Separation of combustion noise in IC engines under cyclo-non-stationary regime
The separation and ranking of combustion and mechanical noise sources is of prime concern for the noise control of internal combustion (IC) engines. Signal processing techniques have been devised recently that can achieve such a separation using the cyclostationary property of IC engine signals. The object of this paper is to extend this framework to the situation where the engine undergoes a transient speed regime, for instance during a run-up. This raises some new and non-trivial questions. First, the assumption of cyclostationarity has to be relaxed and replaced by the vaguer notion of cyclo-non-stationarity. Second  and related to the first point  the practice of cyclic averaging has to be revisited. Third, the design of the separation filter must explicitly incorporate speed dependence. This paper proposes simple but robust solutions to these issues, with a special effort to make them practicable from an industrial point of view. In particular, the cyclic difference operator is introduced in lieu of cyclic averaging, and speed-dependence is captured by use of a flexible basis of B-splines whose knots density is automatically selected from the data. Successful examples of separation are then demonstrated on actual data measured during an engine run-up.
ic internal combustion lpav linear periodically angle-varying lsv linear speed-varying lsi linear speed-invariant pv parameter-varying cs cyclostationary cns cyclo-non-stationary oc operating conditions mle maximum likelihood estimator emle empirical maximum likelihood estimator ls least-squares siso single-inputsingle-output miso multiple-inputsingle-output