Engine performance evaluation using a combustion probe signal analyzer

A two-channel combustion probe signal analyzer to detect variations in the combustion quality in spark ignition engines was built and its performance investigated. The combustion probe signal was obtained by applying a small positive bias to the center electrode of the spark plug of interest. This was accomplished by the insertion of an adaptor between the distributor cap and the spark plug wire. Use of the adapter showed no apparent effect on engine operating characteristics. Experiments investigating the correlation between several engine operating parameters and the combustion quality parameters "impaired combustion" and "slow combustion" were carried out. The parameters varied were A/F (air to fuel ratio), spark advance, engine speed, nonenriched cold start, and NOxand hydrocarbon concentrations in the exhaust. Dynamometer mounted 400 CID production engine was used. Good agreement was found to exist between the variation in the combustion probe signal analyzer\´s counts and progressively induced impairments of the combustion process.