Browse Topic: Scavenging

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On the Effect of the Injector Position on Fuel-Air Mixture Preparation in a Two-Stroke GDI Engine2018-32-004010/30/2018
Modern injection systems are characterized by low cost, light weight and diversified components based on a mature technology. In addition, the constant growth of computational resources allows an in-depth understanding and control of the injection process. In this scenario, increasing interest is presently being paid to understand if an application of such technologies to small two-stroke engines could lead to a return to popularity in place of the more widespread use of the four-stroke engine. Indeed, the possibility of achieving a drastic reduction of both specific fuel consumption and pollutant emissions would completely reverse the future prospect of the two-stroke engine. The authors in previous studies developed a low pressure direct injection (LPDI) system for a 300 cm3 two-stroke engine that was ensuring a performance consistent with a standard four-stroke engine of similar size. The main drawbacks of the system were the large time required for delivering the fuel and the incomplete vaporization in some working conditions, due to the large size of the injected droplets. In this study, the use of a single high pressure injector with an operating pressure of 100 bar was analyzed. An optimization study was carried out in order to identify the best injector configuration for the GDI system. The results of the preliminary 3-D CFD study are here reported. The effect of the injector positioning and injection timing on the spray vaporization, mixture homogenization and fuel short-circuit was evaluated at different engine operating points. The results will show that also in case of a high pressure injection the best performance can be obtained when a suitable interaction between the liquid jet of fuel and the flow of scavenging air is ensured, as well as with the appropriate choice of the injection timing.
Balduzzi, Francesco, Romani, Luca, Tanganelli, Andrea, Bigalli, Simone, Ferrara, Giovanni
Numerical Analysis of Scavenging Process in a Large Marine Two-Stroke Diesel Engine2017-01-220110/8/2017
For uniflow scavenged two-stroke marine diesel engines, the main function of scavenging process is to replace the burned gas with fresh charge. The end state of scavenging process is integral to the subsequent compression and combustion, thereby affecting the engine’s fuel economy, power output and emissions. In this paper, a complete working cycle of a large marine diesel engine was simulated by using the 3D-CFD software CONVERGE. The model was validated by mesh sensitivity test and experiment data. Based on this calibrated model, the influences of swirl ratio and exhaust valve closing (EVC) timing on the scavenging process were investigated. The parameters evaluating the performance of scavenging process were introduced. The results show that, by adjusting the swirl orientation angle(SOA) from SOA=10° to SOA=30°, different swirl ratios are generated and have obvious differences in flow characteristics and scavenging performance. Advancing or delaying the EVC has limited effects on scavenging efficiency, but have obvious effects on the retaining and charging efficiency. In addition, adjusting the EVC timings also have obvious effects on the in-cylinder pressure and temperature, thus affecting the engine’s fuel economy and emission.
Cao, Zhongye, Wang, Tianyou, Sun, Kai, Cui, Lei, Gui, Yong
Numerical Analysis of the Steady-State Scavenging Flow Characteristics of a Two-Stroke Marine Engine2017-01-05583/28/2017
The scavenging process in two-stroke marine engines not only transports burnt gas out of the cylinder but also provides fresh air for the next cycle, thereby significantly affecting the engine performance. In order to enhance fuel-air mixing, the scavenging process usually generates swirling flow in uniflow-type scavenging engines. The scavenging stability directly determines the scavenging efficiency and even influences fuel-air mixing, combustion, and emission of the engine. In the present study, a computational fluid dynamics (CFD) analysis of the scavenging process in a steady-state scavenging flow test is conducted. A precession phenomenon is found in the high swirl model, and Proper Orthogonal Decomposition (POD) method is used to analyze the reason and the multi-scale characteristics of the precession phenomenon.
Cui, Lei, Wang, Tianyou, Sun, Kai, Lu, Zhen, Che, Zhizhao, Sun, Yanzhe
Design of a Fuel-Efficient Two-Stroke Diesel Engine for Medium Passenger Cars: Comparison between Standard and Reverse Uniflow Scavenging Architectures2017-01-06453/28/2017
In spite of the increasingly stringent emission standards, the constant growth of road traffic contributes to climate change and induces detrimental effects on the environment. The European REWARD project (REal World Advanced Technologies foR Diesel Engines) aims to develop a new generation of Diesel engines complying with stricter post Euro 6 legislation and with lower CO2 emissions. Among the different technologies developed, a fuel-efficient two-stroke Diesel engine suited for C-segment passenger cars will be designed and experimentally evaluated. One major challenge for two-stroke engines is the achievement of an efficient scavenging. As the emptying of the in-cylinder burnt gases and the filling by fresh gases is performed at the same time, the challenge consists in removing as much burnt gases as possible while avoiding the by-pass of fresh air toward the exhaust line. For the considered application, the uniflow scavenging architecture, which is featured by ports located in the bottom of the cylinder and valves in the head, is selected. Two possible arrangements for the intake and the exhaust are compared: either the standard configuration for which the intake is ensured by the ports and the exhaust by the valves or the reverse configuration. Both standard and reverse configurations are first compared through 0D system simulations, performed with LMS Imagine.Lab Amesim and then by 3D CFD simulations with CONVERGE. The standard configuration is favored, thanks to better ISFC performances, especially at low and medium loads operating conditions. In addition, the scavenging is strongly penalized for the reverse architecture due to the drag downstream the intake valves.
