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Numerical Simulation and Optimization for Combustion of an Opposed Piston Two-Stroke Engine for Unmanned Aerial Vehicle (UAV)

Beijing Institute of Technology-Zhenfeng Zhao, Fujun Zhang
Harbin Institute of Technology, Shenzhen-Lei Zhou, Hao Li, Zeyu Chen
  • Technical Paper
  • 2020-01-0782
To be published on 2020-04-14 by SAE International in United States
The opposed-piston two-stroke engine is more suitable for the UAV, due to its smaller size, better self-balancing, stable operation and lower noise. Consequently, in this work, based on the experimental data of a prototype opposed piston two-stroke engine, the numerical simulation model are established by AVL-FIRE. The mesh grid and solver parameters of the numerical model are discussed for guaranteeing the accuracy of numerical simulation, and then the ventilation efficiency of the engine with different dip angles and elevation angles have been studied and optimized. Moreover, the fuel spray process and subsequent combustion as well as NOx emissions have been analyzed in details. Finally, the engine combustion parameters have been optimized by orthogonal test design method.
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Optical Characterization of the Combustion Process Inside a Large-Bore Fual-Fuel Two-Stroke Marine Engine by Using Multiple High-Speed Cameras

Lund University-Alexios Matamis, Mattias Richter
MAN Energy Solutions-Johan Hult, Eric Baudoin, Stefan Mayer
  • Technical Paper
  • 2020-01-0788
To be published on 2020-04-14 by SAE International in United States
Dual-fuel engines for marine propulsion are gaining in importance due to operational and environmental benefits. Here the combustion in a dual-fuel marine engine operating on diesel and natural gas is studied using a multiple high-speed camera arrangement. By recording the natural flame emission from three different directions the flame position inside the engine cylinder can be spatially mapped and tracked in time. Through space carving a rough estimate of the three-dimensional (3D) flame contour can be obtained. From this contour properties like flame length and height, as well as ignition locations can be extracted. The multi-camera imaging is applied to a dual-fuel marine two-stroke engine with a bore diameter of 0.5 m and a stroke of 2.2 m. Both liquid and gaseous fuels are directly injected at high pressure, using separate injection systems. Optical access is obtained using borescope inserts, resulting in a minimum disturbance to the cylinder geometry. In this type of engine, with fuel injection from positions at the rim of the cylinder, the flame morphology becomes asymmetric. The optical spatial mapping and…
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The Study on the Characteristics of Different Intake Port Structures in Scavenging and Combustion Processes on a Two-Stroke Poppet Valve Diesel Engine

China North Engine Research Institute-Yan Zhang, Wei Liu, Shuyong Zhang
Tianjin University-Mengmeng Dong, Yiqiang Pei, Jing Qin, Chenxi Wang
  • Technical Paper
  • 2020-01-0486
To be published on 2020-04-14 by SAE International in United States
Two-stroke engines have to face the problems of insufficient charge for short intake time and the loss of intake air caused by long valve overlap. In order to promote the power of a two-stroke poppet valve diesel engine, measures are taken to help optimize intake port structure. In this work, the scavenging and combustion processes of three common types of intake ports including horizontal intake port (HIP), combined swirl intake port (CSIP) and reversed tumble intake port (RTIP) were studied and their characteristics are summarized based on three-dimensional simulation. Results show that the RTIP has better performance in scavenging process for larger intake air trapped in the cylinder. Its scavenging efficiency reaches 84.7%, which is 1.7% higher than the HIP and the trapping ratio of the RTIP reaches 72.3% due to less short-circuiting loss, 11.2% higher than the HIP. The RTIP also behaves better in mixture formation and combustion performance with higher air utilization and superior heat release as well as work capacity. The CSIP has the advantage of higher thermal efficiency but have to…
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Replacement of a 50cc Two-stroke Engine with an Electric Powertrain

