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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.

Increasingly stringent emission regulations force manufacturers of two wheelers to develop low emission motorcycle concepts. Especially for small two-stroke engines with symmetrical port timing structure, causing high HC-emissions due to scavenge losses, this is a challenging demand that can only be met with alternative mixture formation strategies and by intensifying the use of modern development tools. Changing from EU4 to EU5, emission legislation will not only have an impact on the improvement of internal combustion but will also drastically change the after-treatment system. Nowadays, small two-stroke engines make use of a simple carburetor for external mixture preparation. The cylinders are scavenged by air/fuel mixtures. Equipped with exhaust gas after-treatment systems, such as secondary air with two or three catalytic converters, the emission limits for EURO 4 homologation can be achieved with carbureted engines.

Small engines in small lightweight vehicles represent a good compromise between performance, comfort and environmental-oriented design. This becomes an issue worldwide. In big cities, lightweight vehicles have a great potential and advantages with regard to these issues. To reduce emissions in some big cities, governmental regulation requests the local cars being operated on CNG (Compressed Natural Gas). This gives bi-fuel (petrol and CNG) or CNG-mono-fuel vehicles a chance [1, 2]. MAGNA STEYR designed a bi-fuel 3-wheeler concept car and carried out simulations to find a good compromise between small engine and good performance. Styling studies, lightweight base-frame studies and an engine concept was developed for a 3-wheeler, but a module system should allow a taxi or cargo variant for either a 3-wheeler or a 4-wheeler.

Meeting upcoming emission limits such as EURO 5 with comparatively simple and low-cost vehicles will be very challenging. On the engine side, a big effort in terms of fuelling, combustion optimization as well as exhaust gas aftertreatment will be necessary without any doubt. Besides that, additional system optimization potential can be gained by a systematic adaptation of the drive train. One approach is to use a CVT (Continuously Variable Transmission) system to run engines in specific ranges with good fuel economy. However, existing belt driven CVTs show comparatively poor efficiencies. To overcome this drawback, the integration of a novel Continuously Variable Planetary Transmission (CVP), designed and developed by Fallbrook Technologies, was investigated in detail. For this purpose, a longitudinal dynamics simulation in Matlab-Simulink was carried out to compare a standard mass production vehicle drive train with several CVP setups.

The reduction of environmentally harmful gases and the ambitions to reduce the exploitation of fossil resources lead to stricter legislation for all mobile sources. Legislative development significantly affected improvements in emissions and fuel consumptions over the last years, mainly measured under laboratory conditions. But real world operating scenarios have a major influence on emissions and it is already well known that these values considerably differ from officially published figures [1]. There are regulated emissions by the European Commission by means of real driving scenarios for passenger cars. A methodology to measure real drive emissions RDE is therefore well approved for automotive applications but was not adapted for two-wheeler-applications yet [2]. Hence measurements have been performed on-road and on chassis dynamometer for motorcycles with the state of the art RDE measurement equipment to be prepared for possible future legislation.

This paper introduces a research project on a spark ignition engine used in non-road applications. The aim is to illustrate the present situation as basis for comparison and to identify possible improvement potential in terms of performance, efficiency or exhaust and noise emissions. The study is carried out in two steps. First a standard walk-behind lawn mower is equipped with measuring instrumentation for recording the cutting forces and the engine variables during real world operation. The tests are carried out on three different lawn types and two different blade types are investigated. Consequently, in a second step the engine is analysed on the engine test bench in stationary and transient operating mode. A complete engine mapping is done regarding all relevant variables. Additionally to the outdoor tests, fuel consumption and engine out emissions are measured on the engine dynamometer. The recorded data enables a detailed analysis of the engine behaviour.

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.

Looking at the market for 2-wheelers driven by small capacity four stroke engines, it turns out that the legislation for exhaust emissions is mostly combined with a regulation of vehicle speed. Most of the vehicles in this category are still driven by engines equipped with carburetors which, unlike fuel injection systems, do not give the possibility to cut off fuel metering when high speed is achieved. When a carburetor is applied with a simple ignition unit, a reduction of spark advance is the only way to ensure correct vehicle speed, but there are a lot of disadvantages in terms of exhaust emissions and fuel economy coming up with this method of engine power restriction. This leads to the idea of using exhaust gas recirculation (EGR) to reduce engine power when necessary.

The concept of a loop scavenged two-stroke engine, controlling the intake and exhaust port by the moving piston, is a proven way to realize a simple and cheap combustion engine. But without any additional control elements for the gas exchange this concept quickly reaches its limits for current emission regulations. In order to fulfil more stringent emission and fuel consumption limits with a two-stroke engine, one of the most important measures is to avoid scavenging losses of fuel and oil. Additionally, it is necessary to follow a lambda = 1 concept for a 3-way exhaust gas after-treatment. Therefore, using internal mixture preparation systems in combination with different concepts to control the gas exchange process, the two-stroke engine could become a choice for automotive applications, especially as a Range Extender in a Plugin Hybrid Electric Vehicle (PHEV).

