การศึกษาขีดจำกัดการเผาไหม้ที่ส่วนผสมบางในเครื่องยนต์ เอส ไอ สองจังหวะ / ประพันธ์ ดลวิชัย = Lean burn limit study in a two stroke SI engine / Prapun Dolwichai
This work is lean burn limit study in a two stroke SI engine, 356 cc. Daihatsu ZM-9XK. The research has been devided into 3 parts. The first part was the test for OEM performance and fuel consumption using gasoline octane 91. The second part was lean burn limit investigation of engine performance and stability condition. To perform this part, a fuel injection system which fuel is metering by adjusting injector duty cycle. In the third part, analytical results of the first and second parts (performance and fuel consumption) were compared. To demonstrate a potential of fuel economy improvement, a model engine driving electric generator was investigated as a case study. Test results in the first and second parts were corrected according to AS2789.1-1985 recommendation before analyzed and compared. It was found that OEM engine has maximum thermal efficiency = 18.7% and lowest equivalence ratio = 1.31 without engine unstable condition. The results of testing with injection system show maximum thermal efficiency = 21.68% and lowest equivalence ratio = 0.93. The results of lean burn operation with injector system show that the obtained engine thermal efficiencies improvement ranges between 2.35% to 75.1% and the engine can be operated with leaner mixture than OEM. A case study of engine driving electric generator when operating at maximum engine thermal efficiency shows that the obtained electricity is 5.361 kW. The lean burn engine can improve fuel economy up to 15.13% compared with OEM while decreased power output is acceptable.