Galpin, Jeremy, Colliou, Thierry, Laget, Olivier, Rabeau, Fabien, De Paola, Gaetano, Rahir, Pascal
The Effect of Port Timing and Exhaust Back Pressure on Uniflow Scavenging for a High Power Density OPE Engine2016-01-80789/27/2016
Currently the downsizing of IC Engine has become the mainstream to meet fuel economy and emission regulations. It is required that higher power output while with lighter weight that is actually a daunting challenge for a common four-stroke IC engine, because it needs lots of new technologies and high manufacturing cost. For recent years the two-stroke opposed piston engine has drawn much attention in many developed countries for fundamental advantages itself. Double firing frequency means the increased power density brings about smaller engine size and lighter weight. However, the low scavenge efficiency has been assumed the main disadvantage for a two-stroke engine for a long period, and adverse to combustion efficiency. The uniflow scavenging process was investigated by the transient CFD simulation for multiple Cases. The influence of port timing and exhaust back pressure on scavenging was analyzed for two different intake port layouts. The calculated results are shown that exhaust back pressure dominates the charge air leakage and trapped air mass in cylinder. The pressure drop between intake port and exhaust port is whether too high or low all will cause a non-ideal scavenge efficiency affected by final trapped air mass. In addition, the port timing is also quite important to efficiently control the fresh air escape from cylinder, and improves the scavenging process. The intake port orientation based on a datum line will impose a slight effect on scavenge efficiency compared to port timing and exhaust back pressure. In terms of results in all Cases the relative perfect design scheme is Case02 with positive tilt angle for new port timing, and it’s scavenge efficiency is over 90% at 3500rpm with full load and rated power speed in a two-stroke opposed piston engine.
Changming, He, Sichuan, Xu
Three-Dimensional CFD Analysis of Semi-Direct Injection Hydraulic Free Piston Engine2016-01-10184/5/2016
In this paper, a new method for the driving of the hydraulic free piston engine (HFPE) is proposed. Hydraulic differential drive achieves the compression stroke automatically rather than special recovery system, which has a great influence on the engine dynamic performance. The purpose of this paper is to solve the key operation and control problems for HFPE to commix fuel with air. HFPE adopts two-stroke loop-scavenging and semi-direct injection. The semi-direct injection nozzle is located in the liner wall inside the main intake port, with the axes oriented towards the piston at the Bottom Dead Center (BDC). Different scavenging pressures and injection angles result in different impacts on the mixture of fuel and air in the cylinder. This study analyzes the changes of the combustion heat release rate by simulation. The result shows that the gasoline back-flow and short circuit loss is minimal, and the mixture of fuel and air is uniform, with the initial pressure of 0.13MPa and injection angle of 120°CA. Moreover, heat release of HFPE is enhanced, which complies with the requirements of the original design. The study can provide the theoretical basis for exploring the scavenging characteristics and operation mechanism of HFPE.
Wang, Shan, Zhao, ZhenFeng, Zhang, Shuanlu, Liu, Jinxiang, Liu, Yuhang
Investigation of the Gas Exchange (Scavenging) on a Single-Scroll Turbocharged Four Cylinder GDI Engine2016-01-10244/5/2016
For scavenging the combustion chamber during the gas exchange, a temporary positive pressure gradient between the intake and the exhaust is required. On a single-scroll turbocharged four cylinder engine, the positive pressure gradient is not realized by the spatial separation of the exhaust manifold (twin-scroll), but by the use of suitable short exhaust valve opening times. In order to avoid any influence of the following firing cylinder onto the ongoing scavenging process, the valve opening time has to be shorter than 180 °CA. Such a short valve opening time has both, a strong influence on the gas exchange at the low-end torque and at the maximum engine power. This paper analyzes a phenomenon, which occurs due to short exhaust valve opening durations and late valve timings: A repeated compression of the burned cylinder charge after the bottom dead center, referred to as “recompression” in this paper. By means of a new energetic analysis (available technical work capacity) the energetic contribution of the recompression to the boost pressure generation has been examined and is presented in this paper. Furthermore two different variable exhaust valve train systems in combination with a part-scroll-separation exhaust manifold are compared in this paper. The aim is to reduce fuel consumption at the nominal power. The two exhaust valve train systems increase the valve opening duration by either a two step system or by a system with the ability to offset the valve timing. It is shown in simulation results how both systems in combination with a prolonged part-scroll-separation in the exhaust manifold reach a potential to reduce fuel consumption up to 10 %.