TWIG Power-Jesse Beeker
  • Technical Paper
  • 2019-32-0623
Published 2020-01-24 by Society of Automotive Engineers of Japan in Japan
As global regulations look to create a dramatic reduction in CO2 emission and other forms of pollution, companies with products that rely on engine technology must be ready to take on the electrification challenge. Applications that remain using two-stroke engine technology continue to exist due to their very high power density requirements. However, their history of higher pollution compared to four-stroke engines makes them a target to be regulated out of existence.Such high power two-stroke applications include high performance off-road motorcycles. In this type of product, electrification can solve not only pollution challenges but market challenges, such as ridership and public perception. By addressing the core problems presented by the two-stroke engine and turning challenges into opportunity, a strong attraction is created to convert a two-stroke engine motorcycle to an electric vehicle.With Automotive electric vehicle technology paving the way, the basis for cost effective electric motorcycle powertrain is explored for a 50cc off-road motorcycle application. The 50cc engine and motorcycle represent a special product where size, performance, and cost have a high sensitivity. The 50cc…
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Development of a Novel Hybrid-Piston for Application in High Performance Two-Stroke Engines

Fraunhofer IWS, 01277 Dresden, Germany-Axel Jahn, Frieder Zimmermann, Uwe Stamm
Mahle König Kommanditgesellschaft GmbH & Co KG, 6830 Ran-Christian Bechter, Thomas Herb
  • Technical Paper
  • 2019-32-0508
Published 2020-01-24 by Society of Automotive Engineers of Japan in Japan
The current development trends for high performance two-stroke engines have been identified in raising combustion pressures and therefore higher cylinder temperatures [1] [2]. Thus, the requirements on piston assembly are increased in such a way that pistons based on aluminium-silicon alloys – as most commonly used in high performance two-stroke engines - reach their application limit. A suitable solution has been shown by research work such as that conducted by Mahle König, by using a piston consisting of different materials. With this approach, the higher stressed piston crown consists of steel, while the lower stressed piston skirt is made out from aluminium. Previous basic examinations showed the high potential of the hybrid piston concept in terms of pressure and temperature increase, while also showing the need for a temperature-stable and pressure-tight joint between crown and skirt.This paper will focus on the development of two novel hybrid-piston concepts, where the piston crown and the piston skirt are connected in different ways. The first hybrid concept presented uses the piston pin in order to realize a plugconnection…
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Intermittent Injection for a Two-Stroke Direct Injection Engine

Università degli Studi di Firenze-Francesco Balduzzi, Luca Romani, Lorenzo Bosi, Giovanni Ferrara
  • Technical Paper
  • 2019-32-0524
Published 2020-01-24 by Society of Automotive Engineers of Japan in Japan
Cycle-to-cycle variation is one of the main factors for high fuel consumption and emissions of a two-stroke engine during the low-load and low-speed running. The increase of residual gas ratio due to the lower delivered amount of fresh scavenging air leads to a lower flame front speed and, therefore, to a slow combustion or even misfiring. The consequence is a very high level of unburnt hydrocarbons, since a large amount of fuel does not take part in the combustion process.The use of a direct injection system allows a more flexible management of the injection of fuel over subsequent engine cycles. Under a low-load condition, the low request in terms of brake mean effective pressure (BMEP) can be achieved by performing a load control based on an intermittent injection, thus reducing the need for intake throttling and avoiding the loss of fresh fuel resulting from cycles without combustion. In more detail, the supply of fuel to the combustion chamber can be skipped for one or more cycles, thus performing a number of consecutive scavenging cycles with…
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Calcium in Oil Effects on Pre-ignition of Two-stroke Engine

