Use of a mechanical analogy to couple the time-domain of a one-cylinder cold-engine model with the input impedance of its intake system

The acoustic waves generated by a reciprocating engine in the air intake system have a strong influence on filling the engine with air and thus on its global performance. This coupling between in duct acoustic and in-engine thermo-dynamic phenomena is the purpose of the present paper which reports a numerical technique to couple a cold engine characterized by its geometry and the movement of the piston and the valves with an air-intake system characterized by its experimental input impedance. The pressure in two different air-intake systems is computed and compared to experimental results obtained with an engine rotating at 16 different speeds. The results are in fair to very fair agreement.The numerical procedure allowed the computation of the volumetric efficiency that corresponds to the amount of air trapped in the cylinder and thus potentially available for the combustion. The comparison between the efficiency after one cycle and the converged efficiencies versus the engine speed enabled us, using data from the literature, to discern two different influences of the acoustic phenomena on the engine performance.

► An engine model is numerically coupled to the impedance of its air intake system.
► Pressure is measured in two air intake systems successively connected to an engine.
► Numerical and experimental results agree fairly well from 1500 to 3000 rpm.
► The intake transient fills the engine with more air over a large range of speeds.
► The acoustic resonances fill the engine with more air at specific engine speeds.