Wolany, Adalbert, Glahn, Claus, Berner, Hans-Juergen, Bargende, Michael
Engine Downsizing through Two-Stroke Operation in a Four-Valve GDI Engine2016-01-06744/5/2016
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 at 800 rpm and 1600 rpm and the overall engine performance was presented. Gaseous and smoke emissions were measured and examined, as well as an analysis of the spark ignition combustion process. The results demonstrated that very high torque at low engine speeds could be obtained at relatively low in-cylinder pressures and reasonable fuel consumption results.
Dalla Nora, Macklini, Lanzanova, Thompson, Zhang, Yan, Zhao, Hua
Port Design Criteria for 2-Stroke Loop Scavenged Engines2016-01-06104/5/2016
Interest in 2-stroke engines has been recently renewed by several prototypes, developed for the automotive and/or the aircraft field. Loop scavenging, with piston controlled ports is particularly attractive, but the configurations successfully developed in the past for motorbike racing (in particular, the 125cc unit displacement, crankcase pump engines), are not suitable for automotive applications. Therefore, new criteria are necessary to address the scavenging system design of the new generation of 2-stroke automobile/aircraft engines. The paper reviews the transfer ports optimization of a loop scavenged 2-stroke cylinder, whose main parameters were defined in a previous study. The optimization has been carried by means of a parametric grid, considering 3 parameters (2 tilt angles, and the focus distance), and 3 different engine speeds (2000-3000-4000 rpm, assuming a Diesel engine). A set of scavenging CFD-3d simulations have been performed by using a customized version of KIVA-3V. The numerical approach was experimentally calibrated in a previous project (see appendix 1) The simulations results are presented by means of maps showing the influence of the geometrical parameters on the main scavenging coefficients. Finally, a refined mesh has been constructed for the optimum configuration found in the previous parametric analysis, and a set of multi-cycle simulations have been performed. The results demonstrated the very good efficiency of the scavenging process, close to a perfect displacement for delivery ratio up to 1.5, or for residuals fraction higher than 50%
Mattarelli, Enrico, Rinaldini, Carlo Alberto, Savioli, Tommaso
Turbocharger Matching Method for Reducing Residual Concentration in a Turbocharged Gasoline Engine2015-01-12784/14/2015
In a turbocharged engine, preserving the maximum amount of exhaust pulse energy for turbine operation will result in improved low end torque and engine transient response. However, the exhaust flow entering the turbine is highly unsteady, and the presence of the turbine as a restriction in the exhaust flow results in a higher pressure at the cylinder exhaust ports and consequently poor scavenging. This leads to an increase in the amount of residual gas in the combustion chamber, compared to the naturally-aspirated equivalent, thereby increasing the tendency for engine knock. If the level of residual gas can be reduced and controlled, it should enable the engine to operate at a higher compression ratio, improving its thermal efficiency. This paper presents a method of turbocharger matching for reducing residual gas content in a turbocharged engine. The turbine is first scaled to a larger size as a preliminary step towards reducing back pressure and thus the residual gas concentration in-cylinder. However a larger turbine causes a torque deficit at low engine speeds. So in a following step, pulse separation is used. In optimal pulse separation, the gas exchange process in one cylinder is completely unimpeded by pressure pulses emanating from other cylinders, thereby preserving the exhaust pulse energy entering the turbine. A pulse-divided exhaust manifold enables this by isolating the manifold runners emanating from certain cylinder groups, even as far as the junction with the turbine housing. This combination of appropriate turbine sizing and pulse-divided exhaust manifold design is applied to a Proton 1.6-litre CamPro CFE turbocharged gasoline engine model. The use of a pulse-divided exhaust manifold allows the turbine to be increased in size by 2.5 times (on a mass flow rate basis) while maintaining the same torque and power performance. As a consequence, lower back pressure and improved scavenging reduces the residual concentration by up to 43%, while the brake specific fuel consumption improves by approx. 1%, before any modification to the compression ratio is made.
Ismail, Muhammad Izzal, Costall, Aaron, Martinez-Botas, Ricardo, Rajoo, Srithar
Scheme Design and Performance Simulation of Opposed-Piston Two-Stroke Gasoline Direct Injection Engine2015-01-12764/14/2015
In this paper, a new-type balanced opposed-piston two-stroke (OP2S) gasoline direct injection (GDI) engine is developed by Beijing Institute of Technology. OP2S-GDI engine has some potential advantages such as simple structure, good balance, compact, high power density and thermal efficiency. The structural feature of OP2S-GDI engine leads to the performance difference compared with conventional engines. In order to study and verify the characteristics of this kind of engine, the dynamics characteristics and design scheme of opposed crank-connecting rod mechanism, in-cylinder scavenging process, mixture formation and combustion process are investigated. The influence of parameters on engine performance is investigated, including opposed-piston motion phase difference, intake and exhaust port timing, injection and ignition timing. In addition, the arrangement form of opposed crank-connecting rod mechanism is investigated as a main factor to affect the integral forced status and system balance for OP2S-GDI engine.
