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Experimental Investigation of Combustion and Emission Characteristics of Stoichiometric Stratified Flame Ignited (SFI) Hybrid Combustion in a 4-Stroke PFI/DI Gasoline Engine

Brunel University-Hua Zhao
China North Engine Research Institute-Yan Zhang, Yufeng Li, Honglin Bai
Published 2019-04-02 by SAE International in United States
Controlled Auto-Ignition (CAI), also known as Homogeneous Charge Compression Ignition (HCCI), can improve the fuel economy of gasoline engines and simultaneously achieve ultra-low NOx emissions. However, the difficulty in combustion phasing control and violent combustion at high loads limit the commercial application of CAI combustion. To overcome these problems, stratified mixture, which is rich around the central spark plug and lean around the cylinder wall, is formed through port fuel injection and direct injection of gasoline. In this condition, rich mixture is consumed by flame propagation after spark ignition, while the unburned lean mixture auto-ignites due to the increased in-cylinder temperature during flame propagation, i.e., stratified flame ignited (SFI) hybrid combustion. The combustion and emissions characteristics in the SFI combustion were experimentally investigated in a naturally aspirated single-cylinder 4-stroke gasoline engine at medium-high loads when direct injection timing was kept at -60 °CA after top dead center and direct injection ratio was less than or equal to 0.4 at stoichiometry. The results show that advanced spark timing or decreased direct injection ratio alters the SFI…
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The Application of Controlled Auto-Ignition Gasoline Engines -The Challenges and Solutions

Brunel University-Hua Zhao
China North Engine Research Institute-Yan Zhang, Yufeng Li, Honglin Bai
Published 2019-04-02 by SAE International in United States
Controlled Auto-Ignition (CAI) combustion, also known as Homogeneous Charge Compression Ignition (HCCI), has the potential to simultaneously reduce the fuel consumption and nitrogen oxides emissions of gasoline engines. However, narrow operating region in loads and speeds is one of the challenges for the commercial application of CAI combustion to gasoline engines. Therefore, the extension of loads and speeds is an important prerequisite for the commercial application of CAI combustion. The effect of intake charge boosting, charge stratification and spark-assisted ignition on the operating range in CAI mode was reviewed. Stratified flame ignited (SFI) hybrid combustion is one form to achieve CAI combustion under the conditions of highly diluted mixture caused by the flame in the stratified mixture with the help of spark plug. CAI combustion in two-stroke gasoline engine can be used to enhance the torque of a four-stroke gasoline engine with the same displacement at the same indicated mean effective pressure. Poppet-valved two-stroke gasoline engines with normal valve lift and variable valve timing device, and uniflow two-stroke engine with gas exchange process completed by…
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Effects of Intake Port Structures and Valve Timings on the Scavenging Process in a Two-Stroke Poppet Valve Diesel Engine

China North Engine Research Institute-Wei Liu, Yan Zhang, Bo Yu, Yaozong Li, Ziyu Wang
Published 2019-04-02 by SAE International in United States
The two-stroke operation is one of the most effective approaches to significantly increase the torque and power of a 4-stroke engine without the necessary requirement of intensifying the engine. Scavenging process is one of the key factors determining the performance of the two-stroke engine. In this work, a structure of top entry intake ports with poppet valves was employed on a 2-stroke single cylinder diesel engine with the conventional horizontal intake ports replaced. By this way, the reversed tumble flows in the cylinder were formed during the intake process to improve the scavenging performance of 2-stroke operation. In the meanwhile, the effects of valve timings and intake port structures on scavenging processes were estimated respectively through the1D and 3D simulation of the gas exchange process.Results show that compared to the conventional horizontal intake port case, the reversed tumble flow created by the top-entry intake port led to a lower air short-circuiting rate and a higher scavenging efficiency. Furthermore, by advancing the exhaust valve opening the exhaust gas was discharged more sufficiently and the intake backflow…
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Simulation of the Effect of Intake Pressure and Split Injection on Lean Combustion Characteristics of a Poppet-Valve Two-Stroke Direct Injection Gasoline Engine at High Loads

