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Practicability and Influencing Factors of a Lean Burn Mode for Two-Stroke Engines in Hand-Held Powertools

Andreas Stihl AG & Co KG-Florian Schumann, Tim Gegg
Graz University of Technology-Pascal Piecha, Christoph Ninaus, Stephan Schmidt, Roland Kirchberger
  • Technical Paper
  • 2017-32-0043
Published 2017-11-05 by Society of Automotive Engineers of Japan in Japan
For many applications, such as scooters, hand-held power tools and many off-road vehicles, two-stroke engines are used as a preferred propulsion unit. These engines convince by a good power to weight ratio, a high durability and low maintenance technology and are therefore the first choice in this field of application. In general, already much development effort has been expended to improve those systems. However, an increasing environmental awareness, the protection of health and the shortage of fossil resources are the driving factors to further enhance the internal combustion process of those adapted two-stroke engines. The current focus here is on the reduction of emissions and fuel consumption with an at least constant power output.An approach to address an improvement of engine efficiency can be covered by applying a lean combustion burn mode. In almost all combustion technology sectors, including furnaces, gas turbines and many internal combustion engines, a lean combustion is utilized. Possible advantages of a combustion process under lean conditions are low pollutant emissions and high efficiencies, because flame temperatures are typically low. Nevertheless,…
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Optical Analysis on the Mixture Preparation and Combustion Behavior of Small Two-Stroke SI Engines Fueled with Alcohol-Blends

ANDREAS STIHL AG & Co. KG-Tilman Seidel, Stefan Schweiger, Florian Schumann, Tim Gegg
MOT GmbH-Justus Weßling, Fabian Rauber, Fabian Titus, Kai W. Beck
  • Technical Paper
  • 2017-32-0078
Published 2017-11-05 by Society of Automotive Engineers of Japan in Japan
Small gasoline engines are used in motorcycles and handheld machinery, because of their high power density, low cost and compact design. The reduction of hydrocarbon emissions and fuel consumption is an important factor regarding the upcoming emission standards and operational expenses. The scavenging process of the two-stroke engine causes scavenging losses [1]. A reduction in hydrocarbon emissions due to scavenging losses can be achieved through a better understanding of the inner mixture formation. The time frame for fuel vaporization is limited using two-stroke SI engines by the high number of revolutions. With crank angle resolved optical methods it is possible to analyze the mixture formation behavior and combustion. A topic of these investigations is the use of alternative fuels such as alcohol- or butanol-blends and the analysis of their impact on the engine behavior. These fuels show high potential for further reduction of exhaust emissions while simultaneously increasing the engine power output.
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Experimental Investigations Regarding the Potential of an Electronic Ignition Timing Control for a Lawn Mower Engine

Andreas Stihl AG & Co KG-Jan-Philipp Banzhaf, Tim Gegg
Graz University of Technology-Michael Zisser, Hans-Juergen Schacht, Reinhard Stelzl, Bernhard Schweighofer, Hannes Wegleiter, Stephan Schmidt
Published 2016-11-08 by SAE International in United States
In order to fulfill future regulations regarding emissions and CO2 reduction, the small engine market inclines to migrate from carburetor systems to cleaner, more efficient electronic ignition controls and electronic fuel injection systems. When implementing such mechatronic systems in small engine applications, one has to consider specific boundary conditions like the lack of relevant sensors, limited possibilities in terms of space and of course the necessity to keep the costs as low as possible. Especially in the non-road mobile machinery (NRMM) segment, the absence of sensors makes it difficult to apply standard electronic control systems, which are based on engine related input signals provided by sensors. One engine related signal, which is even provided by the simplest engine setup, is some form of the crankshaft speed since it is essential for the functionality of the engine. In this paper, the potential of an electronic ignition timing control system based on this signal as well as experimental experiments are presented. A single cylinder lawn mower SI engine is used for the experiments, since it is representative…
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Investigations and Analysis of Working Processes of Two-Stroke Engines with the Focus on Wall Heat Flux