Ma, Fukang, Zhao, Changlu, Zhang, Shuanlu, Wang, Hao
Comparison between 2 and 4-Stroke Engines for a 30 kW Range Extender2014-32-011411/11/2014
The paper compares two different design concepts for a range extender engine rated at 30 kW at 4500 rpm. The first project is a conventional 4-Stroke SI engine, 2-cylinder, 2-valve, equipped with port fuel injection. The second is a new type of 2-Stroke loop scavenged SI engine, featuring a direct gasoline injection and a patented rotary valve for enhancing the induction and scavenging processes. Both power units have been virtually designed with the help of CFD simulation. Moreover, for the 2-Stroke engine, a prototype has been also built and tested at the dynamometer bench, allowing the authors to make a reliable theoretical comparison with the well assessed 4-Stroke unit. Even if the optimized design of each one of the two engines is similar to that of existing prototypes, the paper is not intended to be a benchmarking, but a general study, aimed to define the fundamental project guidelines and compare different solutions under the same conditions, including the unavoidable arbitrary hypotheses. The main results of the comparison may be summarized as follows: the 2-Stroke engine is more compact and light (−38% of frontal area, 35 vs. 50 kg); its fuel efficiency is slightly better, and further improvements are possible running on stratified charge; the reduction of NOx in the 2-S catalyst may not be complete, due to the unavoidable air short-circuit.
Mattarelli, Enrico, Rinaldini, Carlo Alberto, Cantore, Giuseppe, Agostinelli, Enrico
Performance Sensitivity to Exhaust Valves and Turbine Parameters on a Turbocompound Engine with Divided Exhaust Period2014-01-259710/13/2014
Turbocompound can utilize part of the exhaust energy on internal combustion engines; however, it increases exhaust back pressure, and pumping loss. To avoid such drawbacks, divided exhaust period (DEP) technology is combined with the turbocompound engine. In the DEP concept the exhaust flow is divided between two different exhaust manifolds, blowdown and scavenging, with different valve timings. This leads to lower exhaust back pressure and improves engine performance. Combining turbocompound engine with DEP has been theoretically investigated previously and shown that this reduces the fuel consumption and there is a compromise between the turbine energy recovery and the pumping work in the engine optimization. However, the sensitivity of the engine performance has not been investigated for all relevant parameters. The main aim of this study is to analyze the sensitivity of this engine architecture in terms of break specific fuel consumption to different parameters concerning the gas exchange such as blowdown valve timing, scavenging valve timing, blowdown valve size, scavenging valve size, discharge coefficients of blowdown and scavenging ports, turbine efficiency, turbine size and power transmission efficiency. This study presents the sensitivity analysis of the turbocompound DEP engine to these parameters and defines a set of important parameters that should be examined in experimental studies.
Aghaali, Habib, Angstrom, Hans-Erik
Simulation Study of Divided Exhaust Period for a Regulated Two-stage Downsized SI Engine2014-01-255010/13/2014
The Divided Exhaust Period (DEP) concept is an approach which has been proved to significantly reduce the averaged back pressure of turbocharged engines whilst still improving its combustion phasing. The standard layout of the DEP system comprises of two separately-functioned exhaust valves with one valve feeding the blow-down pulse to the turbine whilst the other valve targeting the scavenging behaviour by bypassing the turbine. Via combining the characteristics of both turbocharged engines and naturally aspirated engines, this method can provide large BSFC improvement. The DEP concept has only been applied to single-stage turbocharged engines so far. However, it in its basic form is in no way restricted to a single-stage system. This paper, for the first time, will apply DEP concept to a regulated two-stage (R2S) downsized SI engine. By controlling the timing of the exhaust valves separately to feed the exhaust mass flow to the high-pressure turbine or the low-pressure turbine or the exhaust pipe, it is anticipated that such system could achieve even better breathing characteristics than the standard one-stage turbocharged engine. The simulation was carried out on a heavily downsized R2S turbocharged SI engine model. As the major objective of this project is to explore the gas exchange process for the DEP-based R2S downsized engine, the knock model in the system is ignored. The results showed that PMEP is significantly improved over the entire engine speed and BSFC was decreased by up to 3% with minimum modification of the original system. The system also showed the potential benefit for knock sensitivity and it is considered that by adding the knock model, there will be some more BSFC improvement.
Hu, Bo, Brace, Chris, Akehurst, Sam, Copeland, Colin, Turner, J.W.G.