The new generation of metallic substrates for catalytic converters used in the two and three wheeler industry is capable of improving conversion behavior even with smaller catalyst size. The lowering of production costs due to less use of precious metal is possible. This novel technological application in motorcycle vehicle class improves exhaust emission performance and introduces a new competitive product on the market. Specially developed foil structures, which transform a laminar exhaust gas flow to a turbulent one, significantly improve exhaust gas mixing behavior in the catalyst. This publication is dealing with the analysis of different metallic substrate foil structures for the catalyst conversion performance and the light-off characteristics for the leading state of the art four stroke 150 cm3 motorcycle technology developed for the Asian market.

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.

In the course of the last few years a continuous increase of the injection pressure level of gasoline direct injection systems appeared. Today's systems use an injection pressure up to 200bar and the trend shows a further increase for the future. Although several benefits go along with the increased injection pressure, the disadvantages such as higher system costs and higher energy demand lead to the question of the lowest acceptable injection pressure level for low cost GDI combustion systems. Lowering injection pressure and costs could enable the technological upgrading from MPFI to GDI in smaller engine segments, which would lead to a reduction of CO2 emission. This publication covers the investigation of a low pressure GDI system (LPDI) with focus on small and low cost GDI engines. The influence of the injection pressure on the fuel consumption and emission behavior was investigated using a 1.4l series production engine.

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.

Aiming to investigate the influence of methanol blends on the combustion process of a PFI four-stroke boxer engine, four mixtures of pure methanol and oxygen-free gasoline (M0) are prepared. The fuels tested are labelled by M15, M25, M35 and M50, where the number represents the percentual in volume of methanol within the mixture. In order to establish a base for comparisons, standard gas-station gasoline (S95) is also tested. Backwards compatibility is evaluated through test-bed measurements, when the engine operates without any modifications in the ECU. Over the whole operational area of the engine map, M15 and M25 can be used in the motorcycle application. Raw emissions of THC, CO2, CO and NOx decrease with the increase of methanol for almost all the conditions tested. It is observed that knock resistance is higher for higher methanol contents. At WOT, power is increased with the methanol proportion, being M50 and M35 more powerful than standard gasoline.

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.

The automotive industry has made great efforts in reducing fuel consumption. The efficiency of modern spark ignition (SI) engines has been increased by improving the combustion process and reducing engine losses such as friction, gas exchange and wall heat losses. Nevertheless, further efficiency improvement is indispensable for the reduction of CO2 emissions and the smart usage of available energy. In the previous years the Atkinson Cycle, realized over the crank train and/or valve train, is attracting considerable interest of several OEMs due to the high theoretical efficiency potential. In this publication a crank train-based Atkinson cycle engine is investigated. The researched engine, a 4-stroke 2 cylinder V-engine, basically consists of a special crank train linkage system and a novel Mono-Shaft valve train concept.

The enhancement of efficiency will play a more and more important role in the development of future (small) internal combustion engines. In recent years, the Atkinson cycle, realized over the crank drive, has attracted increasing attention. Several OEMs have been doing investigations on this efficiency-increasing principle with in the whole range from small engines up to automotive ones. In previous publications, the authors stated that an indicated efficiency of up to 48% could be reached with an Atkinson cycle-based engine. However, these studies are based on 1D-CFD simulation. To verify the promising simulation results, a prototype engine, based on the Atkinson principle, was designed and experimentally tested. The aim of the present study is to evaluate and validate the (indicated) engine efficiency gained by experimental tests compared to the predicted simulation results. In order to investigate part load behavior, several valve timing strategies were also developed and tested.

Meeting future legislative targets for SI engines by means of low cost technologies is a big challenge for engineers. Despite the use of simple and cost efficient components these engines have to fulfill customer requirements in terms of power and fuel economy, representing the most important selling arguments. Without the possibility of integrating modern technologies like fuel injection systems for mixture preparation instead of simple carburetors, it is very complex to find viable solutions that enable the achievement of these targets. A main key to improve emission behavior, fuel economy and performance on carbureted engines is to get an insight in the mixture preparation process, especially under transient conditions.

In recent years, E-mobility relevance has increased in the automotive sector, yet pure electric vehicles struggle to establish themselves in the still internal combustion engine (ICE) dominated sector of L-category and powersport applications. Battery electric hybrid L-category vehicles, as considered in this paper, combine both ICE and electric powertrains. Nowadays, numerous ICE L-category vehicles use rubber V-belt continuous variable transmissions (CVT) due to their reliability and user-friendliness, which often outweighs the drawback of relatively low efficiency. This paper not only aims to show, with the help of longitudinal dynamic simulation (LDS), how a state-of-the-art L-category ICE powertrain with special focus on the CVT can benefit from hybridization in terms of overall efficiency, but furthermore points out where the efficiency increase actually comes from and how this new knowledge can be implemented intelligently into a hybrid strategy.

Professional users in particular will continue to rely on internal combustion engine drives in the future due to high power requirements and high daily energy consumption. Especially if they have to work in rural areas without the possibility of recharging batteries, such as in forestry or maintenance of road verges or railway lines. For these applications, it must be possible to run sustainable fuels for defossilization and drastically reduced CO2 emissions. This paper provides insights into a possible future fuel market and describes its evolution towards a more sustainable future from the perspective of a handheld equipment manufacturer. As developments in the fuel market are currently difficult to predict, manufacturers of hand-held power tools with combustion engines need to be prepared for changes in the composition of fuels that might become available on the market.