SAE International Journal of Engines

Andreas Stihl AG & Co KG-Florian Schumann, Stephan Meyer, Tim Gegg
BRP-Powertrain GmbH & Co KG-Stefan Leiber
  • Journal Article
  • 2016-32-0028
Published 2016-11-08 by SAE International in United States
Small displacement two-stroke engines are widely used as affordable and low-maintenance propulsion systems for motorcycles, scooters, hand-held power tools and others. In recent years, considerable progress regarding emission reduction has been reached. Nevertheless, a further improvement of two-stroke engines is necessary to cover protection of health and environment. In addition, the shortage of fossil fuel resources and the anthropogenic climate change call for a sensual use of natural resources and therefore, the fuel consumption and engine efficiency needs to be improved.With the application of suitable analyses methods it is possible to find improving potential of the working processes of these engines. The thermodynamic loss analysis is a frequently applied method to examine the working process and is universally adaptable. Within this paper, a series production small displacement two-stroke engine is experimentally investigated on the test bench and adapted with measuring equipment in order to analyze the working process with focus on the wall heat flux. Due to high speed and vibrations, these investigations are complex. This publication considers an assessment of correlation predictability of heat…
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Advantages and Challenges of Lean Operation of Two-Stroke Engines for Hand-Held Power Tools

SAE International Journal of Engines

ANDREAS STIHL AG & Co. KG-Armin Kölmel, Stephan Meyer, Tim Gegg
Graz University of Technology-Alexander Trattner, Helmut Grassberger, Oliver Schoegl, Stephan Schmidt, Roland Kirchberger, Helmut Eichlseder
  • Journal Article
  • 2014-32-0009
Published 2014-11-11 by SAE International in United States
One of the most significant current discussions worldwide is the anthropogenic climate change accompanying fossil fuel consumption. Sustainable development in all fields of combustion engines is required with the principal objective to enhance efficiency. This certainly concerns the field of hand-held power tools as well. Today, two-stroke SI engines equipped with a carburetor are the most widely used propulsion technology in hand-held power tools like chain saws and grass trimmers.To date, research tended to focus on two-stroke engines with rich mixture setting. In this paper the advantages and challenges of leaner and/or lean operation are discussed. Experimental investigations regarding the influence of equivalence ratio on emissions, fuel consumption and power have been performed. Accompanying 3D-CFD simulations support the experiments in order to gain insight into these complex processes. The investigations concentrate on two different mixture formation processes, i.e. CCI (crankcase injection) and LPDI (low pressure direct injection). Further focus is put onto combustion phenomena of lean mixtures. The main issue addressed in this paper is the impact of mixture setting on fuel consumption. Therefore, the…
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Future Engine Technology in Hand-Held Power Tools

SAE International Journal of Engines

Andreas STIHL AG & Co. KG-Armin Kölmel, Michael Raffenberg, Tim Gegg
Graz University of Technology-Alexander Trattner, Stephan Schmidt, Roland Kirchberger, Helmut Eichlseder
  • Journal Article
  • 2012-32-0111
Published 2012-10-23 by SAE International in United States
Today mankind is using highly sophisticated tools which contribute to maintain the standard of living. Nevertheless, these tools have to be further improved in the near future in order to protect health and environment as well as to ensure prosperity. Two-stroke engines equipped with a carburettor are the most used propulsion technology in hand-held power tools like chain saws and grass trimmers. The shortage of fossil resources and the necessary reduction of carbon dioxide emissions ask for improved engine efficiency. Concurrently, customers demand for an easy usage with high performance at all operating conditions, e.g. varying ambient temperature and pressure and different fuels. Moreover, world-wide emission limits will be even stricter in future.The improvement of the emission level, fuel consumption and customer benefits, while keeping the present advantages of two-stroke engines, like high specific power and simplicity, are the goals of this research work. This paper describes the experimental results of several low-cost electrical mixture formation systems (low pressure direct injection, semi-direct injection and external mixture formation) in combination with a two-stroke engine. 3D-CFD simulations…
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Combustion Analysis on Small Two-Stroke SI-Engines for Handheld Power Tools