1-D Simulation Study of Divided Exhaust Period for a Highly Downsized Turbocharged SI Engine - Scavenge Valve Optimization2014-01-16564/1/2014
Fuel efficiency and torque performance are two major challenges for highly downsized turbocharged engines. However, the inherent characteristics of the turbocharged SI engine such as negative PMEP, knock sensitivity and poor transient performance significantly limit its maximum potential. Conventional ways of improving the problems above normally concentrate solely on the engine side or turbocharger side leaving the exhaust manifold in between ignored. This paper investigates this neglected area by highlighting a novel means of gas exchange process. Divided Exhaust Period (DEP) is an alternative way of accomplishing the gas exchange process in turbocharged engines. The DEP concept engine features two exhaust valves but with separated function. The blow-down valve acts like a traditional turbocharged exhaust valve to evacuate the first portion of the exhaust gas to the turbine. While the scavenge valve feeding the latter portion of the exhaust gas directly into the low resistant exhaust pipe behaves similarly to valves in a naturally aspirated engine. By combining the characteristics of both turbocharged and naturally aspirated engines, high backpressure between the turbine inlet and the exhaust port is maintained in the blowdown phase while significant reduction of the backpressure could be achieved in the latter displacement phase. This is directly beneficial for pumping work and residual gas scavenging. Combustion phasing & stability and turbocharger efficiency could also benefit from such concept. This simulation study was carried out using a validated 1D model of a highly downsized SI engine. Two degrees of freedom including the lift and the duration of the scavenge valve were optimized to achieve minimum BSFC. The potential for higher attainable BMEP was also briefly investigated at low engine speed.
Hu, Bo, Akehurst, Sam, Brace, Chris, Copeland, Colin, Turner, James
Responsiveness of a 30 Bar BMEP 3-Cylinder Engine: Opportunities and Limits of Turbocharged Downsizing2014-01-16464/1/2014
Thanks to direct injection and turbocharging, downsizing technology has found widespread acceptance in series production engines. Fuel consumption for NEDC and also real world driving conditions can be reduced significantly depending on the extend of downsizing. For future applications 3 cylinder gasoline engines have already been announced for up to 140 kW by premium OEMs. Recent developments focus on well-adjusted downsizing rates taking into account merits and demerits of conventional charging technologies. One of the biggest challenge in the development process is to meet the customer's demands regarding vehicle driveability for downsized turbocharged gasoline engines for real world driving conditions. Scavenging has proven to be very beneficial to meet the required vehicle responsiveness. Pressure charged production engines are now delivering more than 200 % of the BMEP that was typical for naturally aspirated engines a few years ago. With the introduction of direct injection the way was cleared for scavenging combustion method without an increase in engine-out hydrocarbon emissions. Today with respect to real world vehicle test procedures, emission analysis for the whole operating region needs to be considered. Latest disclosure of the European Commission can be concluded as follows: there has been little change in total NOx emissions during the last 15 years 69 % of NO2 and NOx emissions are caused by local traffic RDE test procedures for gaseous emissions will be introduced in September 2017 [1]. A distinction of diesel and gasoline application cannot be expected in context of future emission legislation. The Institute for Internal Combustion Engines and Powertrain Systems (VKM) of the TU Darmstadt started a measurement campaign - steady state as well as transient - in order to investigate the different options namely standard scavenging, stoichiometric scavenging and electrified air path way to investigate the capability of passing real world driving emission test procedures of extreme downsizing concepts. The research activities on downsizing engines and engines for hybrid drive trains are carried out together with project partner, MAHLE International GmbH.
Martin, Sebastian, Beidl, Christian, Mueller, Rolf
Effect of Piston Dynamic on the Working Processes of an Opposed-Piston Two-Stroke Folded-Cranktrain Engine2014-01-16284/1/2014
An opposed-piston two-stroke folded-cranktrain diesel engine was studied in this paper. In order to achieve asymmetric scavenging, asymmetric angle between two crank throws were designed. However asymmetric crank-throw angle has direct effect on the piston dynamic, which affects engine performance. This paper investigated the characteristics of the piston dynamic on an opposed-piston two-stroke folded-cranktrain diesel engine; effects of the asymmetric angle on the piston displacement, velocity and acceleration were analyzed; further researches were done to studied the effect of piston dynamic on the gas exchange performance and in-cylinder performance. The results show that, larger asymmetric angle is positive for the scavenging efficiency but negative for combustion. The 8.5° CA asymmetric angle showed better fuel economical and IMEP due to better mix and combustion at 2200 r/min, while the 6° CA asymmetric angle showed better fuel economical and IMEP due to better scavenging efficiency at 1000 r/min.
