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High performance engines are used in many different powersports applications. In several of these applications 2-stroke engines play an important role. The direct injection technology is a key technology for 2-stroke engines to fulfill both the customers’ request for high power and the environmental requirements concerning emissions and efficiency. As the load spectrum differs from one application to the other, it was interesting to find out if different injection technologies can answer the needs for different applications more efficiently regarding performance but also economic targets. Therefore, the results of the BRP Rotax 600 cm3 E-TEC (direct injection system) engine are compared to the same base engine but adopted with the LPDI (low pressure direct injection) technology developed by IVT at Graz University of Technology. The systems were compared on the engine testbench over 17 rpm / load points representing different product usage profiles.

Millions of small displacement single-cylinder engines are used for the propulsion of scooters, motorcycles, small boats and others. These SI-engines represent the basis of an affordable mobility in many countries, but at the same time their efficiency is quite low. Today, the limited fossil fuel resources and the anthropogenic climate require a sustainable development of combustion engines, the reduction of fuel consumption being an important factor. A variety of different strategies (turbo-charging, cylinder deactivation, direct injection, etc.) are investigated here to increase the efficiency of multi-cylinder engines. In the case of small displacement single-cylinder engines, other strategies are required because of their special design and the high pressure on costs. In the context of this paper different layout parameters which have an influence on the working process are investigated, with the aim of increasing the efficiency of small displacement single-cylinder engines.

In consideration of the fact that in extreme Enduro competitions two-stroke motorcycles are still dominating, the Institute of Internal Combustion Engines and Thermodynamics, Graz University of Technology, with a long tradition in two-stroke technology, has developed a new 300 cm3 two-stroke motorcycle engine. The 2-stroke LPDI (Low Pressure Direct Injection) technology was originally developed for the 50 cm3 Scooter and moped market in Europe. In 50 cm3 applications the LPDI technology fulfils the EURO 4 emission standard (2017) [1]. In a next step the LPDI technology was applied to a 250 cm3 Enduro engine demonstrator vehicle. Based on the results of the demonstrator, a complete new high performance 300 cm3 engine was developed. The development of this new engine will be described in this publication. Some interesting aspects of the layout with 3D-CFD methods and also 1D-CFD simulation to optimize the exhaust system by DoE methods are discussed in the paper.

The Institute for Internal Combustion Engines and Thermodynamics, Graz University of Technology, has presented several applications of its 2-stroke LPDI (low pressure direct injection) technology in the previous years ([1], [2], [3]). In order to improve the competitiveness of the 2-stroke LPDI technology, an air cooled 50cm3 scooter application has been developed. All previous applications have been liquid cooled. This air cooled application demonstrates the EURO 4 (2017) ability of the technology and shows that the 2S-LPDI technology can also be applied to low cost air-cooled engines. Hence, the complete scooter and moped fleet can be equipped with this technology in order to fulfil both the emission standards and the COP (conformity of production) requirements of Euro 4 emission stage. The paper presents the Euro 4 Scooter results and describes the efficient conversion process of the existing carburetor engine to the LPDI version.

Nowadays, politicians are forced by air pollution prevention to demand zero emission vehicles (ZEV) in the form of pure electric vehicles. The poor capacity to weight factor of actual batteries compared to any kind of liquid or gaseous hydro-carbon fuel is the main reason for the retarded implementation of ZEV. Solutions offered by automobile manufacturers are mild to full hybrid powertrains based on the well established ICE platform. The difficulty of those approaches of electrification is to compete with the performance and benefit costumers expect from standard automobiles. Pure electric vehicles are rare and often disappointing regarding range and/or performance. Additionally the costs for such vehicles, which are mainly driven by the battery prices, are comparatively high, impeding their market entrance and acceptance. Low price electric city scooters are actually offered as pure electric vehicles in a wide variety of different models.

