time available for proper air–fuel mixing at high speeds using the current fuel injector. The large amounts of hot residual gas trapped induced controlled auto-ignition combustion at high speeds, and thus the abrupt heat release limited higher loads.
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CAI combustion of gasoline and its mixture with ethanol in a 2-stroke Poppet Valve DI gasoline engine
Fuel, 2013Co-Authors: Yan Zhang, Hua Zhao, Mohammed Moore Ojapah, Alasdair CairnsAbstract:Controlled Auto Ignition (CAI), also known as Homogeneous Charge Compression Ignition (HCCI), is one of the most promising combustion technologies to reduce the fuel consumption and NOx emissions. Currently, CAI combustion is constrained at part load operation conditions because of misfire at low load and knocking combustion at high load, and the lack of effective means to control the combustion process. Extending its operating range including high load boundary towards full load and low load boundary towards idle in order to allow the CAI engine to meet the demand of whole vehicle driving cycles, has become one of the key issues facing the industrialisation of CAI/HCCI technology. Furthermore, this combustion mode should be compatible to different fuels, and can switch back to conventional spark ignition operation when necessary. In this paper, the CAI operation is demonstrated on a 2-stroke gasoline direct injection (GDI) engine equipped with a Poppet Valve train. The results shown that the CAI combustion can be readily achieved in the 2-stroke cycle of a Poppet Valve engine and the range of CAI combustion can be significantly extended compared to the 4-stroke cycle operation. In addition, the effects of ethanol concentration on 2-stroke CAI operational range, combustion process, emissions and efficiencies are studied and presented.
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measurement of short circuiting and its effect on the controlled autoignition or homogeneous charge compression ignition combustion in a two stroke Poppet Valve engine
Proceedings of the Institution of Mechanical Engineers Part D: Journal of Automobile Engineering, 2012Co-Authors: Yan Zhang, Hua ZhaoAbstract:Controlled autoignition or homogeneous charge compression ignition combustion in four-stroke spark ignition engines has been the subject of extensive research over the last decade. In order to exte...
Zhao H - One of the best experts on this subject based on the ideXlab platform.
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Experimental investigation of the air-fuel charging process in a four-Valve supercharged two-stroke cycle GDI engine
'Springer Science and Business Media LLC', 2019Co-Authors: Td ,metzka Lanzanova, Me ,santos Martins, Pr ,moreira Machado, Zhao HAbstract:Fuel consumption standards imposed in several countries for the next years have prompted the development of hybrid passenger cars with ever smaller internal combustion engines. In such powertrain, fuel consumption is as important as engine packaging and power density, so two-stroke engines may be an option due to their higher combustion frequency compared to four-stroke engines. Therefore, the present research investigates the air–fuel charging process of an overhead four-Valve direct injection supercharged engine operating in the two-stroke cycle. The optimum start of fuel injection was evaluated for commercial gasoline by means of indicated and combustion efficiencies where a trade-off was found between early and late fuel injections. By advancing the injection timing, more fuel was prone to short circuit to the exhaust during the Valve overlap, while late injections resulted in poor charge preparation. The gas exchange parameters, i.e. charging and trapping efficiencies, were obtained from seventy operating points running at fuel-rich conditions. The Benson–Brandham mixing-displacement scavenging model was then fit to the experimental data with a coefficient of determination better than 0.95. With such model, the air trapping and charging efficiencies could be estimated solely based on the scavenge ratio and exhaust lambda, regardless of the engine load, speed, or air/fuel ratio employed. Further twenty-five different lean-burn testing points were tested to certify the proposed methodology applied to the Poppet Valve two-stroke engine. The in-cylinder lambda was calculated and found different from the exhaust lambda due to mixing between burned gases and intake air during the scavenging process
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High load performance and combustion analysis of a four-Valve direct injection gasoline engine running in the two-stroke cycle
