Existing air-fuel ratio control systems for lean burn gas engines are rather complicated. In order to develop small lean burn gas engine, it was necessary to develop a gas mixer which provides mixture of the required air-fuel ratio over the various load without any feed back control.
Venturi type gas mixers were employed, because they have simple structure and relatively constant air-fuel ratio characteristic over wide range of flow conditions. Various venturi mixers, with different throat diameter, different position of the throat, different position of the fuel gas inlet, different shape of the fuel gas inlet, were tested by steady flow test installation.
Based on these test results, a prototype gas mixer for a 40 kw premixed turbocharged open chamber lean burn gas engine was designed and tested by steady flow test installation and real gas engine. As a result, it became evident the pressure loss of the mixer was remarkably improved compared with the conventional venturi mixer, and the fuel-air ratio characteristic became optimized.