Air Fuel Ratio Estimation of a Glow Engine through Sound 978509
We examined if air fuel ratio could be estimated by engine sound for a two-stroke glow engine. A time resolved FFT (Fast Fourier Transform) was adopted to analyze the engine sound.
As a result, strong acoustic radiation were shown twice at TDC and BDC in the frequency range below 2.5 kHz in each cycle. For the case of high air fuel ratio, a peak of sound pressure in the range of 2.5 to 5 kHz exists in between TDC and BDC. This sound is supposed to be a noise due to anomalous combustion. Since the noise appears just after the combustion noise, the anomalous combustion noise is supposed to be a knocking noise.
When the periodic noise in the range up to 2.5 kHz appears weakly twice in one cycle, the air fuel ratio is approaching low limit for a stable run of the engine at 12000 rpm. When the periodic noise in the range of 2.5 to 5 kHz appears once in one cycle between the periodic noise in the range up to 2.5 kHz, the air fuel ratio is approaching high limit.
Koji Murakami, Mitsuaki Tanabe, Kiyoshi Aoki
College of Science and Technology, Nihon Univ.
Small Engine Technology Conference & Exposition