'Elsevier BV', 2015Co-Authors: Dalla Nora M, Zhao HAbstract:With the introduction of CO2 emissions legislation or fuel economy standards in Europe and many countries, significant effort is being made to improve spark ignition gasoline engines because of their dominant market share in passenger cars and potential for better fuel economy. Amongst several approaches, the engine downsizing technology has been adopted by the automotive companies as one of the most effective methods to reduce fuel consumption of gasoline engines. However, aggressive engine downsizing is constrained by excessive thermal and mechanical loads as well as knocking combustion and low speed pre-ignition (also known as super-knock). In order to overcome such difficulties, a gasoline direct injection single cylinder engine was modified to run under the two-stroke cycle by operating the intake and exhaust Valves around bottom dead centre (BDC) at every crankshaft revolution. The combustion products were scavenged by means of a reversed tumble flow of compressed air during the positive Valve overlap period at BDC. The engine output was determined by the charging and trapping efficiencies, which were directly influenced by the intake and exhaust Valve timings and boost pressures. In this research a Valve timing optimisation study was performed using a fully flexible Valve train unit, where the intake and exhaust Valve timings were advanced and retarded independently at several speeds and loads. A supercharger was used to vary the load by increasing the intake pressure. The effects of Valve timing and boost pressure in this two-stroke Poppet Valve engine were investigated by a detailed analysis of the gas exchange process and combustion heat release. Gaseous and smoke emissions were measured and analysed. The results confirmed that the two-stroke cycle operation enabled the indicated mean effective pressure to reach 1.2MPa (equivalent to 2.4MPa in a four-stroke cycle) with an in-cylinder pressure below 7MPa at an engine speed as low as 800rpm. The engine operation was limited by scavenging inefficiencies and short time available for proper air-fuel mixing at high speeds using the current fuel injector. The large amounts of hot residual gas trapped induced controlled auto-ignition combustion at high speeds, and thus the abrupt heat release limited higher loads.The Brazilian council for scientific and technological development (CNPq – Brasil
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Investigation of combustion, performance and emission characteristics of 2-stroke and 4-stroke spark ignition and CAI/HCCI operations in a DI gasoline
'Elsevier BV', 2014Co-Authors: Zhang Y, Zhao HAbstract:In order to develop more efficient and cleaner gasoline engines, a number of new engine operating strategies have been proposed and researched on different engines, including the spark ignition (SI) and controlled autoignition (CAI) or HCCI in both 2-stroke and 4-stroke cycles in a Poppet Valve engine. In this work, a single cylinder direct injection gasoline engine equipped with an electro-hydraulic Valve-train system has been commissioned and used to achieve seven different operating modes, including: 4-stroke throttle-controlled SI, 4-stroke intake Valve throttled SI, 4-stroke positive Valve overlap SI, 4-stroke negative Valve overlap CAI, 4-stroke exhaust rebreathing CAI, 2-stroke CAI and 2-stroke SI. Their performance and emission characteristics were analysed and compared at a typical engine calibration operating condition of 1500. rpm and 3.6. bar IMEP in 4-stroke or 1.8. bar IMEP in 2-stroke. Results show that 4-stroke positive Valve overlap SI, 4-stroke NVO CAI and exhaust rebreathing CAI modes have better fuel economy and lower NOx emissions than the conventional throttled 4-stroke SI operation. The 2-stroke CAI operation was found to produce higher combustion efficiency and lower ISFC but lower brake efficiency than the 4-s-stroke operations at the same power output due to the supercharger's efficiency. But, at the same IMEP as the 4-stroke operation, the 2-stroke CAI operation results in 29% reduction in BSFC, indicating its potential synergy with highly downsized direct injection gasoline engines for much better fuel economy and performance.The Engineering and Physical Sciences Research Council (EPSRC), UK, and the technical support to the engine control by Ricardo UK
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CAI combustion of gasoline and its mixture with ethanol in a 2-stroke Poppet Valve DI gasoline engine
'Elsevier BV', 2013Co-Authors: Zhang Y, Zhao H, Ojapah M, Cairns AAbstract:This article has been made available through the Brunel Open Access Publishing Fund.Controlled Auto Ignition (CAI), also known as Homogeneous Charge Compression Ignition (HCCI), is one of the most promising combustion technologies to reduce the fuel consumption and NOx emissions. Currently, CAI combustion is constrained at part load operation conditions because of misfire at low load and knocking combustion at high load, and the lack of effective means to control the combustion process. Extending its operating range including high load boundary towards full load and low load boundary towards idle in order to allow the CAI engine to meet the demand of whole vehicle driving cycles, has become one of the key issues facing the industrialisation of CAI/HCCI technology. Furthermore, this combustion mode should be compatible to different fuels, and can switch back to conventional spark ignition operation when necessary. In this paper, the CAI operation is demonstrated on a 2-stroke gasoline direct injection (GDI) engine equipped with a Poppet Valve train. The results shown that the CAI combustion can be readily achieved in the 2-stroke cycle of a Poppet Valve engine and the range of CAI combustion can be significantly extended compared to the 4-stroke cycle operation. In addition, the effects of ethanol concentration on 2-stroke CAI operational range, combustion process, emissions and efficiencies are studied and presented. © 2013 Elsevier Ltd. All rights reserved
Macklini Dalla Nora - One of the best experts on this subject based on the ideXlab platform.
