The two-stroke SI engine remains the dominant concept for handheld power tools. Its main advantages are a good power-to-weight ratio, simple mechanical design and low production costs. Because of these reasons, the two-stroke SI engine will remain the dominant engine in such applications for the foreseeable future. Increasingly stringent exhaust emission laws, in conjunction with the drive for more efficiency, have made new scavenging and combustion processes necessary. The main foci are to reduce raw emissions of unburned hydrocarbons via intelligent guidance of the fresh air-fuel mixture and to improve performance to reduce specific emissions. The flow velocity in the electrode gap of the spark plug is of great interest for the ignition of the air-fuel-mixture and the early combustion phase of all kinds of SI engines. In these investigations, the flow velocity in the spark plug gap of a two-stroke gasoline engine with stratified scavenging was measured under various conditions. Two spatial directions in the spark plug gap were measured without influencing the in-cylinder flow. The measurements were performed using LDA (Laser Doppler Anemometry), a non-intrusive optical velocity measurement technology. For the application of the LDA equipment, the placement of one optical access in the cylinder head was necessary. The access is located in the plane of the spark plug gap coaxial with the crankshaft.
The investigations were done in non-fired operating points; the engine was powered by an asynchronous motor. Variation parameters included the engine speed in a range from idle speed up to 9500 rpm; engine loads and volumetric efficiencies at various throttle valve positions. In addition, the influences of different orientations of the spark plug electrode were also investigated.
