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Acoustic standing waves are excited in internal combustion chambers by both normal combustion and autoignition. The energy in these acoustic modes can be transmitted through the engine block and radiated as high-frequency engine noise. Using finite-element models of two different (four-valve and two-valve) production engine combustion chambers, the mode shapes and relative frequencies of the in-cylinder volume acoustic modes are calculated as a function of crank angle. The model is validated by comparison to spectrograms of experimental time-sampled waveforms (from flush-mounted cylinder pressure sensors and accelerometers) from these two typical production spark-ignited engines.

This paper describes a digital Phase-Locked Loop (PLL) frequency synthesizer designed for AM/FM radios. The synthesizer utilizes an upconversion technique which enables tuning of both the AM and FM bands using one Voltage Controlled Oscillator (VCO) operating between 98 and 118 MHz. The scheme reduces the cost associated with the AM front end as a result of eliminating three matched varactor diodes and the labor involved in the five to six adjustments for alignment.