The emission behaviour of an internal combustion engine under test-bed conditions shows differences to the emission behaviour under real in-use conditions. Because of this fact, the developers of combustion engines and the legislator are focussing on the measurement and optimization of real in-use emissions.
To this day, the research, the adjustment of the carburettor and the legislation of small handheld engines is performed under test bench conditions, especially conditioned fuel pressure and temperature, as well as air temperature. Also the engines are laid out for two operation points: rated speed with full open throttle and idle speed. This test-procedure is used for all kinds of handheld off-road applications and does not consider the load profile of the different power tools. Especially applications with transient load profiles, for example chainsaws, work in more than two operating points in real use. The engine performance and driveability gets adjusted in transient cycles after the two point optimization, not regarding any emissions or the fuel consumption. This procedure is carried out because the measurement of the fuel consumption in a transient cycle is difficult. The examination of the fuel consumption of small two-stroke SI engines is aggravated due to low consumption flow rates and pressures. This requires a special equipment and particular measuring. It is crucial, that the measuring principle does not have influence on the actual combustion and it has to manage varying fuel flows.
In this investigation the engine was run both under laboratory and under real in-use conditions. The emissions for all tests in these operating points were analyzed. The concentrations of the exhaust gas components were measured on-line while the test engine was running under the operating conditions. This offers a new solution in determining exhaust emissions and fuel consumption from small two-stroke SI engines.