The future exhaust emission legislation limits and the procedures for running the test cycles will have an important influence on future range extender concepts. Due to the special steady state operation strategy of the range extender engines, it is possible to create a simple methodology for comparing engine test bench emissions with the emission limits of exhaust gas legislations. Therefore the energy demand of a predefined vehicle was simulated with PHEM, a longitudinal dynamic simulation tool. According to that, the influence of different exhaust gas after treatment systems and preheating options on the tolerated raw emission concentration will be analyzed. With this information, a few chosen range extender engine concepts will be compared concerning their suitability for future exhaust emission legislations. The selection of the range extender concepts was carried out with the methotology of a value benefit analysis.

Based on the fundamental analysis of the two-stroke process (SETC 2005-32-0098) and the development of a stratified scavenged small capacity two-stroke engine (SETC 2006-32-0065), a further approach to achieve low emissions in this engine category is the main subject of this publication. The principles of the system are described by design activities, results of the 3D-CFD simulation and the visualization of the spray in the cylinder. The benefit of this system on exhaust emissions is demonstrated by engine test bench as well as chassis dynamometer results. The achievable reduction of exhaust emissions, especially with an applied oxidation catalytic converter, is remarkable and the potential to fulfill future emission limits has already been demonstrated.

Future exhaust emission targets and increasing customer demands call for the implementation of enhanced engine technologies, as well known from automotive applications, into small capacity engine categories. Especially the applied engineering solutions in the market of motor vehicles driven by engines up to 50 cm3 displacement have been significantly changed in the last years. Beside low cost technologies (air cooled two stroke or four stroke engines with carburetor), enhanced mixture preparation and exhaust gas after treatment systems come to use. Highly technological two stroke engines are equipped with direct fuel injection systems in combination with efficient exhaust gas after treatment methods; in four stroke engine applications intake port fuel injection systems in combination with oxidation catalysts or 3-way catalytic conversion are established on the market.

State of the art technologies of 2 and 4 stroke engines have to fulfill severe future exhaust emission regulations, with special focus on the aspects of rising performance and low cost manufacturing, leading to an important challenge for the future. In special fields of applications (e.g. mopeds, hand held or off-road equipment) mainly engines with simple mixture preparation systems, partially without exhaust gas after treatment are used. The comparison of 2 and 4 stroke concepts equipped with different exhaust gas after treatment systems provides a decision support for applications in a broad field of small capacity engine classes.

Based on the fundamental analysis of the two-stroke process and the first results of the 3D-CFD simulation (Paper No: SETC 2005-32-0098), the development of a small capacity two-stroke engine is the subject of this publication. The developed 50 cm3 two-stroke engine is applied with a low pressure fuel injection system and allows, due to the special positioning of the fuel injector, two different scavenge modes. The first mode is a standard homogenous scavenge mode and the second one is for a stratified scavenged engine operation. Both modes can be achieved only by the adjustment of the injection timing without any restrictions concerning possible phasing. The system only deals with one fuel injector; special constraints concerning the transition between stratified and homogenous operation are not required. Any possible mixture can be applied between stratification and homogenous mode.

More and more restrictive regulations, as the pending Euro3 emission legislation, demand for a lowering of exhaust emissions of two stroke engines. The reduction of scavenge losses is one of the key requirements for the development of two-stroke engines. Besides it is important to maintain the excellent torque and power behavior of the two stroke units. This publication gives a summary of previous and present development results of test bench and chassis dynamometer measurements and of 3D CFD simulations. All these results are targeted on a reduction of the scavenge losses and therewith HC-emissions. Therefore the focus is put on different injection strategies, such as semi-direct and air-assisted injection. Additionally, the potential of the high pressure gasoline direct injection is presented, even if this technology is still too expensive for the small capacity engine market, e.g. the European 50 cc scooter class.

The present paper describes in detail the development of such a combustion process, starting from the initial design, referring to the simulation of the entire system with the description of the injection, vaporisation and combustion, through to the test bench experiments. The particular focus of the presentation lies on the application of 3D-CFD simulation technologies for modelling the entire system, including the high-pressure direct injection. This paper looks into the analysis and validation of the simulation data, as well as into the thermodynamic analysis and evaluation of the data measured in the tests. The results regarding the performance, emissions and other parameters are represented in comparison with other combustion processes, thus showing the potential of the newly designed combustion process.