Fuel properties detecting apparatus for an internal combustion engine

A fuel properties detecting apparatus for an internal combustion engine wherein an intake air quantity and an air-fuel ratio in exhaust gas are measured, a basic fuel injection quantity is calculated on the basis of said intake air quantity, and an amount of fuel to be injected is feed-back controlled in response to said air-fuel ratio, comprising:

• a pressure detecting means to detect an inner pressure of a cylinder,
• a crank angle detecting means to detect a crank angle of the engine, and
• a control device comprising means for receiving signals from said pressure detecting means and said crank angle detecting means to thereby calculate an effective calorific value Q of fuel in an ignition cycle on the basis of an inner pressure of a cylinder P(.theta.) at a crank angle in compression and expansion strokes in an ignition cycle, a crank angle .theta. and a cylinder capacity V(.theta.), and to obtain an effective combustion rate K or a low level calorific value Hu of fuel, whereby said control device further comprises means for detecting fuel properties by using at least one of said effective combustion rate K said low level calorific value, Hu, and a ratio of a fuel injection pulse width Ti to said low level calorific value Hu (Ti/Hu).