Brunel University-Hua Zhao
China North Engine Research Institute-Yan Zhang, Yufeng Li, Honglin Bai
Published 2018-09-10 by SAE International in United States
Poppet-valve two-stroke gasoline engines can increase the specific power of their four-stroke counterparts with the same displacement and hence decrease fuel consumption. However, knock may occur at high loads. Therefore, the combustion with stratified lean mixture was proposed to decrease knock tendency and improve combustion stability in a poppet-valve two-stroke direct injection gasoline engine. The effect of intake pressure and split injection on fuel distribution, combustion and knock intensity in lean mixture conditions at high loads was simulated with a three-dimensional computational fluid dynamic software. Simulation results show that with the increase of intake pressure, the average fuel-air equivalent ratio in the cylinder decreases when the second injection ratio was fixed at 70% at a given amount of fuel in a cycle. With the increase of intake pressure, ignition timing advances, combustion duration slightly decreases first and then increases while the maximum pressure rise rate first increases and then drops. High intake pressure can prevent the occurrence of knock through decreased fuel-air equivalent ratio around the cylinder. The second injection timing can also influence combustion…
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The Reduction of Mechanical and Thermal Loads in a High-Speed HD Diesel Engine Using Miller Cycle with Late Intake Valve Closing

China North Engine Research Institute-Yan Zhang, Ziyu Wang, Honglin Bai, Chao Guo, Jinlong liu, Yufeng Li
Published 2017-03-28 by SAE International in United States
Mechanical load and thermal load are the two main barriers limiting the engine power output of heavy duty (HD) diesel engines. Usually, the peak cylinder pressure could be reduced by retarding combustion phasing while introducing the drawback of higher thermal load and exhaust temperature. In this paper, Miller cycle with late intake valve closing was investigated at high speed high load condition (77 kW/L) on a single cylinder HD diesel engine. The results showed the simultaneous reduction of mechanical and thermal loads. In the meanwhile, higher boosting pressure was required to compensate the Miller loss of the intake charge during intake and compression process. The combustion temperature, cylinder pressure, exhaust temperature and NOx emission were reduced significantly with Miller cycle at the operating condition. Furthermore, the combustion process, smoke number and fuel consumption were analysed.
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Engine Downsizing through Two-Stroke Operation in a Four-Valve GDI Engine

Brunel University London-Macklini Dalla Nora, Thompson Lanzanova, Yan Zhang, Hua Zhao
Published 2016-04-05 by SAE International in United States
With the introduction of CO2 emissions legislation in Europe and many countries, there has been extensive research on developing high efficiency gasoline engines by means of the downsizing technology. Under this approach the engine operation is shifted towards higher load regions where pumping and friction losses have a reduced effect, so improved efficiency is achieved with smaller displacement engines. However, to ensure the same full load performance of larger engines the charge density needs to be increased, which raises concerns about abnormal combustion and excessive in-cylinder pressure. In order to overcome these drawbacks a four-valve direct injection gasoline engine was modified to operate in the two-stroke cycle. Hence, the same torque achieved in an equivalent four-stroke engine could be obtained with one half of the mean effective pressure. A wet sump was employed to avoid the inherent lubrication and durability issues of conventional two-stroke engines, and the scavenging process was ensured via external boosting. The adoption of direct fuel injection removed the problem of fuel short-circuiting present in mixture scavenged engines. Several loads were tested…
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Application of Beamforming to Side Mirror Aeroacoustic Noise Optimization

