Development of an Oil Degradation Sensor Based on Detection of Free Radicals

This paper proposes an oil degradation sensor that informs the best time for oil replacement to achieve the right balance with oil conservation and engine protection. We found that free radicals in the engine oil generate by chain decomposition reactions of hydrocarbons by heat and the amount of them increases with an increase in running distance. Based on theoretical analysis and experiment results, the free radical concentrations have high correlations with pH and base number. The sensor using the principle of electron spin resonance (ESR) can measure the amount of free radical molecules in a non-contact method. The sensor successfully detected free radicals produced by the degradation of actual engine oil.