Yamabiko-Corp.-Kuniyoshi Eto, Masaki Kihara
  • Technical Paper
  • 2019-32-0579
Published 2020-01-24 by Society of Automotive Engineers of Japan in Japan
Investigations of the influence of calcium on pre-ignition in a two-stroke engine have shown that the lower the calcium concentration, the lower the frequency of pre-ignition. Pre-ignition problems can occur in small, air-cooled, two-stroke engines such as a chainsaw. In contrast, in a supercharged automobile engine, it has been reported that calcium, which is a detergent component in engine oil, causes low-speed pre-ignition. The oil for two-stroke engines also contains calcium and is mixed with the fuel and lubricated before being supplied to the combustion chamber. This makes, two-stroke engines more likely to be affected by oil components. Based on this, we investigated the influence of calcium on pre-ignition of a two-stroke engine. First, we investigated driving conditions in which pre-ignition is likely to occur, such as warming up the engine. Under this condition, oil with calcium concentrations ranging from 0 ppm to 1,500 ppm were tested at a mixing ratio of 2%. The results show that the lower the calcium concentration, the lower the incidence rate of pre-ignition. Which could also occur at 0…
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Analysis on flow motion and combustion process in pre-chamber and main chamber for low-speed two-stroke dual-fuel engine

China Ship Power Institute Co. Ltd.-Teng Liu
Harbin Engineering University-Long Liu, Yue Wu, Qian Xiong
  • Technical Paper
  • 2019-01-2175
Published 2019-12-19 by SAE International in United States
Low-speed two-stroke dual-fuel engines has been paid more attention due to the energy efficiency design index and Tier III emissions limitations issued by International Marine Organization. Although the dual-fuel engines have strong merits on emissions reduction, which can reach the IMO Tier III without aftertreatment, the power output is much lower than that of diesel engines. Therefore, the dual-fuel engine is also needed to improve continuously. However, the mixing and combustion processes in the engine have not been fully understood. In this study, a 3D-CFD model of the dual-fuel engine was established using CONVERGE to explore the mixing and combustion processes. Locally embedding fine grids are considered at scavenging ports, natural gas injection ports, pre-chamber. The model was validated by experimental in-cylinder pressure. Then, the flow motion, mixing of natural gas and air, flow in pre-chamber, torch and combustion in main-chamber were analyzed based on swirl variation, flow velocity distribution, equivalence ratio distribution and torch propagation.
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A Study of Injection Directions on Improvement of Engine Performance and NOx Emission in A Low-speed Marine Engine

Key Laboratory for Power Machinery and Engineering of M.O.E,-Qian Sun, Wenxia Ji, Zhen Huang, Lei Zhu*
  • Technical Paper
  • 2019-01-2322
Published 2019-12-19 by SAE International in United States
A computational fluid dynamics (CFD) simulation model for a two-stroke low-speed marine engine has been established in CONVERGE software, to study the impact of different injection directions on fuel consumption and emissions of the engine. The goal of this research was to investigate injection angles in horizontal and vertical directions respectively. According to the simulation results, “trade-off” relationship was found in both directions between fuel consumption and NOx emission. Based on these results, 8° and -16° were considered as optimal injection angles in horizontal and vertical directions. With the optimized injection angles, lower NOx emission can be achieved with a little penalty on fuel consumption.
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Experimental study of cylinder oil stripping behavior at the scavenge port of a low-speed two-stroke engine

Dalian University of Technology-Min Pan, Liyan Feng, Zhen Gong, Zhengran Yu, Hongjie Sun, Zixin Wang, Peng Yan
  • Technical Paper
  • 2019-01-2335
Published 2019-12-19 by SAE International in United States
The stripping of cylinder oil at the scavenging ports of low-speed two-stroke marine engines is one of the main sources of floating oil droplets existing in cylinders. The combustion of these oil droplets is one of the major reasons of PM emissions and pre-ignition for dual-fuel engines. In order to investigate the stripping behavior, a prototype model and a test bench were set up to carry out the experiment of cylinder oil stripping behavior and single droplet deformation under different conditions. Meanwhile, a CFD model was established to analyze the actual scavenging flow field, and the verification results were obtained: in the case of excessive lubrication, a considerable amount of cylinder oil remains on the upper surface of the scavenge ports. Such cylinder oil can be blown into the cylinder when the ports are opened. Then the oil droplets floating in the cylinder or attaching to the exhaust valve form potential spontaneous combustion points, which leads to the worsening of PM emissions and the threat of pre-ignition, the most harmful abnormal combustion for Otto-cycle dual-fuel…
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