The robustness control for homogeneous charge compression ignition (HCCI) using a crank angle sensor and a knock sensor has been estimated. On the other hand, an ion current sensor is used as a countermeasure against abnormal combustion with downsized and higher compression ratio engines. This sensor can generally be adopted in engine systems. Therefore, we examined the application of an ion current sensor to robustness control for HCCI.The purpose of this research was to develop a method of detecting combustion conditions to make HCCI engines more robust. Therefore, we evaluated the performance of the ion current sensor. Experimental results comparing ion intensity detection in HCCI.The detection value of the ion current sensor changed based on the form of combustion. Experimental results showed that the heat release rate increased with an increase in ion signals appear during the same time at approximately in both spark ignition (SI) and HCCI. It was assumed that ion signals appearing during the main combustion period. Although the maximum heat release rate of HCCI is higher than one of SI, the maximum ion signal of HCCI is lower than that of SI.Experimental results of comparing detecting ion intensity (II) in HCCI and various other forms of combustions (stoichiometric SI, lean SI, and exhaust gas recirculation (EGR) SI) showed that as maximum cylinder temperature decreased, II decreased. These results showed that an ion current signal decreased due to lower temperature combustion. However, this correlation was the result of detecting nitrogen oxides (NOx). Therefore, an ion current sensor is applicable to NOx detection device for robustness control in HCCI.