Fuel property judgement device for internal combustion engine

A fuel property judgement apparatus for an internal combustion engine, comprising:

• a crank angle sensor for generating a crank angle signal corresponding to an rpm of the internal combustion engine and a crank angle position;
• a starter switch for outputting a start signal at the time of starting operation of the internal combustion engine;
• an initial combustion detecting means for detecting an initial combustion at the time of starting operation of the internal combustion engine in response to the start signal;
• a turn-on number counting means for counting a turn-on number of the crank angle signal during a period from the operation start of the internal combustion engine to the detection of the initial combustion;
• a standard number setting means for setting a standard number which is a judgement standard for the fuel property of the internal combustion engine;
• a turn-on number comparing means for comparing the turn-on number with the standard number to yield a comparison result;
• a fuel property judgement means for determining the fuel property on the basis of the comparison result of said turn-on number comparing means;
• and
• an ion current detecting device for detecting an ion current generated in the vicinity of an ignition plug at the time of an ignition control operation of the internal combustion engine, wherein said initial combustion detecting means detects the initial combustion on the basis of the ion current.