Zhang, Zhenyu, Zhao, Changlu, Wu, Dan, Zhang, Fujun, Luo, Guoliang
Preliminary Design of a Two-Stroke Uniflow Diesel Engine for Passenger Car2013-01-17194/8/2013
The target of substantial CO₂ reductions in the spirit of the Kyoto Protocol as well as higher engine efficiency requirements has increased research efforts into hybridization of passenger cars. In the frame of this hybridization, there is a real need to develop small Internal Combustion Engines (ICE) with high power density. The two-stroke cycle can be a solution to reach these goals, allowing reductions of engine displacement, size and weight while maintaining good NVH, power and consumption levels. Reducing the number of cylinders, could also help reduce engine cost. Taking advantage of a strong interaction between the design office, 0D system simulations and 3D CFD computations, a specific methodology was set up in order to define a first optimized version of a two-stroke uniflow diesel engine. The main geometrical specifications (displacement, architecture) were chosen at the beginning of the study based on a bibliographic pre-study and the power target in terms. Using 3D CFD, the expansion/scavenging/compression phases were computed in order to evaluate the scavenging characteristic and the in-cylinder aerodynamics level which mainly depend on the combustion chamber geometry and on the intake and the exhaust manifolds and strategies. The scavenging characteristic was then used in 0D computations in order to evaluate each engine configuration in terms of power and consumption on the entire engine map. Indications were then deduced in order to guide the design office for the engine optimization. One configuration was chosen to be built and tested on the test-bench. In the present paper the specific methodology is described and several indications are given for the preliminary design of such a two-stroke diesel engine.
Laget, Olivier, Ternel, Cyprien, Thiriot, Julien, Charmasson, Sébastien, Tribotté, Pascal, Vidal, Fabrice
Wind-Driven Wireless Networked System of Mobile Sensors for Mars ExplorationTBMG-154741/1/2013
A revolutionary way is proposed of studying the surface of Mars using a wind-driven network of mobile sensors: GOWON. GOWON would be a scalable, self-powered and autonomous distributed system that could allow in situ mapping of a wide range of environmental phenomena in a much larger portion of the surface of Mars compared to earlier missions. It could improve the possibility of finding rare phenomena such as “blueberries” or bio-signatures and mapping their occurrence, through random wind-driven search. It would explore difficult terrains that were beyond the reach of previous missions, such as regions with very steep slopes and cluttered surfaces. GOWON has a potentially long life span, as individual elements can be added to the array periodically. It could potentially provide a costeffective solution for mapping wide areas of Martian terrain, enabling leaving a long-lasting sensing and searching infrastructure on the surface of Mars.
Development of a Compact Intake Porting Design for a 2-Stroke DI Outboard Engine2012-32-011610/23/2012
Early implementations of direct injection technology were primarily adaptations of fuel systems to existing loop scavenge carbureted engines that did not leverage the strong interaction between the scavenge flow and fuel distribution in the cylinder. Emissions reduction techniques have been limited to engine calibration strategies using injection timing to minimize lost fuel at the expense of mixture preparation and power. This work focuses on manipulating the scavenging pattern to reduce lost fuel while improving mixture preparation and trapped oxygen. The project goals were to design an intake porting specifically for a 3.4 liter V6 2-stroke DI outboard engine that meets EPA 3 star NTE emissions regulations while increasing power by 10 percent and increasing fuel economy 10 percent over production baseline. Project constraints on the radial space available for the intake ports limited traditional guidance provided by the port walls and required alternative methods to target the scavenge flow. The multi-dimensional CFD code KIVA-3V2 was used to simulate and design the intake ports. The model setup is a single cylinder with pressure boundary conditions incorporating an outwardly opening hollow cone fuel injector. CFD results, both integrated and spatially resolved, are evaluated on the basis of scavenging, mixture preparation and lost fuel out the exhaust port. Correlation of scavenging performance was achieved by comparing delivered oxygen levels calculated from emissions data to simulation results. For mixture preparation, a qualitative correlation was achieved by using experimental metrics including specific fuel consumption and power output sensitivity to injection timing. Simulation and experimental results are presented for two compact porting designs that strike different balances between lost fuel and mixture preparation. One of these new configurations had a unique scavenge pattern that allowed for substantially increased fuel penetration while maintaining good fuel trapping. This penetration allowed for improved interaction with exhaust plug induced flow and an associated improvement in mixture preparation.
Westhoff, Paul, Johnson, Justin
Numerical and Experimental Investigation of Fuel Effects on Knock Occurrence and Combustion Noise in a 2-Stroke Engine2012-01-08274/16/2012
Knock occurrence is a widely recognized phenomenon to be controlled during the development and optimization of S.I. engines, since it bounds both compression ratio and spark advance, hence reducing the potential in gaining a lower fuel consumption. As a consequence, a clear understanding of the engine parameters affecting the onset of auto-ignition is mandatory for the engine setup. In view of the complexity of the phenomena, the use of combined experimental and numerical investigations is very promising. The paper reports such a combined activity, targeted at characterizing the combustion behavior of a small unit displacement two-stroke SI engine operated with either Gasoline or Natural Gas (CNG). In the paper, detailed multi-cycle 3D-CFD analyses, starting for preliminary 1D computed boundary conditions, are performed to accurately characterize the engine behavior in terms of scavenging efficiency and combustion. In order to assess the accuracy of the adopted numerical approach, comparisons between numerical forecasts and experimental measurements of instantaneous in-cylinder pressure histories are carried out for both gasoline- and CNG-fueled engine operations. 3D analyses are also used to investigate the knock sensitivity of the engine to variations of spark timings in a limited set of operating conditions. The activity is simultaneously developed within a 1D modeling framework, where a detailed quasi-dimensional combustion and knock model is applied to perform a wider investigation of engine performance and knock occurrence for both Gasoline and Natural Gas fuelling. Results from 3D simulations are here used to improve the 1D simulations through a better description of scavenging and combustion processes. Once validated, 1D analyses are in particular finalized to find the knock-limited spark advance by changing both compression ratio and spark timing in order to reduce the fuel consumption. In this phase, a dedicated routine is also developed to have information on combustion related noise, which may limit fuel consumption improvements. Further confirmations on the validity of the 1D approach to the modeling of the knock onset are derived from full-3D knocking analyses over a limited set of engine operating conditions. Advantages and limitations of CNG operations of the engine are briefly pointed out at the end of the paper.