ANDREAS STIHL AG & Co. KG-Tim Gegg, Armin Kölmel
Karlsruhe Institute of Technology (KIT)-Kai W. Beck
Published 2010-09-28 by SAE International in United States
Optical measurement techniques were successfully appointed in four stroke combustion diagnostics because of low interaction and high efficiency. In the field of high speed small engines only less experience exists concerning optical measurement. These engines require sophisticated measurement techniques concerning available space and resolution.Numerous investigations with different measurement techniques to analyze the combustion will be presented in this paper. Engine operation, combustion phenomenons and the limits of some techniques are shown by means of concrete examples. The use of fibre optic endoscopes allows the analysis of flame propagation. Furthermore it is possible to locate glow ignition. By means of spectroscopic measurement the mixture preparation and burning temperature curves could be analyzed by adding special reactants to the fuel.
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Experimental Investigations of Two-Stroke SI Combustion with Simultaneous Cycle-Based Fuel Consumption Measurements

ANDREAS STIHL AG & Co. KG-Tim Gegg, Armin Kölmel
AVL Deutschland GmbH-Hans Van den Hoevel, Martin Duerrwaechter
Published 2010-09-28 by SAE International in United States
Unstable combustion and high cyclic variations of the in-cylinder pressure associated with low engine running smoothness and high emissions are mainly caused by cyclic variations of the fresh charge composition, the variability of the ignition and the fuel mass. These parameters affect the inflammation, the burn rate and thus the whole combustion process. In this paper, the effects of fluctuating fuel mass on the combustion behavior are shown. Small two-stroke engines require special measuring and testing equipment, especially for measuring the fuel consumption at very low fuel flow rates as well as very low fuel supply pressures. To realize a cycle-resolved measurement of the injected fuel mass, fuel consumption measurement with high resolution and high dynamic response is not enough for this application. It is also very important that this measurement technique can cope with fluctuating fuel flows and does not influence the combustion and hence the engine performance - due to the pressure drop over the flow meter. To analyze the effects, the cycle-resolved measurement of the fuel mass was simultaneously adapted with ion…
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Spectroscopic Measurements in Small Two-Stroke SI Engines

Andreas STIHL AG & Co. KG, Waiblingen, Germany-Tim Gegg, Armin Kölmel
Universität Karlsruhe (TH), Germany-Kai W. Beck, Thomas Heidenreich, Steve Busch, Ulrich Spicher
  • Technical Paper
  • 2009-32-0030
Published 2009-11-03 by Society of Automotive Engineers of Japan in Japan
This paper demonstrates the potential of optical sensors in the combustion chamber of a small two-stroke SI engine to detect conditions that hinder an optimal combustion process using emission bands and/or emission lines. The primary focus is on the spectroscopic examination of the combustion radiation emissions cycle-by-cycle. For this purpose, spark-ignition type combustion events, as well as the influence of both the air-fuel-ratio and the fuel type, are investigated on a crank angle resolved basis.Furthermore, an assessment of the radiation emissions of the OH, CH and C2 radicals is made. As a next step, the calculation of a temperature profile inside the combustion chamber is attempted by means of the line-emission-method regarding the thermally excited alkaline metals sodium and potassium. These data enable recognition of diffusion combustion and the detection of inadequate mixture quality.
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Ion-Current Measurement in Small Two-Stroke SI Engines

Andreas STIHL AG & Co. KG-Tim Gegg, Armin Kölmel, Andreas Paa
Pulse GmbH, NL-Tycho Weissgerber, Marc Westecker
Published 2008-09-09 by SAE International in United States
The cyclic changes of the cylinder pressure are mainly influenced by the primary inflammation phase, which in turn depends on the local air/fuel ratio and the residual-gas fraction at the spark plug. The ion-current measurement technique is based on the conductivity of the mixture during the internal combustion. It is therefore possible to use the signal for combustion diagnostics when using the spark plug as a sensor.This article demonstrates the potential of ion sensing at the spark plug and in the combustion chamber to detect sources of interference which prevent an optimal combustion process. Comparing the ion signals of consecutive combustion cycles delivers explanations of phenomena that could not yet be sufficiently characterized by cylinder-pressure indication. The results allow new fundamental approaches to the optimization of the combustion process.
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