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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.

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.

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.