Measurement of Air Distribution in a Multicylinder Engine by Means of a Mass Flow Probe

To lower emissions from a multicylinder engine, the air-fuel ratio must be optimized in all cylinders. If uniform fuel distribution is achieved, then the cylinder-to-cylinder air distribution is of particular interest. A probe system has been developed to measure mass flow rates to individual cylinders during operation of a complete engine. Fast response measurements of pressure, temperature, and flow velocity are made in the intake port near the valve during the intake portion of the cycle. High-speed collection of the large volume of data was accomplished through on-line use of an IBM 1800 computer. A V8 455 CID (7457 cm³) engine with stock intake and single exhaust system was used in the initial application of the mass flow probe. Measurements of 30-40 individual cycles were combined to calculate the mean volumetric efficiency for each cylinder. When measurements for all of the cylinders had been made, the cylinder-to-cylinder distributions were computed as deviations from the overall average. Variations of ±8% were typical during motored operation, with some cylinders deviating by as much as ±12%. Fired operation produced variations greater than ±15%. No characteristic distribution was found to extend throughout the speed and load range tested. Typical cycle-to-cycle variations in the volumetric efficiency for individual cylinders were found to be ±8%.