FAW R&D Center-Lingzhi Li, Jun Li, Bingwu Lu, Yingjie Liu, Zhi Zhang, Hailong Cheng, Yan Zhang, Hangsheng Hou
Published 2016-04-05 by SAE International in United States
Excessive wind noise is one of the most complained problems by owners of new vehicles as evidenced by JD Power Initial Quality Study (IQS) in recent years. After the vehicle speed surpasses 100 km/h, wind noise is gradually becoming the dominant noise source. In an effort to reduce aeroacoustic noise level, Beamforming (BF) is a very effective noise source identification technique used during vehicle wind noise development phases. In this work, based on the planar BF methodology, a large semi-circle microphone array is designed in accordance with the desired resolution and dynamic range pertaining to actual noise source distribution on a typical passenger vehicle. Acoustic array calibration and mapping deformation correction are accomplished by multi-point source method, and the Doppler Effect due to wind is corrected by the location calibration method. The established system is applied to identifying the exterior noise sources on the driver-side of a passenger vehicle in the wind tunnel. The noise sources induced aerodynamically in the area of front wheel housing, rear wheel housing and side mirror are separated successfully. Furthermore,…
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Study on Subcritical/Supercritical Spray Characteristics of a Multi-Hole Gasoline Direct Injector

Tianjin University-Miao Zhang, Yiqiang Pei, Yi Liu, Yan Zhang
Published 2016-04-05 by SAE International in United States
Investigations using supercritical spray platform,which allows gasoline at low sub-critical state,subcritical state and supercritical state respectively,were made to demonstrate the Subcritical/ Supercritical Spray Characteristics of a Multi-Hole Gasoline Direct Injector.The experimental results show that the spray pattern and spray characteristics (i.e. spray penetration distance,spray area and spray perimeter) varied greatly under different state. In subcritical state,the spray characteristics of gasoline is similar to the phenomenon of "flash bfueling",appearing spray entrainment and spray collapse,then spray penetration distance and area drop significantly.In supercritical state,the six-hole gasoline spray is composed by the thick-core region and the thin-diffusion region,and Mach disk is observed at the outlet of the nozzle,then spray penetration distance and area increases sharply. In addition,by comparing the spray characteristics of six-hole and single-hole GDI injector,result shows the single-hole injector is more conducive to the development of supercritical gasoline.
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Investigation of Valve Timings on Lean Boost CAI Operation in a Two-stroke Poppet Valve DI Engine

Brunel University-Yan Zhang, Macklini DallaNora, Hua Zhao
Published 2015-09-01 by SAE International in United States
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. In order to take advantage of the inherent ability to retain a large and varied amount of residual at part-load condition and its potential to achieve extreme engine downsizing of a poppet valve engine running in the 2-stroke cycle, a single cylinder 4-valves camless direct injection gasoline engine has been developed and employed to investigate the CAI combustion process in the 2-stroke cycle mode. The CAI combustion is initiated by trapped residual gases from the adjustable scavenging process enabled by the variable intake and exhaust valve timings. In addition, the boosted intake air is used to provide the in-cylinder air/fuel mixture for maximum combustion efficiency. In this study, the lean boost operation has been implemented and results show that CAI combustion can be operated between a speed range from 800rpm to 3000rpm (limited by the speed of the camless system) and an IMEP range from 1.1bar to…
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Comparison of Performance, Efficiency and Emissions between Gasoline and E85 in a Two-Stroke Poppet Valve Engine with Lean Boost CAI Operation

Brunel University-Yan Zhang, Macklini Dalla Nora, Hua Zhao
Published 2015-04-14 by SAE International in United States
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. Most research on CAI/HCCI combustion operations have been carried out in 4-stroke gasoline engines, despite it was originally employed to improve the part-load combustion and emission in the two-stroke gasoline engine. However, conventional ported two-stroke engines suffer from durability and high emissions. In order to take advantage of the high power density of the two-stroke cycle operation and avoid the difficulties of the ported engine, systematic research and development works have been carried out on the two-stroke cycle operation in a 4-valves gasoline engine. CAI combustion was achieved over a large range of operating conditions when the relative air/fuel ratio (lambda) was kept at one as measured by an exhaust lambda sensor. Because of the presence of air short-circuiting in the two-stroke cycle operation, lean boost CAI combustion was implemented from 800rpm to 3000rpm and an IMEP range from 1.1bar to 7.8bar, and significant improvements in emissions…
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