COMBUSTION RANDOMNESS AND DIESEL ENGINE NOISE: THEORY AND INITIAL EXPERIMENTS

Abstract Theoretical reasoning and preliminary experimental results show that the cycle to cycle variations in the turbulent combustion process in a Diesel engine are responsible for a substantial amount of noise radiated from the engine. These results shown that a new interpretation is required of past results which have compared the cylinder pressure spectrum and the radiated noise spectrum. A two-time variable procedure is used to construct a theory of the three dimensional, unsteady Diesel engine combustion chamber pressure development. This theory is used to extract the spectral behavior of the chamber pressure when the heat release rate contains both periodic and random components. It is then theoretically shown, by use of the theory and past experience on combustion noise, that the randomness can be expected to dominate the periodic part of the pressure-time trace above some lower frequency bound of the order of 1000 Hz. Initial experiments to confirm the theoretical findings are performed under no-load conditions for a single cylinder, air-cooled Diesel engine.