EGR ratio measuring device

An EGR ratio measuring device to measure an EGR ratio of an internal combustion engine based on a concentration of CO2 in an intake air introduced into a combustion chamber of the internal combustion engine and a concentration of CO2 in an exhaust gas discharged from the combustion chamber, and comprising

• a pair of nondispersive infrared gas analyzers that have a function of correcting a water influence and that can measure a concentration of CO2 in a gas containing water,
• an intake air introduction line that is connected to an intake air pipe of the internal combustion engine and that introduces a part of the intake air into one of the nondispersive infrared gas analyzers without removing the water,
• an exhaust gas introduction line that is connected to an exhaust gas pipe of the internal combustion engine and that introduces a part of the exhaust gas into the other nondispersive infrared gas analyzer without removing the water, and
• a temperature adjusting mechanism that keeps a temperature of whole of the intake air introduction line and the exhaust gas introduction line and a temperature of the nondispersive infrared gas analyzers so as not to condense dew and that keeps the temperature of the nondispersive infrared gas analyzer higher than the temperature of the intake air introduction line and the temperature of the exhaust gas introduction line.