Bozza, Fabio, Fontanesi, Stefano, Gimelli, Alfredo, Severi, Elena, Siano, Daniela
An Innovative Solution for Two-Stroke Engines to Reduce the Short-Circuit Effects2012-01-01804/16/2012
Two-stroke engines complete the process cycle in one crankshaft revolution: the scavenging process takes place when the piston is close to the bottom dead center, with the opportunity to open and close the cylinder ports by means of the piston motion, greatly reducing the number of moving parts. This solution however, typically used in small engines, imposes a symmetrical timing with respect to the bottom dead center, leading to a lower scavenging efficiency than a four-stroke engine. Except for the short rpm range of dynamic tuning, two-stroke engines are affected by the short-circuit of fresh air-fuel mixture during the scavenging process: this phenomenon results in a fuel loss, subsequent lower torque and higher specific consumption, and also in an inevitable increase in pollutant emissions. This paper presents one possible mechanical solution to reduce the short-circuit in the whole rpm engine range, to keep the typical advantages of two-stroke engines (simple construction, high specific power and working regularity for a single cylinder engine of a given displacement) and, at the same time, to avoid the usual problems of the two-stroke cycle. An asymmetric timing of the exhaust port is certainly a benefit, and for this reason an innovative design solution was conceived: a rotating valve, directly driven from the crankshaft, was positioned in correspondence with the exhaust port. During every cycle, this valve prevents the leakage of the fresh charge from the exhaust port in the last phase of the scavenging process. At the same time, thanks to its particular geometry, it allows the exhaust flow during the discharge. In other words, the valve converts the typical fluid dynamic effect of the outlet overpressure wave into a mechanical system for all rpm range and not only for the tuning speed. The benefits of this solution were analyzed both in terms of global performance with a 1-D simulation code, and of fluid dynamics behavior of the system through 3-D CFD simulations. The main results, presented in this paper, show significant improvements when compared to analogous traditional two-stroke engines.
Ferrara, Giovanni, Balduzzi, Francesco, Vichi, Giovanni
2-Stroke CAI Combustion Operation in a GDI Engine with Poppet Valves2012-01-11184/16/2012
In order to extend the CAI operation range in 4-stroke mode and maximize the benefit of low fuel consumption and emissions in CAI mode, 2-stroke CAI combustion is revived operating in a GDI engine with poppet valves, where the conventional crankcase scavenging is replaced by boosted scavenging. The CAI combustion is achieved through the inherence of the 2-Stroke operation, which is retaining residual gas. A set of flexible hydraulic valve train was installed on the engine to vary the residual gas fraction under the boosting condition. The effects of spark timing, intake pressure and short-circuiting on 2-stroke CAI combustion and its emissions are investigated and discussed in this paper. Results show the engine could be controlled to achieve CAI operation over a wide range of engine speed and load in the 2-stroke mode because of the flexibility of the electro-hydraulic valvetrain system.
Zhang, Yan, Ojapah, Mohammed, Cairns, Alasdair, Zhao, Hua
Development of Catalytic Converter for 2 - Stroke Engine Powered Vehicles2004-01-10903/8/2004
Scooters and motorcycles are favoured as economical forms of transportation throughout much of Asia. This is particularly true of vehicles with 2 stroke power plants, thanks to the high specific output produced by the simple, less costly engine. However a serious disadvantage of these vehicles is that they emit considerably higher volumes of gaseous pollutants per driven kilometer than do other automobiles. This paper presents new development of a catalytic converter for 2 stroke powered vehicles which uses metallic catalyst support coated with platinum. With an improved inlet header design the conversion efficiency has improved significantly and maximum power loss was than 5 % over the entire speed range.
Tamilporai, P., Chandrasekaran, S., Subramaniyam, S., Jancirani, J.
A Model Method for the Evaluation of the Scavenging System in a Two-Stroke Engine8501762/1/1985
Due to inadequate scavenging process two-stroke petrol engines suffer from substantial specific consumption as well as from poor emission of the toxical components in the exhaust gasses. The paper describes two different scavenging systems: the conventional-so called single phase (Schnürle) one, and the second most sophisticated two phase scavenging system. The effectiveness of the two systems was defined by means of the qualitative scavenging efficiency factor and the model methode was applied for this purpose. Instead of gasseous liquid working media were used on the model engine. A mathematical model based on the principles of the approximate similarity was also developed. It makes us possible to establish the relationships between the most important parameters on the model engine and on the real engine. A special testing device makes us possible the quantitative evaluation of the predictet values and the simulation of the working medium exchange process at different working conditions.
