In order to optimize the 2-stroke uniflow engine performance on vehicle applications, numerical analysis has been introduced, 3D CFD model has been built for the optimization of intake charge organization. The scavenging process was investigated and the intake port design details were improved. Then the output data from 3D CFD calculation were applied to a 1D engine model to process the analysis on engine performance. The boost system optimization of the engine has been carried out also. Furthermore, a vehicle model was also set up to investigate the engine in-vehicle performance.

Ma, Jun, Zhao, Hua, Freeland, Paul, Hawley, Martyn, Xia, Jun

Responsiveness of a 30 Bar BMEP 3-Cylinder Engine: Opportunities and Limits of Turbocharged Downsizing

2014-01-16464/1/2014

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 Engine

2014-01-16284/1/2014

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 Car

2013-01-17194/8/2013

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 Exploration

TBMG-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 Engine

2012-32-011610/23/2012

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 Engine

2012-01-08274/16/2012

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

2-Stroke CAI Combustion Operation in a GDI Engine with Poppet Valves

2012-01-11184/16/2012

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

An Innovative Solution for Two-Stroke Engines to Reduce the Short-Circuit Effects

2012-01-01804/16/2012

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

Development of Catalytic Converter for 2 - Stroke Engine Powered Vehicles

2004-01-10903/8/2004

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 Engine

850176

2/1/1985

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