Patent ID: 8307695

Claim:
A cetane number estimation method for estimating a cetane number of fuel combusted in a diesel engine in which a regular injection is performed by injecting fuel of an amount corresponding to an engine operation state and a preliminary injection is performed by injecting fuel of an amount predetermined for estimation of the cetane number of fuel, comprising: a first process in which the preliminary injection is preformed multiple times at different compression end temperatures with a fuel tank containing fuel having a predetermined cetane number, and an engine torque increase that has been caused by each preliminary injection is calculated and the relation between the compression end temperatures at the respective preliminary injections and the engine torque increases caused by the respective preliminary injections is determined, and the compression end temperature and the engine torque increase at a predetermined reference point on the relation are recorded in a data storage; a second process in which the preliminary injection is performed at the compression end temperature recorded in the data storage and an engine torque increase caused by the preliminary injection is calculated; and a third process in which a cetane number of fuel is estimated based on a relation between the engine torque increase recorded in the data storage and the engine torque increase calculated in the second process.