Patent ID: 6903822

Claim:
An apparatus for measuring density of fuel in an engine comprising: a measuring light introducing passage introducing a measuring light to a measuring passage in a combustion chamber of the engine, the measuring light including a specific wavelength which is selectively absorbed by the fuel; a light receiving element receiving the measuring light having transmitted through the measuring passage; a light-intensity detector detecting intensity of light having the specific wavelength, the light received by the light receiving element being introduced to the light-intensity detector; an interception controller intercepting the measuring light from introducing to the measuring passage; and a fuel density calculator programmed to: calculate intensity of the measuring light having transmitted through the measuring passage by subtracting, from a first light-intensity detected at a predetermined crank angle by the light-intensity detector when the measuring light is introduced to the measuring passage, a second light-intensity detected by the light-intensity detector at the same predetermined crank angle when the measuring light is intercepted by the interception controller; and calculate fuel density based on the intensity of the measuring light having transmitted through the measuring passage and intensity of the measuring light before transmitting through the measuring passage.