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High load performance and combustion analysis of a four-Valve direct injection gasoline engine running in the two-stroke cycle
Applied Energy, 2015Co-Authors: Macklini Dalla Nora, Hua ZhaoAbstract:With the introduction of CO2 emissions legislation or fuel economy standards in Europe and many countries, significant effort is being made to improve spark ignition gasoline engines because of their dominant market share in passenger cars and potential for better fuel economy. Amongst several approaches, the engine downsizing technology has been adopted by the automotive companies as one of the most effective methods to reduce fuel consumption of gasoline engines. However, aggressive engine downsizing is constrained by excessive thermal and mechanical loads as well as knocking combustion and low speed pre-ignition (also known as super-knock). In order to overcome such difficulties, a gasoline direct injection single cylinder engine was modified to run under the two-stroke cycle by operating the intake and exhaust Valves around bottom dead centre (BDC) at every crankshaft revolution. The combustion products were scavenged by means of a reversed tumble flow of compressed air during the positive Valve overlap period at BDC. The engine output was determined by the charging and trapping efficiencies, which were directly influenced by the intake and exhaust Valve timings and boost pressures. In this research a Valve timing optimisation study was performed using a fully flexible Valve train unit, where the intake and exhaust Valve timings were advanced and retarded independently at several speeds and loads. A supercharger was used to vary the load by increasing the intake pressure. The effects of Valve timing and boost pressure in this two-stroke Poppet Valve engine were investigated by a detailed analysis of the gas exchange process and combustion heat release. Gaseous and smoke emissions were measured and analysed. The results confirmed that the two-stroke cycle operation enabled the indicated mean effective pressure to reach 1.2MPa (equivalent to 2.4MPa in a four-stroke cycle) with an in-cylinder pressure below 7MPa at an engine speed as low as 800rpm. The engine operation was limited by scavenging inefficiencies and short time available for proper air–fuel mixing at high speeds using the current fuel injector. The large amounts of hot residual gas trapped induced controlled auto-ignition combustion at high speeds, and thus the abrupt heat release limited higher loads.
Rapetto Nicola - One of the best experts on this subject based on the ideXlab platform.
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Mixture formation analysis in a direct-injection NG SI engine under different injection timings
'Elsevier BV', 2015Co-Authors: Baratta Mirko, Rapetto NicolaAbstract:This paper investigates into the mixture formation in a direct injection, turbocharged, spark-ignition, CNG engine. The engine features a pent-roof combustion chamber, a bowl in piston and an outward-opening Poppet Valve injector, which is located centrally in the chamber dome. In the last few years, many studies have been conducted focusing on direct injection natural gas engines, and the end-of-injection timing has been identified as the main parameter affecting the quality and completeness of the mixture formation process. This paper aims at contributing to the progress of this research field, by means of the presentation and discussion of a large number of experimental and numerical data. The results obtained from the authors’ CFD model, which has been developed and validated within the InGAS Collaborative Project of the EC, are in fact introduced and correlated to the outcomes of the experimental activity done by AVL GmbH, Graz, as part of the same research project. This synergy allowed a deep understanding of the mixture formation process, over a wide range of operating conditions. As a matter of fact, the mixture formation process in a direct injection gaseous-fuel engine differs significantly from direct-injection engines fuelled by gasoline. In fact, the gas jet momentum is lower, reducing the penetration, and the mixture formation strongly relies on the charge motion generated during the intake stroke. More precisely, the work presented in this paper showed that several factors exert an influence on the fuel-air mixing process: jet shape, interaction with piston and/or with the charge motion, and time available for mixing between the end-of-injection and the spark timing, and these may combine differently depending on the specific working point. On an average, at low load and low-medium speeds, the injection should better take place during the second part of the induction stroke. On the other hand, at high speed or high load the injection timing needs to be advanced till around 250°-300° CA degrees before firing TDC, in order to increase the time available for mixing as much as possible
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Mixture formation analysis in a direct-injection NG SI engine under different injection timings
