Search Results

This paper reviews the current and new mini-four-stroke engine technologies that are suitable to be implemented in light-weight outdoor power equipment. A new mixture lubrication setup has been developed for a very compact mini-four-stroke engine. Special emphasis is laid on the design of the combustion chamber and the valve train. The paper derives how to systematically translate the user demands of a light weight engine to the new mini-four-stroke engine. The new STIHL 4-MIX-engine features an integral one-component cylinder including the cylinder head, two valves and a very simple drive train consisting of a plastic cam including a decompression mechanism. The valve train stands speeds in excess of 12000 rpm and it is also lubricated by the new mixture lubrication setup. The piston is used as an oil-mist pump. The engine has an output of 1.0 kW out of 31.4 cm3. Pressure indication work is used in order to optimize the combustion process.

When developing effective exhaust emission reduction measures, a better understanding of the complex working cycle in crankcase scavenged two-stroke gasoline engines. However, in a two-stroke gasoline engine detailed measurement and analysis of combustion data requires significantly more effort, when compared to a lower speed four-stroke engine. Particularly demanding are the requirements regarding the high speed (>10,000 rpm) which inevitably goes along with heavy vibrations and high temperatures of the air cooled cylinders. Another major challenge to the measuring equipment is the increased cleaning demand of the optical sensor surface due to the two-stroke gasoline mixture. In addition, the measuring equipment has to be adapted to the small size engines. Therefore, only a fiber optical approach can deliver insight into the cylinder for analyzing the combustion performance.

Due to emission regulations for hand-held power tools more and more stratified-charge two-stroke engines enter into the market [Sawada et al. 1998, Zahn et al. 2000]. These engines require investigations and treatment for tuning the transient behaviour that are beyond the methods of the tuning for conventional engines. Especially the in-cylinder air-to-fuel-ratio cannot be determined from simple exhaust gas analysis any more. This paper presents an exhaust gas sampling system to enable the use of a standard lambda meter for a fast response measurement of air to fuel ratio out of the combustion chamber. The gas is sampled by means of a small restriction directly out of the combustion chamber. In case of miss-fire the hydrocarbon concentration in the sample is too high for the lambda sensor. With a dilution or a pre-converter system the hydrocarbon concentration can be adjusted to the range of the lambda sensor. Verification has been done with several tests.