Mirko, Ćudina, Radislav, Pavletič
A Study on the Influnce of Intel Angel and Reynolds Number on the Flow-Pattern of Uniflow Scavenging Air8410568/1/1984
A cylinder of a model uniflow scavenging engine filled with air at room temperature was scavenged with hot air, and arrival time of the scavenging air was detected with a thermocouple at 20 positions in the cylinder. And shape of front surface of the scavenging air was obtained from these data: The front surface with medium intensity swirl port has a peak in the central part at low running speed, but as the speed increases, it becomes flat causing scavenging efficiency the highest. And finally, a depression appears at its center at very high running speed. Assuming this phenomenon to be analogous to “vortex breakdown” investigated by T.Sarpkaya and others, the authors have proposed a method to determine a geometry of scavenging port that gives the highest scavenging efficiency at a desired Reynolds number, and verified its availability.
Nishimoto, Keiichi, Kamimoto, Takeyuki
Air Motion in a Two Stroke Engine Cylinder - The Effects of Exhaust Geometry8207512/1/1982
Air motion in one cylinder of a Detroit Diesel 6V-92 two stroke diesel engine was studied under steady flow bench test conditions by a laser Doppler anemometer and an axisymmetric finite difference fluid dynamic model. The effects of four different exhaust opening geometries were explored. Measurements and calculations showed that the swirl induced by the 18 angled inlet ports produced non-uniform axial velocity profiles and large peaks in the mid-radius region (between cylinder center and wall). The exhaust opening geometry in the head of the cylinder influenced these axial velocity fields especially in the upper region of the cylinder. The study concluded that more uniform flow, which is favorable to the scavenging process, can be achieved by an exhaust opening located close to the cylinder periphery.
Sung, Nak Won, Patterson, Donald J.
Further Developments in Scavenging Analysis for Two-Cycle Engines8000382/1/1980
In 1968 Professor Alfred Jante published an SAE paper detailing a method of assessing the scavenging behaviour of a two-cycle engine. It was a simple technique involving motoring the engine and measuring the (cylinder head removed) velocity contours at the cylinder head level using pitot tubes. It attracted wide attention in industry, but with varying degrees of acceptance and results. This paper attempts to establish in a logical manner and with a considerable’ volume of experimental data that the method proposed by Jante has real relevance, but to obtain acceptable accuracy in terms of predicting good and bad scavenging for particular engine cylinders the results have to be analysed rather more carefully and completely than the approach adopted by Jante. The experimental work describes motoring and firing tests on one engine with many engine. cylinders of differing scavenging layouts and correlates the scavenge tests motoring with the firing tests which include measured scavenge and trapping efficiency values, cylinder pressure diagrams together with the usual engine performance parameters.
Blair, G. P., Kenny, R. G.
Scavenging Model Solves Problems in Gas Burning Engine7105792/1/1971
An application of model tests based on laws of similarity is developed in this paper for the analysis of the scavenging and gaseous mixing process in gas-burning engines. Systematic tests disclosed that only the Strouhal model law and the density ratio between the substances involved (Euler's similarity law) are significant. It is also pointed out that fluids are particularly convenient for examination of the scavenging and mixing processes (simple quantitative measurement, and ease of visualization). The model tests deliver qualitative and quantitative predictions on scavenging and mixture formation in the actual engine.
Dedeoglu, Nabi
Scavenging and Other Problems of Two-Stroke Cycle Spark-Ignition Engines6804682/1/1968
Applicable fundamentals of aerodynamics are summarized as a help in designing optimum scavenging flow ducts. Certain patterns of “scavenging pictures” serve as criteria for stability and are derived from requirements for scavenging air flow in the cylinder. For a good performance of the engine, further requirements must be met with regard to exhaust and intake pressure fluctuations, antiknock properties, and the formation and distribution of the fuel-air mixture. Engine performance characteristics of a 3 cyl 2 stroke cycle, spark ignition engine of 61 cu in. displacement are shown. The excellent performance indicates good potentials of the 2 stroke cycle engine.
Jante, Alfred
HIGH-SPEED, HIGH-OUTPUT, LOOP-SCAVENGED TWO-CYCLE DIESEL ENGINES5700621/1/1957
THIS paper deals with the problems connected with high-speed loop-scavenged 2-stroke diesel engines. The theoretical processes of scavenging are described, and methods for their calculation are discussed. It is shown that it is possible to predetermine, to a considerable extent, the most important characteristic values of scavenging and, thus, to shorten the development work. Various arrangements for the supercharging of 2-stroke engines are treated, and the problem of turbocharging this type of engine is described.
List, Prof. Dr. Hans
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