Elsevier Ltd, 2015Co-Authors: Baratta Mirko, Rapetto NicolaAbstract:This paper investigates into the mixture formation in a direct injection, turbocharged, spark-ignition, CNG engine. The engine features a pent-roof combustion chamber, a bowl in piston and an outward-opening Poppet Valve injector, which is located centrally in the chamber dome. In the last few years, many studies have been conducted focusing on direct injection natural gas engines, and the end-of-injection timing has been identified as the main parameter affecting the quality and completeness of the mixture formation process. This paper aims at contributing to the progress of this research field, by means of the presentation and discussion of a large number of experimental and numerical data. The results obtained from the authors' CFD model, which has been developed and validated within the InGAS Collaborative Project of the EC, are in fact introduced and correlated to the outcomes of the experimental activity done by AVL GmbH, Graz, as part of the same research project. This synergy allowed a deep understanding of the mixture formation process, over a wide range of operating conditions. As a matter of fact, the mixture formation process in a direct injection gaseous-fuel engine differs significantly from direct-injection engines fuelled by gasoline. In fact, the gas jet momentum is lower, reducing the penetration, and the mixture formation strongly relies on the charge motion generated during the intake stroke. More precisely, the work presented in this paper showed that several factors exert an influence on the fuel-air mixing process: jet shape, interaction with piston and/or with the charge motion, and time available for mixing between the end-of-injection and the spark timing, and these may combine differently depending on the specific working point. On an average, at low load and low-medium speeds, the injection should better take place during the second part of the induction stroke. On the other hand, at high speed or high load the injection timing needs to be advanced till around 250°-300° CA degrees before firing TDC, in order to increase the time available for mixing as much as possibl
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Fluid-dynamic and numerical aspects in the simulation of direct CNG injection in spark-ignition engines
Elsevier, 2014Co-Authors: Baratta Mirko, Rapetto NicolaAbstract:This paper presents a detailed discussion on the numerical simulation of the underexpanded gas efflux from an outward-opening Poppet-Valve injector into an engine combustion chamber. The aim of the paper is to optimize the numerical simulation strategy for direct gas injection, in view of its application to internal combustion (IC) engines. In the first part of the paper, the widely studied case of a two-dimensional compressible flow is examined, and the main guidelines for the development of an effective numerical model for compressed natural gas (CNG) direct injection simulation are given, with specific reference to IC engines. The second part of the paper is devoted to the description of the numerical model developed and validated by the authors within the Star-CD environment, which is characterized by the presence of two distinct meshes. The first is built manually and covers the region surrounding the injector exit, whereas the second one covers most of the engine chamber and is built using the Es-ICE tool. A careful grid-independence study has been carried out in both the first and second part of the paper, and the influence of the spatial discretization of the convective fluxes has been discussed as well. The analyses have shown that a resolution of 40 cells in the nozzle height should be adopted to describe the typical phenomena that characterize an underexpanded free jet, unless a second order scheme can be implemented. However, as far as the simulation of the jet penetration time-history and its mixing with the surrounding air is concerned, sufficiently accurate results can also be obtained by using 20 cells per nozzle diameter and the first-order upwind scheme. As for the direct injection engine model, 16 cells across the nozzle lift represent a good compromise between accuracy and reliability of the results and the required computational time. The model has been validated with the support of experimental PLIF images in an optical-access engine, and has shown overall good accuracy and reliability, thus suggesting it is suitable for mixture formation analysi
Alasdair Cairns - One of the best experts on this subject based on the ideXlab platform.
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CAI combustion of gasoline and its mixture with ethanol in a 2-stroke Poppet Valve DI gasoline engine
Fuel, 2013Co-Authors: Yan Zhang, Hua Zhao, Mohammed Moore Ojapah, Alasdair CairnsAbstract:Controlled Auto Ignition (CAI), also known as Homogeneous Charge Compression Ignition (HCCI), is one of the most promising combustion technologies to reduce the fuel consumption and NOx emissions. Currently, CAI combustion is constrained at part load operation conditions because of misfire at low load and knocking combustion at high load, and the lack of effective means to control the combustion process. Extending its operating range including high load boundary towards full load and low load boundary towards idle in order to allow the CAI engine to meet the demand of whole vehicle driving cycles, has become one of the key issues facing the industrialisation of CAI/HCCI technology. Furthermore, this combustion mode should be compatible to different fuels, and can switch back to conventional spark ignition operation when necessary. In this paper, the CAI operation is demonstrated on a 2-stroke gasoline direct injection (GDI) engine equipped with a Poppet Valve train. The results shown that the CAI combustion can be readily achieved in the 2-stroke cycle of a Poppet Valve engine and the range of CAI combustion can be significantly extended compared to the 4-stroke cycle operation. In addition, the effects of ethanol concentration on 2-stroke CAI operational range, combustion process, emissions and efficiencies are studied and presented.